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Default to ninja for faster builds (mac & linux) - #124041

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Default to ninja for faster builds (mac & linux)#124041
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Benchmarking showed ninja provides ~8.8% faster builds on macOS (avg 654s vs 718s per build). This change defaults to using ninja for both MacOS and Linux.

Changes:

  • eng/build.sh: default to using ninja
  • eng/native/build-commons.sh: Default -ninja on macOS, add -ninja false opt-out

Users can opt out with --ninja false (or -ninja false for native builds).

Contributes to #54022 (#54022)

Steve Pfister
Default to ninja on macOS for faster builds
968f944
Benchmarking showed ninja provides ~8.8% faster builds on macOS
(avg 654s vs 718s per build). This change defaults to using ninja
when the host OS is macOS.
Changes:
- eng/build.sh: Default --ninja true on macOS, track explicit user override
- eng/native/build-commons.sh: Default -ninja on macOS, add -ninja false opt-out
Users can opt out with --ninja false (or -ninja false for native builds).
@steveisok
steveisok requested review from a team and CopilotFebruary 5, 2026 13:01
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Pull request overview

This PR improves macOS build performance by defaulting to the Ninja build system instead of Make, achieving approximately 8.8% faster build times (654s vs 718s average). The change is opt-out via --ninja false to maintain flexibility.

Changes:

  • Default ninja build system on macOS for improved performance
  • Add explicit flag tracking to prevent overriding user preferences
  • Update help text to document the new default and opt-out mechanism

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

FileDescription
eng/build.shAdds macOS-specific ninja default with tracking to avoid overriding explicit user settings
eng/native/build-commons.shSets ninja as default on macOS and enhances -ninja flag to accept true/false values

Comment threadeng/native/build-commons.sh Outdated
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docs\workflow\requirements\macos-requirements.md needs to be updated - ninja is no longer optional by default after this change.

@jkotasjkotas added area-Infrastructure and removed needs-area-label An area label is needed to ensure this gets routed to the appropriate area owners labels Feb 5, 2026
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Windows also defaults to ninja. Maybe we should flip the switch: --skipninja and cherry-pick installation script change a2b49ec. It's a tiny script dependency considering everything else required by the build.

@jkotas

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--skipninja

Nit: Avoiding negations in names is a generally better UX design. I like -ninja false better than -skipninja.

@steveisok
Default to Ninja on macOS for faster builds
c98f1b9
- Use single useNinja variable in eng/build.sh instead of tracking explicit-ness
- Initialize __UseNinja=0 in build-commons.sh, then override to 1 on macOS
- Remove __UseNinja=0 initialization from build-runtime.sh and tests/build.sh
so the macOS default takes effect
- Update macOS requirements docs to reflect ninja is now default
@jkoritzinsky

jkoritzinsky commented Feb 5, 2026

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I was just talking with @agocke about requiring Ninja on macOS to make it easier to maintain our Swift usage (as CMake only supports Swift with Ninja and XCode) so we don't need to manually invoke the Swift compiler and do our own object file handling.

I think this is a great first step in that direction!

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@steveisok
Use ninja if installed for both macOS and Linux
f8a3e55
Based on PR feedback, default to using Ninja for native builds on any
Unix platform where ninja is installed, rather than only on macOS.
This aligns with the Mono subtree behavior and provides faster builds
when ninja is available.
CopilotAI review requested due to automatic review settings February 5, 2026 22:48
@steveisoksteveisok changed the title Default to ninja on macOS for faster buildsDefault to ninja if installed for faster builds (mac & linux)Feb 5, 2026
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Pull request overview

Copilot reviewed 5 out of 5 changed files in this pull request and generated 4 comments.

Comment threadeng/build.sh Outdated
Comment threadeng/native/build-commons.sh Outdated
Comment threadeng/build.sh Outdated
Comment threaddocs/workflow/requirements/macos-requirements.md Outdated
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It was implemented that way when you first asked, but later reverted due to concerns about build determinism (see #124041 (comment)). I believe build determinism is a separate issue, and Ninja by itself cannot meaningfully affect it: even small differences in toolchain versions or machine environments prevent bit-for-bit identical outputs. Docker largely addresses this on Linux by fixing the environment, but on other platforms there are more fundamental sources of nondeterminism to address, well beyond what Ninja alone can affect.

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Ok, @am11 votes for use if installed. @jkoritzinsky you appear to be as well.

@jkotas?

I don't have a strong opinion, but if I had to pick, I'd choose ninja by default and only opt out explicitly.

@jkotas

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numbers for the build time improvement on Linux

I see 5% improvement for ./build.sh -s clr -c release in mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-net11.0-cross-amd64 container on standard issue devbox. (~610seconds without ninja, 580seconds with ninja, average of 10+ builds)

I'd choose ninja by default

Yes, I think we should have it on by default for macOS and Linux at least, so that folks do not accidentally forget to install it and get worse build times.

other platforms

I am fine with off by default (or automatic light up) for other platforms if it helps.

jkotas
jkotas reviewed Feb 7, 2026
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Comment threaddocs/workflow/requirements/macos-requirements.md Outdated
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I'm okay with on-by-default as well. I just figured that use-if-available is an easier change to accept if we weren't sure if we wanted to switch.

@steveisok@jkotas
Update docs/workflow/requirements/macos-requirements.md
d1b1447
Co-authored-by: Jan Kotas <jkotas@microsoft.com>
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Pull request overview

Copilot reviewed 5 out of 5 changed files in this pull request and generated 4 comments.

Comment threadeng/native/build-commons.sh
Comment threadeng/build.sh
Comment threadeng/build.sh
Comment threadeng/native/build-commons.sh
Steve Pfister
Fix -ninja argument parsing to not consume the next flag
4655850
When -ninja was followed by another flag (e.g. --ninja --subset clr),
the parser would consume the next argument as a ninja value and break
argument parsing. Now check if $2 starts with '-' before treating it
as a true/false value.
@steveisok

steveisok commented Feb 8, 2026

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I see 5% improvement for ./build.sh -s clr -c release in mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-net11.0-cross-amd64 container on standard issue devbox. (~610seconds without ninja, 580seconds with ninja, average of 10+ builds)

Ran on WSL for a 4 hour loop. 12% better there on average.

jkotas
jkotas reviewed Feb 8, 2026
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Comment threaddocs/workflow/requirements/macos-requirements.md
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Pull request overview

Copilot reviewed 7 out of 7 changed files in this pull request and generated no new comments.

jkotas
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Thanks!

@steveisok
steveisok merged commit 407f9f1 into dotnet:mainFeb 8, 2026
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This broke runtime-libraries enterprise-linux (that was skipped on the PR). #124187
It would be nice if it falls back automatically if Ninja is not present.

@am11am11 mentioned this pull request Feb 21, 2026
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iremyux pushed a commit to iremyux/dotnet-runtime that referenced this pull request Mar 2, 2026
@steveisokSteve Pfister@iremyux
Default to ninja for faster builds (mac & linux) (dotnet#124041)
1d171e2
Benchmarking showed ninja provides ~8.8% faster builds on macOS (avg
654s vs 718s per build). This change defaults to using ninja for both
MacOS and Linux.
Changes:
- eng/build.sh: default to using ninja
- eng/native/build-commons.sh: Default -ninja on macOS, add -ninja false
opt-out
Users can opt out with --ninja false (or -ninja false for native
builds).
Contributes to dotnet#54022
(dotnet#54022)
---------
Co-authored-by: Steve Pfister <steve.pfister@microsoft.com>
@github-actionsgithub-actionsBot locked and limited conversation to collaborators Mar 12, 2026
Sign up for freeto subscribe to this conversation on GitHub. Already have an account? Sign in.

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var __re = new RegExp('^' + "github\\.com" + '
Default to ninja for faster builds (mac & linux) by steveisok · Pull Request #124041 · dotnet/runtime · GitHub
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Default to ninja for faster builds (mac & linux) - #124041
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Default to ninja for faster builds (mac & linux)#124041
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Benchmarking showed ninja provides ~8.8% faster builds on macOS (avg 654s vs 718s per build). This change defaults to using ninja for both MacOS and Linux.
Changes:
  • eng/build.sh: default to using ninja
  • eng/native/build-commons.sh: Default -ninja on macOS, add -ninja false opt-out
Users can opt out with --ninja false (or -ninja false for native builds).
Contributes to #54022 (#54022)
Steve Pfister
Default to ninja on macOS for faster builds
968f944
Benchmarking showed ninja provides ~8.8% faster builds on macOS
(avg 654s vs 718s per build). This change defaults to using ninja
when the host OS is macOS.
Changes:
- eng/build.sh: Default --ninja true on macOS, track explicit user override
- eng/native/build-commons.sh: Default -ninja on macOS, add -ninja false opt-out
Users can opt out with --ninja false (or -ninja false for native builds).
@steveisok
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a team and CopilotFebruary 5, 2026 13:01
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Pull request overview
This PR improves macOS build performance by defaulting to the Ninja build system instead of Make, achieving approximately 8.8% faster build times (654s vs 718s average). The change is opt-out via --ninja false to maintain flexibility.
Changes:
  • Default ninja build system on macOS for improved performance
  • Add explicit flag tracking to prevent overriding user preferences
  • Update help text to document the new default and opt-out mechanism
Reviewed changes
Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.
FileDescription
eng/build.shAdds macOS-specific ninja default with tracking to avoid overriding explicit user settings
eng/native/build-commons.shSets ninja as default on macOS and enhances -ninja flag to accept true/false values
Comment threadeng/native/build-commons.sh
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docs\workflow\requirements\macos-requirements.md needs to be updated - ninja is no longer optional by default after this change.
@jkotasjkotas
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Windows also defaults to ninja. Maybe we should flip the switch: --skipninja and cherry-pick installation script change a2b49ec. It's a tiny script dependency considering everything else required by the build.
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--skipninja
Nit: Avoiding negations in names is a generally better UX design. I like -ninja false better than -skipninja.
@steveisok
Default to Ninja on macOS for faster builds
c98f1b9
- Use single useNinja variable in eng/build.sh instead of tracking explicit-ness
- Initialize __UseNinja=0 in build-commons.sh, then override to 1 on macOS
- Remove __UseNinja=0 initialization from build-runtime.sh and tests/build.sh
so the macOS default takes effect
- Update macOS requirements docs to reflect ninja is now default
@jkoritzinsky
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I was just talking with @agocke about requiring Ninja on macOS to make it easier to maintain our Swift usage (as CMake only supports Swift with Ninja and XCode) so we don't need to manually invoke the Swift compiler and do our own object file handling.
I think this is a great first step in that direction!
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@steveisok
Use ninja if installed for both macOS and Linux
f8a3e55
Based on PR feedback, default to using Ninja for native builds on any
Unix platform where ninja is installed, rather than only on macOS.
This aligns with the Mono subtree behavior and provides faster builds
when ninja is available.
CopilotAI
review requested due to automatic review settings
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@steveisoksteveisok
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Default to ninja on macOS for faster buildsDefault to ninja if installed for faster builds (mac & linux)Feb 5, 2026
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Pull request overview
Copilot reviewed 5 out of 5 changed files in this pull request and generated 4 comments.
Comment threadeng/build.sh
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Comment threaddocs/workflow/requirements/macos-requirements.md
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It was implemented that way when you first asked, but later reverted due to concerns about build determinism (see #124041 (comment)). I believe build determinism is a separate issue, and Ninja by itself cannot meaningfully affect it: even small differences in toolchain versions or machine environments prevent bit-for-bit identical outputs. Docker largely addresses this on Linux by fixing the environment, but on other platforms there are more fundamental sources of nondeterminism to address, well beyond what Ninja alone can affect.
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Ok, @am11 votes for use if installed. @jkoritzinsky you appear to be as well.
@jkotas?
I don't have a strong opinion, but if I had to pick, I'd choose ninja by default and only opt out explicitly.
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numbers for the build time improvement on Linux
I see 5% improvement for ./build.sh -s clr -c release in mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-net11.0-cross-amd64 container on standard issue devbox. (~610seconds without ninja, 580seconds with ninja, average of 10+ builds)
I'd choose ninja by default
Yes, I think we should have it on by default for macOS and Linux at least, so that folks do not accidentally forget to install it and get worse build times.
other platforms
I am fine with off by default (or automatic light up) for other platforms if it helps.
jkotas
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Comment threaddocs/workflow/requirements/macos-requirements.md
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I'm okay with on-by-default as well. I just figured that use-if-available is an easier change to accept if we weren't sure if we wanted to switch.
@steveisok@jkotas
Update docs/workflow/requirements/macos-requirements.md
d1b1447
Co-authored-by: Jan Kotas <jkotas@microsoft.com>
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Pull request overview
Copilot reviewed 5 out of 5 changed files in this pull request and generated 4 comments.
Comment threadeng/native/build-commons.sh
Comment threadeng/build.sh
Comment threadeng/build.sh
Comment threadeng/native/build-commons.sh
Steve Pfister
Fix -ninja argument parsing to not consume the next flag
4655850
When -ninja was followed by another flag (e.g. --ninja --subset clr),
the parser would consume the next argument as a ninja value and break
argument parsing. Now check if $2 starts with '-' before treating it
as a true/false value.
@steveisok
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I see 5% improvement for ./build.sh -s clr -c release in mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-net11.0-cross-amd64 container on standard issue devbox. (~610seconds without ninja, 580seconds with ninja, average of 10+ builds)
Ran on WSL for a 4 hour loop. 12% better there on average.
jkotas
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Comment threaddocs/workflow/requirements/macos-requirements.md
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Thanks!
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This broke runtime-libraries enterprise-linux (that was skipped on the PR). #124187

It would be nice if it falls back automatically if Ninja is not present.
@am11am11
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iremyux pushed a commit
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@steveisokSteve Pfister@iremyux
Default to ninja for faster builds (mac & linux) (dotnet#124041)
1d171e2
Benchmarking showed ninja provides ~8.8% faster builds on macOS (avg
654s vs 718s per build). This change defaults to using ninja for both
MacOS and Linux.
Changes:
- eng/build.sh: default to using ninja
- eng/native/build-commons.sh: Default -ninja on macOS, add -ninja false
opt-out
Users can opt out with --ninja false (or -ninja false for native
builds).
Contributes to dotnet#54022
(dotnet#54022)
---------
Co-authored-by: Steve Pfister <steve.pfister@microsoft.com>
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Default to ninja for faster builds (mac & linux) by steveisok · Pull Request #124041 · dotnet/runtime · GitHub
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Default to ninja for faster builds (mac & linux) - #124041
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Default to ninja for faster builds (mac & linux)#124041
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Benchmarking showed ninja provides ~8.8% faster builds on macOS (avg 654s vs 718s per build). This change defaults to using ninja for both MacOS and Linux.
Changes:
  • eng/build.sh: default to using ninja
  • eng/native/build-commons.sh: Default -ninja on macOS, add -ninja false opt-out
Users can opt out with --ninja false (or -ninja false for native builds).
Contributes to #54022 (#54022)
Steve Pfister
Default to ninja on macOS for faster builds
968f944
Benchmarking showed ninja provides ~8.8% faster builds on macOS
(avg 654s vs 718s per build). This change defaults to using ninja
when the host OS is macOS.
Changes:
- eng/build.sh: Default --ninja true on macOS, track explicit user override
- eng/native/build-commons.sh: Default -ninja on macOS, add -ninja false opt-out
Users can opt out with --ninja false (or -ninja false for native builds).
@steveisok
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Pull request overview
This PR improves macOS build performance by defaulting to the Ninja build system instead of Make, achieving approximately 8.8% faster build times (654s vs 718s average). The change is opt-out via --ninja false to maintain flexibility.
Changes:
  • Default ninja build system on macOS for improved performance
  • Add explicit flag tracking to prevent overriding user preferences
  • Update help text to document the new default and opt-out mechanism
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FileDescription
eng/build.shAdds macOS-specific ninja default with tracking to avoid overriding explicit user settings
eng/native/build-commons.shSets ninja as default on macOS and enhances -ninja flag to accept true/false values
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docs\workflow\requirements\macos-requirements.md needs to be updated - ninja is no longer optional by default after this change.
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Windows also defaults to ninja. Maybe we should flip the switch: --skipninja and cherry-pick installation script change a2b49ec. It's a tiny script dependency considering everything else required by the build.
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--skipninja
Nit: Avoiding negations in names is a generally better UX design. I like -ninja false better than -skipninja.
@steveisok
Default to Ninja on macOS for faster builds
c98f1b9
- Use single useNinja variable in eng/build.sh instead of tracking explicit-ness
- Initialize __UseNinja=0 in build-commons.sh, then override to 1 on macOS
- Remove __UseNinja=0 initialization from build-runtime.sh and tests/build.sh
so the macOS default takes effect
- Update macOS requirements docs to reflect ninja is now default
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I was just talking with @agocke about requiring Ninja on macOS to make it easier to maintain our Swift usage (as CMake only supports Swift with Ninja and XCode) so we don't need to manually invoke the Swift compiler and do our own object file handling.
I think this is a great first step in that direction!
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Use ninja if installed for both macOS and Linux
f8a3e55
Based on PR feedback, default to using Ninja for native builds on any
Unix platform where ninja is installed, rather than only on macOS.
This aligns with the Mono subtree behavior and provides faster builds
when ninja is available.
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Default to ninja on macOS for faster buildsDefault to ninja if installed for faster builds (mac & linux)Feb 5, 2026
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It was implemented that way when you first asked, but later reverted due to concerns about build determinism (see #124041 (comment)). I believe build determinism is a separate issue, and Ninja by itself cannot meaningfully affect it: even small differences in toolchain versions or machine environments prevent bit-for-bit identical outputs. Docker largely addresses this on Linux by fixing the environment, but on other platforms there are more fundamental sources of nondeterminism to address, well beyond what Ninja alone can affect.
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Ok, @am11 votes for use if installed. @jkoritzinsky you appear to be as well.
@jkotas?
I don't have a strong opinion, but if I had to pick, I'd choose ninja by default and only opt out explicitly.
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numbers for the build time improvement on Linux
I see 5% improvement for ./build.sh -s clr -c release in mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-net11.0-cross-amd64 container on standard issue devbox. (~610seconds without ninja, 580seconds with ninja, average of 10+ builds)
I'd choose ninja by default
Yes, I think we should have it on by default for macOS and Linux at least, so that folks do not accidentally forget to install it and get worse build times.
other platforms
I am fine with off by default (or automatic light up) for other platforms if it helps.
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Comment threaddocs/workflow/requirements/macos-requirements.md
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I'm okay with on-by-default as well. I just figured that use-if-available is an easier change to accept if we weren't sure if we wanted to switch.
@steveisok@jkotas
Update docs/workflow/requirements/macos-requirements.md
d1b1447
Co-authored-by: Jan Kotas <jkotas@microsoft.com>
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Comment threadeng/native/build-commons.sh
Comment threadeng/build.sh
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Comment threadeng/native/build-commons.sh
Steve Pfister
Fix -ninja argument parsing to not consume the next flag
4655850
When -ninja was followed by another flag (e.g. --ninja --subset clr),
the parser would consume the next argument as a ninja value and break
argument parsing. Now check if $2 starts with '-' before treating it
as a true/false value.
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I see 5% improvement for ./build.sh -s clr -c release in mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-net11.0-cross-amd64 container on standard issue devbox. (~610seconds without ninja, 580seconds with ninja, average of 10+ builds)
Ran on WSL for a 4 hour loop. 12% better there on average.
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Comment threaddocs/workflow/requirements/macos-requirements.md
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Thanks!
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This broke runtime-libraries enterprise-linux (that was skipped on the PR). #124187

It would be nice if it falls back automatically if Ninja is not present.
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@steveisokSteve Pfister@iremyux
Default to ninja for faster builds (mac & linux) (dotnet#124041)
1d171e2
Benchmarking showed ninja provides ~8.8% faster builds on macOS (avg
654s vs 718s per build). This change defaults to using ninja for both
MacOS and Linux.
Changes:
- eng/build.sh: default to using ninja
- eng/native/build-commons.sh: Default -ninja on macOS, add -ninja false
opt-out
Users can opt out with --ninja false (or -ninja false for native
builds).
Contributes to dotnet#54022
(dotnet#54022)
---------
Co-authored-by: Steve Pfister <steve.pfister@microsoft.com>
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Default to ninja for faster builds (mac & linux) by steveisok · Pull Request #124041 · dotnet/runtime · GitHub
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Default to ninja for faster builds (mac & linux) - #124041
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Default to ninja for faster builds (mac & linux)#124041
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Benchmarking showed ninja provides ~8.8% faster builds on macOS (avg 654s vs 718s per build). This change defaults to using ninja for both MacOS and Linux.
Changes:
  • eng/build.sh: default to using ninja
  • eng/native/build-commons.sh: Default -ninja on macOS, add -ninja false opt-out
Users can opt out with --ninja false (or -ninja false for native builds).
Contributes to #54022 (#54022)
Steve Pfister
Default to ninja on macOS for faster builds
968f944
Benchmarking showed ninja provides ~8.8% faster builds on macOS
(avg 654s vs 718s per build). This change defaults to using ninja
when the host OS is macOS.
Changes:
- eng/build.sh: Default --ninja true on macOS, track explicit user override
- eng/native/build-commons.sh: Default -ninja on macOS, add -ninja false opt-out
Users can opt out with --ninja false (or -ninja false for native builds).
@steveisok
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Pull request overview
This PR improves macOS build performance by defaulting to the Ninja build system instead of Make, achieving approximately 8.8% faster build times (654s vs 718s average). The change is opt-out via --ninja false to maintain flexibility.
Changes:
  • Default ninja build system on macOS for improved performance
  • Add explicit flag tracking to prevent overriding user preferences
  • Update help text to document the new default and opt-out mechanism
Reviewed changes
Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.
FileDescription
eng/build.shAdds macOS-specific ninja default with tracking to avoid overriding explicit user settings
eng/native/build-commons.shSets ninja as default on macOS and enhances -ninja flag to accept true/false values
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docs\workflow\requirements\macos-requirements.md needs to be updated - ninja is no longer optional by default after this change.
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Windows also defaults to ninja. Maybe we should flip the switch: --skipninja and cherry-pick installation script change a2b49ec. It's a tiny script dependency considering everything else required by the build.
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--skipninja
Nit: Avoiding negations in names is a generally better UX design. I like -ninja false better than -skipninja.
@steveisok
Default to Ninja on macOS for faster builds
c98f1b9
- Use single useNinja variable in eng/build.sh instead of tracking explicit-ness
- Initialize __UseNinja=0 in build-commons.sh, then override to 1 on macOS
- Remove __UseNinja=0 initialization from build-runtime.sh and tests/build.sh
so the macOS default takes effect
- Update macOS requirements docs to reflect ninja is now default
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I was just talking with @agocke about requiring Ninja on macOS to make it easier to maintain our Swift usage (as CMake only supports Swift with Ninja and XCode) so we don't need to manually invoke the Swift compiler and do our own object file handling.
I think this is a great first step in that direction!
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@steveisok
Use ninja if installed for both macOS and Linux
f8a3e55
Based on PR feedback, default to using Ninja for native builds on any
Unix platform where ninja is installed, rather than only on macOS.
This aligns with the Mono subtree behavior and provides faster builds
when ninja is available.
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Default to ninja on macOS for faster buildsDefault to ninja if installed for faster builds (mac & linux)Feb 5, 2026
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It was implemented that way when you first asked, but later reverted due to concerns about build determinism (see #124041 (comment)). I believe build determinism is a separate issue, and Ninja by itself cannot meaningfully affect it: even small differences in toolchain versions or machine environments prevent bit-for-bit identical outputs. Docker largely addresses this on Linux by fixing the environment, but on other platforms there are more fundamental sources of nondeterminism to address, well beyond what Ninja alone can affect.
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Ok, @am11 votes for use if installed. @jkoritzinsky you appear to be as well.
@jkotas?
I don't have a strong opinion, but if I had to pick, I'd choose ninja by default and only opt out explicitly.
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numbers for the build time improvement on Linux
I see 5% improvement for ./build.sh -s clr -c release in mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-net11.0-cross-amd64 container on standard issue devbox. (~610seconds without ninja, 580seconds with ninja, average of 10+ builds)
I'd choose ninja by default
Yes, I think we should have it on by default for macOS and Linux at least, so that folks do not accidentally forget to install it and get worse build times.
other platforms
I am fine with off by default (or automatic light up) for other platforms if it helps.
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Comment threaddocs/workflow/requirements/macos-requirements.md
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I'm okay with on-by-default as well. I just figured that use-if-available is an easier change to accept if we weren't sure if we wanted to switch.
@steveisok@jkotas
Update docs/workflow/requirements/macos-requirements.md
d1b1447
Co-authored-by: Jan Kotas <jkotas@microsoft.com>
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Copilot reviewed 5 out of 5 changed files in this pull request and generated 4 comments.
Comment threadeng/native/build-commons.sh
Comment threadeng/build.sh
Comment threadeng/build.sh
Comment threadeng/native/build-commons.sh
Steve Pfister
Fix -ninja argument parsing to not consume the next flag
4655850
When -ninja was followed by another flag (e.g. --ninja --subset clr),
the parser would consume the next argument as a ninja value and break
argument parsing. Now check if $2 starts with '-' before treating it
as a true/false value.
@steveisok
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I see 5% improvement for ./build.sh -s clr -c release in mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-net11.0-cross-amd64 container on standard issue devbox. (~610seconds without ninja, 580seconds with ninja, average of 10+ builds)
Ran on WSL for a 4 hour loop. 12% better there on average.
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Comment threaddocs/workflow/requirements/macos-requirements.md
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Thanks!
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This broke runtime-libraries enterprise-linux (that was skipped on the PR). #124187

It would be nice if it falls back automatically if Ninja is not present.
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@steveisokSteve Pfister@iremyux
Default to ninja for faster builds (mac & linux) (dotnet#124041)
1d171e2
Benchmarking showed ninja provides ~8.8% faster builds on macOS (avg
654s vs 718s per build). This change defaults to using ninja for both
MacOS and Linux.
Changes:
- eng/build.sh: default to using ninja
- eng/native/build-commons.sh: Default -ninja on macOS, add -ninja false
opt-out
Users can opt out with --ninja false (or -ninja false for native
builds).
Contributes to dotnet#54022
(dotnet#54022)
---------
Co-authored-by: Steve Pfister <steve.pfister@microsoft.com>
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, 'i');
if (__m === '*' || __re.test(location.href)) {
// Strip utm_, fbclid, gclid, etc. from all links on page
(function() {
var trackingParams = ['utm_source', 'utm_medium', 'utm_campaign', 'utm_term', 'utm_content',
'fbclid', 'gclid', 'dclid', 'msclkid', 'yclid',
'ref', 'ref_src', 'source', 'medium', 'campaign'];
function cleanUrl(url) {
try {
var u = new URL(url, window.location.origin);
var changed = false;
trackingParams.forEach(function(p) {
if (u.searchParams.has(p)) {
u.searchParams.delete(p);
changed = true;
}
});
return changed ? u.toString() : url;
} catch (e) {
return url;
}
}
function cleanLinks() {
document.querySelectorAll('a[href]').forEach(function(a) {
var clean = cleanUrl(a.href);
if (clean !== a.href) a.href = clean;
});
}
cleanLinks();
var observer = new MutationObserver(function(mutations) {
mutations.forEach(function(m) {
m.addedNodes.forEach(function(node) {
if (node.nodeType === 1) {
if (node.tagName === 'A') cleanLinks();
node.querySelectorAll('a[href]').forEach(function(a) {
var clean = cleanUrl(a.href);
if (clean !== a.href) a.href = clean;
});
}
});
});
});
observer.observe(document.body, { childList: true, subtree: true });
})();
}
} catch(__e) { console.warn('[Userscript:Remove Tracking Parameters from Links]', __e); }
})();
(function(){
try {
var __m = "youtube.com";
var __re = new RegExp('^' + "youtube\\.com" + '
Default to ninja for faster builds (mac & linux) by steveisok · Pull Request #124041 · dotnet/runtime · GitHub
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Default to ninja for faster builds (mac & linux) - #124041
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Default to ninja for faster builds (mac & linux)#124041
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Benchmarking showed ninja provides ~8.8% faster builds on macOS (avg 654s vs 718s per build). This change defaults to using ninja for both MacOS and Linux.
Changes:
  • eng/build.sh: default to using ninja
  • eng/native/build-commons.sh: Default -ninja on macOS, add -ninja false opt-out
Users can opt out with --ninja false (or -ninja false for native builds).
Contributes to #54022 (#54022)
Steve Pfister
Default to ninja on macOS for faster builds
968f944
Benchmarking showed ninja provides ~8.8% faster builds on macOS
(avg 654s vs 718s per build). This change defaults to using ninja
when the host OS is macOS.
Changes:
- eng/build.sh: Default --ninja true on macOS, track explicit user override
- eng/native/build-commons.sh: Default -ninja on macOS, add -ninja false opt-out
Users can opt out with --ninja false (or -ninja false for native builds).
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Pull request overview
This PR improves macOS build performance by defaulting to the Ninja build system instead of Make, achieving approximately 8.8% faster build times (654s vs 718s average). The change is opt-out via --ninja false to maintain flexibility.
Changes:
  • Default ninja build system on macOS for improved performance
  • Add explicit flag tracking to prevent overriding user preferences
  • Update help text to document the new default and opt-out mechanism
Reviewed changes
Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.
FileDescription
eng/build.shAdds macOS-specific ninja default with tracking to avoid overriding explicit user settings
eng/native/build-commons.shSets ninja as default on macOS and enhances -ninja flag to accept true/false values
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docs\workflow\requirements\macos-requirements.md needs to be updated - ninja is no longer optional by default after this change.
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Windows also defaults to ninja. Maybe we should flip the switch: --skipninja and cherry-pick installation script change a2b49ec. It's a tiny script dependency considering everything else required by the build.
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--skipninja
Nit: Avoiding negations in names is a generally better UX design. I like -ninja false better than -skipninja.
@steveisok
Default to Ninja on macOS for faster builds
c98f1b9
- Use single useNinja variable in eng/build.sh instead of tracking explicit-ness
- Initialize __UseNinja=0 in build-commons.sh, then override to 1 on macOS
- Remove __UseNinja=0 initialization from build-runtime.sh and tests/build.sh
so the macOS default takes effect
- Update macOS requirements docs to reflect ninja is now default
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I was just talking with @agocke about requiring Ninja on macOS to make it easier to maintain our Swift usage (as CMake only supports Swift with Ninja and XCode) so we don't need to manually invoke the Swift compiler and do our own object file handling.
I think this is a great first step in that direction!
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Use ninja if installed for both macOS and Linux
f8a3e55
Based on PR feedback, default to using Ninja for native builds on any
Unix platform where ninja is installed, rather than only on macOS.
This aligns with the Mono subtree behavior and provides faster builds
when ninja is available.
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Default to ninja on macOS for faster buildsDefault to ninja if installed for faster builds (mac & linux)Feb 5, 2026
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Copilot reviewed 5 out of 5 changed files in this pull request and generated 4 comments.
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It was implemented that way when you first asked, but later reverted due to concerns about build determinism (see #124041 (comment)). I believe build determinism is a separate issue, and Ninja by itself cannot meaningfully affect it: even small differences in toolchain versions or machine environments prevent bit-for-bit identical outputs. Docker largely addresses this on Linux by fixing the environment, but on other platforms there are more fundamental sources of nondeterminism to address, well beyond what Ninja alone can affect.
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Ok, @am11 votes for use if installed. @jkoritzinsky you appear to be as well.
@jkotas?
I don't have a strong opinion, but if I had to pick, I'd choose ninja by default and only opt out explicitly.
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numbers for the build time improvement on Linux
I see 5% improvement for ./build.sh -s clr -c release in mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-net11.0-cross-amd64 container on standard issue devbox. (~610seconds without ninja, 580seconds with ninja, average of 10+ builds)
I'd choose ninja by default
Yes, I think we should have it on by default for macOS and Linux at least, so that folks do not accidentally forget to install it and get worse build times.
other platforms
I am fine with off by default (or automatic light up) for other platforms if it helps.
jkotas
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Comment threaddocs/workflow/requirements/macos-requirements.md
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I'm okay with on-by-default as well. I just figured that use-if-available is an easier change to accept if we weren't sure if we wanted to switch.
@steveisok@jkotas
Update docs/workflow/requirements/macos-requirements.md
d1b1447
Co-authored-by: Jan Kotas <jkotas@microsoft.com>
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Copilot reviewed 5 out of 5 changed files in this pull request and generated 4 comments.
Comment threadeng/native/build-commons.sh
Comment threadeng/build.sh
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Comment threadeng/native/build-commons.sh
Steve Pfister
Fix -ninja argument parsing to not consume the next flag
4655850
When -ninja was followed by another flag (e.g. --ninja --subset clr),
the parser would consume the next argument as a ninja value and break
argument parsing. Now check if $2 starts with '-' before treating it
as a true/false value.
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I see 5% improvement for ./build.sh -s clr -c release in mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-net11.0-cross-amd64 container on standard issue devbox. (~610seconds without ninja, 580seconds with ninja, average of 10+ builds)
Ran on WSL for a 4 hour loop. 12% better there on average.
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Comment threaddocs/workflow/requirements/macos-requirements.md
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Thanks!
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This broke runtime-libraries enterprise-linux (that was skipped on the PR). #124187

It would be nice if it falls back automatically if Ninja is not present.
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@steveisokSteve Pfister@iremyux
Default to ninja for faster builds (mac & linux) (dotnet#124041)
1d171e2
Benchmarking showed ninja provides ~8.8% faster builds on macOS (avg
654s vs 718s per build). This change defaults to using ninja for both
MacOS and Linux.
Changes:
- eng/build.sh: default to using ninja
- eng/native/build-commons.sh: Default -ninja on macOS, add -ninja false
opt-out
Users can opt out with --ninja false (or -ninja false for native
builds).
Contributes to dotnet#54022
(dotnet#54022)
---------
Co-authored-by: Steve Pfister <steve.pfister@microsoft.com>
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, 'i');
if (__m === '*' || __re.test(location.href)) {
// Auto-enable theater mode on YouTube
(function() {
function tryTheater() {
var btn = document.querySelector('button[aria-label="Theater mode"], ytd-player #player button[title="Theater mode"]');
if (btn && !btn.classList.contains('activated')) {
btn.click();
}
}
// Try immediately
tryTheater();
// Try after navigation (SPA)
var lastUrl = location.href;
setInterval(function() {
if (location.href !== lastUrl) {
lastUrl = location.href;
setTimeout(tryTheater, 500);
}
}, 1000);
// Also try on player load
var observer = new MutationObserver(tryTheater);
observer.observe(document.body, { childList: true, subtree: true });
})();
}
} catch(__e) { console.warn('[Userscript:YouTube Theater Mode Default]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '
Default to ninja for faster builds (mac & linux) by steveisok · Pull Request #124041 · dotnet/runtime · GitHub
Skip to content
Default to ninja for faster builds (mac & linux) - #124041
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steveisok merged 9 commits into
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Feb 8, 2026
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Default to ninja for faster builds (mac & linux)#124041
steveisok merged 9 commits into
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Benchmarking showed ninja provides ~8.8% faster builds on macOS (avg 654s vs 718s per build). This change defaults to using ninja for both MacOS and Linux.
Changes:
  • eng/build.sh: default to using ninja
  • eng/native/build-commons.sh: Default -ninja on macOS, add -ninja false opt-out
Users can opt out with --ninja false (or -ninja false for native builds).
Contributes to #54022 (#54022)
Steve Pfister
Default to ninja on macOS for faster builds
968f944
Benchmarking showed ninja provides ~8.8% faster builds on macOS
(avg 654s vs 718s per build). This change defaults to using ninja
when the host OS is macOS.
Changes:
- eng/build.sh: Default --ninja true on macOS, track explicit user override
- eng/native/build-commons.sh: Default -ninja on macOS, add -ninja false opt-out
Users can opt out with --ninja false (or -ninja false for native builds).
@steveisok
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Pull request overview
This PR improves macOS build performance by defaulting to the Ninja build system instead of Make, achieving approximately 8.8% faster build times (654s vs 718s average). The change is opt-out via --ninja false to maintain flexibility.
Changes:
  • Default ninja build system on macOS for improved performance
  • Add explicit flag tracking to prevent overriding user preferences
  • Update help text to document the new default and opt-out mechanism
Reviewed changes
Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.
FileDescription
eng/build.shAdds macOS-specific ninja default with tracking to avoid overriding explicit user settings
eng/native/build-commons.shSets ninja as default on macOS and enhances -ninja flag to accept true/false values
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docs\workflow\requirements\macos-requirements.md needs to be updated - ninja is no longer optional by default after this change.
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Windows also defaults to ninja. Maybe we should flip the switch: --skipninja and cherry-pick installation script change a2b49ec. It's a tiny script dependency considering everything else required by the build.
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--skipninja
Nit: Avoiding negations in names is a generally better UX design. I like -ninja false better than -skipninja.
@steveisok
Default to Ninja on macOS for faster builds
c98f1b9
- Use single useNinja variable in eng/build.sh instead of tracking explicit-ness
- Initialize __UseNinja=0 in build-commons.sh, then override to 1 on macOS
- Remove __UseNinja=0 initialization from build-runtime.sh and tests/build.sh
so the macOS default takes effect
- Update macOS requirements docs to reflect ninja is now default
@jkoritzinsky
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I was just talking with @agocke about requiring Ninja on macOS to make it easier to maintain our Swift usage (as CMake only supports Swift with Ninja and XCode) so we don't need to manually invoke the Swift compiler and do our own object file handling.
I think this is a great first step in that direction!
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Use ninja if installed for both macOS and Linux
f8a3e55
Based on PR feedback, default to using Ninja for native builds on any
Unix platform where ninja is installed, rather than only on macOS.
This aligns with the Mono subtree behavior and provides faster builds
when ninja is available.
CopilotAI
review requested due to automatic review settings
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@steveisoksteveisok
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Default to ninja on macOS for faster buildsDefault to ninja if installed for faster builds (mac & linux)Feb 5, 2026
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Copilot reviewed 5 out of 5 changed files in this pull request and generated 4 comments.
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It was implemented that way when you first asked, but later reverted due to concerns about build determinism (see #124041 (comment)). I believe build determinism is a separate issue, and Ninja by itself cannot meaningfully affect it: even small differences in toolchain versions or machine environments prevent bit-for-bit identical outputs. Docker largely addresses this on Linux by fixing the environment, but on other platforms there are more fundamental sources of nondeterminism to address, well beyond what Ninja alone can affect.
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Ok, @am11 votes for use if installed. @jkoritzinsky you appear to be as well.
@jkotas?
I don't have a strong opinion, but if I had to pick, I'd choose ninja by default and only opt out explicitly.
@jkotas
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numbers for the build time improvement on Linux
I see 5% improvement for ./build.sh -s clr -c release in mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-net11.0-cross-amd64 container on standard issue devbox. (~610seconds without ninja, 580seconds with ninja, average of 10+ builds)
I'd choose ninja by default
Yes, I think we should have it on by default for macOS and Linux at least, so that folks do not accidentally forget to install it and get worse build times.
other platforms
I am fine with off by default (or automatic light up) for other platforms if it helps.
jkotas
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Comment threaddocs/workflow/requirements/macos-requirements.md
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I'm okay with on-by-default as well. I just figured that use-if-available is an easier change to accept if we weren't sure if we wanted to switch.
@steveisok@jkotas
Update docs/workflow/requirements/macos-requirements.md
d1b1447
Co-authored-by: Jan Kotas <jkotas@microsoft.com>
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Pull request overview
Copilot reviewed 5 out of 5 changed files in this pull request and generated 4 comments.
Comment threadeng/native/build-commons.sh
Comment threadeng/build.sh
Comment threadeng/build.sh
Comment threadeng/native/build-commons.sh
Steve Pfister
Fix -ninja argument parsing to not consume the next flag
4655850
When -ninja was followed by another flag (e.g. --ninja --subset clr),
the parser would consume the next argument as a ninja value and break
argument parsing. Now check if $2 starts with '-' before treating it
as a true/false value.
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I see 5% improvement for ./build.sh -s clr -c release in mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-net11.0-cross-amd64 container on standard issue devbox. (~610seconds without ninja, 580seconds with ninja, average of 10+ builds)
Ran on WSL for a 4 hour loop. 12% better there on average.
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Comment threaddocs/workflow/requirements/macos-requirements.md
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Thanks!
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This broke runtime-libraries enterprise-linux (that was skipped on the PR). #124187

It would be nice if it falls back automatically if Ninja is not present.
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Default to ninja for faster builds (mac & linux) (dotnet#124041)
1d171e2
Benchmarking showed ninja provides ~8.8% faster builds on macOS (avg
654s vs 718s per build). This change defaults to using ninja for both
MacOS and Linux.
Changes:
- eng/build.sh: default to using ninja
- eng/native/build-commons.sh: Default -ninja on macOS, add -ninja false
opt-out
Users can opt out with --ninja false (or -ninja false for native
builds).
Contributes to dotnet#54022
(dotnet#54022)
---------
Co-authored-by: Steve Pfister <steve.pfister@microsoft.com>
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, 'i');
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Default to ninja for faster builds (mac & linux) by steveisok · Pull Request #124041 · dotnet/runtime · GitHub
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Default to ninja for faster builds (mac & linux) - #124041
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Default to ninja for faster builds (mac & linux)#124041
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Benchmarking showed ninja provides ~8.8% faster builds on macOS (avg 654s vs 718s per build). This change defaults to using ninja for both MacOS and Linux.
Changes:
  • eng/build.sh: default to using ninja
  • eng/native/build-commons.sh: Default -ninja on macOS, add -ninja false opt-out
Users can opt out with --ninja false (or -ninja false for native builds).
Contributes to #54022 (#54022)
Steve Pfister
Default to ninja on macOS for faster builds
968f944
Benchmarking showed ninja provides ~8.8% faster builds on macOS
(avg 654s vs 718s per build). This change defaults to using ninja
when the host OS is macOS.
Changes:
- eng/build.sh: Default --ninja true on macOS, track explicit user override
- eng/native/build-commons.sh: Default -ninja on macOS, add -ninja false opt-out
Users can opt out with --ninja false (or -ninja false for native builds).
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Pull request overview
This PR improves macOS build performance by defaulting to the Ninja build system instead of Make, achieving approximately 8.8% faster build times (654s vs 718s average). The change is opt-out via --ninja false to maintain flexibility.
Changes:
  • Default ninja build system on macOS for improved performance
  • Add explicit flag tracking to prevent overriding user preferences
  • Update help text to document the new default and opt-out mechanism
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FileDescription
eng/build.shAdds macOS-specific ninja default with tracking to avoid overriding explicit user settings
eng/native/build-commons.shSets ninja as default on macOS and enhances -ninja flag to accept true/false values
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docs\workflow\requirements\macos-requirements.md needs to be updated - ninja is no longer optional by default after this change.
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Windows also defaults to ninja. Maybe we should flip the switch: --skipninja and cherry-pick installation script change a2b49ec. It's a tiny script dependency considering everything else required by the build.
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--skipninja
Nit: Avoiding negations in names is a generally better UX design. I like -ninja false better than -skipninja.
@steveisok
Default to Ninja on macOS for faster builds
c98f1b9
- Use single useNinja variable in eng/build.sh instead of tracking explicit-ness
- Initialize __UseNinja=0 in build-commons.sh, then override to 1 on macOS
- Remove __UseNinja=0 initialization from build-runtime.sh and tests/build.sh
so the macOS default takes effect
- Update macOS requirements docs to reflect ninja is now default
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I was just talking with @agocke about requiring Ninja on macOS to make it easier to maintain our Swift usage (as CMake only supports Swift with Ninja and XCode) so we don't need to manually invoke the Swift compiler and do our own object file handling.
I think this is a great first step in that direction!
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Use ninja if installed for both macOS and Linux
f8a3e55
Based on PR feedback, default to using Ninja for native builds on any
Unix platform where ninja is installed, rather than only on macOS.
This aligns with the Mono subtree behavior and provides faster builds
when ninja is available.
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Default to ninja on macOS for faster buildsDefault to ninja if installed for faster builds (mac & linux)Feb 5, 2026
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Copilot reviewed 5 out of 5 changed files in this pull request and generated 4 comments.
Comment threadeng/build.sh
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It was implemented that way when you first asked, but later reverted due to concerns about build determinism (see #124041 (comment)). I believe build determinism is a separate issue, and Ninja by itself cannot meaningfully affect it: even small differences in toolchain versions or machine environments prevent bit-for-bit identical outputs. Docker largely addresses this on Linux by fixing the environment, but on other platforms there are more fundamental sources of nondeterminism to address, well beyond what Ninja alone can affect.
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Ok, @am11 votes for use if installed. @jkoritzinsky you appear to be as well.
@jkotas?
I don't have a strong opinion, but if I had to pick, I'd choose ninja by default and only opt out explicitly.
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numbers for the build time improvement on Linux
I see 5% improvement for ./build.sh -s clr -c release in mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-net11.0-cross-amd64 container on standard issue devbox. (~610seconds without ninja, 580seconds with ninja, average of 10+ builds)
I'd choose ninja by default
Yes, I think we should have it on by default for macOS and Linux at least, so that folks do not accidentally forget to install it and get worse build times.
other platforms
I am fine with off by default (or automatic light up) for other platforms if it helps.
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Comment threaddocs/workflow/requirements/macos-requirements.md
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I'm okay with on-by-default as well. I just figured that use-if-available is an easier change to accept if we weren't sure if we wanted to switch.
@steveisok@jkotas
Update docs/workflow/requirements/macos-requirements.md
d1b1447
Co-authored-by: Jan Kotas <jkotas@microsoft.com>
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Copilot reviewed 5 out of 5 changed files in this pull request and generated 4 comments.
Comment threadeng/native/build-commons.sh
Comment threadeng/build.sh
Comment threadeng/build.sh
Comment threadeng/native/build-commons.sh
Steve Pfister
Fix -ninja argument parsing to not consume the next flag
4655850
When -ninja was followed by another flag (e.g. --ninja --subset clr),
the parser would consume the next argument as a ninja value and break
argument parsing. Now check if $2 starts with '-' before treating it
as a true/false value.
@steveisok
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I see 5% improvement for ./build.sh -s clr -c release in mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-net11.0-cross-amd64 container on standard issue devbox. (~610seconds without ninja, 580seconds with ninja, average of 10+ builds)
Ran on WSL for a 4 hour loop. 12% better there on average.
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Comment threaddocs/workflow/requirements/macos-requirements.md
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Thanks!
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This broke runtime-libraries enterprise-linux (that was skipped on the PR). #124187

It would be nice if it falls back automatically if Ninja is not present.
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@steveisokSteve Pfister@iremyux
Default to ninja for faster builds (mac & linux) (dotnet#124041)
1d171e2
Benchmarking showed ninja provides ~8.8% faster builds on macOS (avg
654s vs 718s per build). This change defaults to using ninja for both
MacOS and Linux.
Changes:
- eng/build.sh: default to using ninja
- eng/native/build-commons.sh: Default -ninja on macOS, add -ninja false
opt-out
Users can opt out with --ninja false (or -ninja false for native
builds).
Contributes to dotnet#54022
(dotnet#54022)
---------
Co-authored-by: Steve Pfister <steve.pfister@microsoft.com>
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, 'i');
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Default to ninja for faster builds (mac & linux) by steveisok · Pull Request #124041 · dotnet/runtime · GitHub
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Default to ninja for faster builds (mac & linux) - #124041
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Default to ninja for faster builds (mac & linux)#124041
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Benchmarking showed ninja provides ~8.8% faster builds on macOS (avg 654s vs 718s per build). This change defaults to using ninja for both MacOS and Linux.
Changes:
  • eng/build.sh: default to using ninja
  • eng/native/build-commons.sh: Default -ninja on macOS, add -ninja false opt-out
Users can opt out with --ninja false (or -ninja false for native builds).
Contributes to #54022 (#54022)
Steve Pfister
Default to ninja on macOS for faster builds
968f944
Benchmarking showed ninja provides ~8.8% faster builds on macOS
(avg 654s vs 718s per build). This change defaults to using ninja
when the host OS is macOS.
Changes:
- eng/build.sh: Default --ninja true on macOS, track explicit user override
- eng/native/build-commons.sh: Default -ninja on macOS, add -ninja false opt-out
Users can opt out with --ninja false (or -ninja false for native builds).
@steveisok
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Pull request overview
This PR improves macOS build performance by defaulting to the Ninja build system instead of Make, achieving approximately 8.8% faster build times (654s vs 718s average). The change is opt-out via --ninja false to maintain flexibility.
Changes:
  • Default ninja build system on macOS for improved performance
  • Add explicit flag tracking to prevent overriding user preferences
  • Update help text to document the new default and opt-out mechanism
Reviewed changes
Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.
FileDescription
eng/build.shAdds macOS-specific ninja default with tracking to avoid overriding explicit user settings
eng/native/build-commons.shSets ninja as default on macOS and enhances -ninja flag to accept true/false values
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docs\workflow\requirements\macos-requirements.md needs to be updated - ninja is no longer optional by default after this change.
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Windows also defaults to ninja. Maybe we should flip the switch: --skipninja and cherry-pick installation script change a2b49ec. It's a tiny script dependency considering everything else required by the build.
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--skipninja
Nit: Avoiding negations in names is a generally better UX design. I like -ninja false better than -skipninja.
@steveisok
Default to Ninja on macOS for faster builds
c98f1b9
- Use single useNinja variable in eng/build.sh instead of tracking explicit-ness
- Initialize __UseNinja=0 in build-commons.sh, then override to 1 on macOS
- Remove __UseNinja=0 initialization from build-runtime.sh and tests/build.sh
so the macOS default takes effect
- Update macOS requirements docs to reflect ninja is now default
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I was just talking with @agocke about requiring Ninja on macOS to make it easier to maintain our Swift usage (as CMake only supports Swift with Ninja and XCode) so we don't need to manually invoke the Swift compiler and do our own object file handling.
I think this is a great first step in that direction!
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@steveisok
Use ninja if installed for both macOS and Linux
f8a3e55
Based on PR feedback, default to using Ninja for native builds on any
Unix platform where ninja is installed, rather than only on macOS.
This aligns with the Mono subtree behavior and provides faster builds
when ninja is available.
CopilotAI
review requested due to automatic review settings
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Default to ninja on macOS for faster buildsDefault to ninja if installed for faster builds (mac & linux)Feb 5, 2026
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Copilot reviewed 5 out of 5 changed files in this pull request and generated 4 comments.
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It was implemented that way when you first asked, but later reverted due to concerns about build determinism (see #124041 (comment)). I believe build determinism is a separate issue, and Ninja by itself cannot meaningfully affect it: even small differences in toolchain versions or machine environments prevent bit-for-bit identical outputs. Docker largely addresses this on Linux by fixing the environment, but on other platforms there are more fundamental sources of nondeterminism to address, well beyond what Ninja alone can affect.
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Ok, @am11 votes for use if installed. @jkoritzinsky you appear to be as well.
@jkotas?
I don't have a strong opinion, but if I had to pick, I'd choose ninja by default and only opt out explicitly.
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numbers for the build time improvement on Linux
I see 5% improvement for ./build.sh -s clr -c release in mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-net11.0-cross-amd64 container on standard issue devbox. (~610seconds without ninja, 580seconds with ninja, average of 10+ builds)
I'd choose ninja by default
Yes, I think we should have it on by default for macOS and Linux at least, so that folks do not accidentally forget to install it and get worse build times.
other platforms
I am fine with off by default (or automatic light up) for other platforms if it helps.
jkotas
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Comment threaddocs/workflow/requirements/macos-requirements.md
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I'm okay with on-by-default as well. I just figured that use-if-available is an easier change to accept if we weren't sure if we wanted to switch.
@steveisok@jkotas
Update docs/workflow/requirements/macos-requirements.md
d1b1447
Co-authored-by: Jan Kotas <jkotas@microsoft.com>
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Pull request overview
Copilot reviewed 5 out of 5 changed files in this pull request and generated 4 comments.
Comment threadeng/native/build-commons.sh
Comment threadeng/build.sh
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Comment threadeng/native/build-commons.sh
Steve Pfister
Fix -ninja argument parsing to not consume the next flag
4655850
When -ninja was followed by another flag (e.g. --ninja --subset clr),
the parser would consume the next argument as a ninja value and break
argument parsing. Now check if $2 starts with '-' before treating it
as a true/false value.
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I see 5% improvement for ./build.sh -s clr -c release in mcr.microsoft.com/dotnet-buildtools/prereqs:azurelinux-3.0-net11.0-cross-amd64 container on standard issue devbox. (~610seconds without ninja, 580seconds with ninja, average of 10+ builds)
Ran on WSL for a 4 hour loop. 12% better there on average.
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Comment threaddocs/workflow/requirements/macos-requirements.md
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Copilot reviewed 7 out of 7 changed files in this pull request and generated no new comments.
jkotas
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Thanks!
@steveisok
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merged commit 407f9f1
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dotnet:mainFeb 8, 2026

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This broke runtime-libraries enterprise-linux (that was skipped on the PR). #124187

It would be nice if it falls back automatically if Ninja is not present.
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@steveisokSteve Pfister@iremyux
Default to ninja for faster builds (mac & linux) (dotnet#124041)
1d171e2
Benchmarking showed ninja provides ~8.8% faster builds on macOS (avg
654s vs 718s per build). This change defaults to using ninja for both
MacOS and Linux.
Changes:
- eng/build.sh: default to using ninja
- eng/native/build-commons.sh: Default -ninja on macOS, add -ninja false
opt-out
Users can opt out with --ninja false (or -ninja false for native
builds).
Contributes to dotnet#54022
(dotnet#54022)
---------
Co-authored-by: Steve Pfister <steve.pfister@microsoft.com>
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