[TrimmableTypeMap] Use Crc64 package naming by default with LowercaseCrc64 compatibility by Copilot · Pull Request #11193 · dotnet/android

Copilot · 2026-04-23T07:05:16Z

This updates trimmable type map generation to default to Crc64-based package naming for unregistered types, while preserving backwards compatibility for projects that explicitly set:

<AndroidPackageNamingPolicy>LowercaseCrc64</AndroidPackageNamingPolicy>

Package naming policy support in trimmable typemap
- Wired AndroidPackageNamingPolicy into trimmable typemap generation.
- Added policy-aware hashing:
  - Crc64 (trimmable default) → crc64... using System.IO.Hashing.Crc64 with length mixing
  - LowercaseCrc64 → crc64... using the existing legacy/custom CRC64 implementation for compatibility with previous naming
- Removed trimmable XxHash64 handling, as it no longer provides value for this path.
- Kept Mono.Android namespace-preserving behavior unchanged.
Default policy update
- Crc64 is now the default only for trimmable typemap generation.
- The global AndroidPackageNamingPolicy default remains LowercaseCrc64 for non-trimmable typemap paths.
Hashing implementation refactor
- Moved scanner hashing logic out of JavaPeerScanner into a dedicated static ScannerHashingHelper for easier focused testing.
- Added dedicated ScannerHashingHelper.ToCrc64() for System.IO.Hashing.Crc64.
- Updated UTF-8 buffer handling for the fast Crc64 path to use stackalloc with new byte[N] fallback for larger buffers (>256 bytes).
- Added length mixing (crc64 ^ byteLength) in ToCrc64() to avoid equal outputs for different-length all-zero inputs.
- Kept legacy CRC64 compatibility behavior intact.
Targeted test updates
- Updated scanner expectations for crc64 trimmable defaults.
- Added coverage to verify:
  - default Crc64 output,
  - legacy LowercaseCrc64 compatibility output.
- Removed XxHash64-specific scanner expectations.
- Kept fixed-vector tests for legacy CRC64 known input/output pairs to validate backward compatibility behavior.
- Converted Crc64 known-output validation into a [Theory] with multiple input/output vectors.
- Added a regression test to ensure different-length zero-byte inputs produce different Crc64 outputs.
Related plumbing updates
- Passed package naming policy through the trimmable typemap target/task into TrimmableTypeMapGenerator and scanner hashing logic.
- Merged latest main conflict changes so trimmable typemap generation keeps both package naming policy support and MaxArrayRank plumbing.

returnpackageNamingPolicyswitch{HashedPackageNamingPolicy.LowercaseCrc64=>"crc64"+ScannerHashingHelper.ToLegacyCrc64(ns,assemblyName),HashedPackageNamingPolicy.Crc64=>"crc64"+ScannerHashingHelper.ToCrc64(ns,assemblyName),
_ =>thrownewInvalidOperationException($"Unsupported package naming policy: {packageNamingPolicy}"),};

simonrozsival · 2026-04-23T09:25:13Z

@copilot I would prefer changing the prefix from crc64 to xx64 to reflect the change.

Copilot · 2026-04-23T09:57:50Z

@copilot I would prefer changing the prefix from crc64 to xx64 to reflect the change.

Updated in 1049678: auto-generated TrimmableTypeMap package names now use the xx64 prefix (with XxHash64), and related unit/integration test expectations were updated accordingly.

jonathanpeppers

Note that there is the property:

<AndroidPackageNamingPolicy>LowercaseCrc64</AndroidPackageNamingPolicy>

We will probably want to introduce a new one for XxHash64.

It is a slight breaking change, because people could have a hardcoded package name in a script for launching their main activity, etc.

So, I think what we did in some really old Xamarin.Android release, we changed the default but allowed projects to still use the old one.

simonrozsival · 2026-04-23T15:03:09Z

It is a slight breaking change, because people could have a hardcoded package name in a script for launching their main activity, etc.

So funny thing is that the CSC64 we have in our C++(or C#?) code and CSC64 that is in System.IO.Hashing produce different results. I decided to use the System.IO.Hashing one in the trimmable typemap so that would be a breaking change anyway. I will need to revisit this and try to make the LowercaseCrc64 option be consistent with previous naming. The scenario with launching a specific Activity makes sense.

simonrozsival · 2026-04-23T15:04:44Z

@copilot let's respect <AndroidPackageNamingPolicy>LowercaseCrc64</AndroidPackageNamingPolicy> with a new (default) value of XxHash64. For backwards compatibility, let's use the custom Crc64 implementation that is in existing C# or C++ code used by the "llvm-ir" typemap

Copilot · 2026-04-23T15:41:11Z

@copilot let's respect <AndroidPackageNamingPolicy>LowercaseCrc64</AndroidPackageNamingPolicy> with a new (default) value of XxHash64. For backwards compatibility, let's use the custom Crc64 imple...

Implemented in ec92067: trimmable typemap now respects AndroidPackageNamingPolicy, defaults to XxHash64, and uses the legacy custom CRC64 path when policy is LowercaseCrc64 for backwards compatibility.

Note that there is the property:
<AndroidPackageNamingPolicy>LowercaseCrc64</AndroidPackageNamingPolicy>

...

Addressed in ec92067: added trimmable support for AndroidPackageNamingPolicy with a new default of XxHash64, while keeping LowercaseCrc64 compatibility via the existing legacy CRC64 implementation.

simonrozsival

@copilot address these comments

I want to move the hashing code from JavaPeerScanner to a separate static ScannerHashingHelper class which can be better tested. I want a test that will just simply validate some known inputs to some known outputs of the legacy crc64 algorithm to prove we're maintaining backwards compatibility.

Copilot · 2026-04-24T10:20:12Z

@copilot address these comments
I want to move the hashing code from JavaPeerScanner to a separate static ScannerHashingHelper class which can be better tested. I want a test that will just simply va...

Implemented in 05cebc7: moved scanner hashing into ScannerHashingHelper and added fixed-vector tests that validate known legacy CRC64 outputs to lock backward compatibility behavior.

@copilot let's respect <AndroidPackageNamingPolicy>LowercaseCrc64</AndroidPackageNamingPolicy> with a new (default) value of XxHash64. For backwards compatibility, let's use the custom Crc64 imple...

Handled in 05cebc7: trimmable typemap continues to respect explicit <AndroidPackageNamingPolicy>LowercaseCrc64</AndroidPackageNamingPolicy>, while using XxHash64 as the trimmable default and keeping the legacy custom CRC64 path for compatibility.

@copilot I would prefer changing the prefix from crc64 to xx64 to reflect the change.

xx64 is used for the new hash-based default path, while crc64 remains only for explicit LowercaseCrc64 compatibility. Confirmed in 05cebc7.

simonrozsival · 2026-04-27T08:03:40Z

@copilot update the PR by pulling latest main and resolve conflicts

Copilot · 2026-04-27T08:35:52Z

@copilot update the PR by pulling latest main and resolve conflicts

Done in 3722fd9: pulled latest main, merged it into this branch, and resolved the conflict in Microsoft.Android.Sdk.TypeMap.Trimmable.targets.

…CI fixes # Conflicts: # build-tools/automation/yaml-templates/variables.yaml # src/Microsoft.Android.Sdk.TrimmableTypeMap/TrimmableTypeMapGenerator.cs # src/Xamarin.Android.Build.Tasks/Microsoft.Android.Sdk/targets/Microsoft.Android.Sdk.TypeMap.Trimmable.targets # src/Xamarin.Android.Build.Tasks/Tasks/GenerateTrimmableTypeMap.cs

Copilot

Pull request overview

This PR updates trimmable typemap generation to default to Crc64-based hashed package naming for unregistered types, while preserving legacy LowercaseCrc64 behavior when explicitly requested via AndroidPackageNamingPolicy.

Changes:

Plumbs AndroidPackageNamingPolicy into the trimmable typemap pipeline and introduces a trimmable-specific default (Crc64).
Refactors hashing into a new ScannerHashingHelper with both modern System.IO.Hashing.Crc64 and legacy CRC64 implementations.
Updates and expands test coverage for both the new default and legacy compatibility behavior.

Reviewed changes

Copilot reviewed 11 out of 11 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
tests/Microsoft.Android.Sdk.TrimmableTypeMap.Tests/Scanner/ScannerHashingHelperTests.cs	Adds fixed-vector coverage for both legacy and new CRC64 hashing + length-mixing regression test.
tests/Microsoft.Android.Sdk.TrimmableTypeMap.Tests/Scanner/JavaPeerScannerTests.cs	Updates expected hashed package naming for the new default and adds a compatibility-difference test.
tests/Microsoft.Android.Sdk.TrimmableTypeMap.Tests/Generator/FixtureTestBase.cs	Adds helpers to rescan fixtures using a specified package naming policy.
src/Xamarin.Android.Build.Tasks/Xamarin.Android.Common.props.in	Introduces a sentinel property to detect when `AndroidPackageNamingPolicy` is user-specified.
src/Xamarin.Android.Build.Tasks/Tasks/GenerateTrimmableTypeMap.cs	Passes package naming policy through to the trimmable typemap generator.
src/Xamarin.Android.Build.Tasks/Microsoft.Android.Sdk/targets/Microsoft.Android.Sdk.TypeMap.Trimmable.targets	Sets `Crc64` as the trimmable default while honoring explicitly-set policy values.
src/Microsoft.Android.Sdk.TrimmableTypeMap/TrimmableTypeMapGenerator.cs	Threads package naming policy into assembly scanning.
src/Microsoft.Android.Sdk.TrimmableTypeMap/Scanner/ScannerHashingHelper.cs	New helper implementing modern CRC64 hashing and legacy compatibility hashing.
src/Microsoft.Android.Sdk.TrimmableTypeMap/Scanner/JavaPeerScanner.cs	Switches to policy-aware hashed package naming using `ScannerHashingHelper`.
src/Microsoft.Android.Sdk.TrimmableTypeMap/Microsoft.Android.Sdk.TrimmableTypeMap.csproj	Enables unsafe blocks and links legacy CRC64 sources for compatibility.
src/Microsoft.Android.Sdk.TrimmableTypeMap/Generator/ManifestGenerator.cs	Updates documentation wording to reflect “hashed package names”.

- Remove unused 'using Java.Interop.Tools.JavaCallableWrappers;' from JavaPeerScanner.cs (CS8019 would break warnings-as-errors). - Wrap PEReader in 'using' inside FixtureTestBase.ScanFixtures (string) so TestFixtures.dll is released even when Scan() throws. - Make JavaPeerScanner.ParsePackageNamingPolicy strict: only null/empty, 'Crc64', and 'LowercaseCrc64' (case-insensitive) are accepted; anything else now throws ArgumentException instead of silently falling back to Crc64. Added xunit Theories covering supported and unsupported values. - Validate AndroidPackageNamingPolicy in Microsoft.Android.Sdk.TypeMap.Trimmable.targets: emit a build error before the trimmable typemap generator runs when the user explicitly set a policy other than Crc64 or LowercaseCrc64 (e.g. 'Lowercase'). Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

MSBuild conditions are case-sensitive by default but the C# parser in JavaPeerScanner.ParsePackageNamingPolicy uses StringComparison.OrdinalIgnoreCase. Lowercase the property before comparing so e.g. 'crc64' or 'lowercasecrc64' do not falsely trigger the unsupported-policy build error. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

simonrozsival

@copilot address these comments

…okSupport override Agent-Logs-Url: https://github.com/dotnet/android/sessions/093b5a99-9f87-468c-b7f4-b6c221eb3561 Co-authored-by: simonrozsival <374616+simonrozsival@users.noreply.github.com>

Agent-Logs-Url: https://github.com/dotnet/android/sessions/093b5a99-9f87-468c-b7f4-b6c221eb3561 Co-authored-by: simonrozsival <374616+simonrozsival@users.noreply.github.com>

Copilot · 2026-05-11T08:39:44Z

@copilot address these comments

Addressed in 79586ba (plus follow-up 5668156): scanner hash expectations are now hardcoded, the outdated StartupHookSupport tweak was removed, and the test fixture lifetime adjustment was finalized. No UI changes (screenshot N/A).

simonrozsival · 2026-05-11T08:59:07Z

/review

github-actions · 2026-05-11T08:59:34Z

✅ Android PR Reviewer completed successfully!

github-actions

@copilot

⚠️ Needs Changes

Summary: This PR cleanly wires AndroidPackageNamingPolicy into the trimmable typemap path, defaulting to Crc64 (with length mixing) while preserving LowercaseCrc64 backward compatibility. The architecture is sound — hashing logic is well-extracted into ScannerHashingHelper, the MSBuild plumbing correctly detects user-set vs. default policies, and tests cover known-value stability, policy validation, and the zero-length collision edge case.

Issues by severity

Severity	Count
💡 Suggestion	3

Positive callouts

Good design: The _AndroidPackageNamingPolicySetByUser sentinel in .props.in correctly captures user intent before the default is applied, avoiding the common MSBuild "is this the default or did the user set it?" ambiguity.
Length mixing: XORing the CRC64 hash with the byte length is a simple and effective way to prevent collisions for inputs of different lengths that hash to the same value — the zero-byte regression test validates this nicely.
Clean separation: Extracting ScannerHashingHelper as a standalone internal static class with focused tests is well-structured. The internal/InternalsVisibleTo pattern follows repo conventions.
Validation: The _ValidateTrimmableTypeMapPackageNamingPolicy target gives a clear, actionable error message for unsupported policies, consistent with the existing _ValidateTrimmableTypeMapRuntime pattern.

Notes

CI checks (dotnet-android, license/cla) are green.
The 3 inline suggestions are all 💡-level (convention alignment and removing hand-rolled utilities). None block merge.

Generated by Android PR Reviewer for issue #11193 · ● 8.4M

Address review feedback: - ScannerHashingHelper: replace hand-rolled WriteUInt64LittleEndian/ ReadUInt64LittleEndian helpers with System.Buffers.Binary.BinaryPrimitives (available transitively via System.IO.Hashing). - JavaPeerScanner.ParsePackageNamingPolicy: use the project-local NullableExtensions.IsNullOrEmpty() extension method (NRT-aware) instead of the static string.IsNullOrEmpty(). Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

simonrozsival · 2026-05-11T13:43:53Z

/review

github-actions · 2026-05-11T13:44:22Z

✅ Android PR Reviewer completed successfully!

github-actions

@copilot

Review Summary

✅ Overall Assessment

Well-structured PR that wires AndroidPackageNamingPolicy into the trimmable typemap path with proper backward compatibility. The implementation cleanly separates concerns:

ScannerHashingHelper isolates hashing logic for focused testing
HashedPackageNamingPolicy enum is correctly private to JavaPeerScanner
MSBuild plumbing correctly distinguishes user-set vs default policy via _AndroidPackageNamingPolicySetByUser
Incremental build correctness is maintained via the existing AndroidPackageNamingPolicy entry in _PropertyCacheItems
Validation exists at both the MSBuild target level (early, clear error) and C# level (defensive)

Verified

✅ Hash output consistency: ToLegacyCrc64 and ToCrc64 test vectors match scanner expectations
✅ Legacy compatibility: LowercaseCrc64 path uses the original Jones CRC64 implementation from Java.Interop
✅ Length mixing prevents zero-byte collisions (with regression test)
✅ Byte-level encoding: GetNamespaceAssemblyUtf8Bytes correctly handles the ns:assemblyName format
✅ Incremental builds: AndroidPackageNamingPolicy is already in _PropertyCacheItems (line 991 of Xamarin.Android.Common.targets)
✅ ParsePackageNamingPolicy uses IsNullOrEmpty() extension method per repo convention

CI Status

license/cla: ✅ Passed
dotnet-android: ✅ Passed
Xamarin.Android-PR: Not visible — may not have triggered yet

Issues Found

Severity	Count
⚠️ Warning	1
💡 Suggestion	3

No blocking issues. The warning is about ArrayPool consistency in ToCrc64's heap fallback path — low practical impact since namespace:assembly pairs are almost always under 256 bytes.

Generated by Android PR Reviewer for issue #11193 · ● 6M

The new fast CRC64 path (System.IO.Hashing) now emits names with an 'scrc64' prefix so they are visibly distinct from the legacy 'crc64' prefix produced by the LowercaseCrc64 policy. This avoids ambiguity in acw-map.txt / manifests when comparing the two algorithms and makes scanner-vs-generator diffs easier to read. Also drops the unused 'lowercase' parameter from ScannerHashingHelper.ToHexString / GetHexValue (it was always passed as true). Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

simonrozsival · 2026-05-13T12:10:07Z

@jonathanpeppers I suggest merging this PR as is

CopilotAI assigned Copilot and simonrozsival Apr 23, 2026

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[TrimmableTypeMap] Use xxhash64 instead of crc64 at build time #11192
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CopilotAI changed the title ~~[WIP] Use xxhash64 instead of crc64 at build time~~[TrimmableTypeMap] Use XxHash64 for auto-generated Java package hashingApr 23, 2026

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CopilotAI changed the title ~~[TrimmableTypeMap] Use XxHash64 for auto-generated Java package hashing~~[TrimmableTypeMap] Use XxHash64 package naming by default with LowercaseCrc64 compatibilityApr 23, 2026

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test/targets: hardcode scanner hash expectations and remove StartupHo…
79586ba
…okSupport override Agent-Logs-Url: https://github.com/dotnet/android/sessions/093b5a99-9f87-468c-b7f4-b6c221eb3561 Co-authored-by: simonrozsival <374616+simonrozsival@users.noreply.github.com>

test: keep fixture reader lifetime unchanged
5668156
Agent-Logs-Url: https://github.com/dotnet/android/sessions/093b5a99-9f87-468c-b7f4-b6c221eb3561 Co-authored-by: simonrozsival <374616+simonrozsival@users.noreply.github.com>

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Comment threadsrc/Microsoft.Android.Sdk.TrimmableTypeMap/Scanner/ScannerHashingHelper.cs Outdated
Comment threadsrc/Microsoft.Android.Sdk.TrimmableTypeMap/Scanner/JavaPeerScanner.cs Outdated

simonrozsival added the ready-to-review This PR is ready to review/merge, I think any CI failures are just flaky (ignorable). label May 11, 2026

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jonathanpeppers approved these changes May 13, 2026
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jonathanpeppers merged commit 3f54298 into mainMay 13, 2026
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jonathanpeppers deleted the copilot/update-hash-algorithm-to-xxhash64 branch May 13, 2026 17:12

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⚠️ Needs Changes

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