Isolate MSBuildTaskHost from the rest of MSBuild Codebase

[DustinCampbell]

Summary

MSBuildTaskHost.exe provides legacy support for running .NET Framework 3.5 tasks. It is itself a .NET Framework 3.5 application and loads the Microsoft.Build.* 3.5.0.0 assemblies from the GAC when .NET 3.5 is installed. Today, common targets force three .NET 3.5 tasks to run in MSBuildTaskHost: RegisterAssembly, UnregisterAssembly, and especially, GenerateResource. For .NET 3.5 builds, it is essentially that the 3.5 version of GenerateResource runs, since the BinaryFormatter output format changed between CLR 2.0 and CLR 4.0.

For more than 15 years, MSBuildTaskHost has been compiled from the same shared source files as the rest of MSBuild. This made sense in the .NET Framework 4.0 era, when the delta between 3.5 and 4.0 was small. But as MSBuild has evolved, this arrangement has become increasingly restrictive. Any shared code that uses modern .NET features (Span<T>, Task<T>, immutable collections, etc.) becomes problematic because MSBuildTaskHost cannot consume them. Shared code changes also risk breaking MSBuildTaskHost and, by extension, the ability to build legacy .NET 3.5 projects.

This PR isolates MSBuildTaskHost into its own self‑contained codebase, decoupled from the rest of MSBuild.

Approach

The isolation work follows these steps:

1. Copy all shared files into MSBuildTaskHost.
2. Remove conditional compilation constants from MSBuildTaskHost’s sources:
   • Dead code paths, including those under NET, RUNTIME_TYPE_NETCORE, or FEATURE_* flags irrelevant to .NET 3.5 (e.g., FEATURE_VISUALSTUDIOSETUP).
   • Always‑true code paths, such as those under CLR2COMPATIBILITY or FEATURE_ASSEMBLY_LOCATION.
3. Remove OS/architecture‑specific code that MSBuildTaskHost does not support (i.e., anything outside Windows/x86/x64).
4. Remove uncalled members and unused types.
5. Remove MSBuild public API types that were added solely to make MSBuildTaskHost compile but do not exist in Microsoft.Build.Framework 3.5.0.0 (e.g., IBuildEngine3, ITaskItem2, RunInSTAAttribute).
6. Clean up each file to reflect its new, isolated context.

Additional Changes Outside MSBuildTaskHost

Refactor handshake components to make the tools directory path deterministic by using the MSBuildTaskHost.exe directory when computing handshake salt. (22fb64e)
Add a test that verifies building a .NET 3.5 WinForms application on Windows/.NET Framework when .NET 3.5 is installed. (9941c15)

Next Steps

Remove dead code paths from all shared MSBuild files now that .NET 3.5 compatibility is no longer required. (In progress)
Audit conditional compilation constants across MSBuild. (In progress)
Move remaining shared code into a dedicated shared binary (Microsoft.Build.Framework). (Requires reworking how string resources are consumed across MSBuild binaries.)

Future Work

Refactor task host communication to introduce a “protocol adapter” layer. Now that MSBuildTaskHost is effectively frozen in time, this adapter would shield it from future protocol changes while allowing MSBuild to evolve independently.

[DustinCampbell]

Summary

MSBuildTaskHost.exe provides legacy support for running .NET Framework 3.5 tasks. It is itself a .NET Framework 3.5 application and loads the Microsoft.Build.* 3.5.0.0 assemblies from the GAC when .NET 3.5 is installed. Today, common targets force three .NET 3.5 tasks to run in MSBuildTaskHost: RegisterAssembly, UnregisterAssembly, and especially, GenerateResource. For .NET 3.5 builds, it is essentially that the 3.5 version of GenerateResource runs, since the BinaryFormatter output format changed between CLR 2.0 and CLR 4.0.

For more than 15 years, MSBuildTaskHost has been compiled from the same shared source files as the rest of MSBuild. This made sense in the .NET Framework 4.0 era, when the delta between 3.5 and 4.0 was small. But as MSBuild has evolved, this arrangement has become increasingly restrictive. Any shared code that uses modern .NET features (Span<T>, Task<T>, immutable collections, etc.) becomes problematic because MSBuildTaskHost cannot consume them. Shared code changes also risk breaking MSBuildTaskHost and, by extension, the ability to build legacy .NET 3.5 projects.

This PR isolates MSBuildTaskHost into its own self‑contained codebase, decoupled from the rest of MSBuild.

Approach

The isolation work follows these steps:

1. Copy all shared files into MSBuildTaskHost.
2. Remove conditional compilation constants from MSBuildTaskHost’s sources:
   • Dead code paths, including those under NET, RUNTIME_TYPE_NETCORE, or FEATURE_* flags irrelevant to .NET 3.5 (e.g., FEATURE_VISUALSTUDIOSETUP).
   • Always‑true code paths, such as those under CLR2COMPATIBILITY or FEATURE_ASSEMBLY_LOCATION.
3. Remove OS/architecture‑specific code that MSBuildTaskHost does not support (i.e., anything outside Windows/x86/x64).
4. Remove uncalled members and unused types.
5. Remove MSBuild public API types that were added solely to make MSBuildTaskHost compile but do not exist in Microsoft.Build.Framework 3.5.0.0 (e.g., IBuildEngine3, ITaskItem2, RunInSTAAttribute).
6. Clean up each file to reflect its new, isolated context.

Additional Changes Outside MSBuildTaskHost

Refactor handshake components to make the tools directory path deterministic by using the MSBuildTaskHost.exe directory when computing handshake salt. (22fb64e)
Add a test that verifies building a .NET 3.5 WinForms application on Windows/.NET Framework when .NET 3.5 is installed. (9941c15)

Next Steps

Remove dead code paths from all shared MSBuild files now that .NET 3.5 compatibility is no longer required. (In progress)
Audit conditional compilation constants across MSBuild. (In progress)
Move remaining shared code into a dedicated shared binary (Microsoft.Build.Framework). (Requires reworking how string resources are consumed across MSBuild binaries.)

Future Work

Refactor task host communication to introduce a “protocol adapter” layer. Now that MSBuildTaskHost is effectively frozen in time, this adapter would shield it from future protocol changes while allowing MSBuild to evolve independently.

[DustinCampbell]

Summary

MSBuildTaskHost.exe provides legacy support for running .NET Framework 3.5 tasks. It is itself a .NET Framework 3.5 application and loads the Microsoft.Build.* 3.5.0.0 assemblies from the GAC when .NET 3.5 is installed. Today, common targets force three .NET 3.5 tasks to run in MSBuildTaskHost: RegisterAssembly, UnregisterAssembly, and especially, GenerateResource. For .NET 3.5 builds, it is essentially that the 3.5 version of GenerateResource runs, since the BinaryFormatter output format changed between CLR 2.0 and CLR 4.0.

For more than 15 years, MSBuildTaskHost has been compiled from the same shared source files as the rest of MSBuild. This made sense in the .NET Framework 4.0 era, when the delta between 3.5 and 4.0 was small. But as MSBuild has evolved, this arrangement has become increasingly restrictive. Any shared code that uses modern .NET features (Span<T>, Task<T>, immutable collections, etc.) becomes problematic because MSBuildTaskHost cannot consume them. Shared code changes also risk breaking MSBuildTaskHost and, by extension, the ability to build legacy .NET 3.5 projects.

This PR isolates MSBuildTaskHost into its own self‑contained codebase, decoupled from the rest of MSBuild.

Approach

The isolation work follows these steps:

1. Copy all shared files into MSBuildTaskHost.
2. Remove conditional compilation constants from MSBuildTaskHost’s sources:
   • Dead code paths, including those under NET, RUNTIME_TYPE_NETCORE, or FEATURE_* flags irrelevant to .NET 3.5 (e.g., FEATURE_VISUALSTUDIOSETUP).
   • Always‑true code paths, such as those under CLR2COMPATIBILITY or FEATURE_ASSEMBLY_LOCATION.
3. Remove OS/architecture‑specific code that MSBuildTaskHost does not support (i.e., anything outside Windows/x86/x64).
4. Remove uncalled members and unused types.
5. Remove MSBuild public API types that were added solely to make MSBuildTaskHost compile but do not exist in Microsoft.Build.Framework 3.5.0.0 (e.g., IBuildEngine3, ITaskItem2, RunInSTAAttribute).
6. Clean up each file to reflect its new, isolated context.

Additional Changes Outside MSBuildTaskHost

Refactor handshake components to make the tools directory path deterministic by using the MSBuildTaskHost.exe directory when computing handshake salt. (22fb64e)
Add a test that verifies building a .NET 3.5 WinForms application on Windows/.NET Framework when .NET 3.5 is installed. (9941c15)

Next Steps

Remove dead code paths from all shared MSBuild files now that .NET 3.5 compatibility is no longer required. (In progress)
Audit conditional compilation constants across MSBuild. (In progress)
Move remaining shared code into a dedicated shared binary (Microsoft.Build.Framework). (Requires reworking how string resources are consumed across MSBuild binaries.)

Future Work

Refactor task host communication to introduce a “protocol adapter” layer. Now that MSBuildTaskHost is effectively frozen in time, this adapter would shield it from future protocol changes while allowing MSBuild to evolve independently.

[DustinCampbell]

Summary

MSBuildTaskHost.exe provides legacy support for running .NET Framework 3.5 tasks. It is itself a .NET Framework 3.5 application and loads the Microsoft.Build.* 3.5.0.0 assemblies from the GAC when .NET 3.5 is installed. Today, common targets force three .NET 3.5 tasks to run in MSBuildTaskHost: RegisterAssembly, UnregisterAssembly, and especially, GenerateResource. For .NET 3.5 builds, it is essentially that the 3.5 version of GenerateResource runs, since the BinaryFormatter output format changed between CLR 2.0 and CLR 4.0.

For more than 15 years, MSBuildTaskHost has been compiled from the same shared source files as the rest of MSBuild. This made sense in the .NET Framework 4.0 era, when the delta between 3.5 and 4.0 was small. But as MSBuild has evolved, this arrangement has become increasingly restrictive. Any shared code that uses modern .NET features (Span<T>, Task<T>, immutable collections, etc.) becomes problematic because MSBuildTaskHost cannot consume them. Shared code changes also risk breaking MSBuildTaskHost and, by extension, the ability to build legacy .NET 3.5 projects.

This PR isolates MSBuildTaskHost into its own self‑contained codebase, decoupled from the rest of MSBuild.

Approach

The isolation work follows these steps:

1. Copy all shared files into MSBuildTaskHost.
2. Remove conditional compilation constants from MSBuildTaskHost’s sources:
   • Dead code paths, including those under NET, RUNTIME_TYPE_NETCORE, or FEATURE_* flags irrelevant to .NET 3.5 (e.g., FEATURE_VISUALSTUDIOSETUP).
   • Always‑true code paths, such as those under CLR2COMPATIBILITY or FEATURE_ASSEMBLY_LOCATION.
3. Remove OS/architecture‑specific code that MSBuildTaskHost does not support (i.e., anything outside Windows/x86/x64).
4. Remove uncalled members and unused types.
5. Remove MSBuild public API types that were added solely to make MSBuildTaskHost compile but do not exist in Microsoft.Build.Framework 3.5.0.0 (e.g., IBuildEngine3, ITaskItem2, RunInSTAAttribute).
6. Clean up each file to reflect its new, isolated context.

Additional Changes Outside MSBuildTaskHost

Refactor handshake components to make the tools directory path deterministic by using the MSBuildTaskHost.exe directory when computing handshake salt. (22fb64e)
Add a test that verifies building a .NET 3.5 WinForms application on Windows/.NET Framework when .NET 3.5 is installed. (9941c15)

Next Steps

Remove dead code paths from all shared MSBuild files now that .NET 3.5 compatibility is no longer required. (In progress)
Audit conditional compilation constants across MSBuild. (In progress)
Move remaining shared code into a dedicated shared binary (Microsoft.Build.Framework). (Requires reworking how string resources are consumed across MSBuild binaries.)

Future Work

Refactor task host communication to introduce a “protocol adapter” layer. Now that MSBuildTaskHost is effectively frozen in time, this adapter would shield it from future protocol changes while allowing MSBuild to evolve independently.

[DustinCampbell]

Summary

MSBuildTaskHost.exe provides legacy support for running .NET Framework 3.5 tasks. It is itself a .NET Framework 3.5 application and loads the Microsoft.Build.* 3.5.0.0 assemblies from the GAC when .NET 3.5 is installed. Today, common targets force three .NET 3.5 tasks to run in MSBuildTaskHost: RegisterAssembly, UnregisterAssembly, and especially, GenerateResource. For .NET 3.5 builds, it is essentially that the 3.5 version of GenerateResource runs, since the BinaryFormatter output format changed between CLR 2.0 and CLR 4.0.

For more than 15 years, MSBuildTaskHost has been compiled from the same shared source files as the rest of MSBuild. This made sense in the .NET Framework 4.0 era, when the delta between 3.5 and 4.0 was small. But as MSBuild has evolved, this arrangement has become increasingly restrictive. Any shared code that uses modern .NET features (Span<T>, Task<T>, immutable collections, etc.) becomes problematic because MSBuildTaskHost cannot consume them. Shared code changes also risk breaking MSBuildTaskHost and, by extension, the ability to build legacy .NET 3.5 projects.

This PR isolates MSBuildTaskHost into its own self‑contained codebase, decoupled from the rest of MSBuild.

Approach

The isolation work follows these steps:

1. Copy all shared files into MSBuildTaskHost.
2. Remove conditional compilation constants from MSBuildTaskHost’s sources:
   • Dead code paths, including those under NET, RUNTIME_TYPE_NETCORE, or FEATURE_* flags irrelevant to .NET 3.5 (e.g., FEATURE_VISUALSTUDIOSETUP).
   • Always‑true code paths, such as those under CLR2COMPATIBILITY or FEATURE_ASSEMBLY_LOCATION.
3. Remove OS/architecture‑specific code that MSBuildTaskHost does not support (i.e., anything outside Windows/x86/x64).
4. Remove uncalled members and unused types.
5. Remove MSBuild public API types that were added solely to make MSBuildTaskHost compile but do not exist in Microsoft.Build.Framework 3.5.0.0 (e.g., IBuildEngine3, ITaskItem2, RunInSTAAttribute).
6. Clean up each file to reflect its new, isolated context.

Additional Changes Outside MSBuildTaskHost

Refactor handshake components to make the tools directory path deterministic by using the MSBuildTaskHost.exe directory when computing handshake salt. (22fb64e)
Add a test that verifies building a .NET 3.5 WinForms application on Windows/.NET Framework when .NET 3.5 is installed. (9941c15)

Next Steps

Remove dead code paths from all shared MSBuild files now that .NET 3.5 compatibility is no longer required. (In progress)
Audit conditional compilation constants across MSBuild. (In progress)
Move remaining shared code into a dedicated shared binary (Microsoft.Build.Framework). (Requires reworking how string resources are consumed across MSBuild binaries.)

Future Work

Refactor task host communication to introduce a “protocol adapter” layer. Now that MSBuildTaskHost is effectively frozen in time, this adapter would shield it from future protocol changes while allowing MSBuild to evolve independently.

[DustinCampbell]

Summary

MSBuildTaskHost.exe provides legacy support for running .NET Framework 3.5 tasks. It is itself a .NET Framework 3.5 application and loads the Microsoft.Build.* 3.5.0.0 assemblies from the GAC when .NET 3.5 is installed. Today, common targets force three .NET 3.5 tasks to run in MSBuildTaskHost: RegisterAssembly, UnregisterAssembly, and especially, GenerateResource. For .NET 3.5 builds, it is essentially that the 3.5 version of GenerateResource runs, since the BinaryFormatter output format changed between CLR 2.0 and CLR 4.0.

For more than 15 years, MSBuildTaskHost has been compiled from the same shared source files as the rest of MSBuild. This made sense in the .NET Framework 4.0 era, when the delta between 3.5 and 4.0 was small. But as MSBuild has evolved, this arrangement has become increasingly restrictive. Any shared code that uses modern .NET features (Span<T>, Task<T>, immutable collections, etc.) becomes problematic because MSBuildTaskHost cannot consume them. Shared code changes also risk breaking MSBuildTaskHost and, by extension, the ability to build legacy .NET 3.5 projects.

This PR isolates MSBuildTaskHost into its own self‑contained codebase, decoupled from the rest of MSBuild.

Approach

The isolation work follows these steps:

1. Copy all shared files into MSBuildTaskHost.
2. Remove conditional compilation constants from MSBuildTaskHost’s sources:
   • Dead code paths, including those under NET, RUNTIME_TYPE_NETCORE, or FEATURE_* flags irrelevant to .NET 3.5 (e.g., FEATURE_VISUALSTUDIOSETUP).
   • Always‑true code paths, such as those under CLR2COMPATIBILITY or FEATURE_ASSEMBLY_LOCATION.
3. Remove OS/architecture‑specific code that MSBuildTaskHost does not support (i.e., anything outside Windows/x86/x64).
4. Remove uncalled members and unused types.
5. Remove MSBuild public API types that were added solely to make MSBuildTaskHost compile but do not exist in Microsoft.Build.Framework 3.5.0.0 (e.g., IBuildEngine3, ITaskItem2, RunInSTAAttribute).
6. Clean up each file to reflect its new, isolated context.

Additional Changes Outside MSBuildTaskHost

Refactor handshake components to make the tools directory path deterministic by using the MSBuildTaskHost.exe directory when computing handshake salt. (22fb64e)
Add a test that verifies building a .NET 3.5 WinForms application on Windows/.NET Framework when .NET 3.5 is installed. (9941c15)

Next Steps

Remove dead code paths from all shared MSBuild files now that .NET 3.5 compatibility is no longer required. (In progress)
Audit conditional compilation constants across MSBuild. (In progress)
Move remaining shared code into a dedicated shared binary (Microsoft.Build.Framework). (Requires reworking how string resources are consumed across MSBuild binaries.)

Future Work

Refactor task host communication to introduce a “protocol adapter” layer. Now that MSBuildTaskHost is effectively frozen in time, this adapter would shield it from future protocol changes while allowing MSBuild to evolve independently.

[DustinCampbell]

Summary

MSBuildTaskHost.exe provides legacy support for running .NET Framework 3.5 tasks. It is itself a .NET Framework 3.5 application and loads the Microsoft.Build.* 3.5.0.0 assemblies from the GAC when .NET 3.5 is installed. Today, common targets force three .NET 3.5 tasks to run in MSBuildTaskHost: RegisterAssembly, UnregisterAssembly, and especially, GenerateResource. For .NET 3.5 builds, it is essentially that the 3.5 version of GenerateResource runs, since the BinaryFormatter output format changed between CLR 2.0 and CLR 4.0.

For more than 15 years, MSBuildTaskHost has been compiled from the same shared source files as the rest of MSBuild. This made sense in the .NET Framework 4.0 era, when the delta between 3.5 and 4.0 was small. But as MSBuild has evolved, this arrangement has become increasingly restrictive. Any shared code that uses modern .NET features (Span<T>, Task<T>, immutable collections, etc.) becomes problematic because MSBuildTaskHost cannot consume them. Shared code changes also risk breaking MSBuildTaskHost and, by extension, the ability to build legacy .NET 3.5 projects.

This PR isolates MSBuildTaskHost into its own self‑contained codebase, decoupled from the rest of MSBuild.

Approach

The isolation work follows these steps:

1. Copy all shared files into MSBuildTaskHost.
2. Remove conditional compilation constants from MSBuildTaskHost’s sources:
   • Dead code paths, including those under NET, RUNTIME_TYPE_NETCORE, or FEATURE_* flags irrelevant to .NET 3.5 (e.g., FEATURE_VISUALSTUDIOSETUP).
   • Always‑true code paths, such as those under CLR2COMPATIBILITY or FEATURE_ASSEMBLY_LOCATION.
3. Remove OS/architecture‑specific code that MSBuildTaskHost does not support (i.e., anything outside Windows/x86/x64).
4. Remove uncalled members and unused types.
5. Remove MSBuild public API types that were added solely to make MSBuildTaskHost compile but do not exist in Microsoft.Build.Framework 3.5.0.0 (e.g., IBuildEngine3, ITaskItem2, RunInSTAAttribute).
6. Clean up each file to reflect its new, isolated context.

Additional Changes Outside MSBuildTaskHost

Refactor handshake components to make the tools directory path deterministic by using the MSBuildTaskHost.exe directory when computing handshake salt. (22fb64e)
Add a test that verifies building a .NET 3.5 WinForms application on Windows/.NET Framework when .NET 3.5 is installed. (9941c15)

Next Steps

Remove dead code paths from all shared MSBuild files now that .NET 3.5 compatibility is no longer required. (In progress)
Audit conditional compilation constants across MSBuild. (In progress)
Move remaining shared code into a dedicated shared binary (Microsoft.Build.Framework). (Requires reworking how string resources are consumed across MSBuild binaries.)

Future Work

Refactor task host communication to introduce a “protocol adapter” layer. Now that MSBuildTaskHost is effectively frozen in time, this adapter would shield it from future protocol changes while allowing MSBuild to evolve independently.

[DustinCampbell]

Summary

MSBuildTaskHost.exe provides legacy support for running .NET Framework 3.5 tasks. It is itself a .NET Framework 3.5 application and loads the Microsoft.Build.* 3.5.0.0 assemblies from the GAC when .NET 3.5 is installed. Today, common targets force three .NET 3.5 tasks to run in MSBuildTaskHost: RegisterAssembly, UnregisterAssembly, and especially, GenerateResource. For .NET 3.5 builds, it is essentially that the 3.5 version of GenerateResource runs, since the BinaryFormatter output format changed between CLR 2.0 and CLR 4.0.

For more than 15 years, MSBuildTaskHost has been compiled from the same shared source files as the rest of MSBuild. This made sense in the .NET Framework 4.0 era, when the delta between 3.5 and 4.0 was small. But as MSBuild has evolved, this arrangement has become increasingly restrictive. Any shared code that uses modern .NET features (Span<T>, Task<T>, immutable collections, etc.) becomes problematic because MSBuildTaskHost cannot consume them. Shared code changes also risk breaking MSBuildTaskHost and, by extension, the ability to build legacy .NET 3.5 projects.

This PR isolates MSBuildTaskHost into its own self‑contained codebase, decoupled from the rest of MSBuild.

Approach

The isolation work follows these steps:

1. Copy all shared files into MSBuildTaskHost.
2. Remove conditional compilation constants from MSBuildTaskHost’s sources:
   • Dead code paths, including those under NET, RUNTIME_TYPE_NETCORE, or FEATURE_* flags irrelevant to .NET 3.5 (e.g., FEATURE_VISUALSTUDIOSETUP).
   • Always‑true code paths, such as those under CLR2COMPATIBILITY or FEATURE_ASSEMBLY_LOCATION.
3. Remove OS/architecture‑specific code that MSBuildTaskHost does not support (i.e., anything outside Windows/x86/x64).
4. Remove uncalled members and unused types.
5. Remove MSBuild public API types that were added solely to make MSBuildTaskHost compile but do not exist in Microsoft.Build.Framework 3.5.0.0 (e.g., IBuildEngine3, ITaskItem2, RunInSTAAttribute).
6. Clean up each file to reflect its new, isolated context.

Additional Changes Outside MSBuildTaskHost

Refactor handshake components to make the tools directory path deterministic by using the MSBuildTaskHost.exe directory when computing handshake salt. (22fb64e)
Add a test that verifies building a .NET 3.5 WinForms application on Windows/.NET Framework when .NET 3.5 is installed. (9941c15)

Next Steps

Remove dead code paths from all shared MSBuild files now that .NET 3.5 compatibility is no longer required. (In progress)
Audit conditional compilation constants across MSBuild. (In progress)
Move remaining shared code into a dedicated shared binary (Microsoft.Build.Framework). (Requires reworking how string resources are consumed across MSBuild binaries.)

Future Work

Refactor task host communication to introduce a “protocol adapter” layer. Now that MSBuildTaskHost is effectively frozen in time, this adapter would shield it from future protocol changes while allowing MSBuild to evolve independently.