Enable parallel compilation features by default

[majocha]

This fixes remaining CI failures and enables by default --parallelcompilation. This includes:

• Parallel reference resolution
• Parallel optimizations Parallel optimization - behind a test flag --test:ParallelOptimization #14390
• Parallel ILxGen IlxGen parallelization #14372
• Graph based type checking Parallel type-checking in compilation (behind a feature flag) #14494

NOTE: For deterministic builds only parallel reference resolution will be enabled.

--parallelcompilation- switch can be used to revert all of the above to previous behavior.

See tracking issue #18989

TODO:

• restore switches
• double check that with everything off things still work

Some il baselines changed because of reordered methods.

This work was encouraged and kindly sponsored by Amplifying F# initiative 🚀

[github-actions]

❗ Release notes required

---

✅ Found changes and release notes in following paths:

Change path	Release notes path	Description
src/Compiler	docs/release-notes/.FSharp.Compiler.Service/11.0.0.md

[T-Gro]

Can I ignore the other three?
This one is fully green now.

[majocha]

Can I ignore the other three? This one is fully green now.

Yes, we can continue with just this one.

[majocha]

System.Exception : EVIL_PROVIDER_NamespaceName_Exception.err EVIL_PROVIDER_NamespaceName_Exception.bsl differ; "diff between [D:\a_work\1\s\artifacts\Temp\FSharp.Test.Utilities\72306301\6278ff13\typeProviders\negTests\EVIL_PROVIDER_NamespaceName_Exception.bsl] and [D:\a_work\1\s\artifacts\Temp\FSharp.Test.Utilities\72306301\6278ff13\typeProviders\negTests\EVIL_PROVIDER_NamespaceName_Exception.err]
diff at line 4
+



Unhandled Exception: System.NullReferenceException: Object reference not set to an instance of an object.

at [email protected](TcImportsLockToken tcitok)

at Internal.Utilities.Library.Lock1.AcquireLock[a](FSharpFunc2 f)

at FSharp.Compiler.CompilerImports.TcImportsSafeDisposal.Finalize()
"

Type providers don't like parallel imports, another random fail in evil provider.

[T-Gro]

Type providers don't like parallel imports, another random fail in evil provider.

I wonder if it because of the evil provider, or if the compiler should not synchronizing access to type provider code for all of them. (I assume that at time of TP creation, nothing in the compiler was parallel and access to TP libraries was always sequential).

[majocha]

Type providers don't like parallel imports, another random fail in evil provider.

I wonder if it because of the evil provider, or if the compiler should not synchronizing access to type provider code for all of them. (I assume that at time of TP creation, nothing in the compiler was parallel and access to TP libraries was always sequential).

I suspect it was because of one missing lock 6b96083
There was a comment that this requires a lock, but the lock was not there.

[majocha]

Type providers don't like parallel imports, another random fail in evil provider.

I wonder if it because of the evil provider, or if the compiler should not synchronizing access to type provider code for all of them. (I assume that at time of TP creation, nothing in the compiler was parallel and access to TP libraries was always sequential).

Yes, the oldest thing I remember was the Reactor, that made everything sequential. But then there's this #10310

[T-Gro]

Ok this makes sense, all access to TP synchronized.
We cannot tell from the outside if TP internals are thread safe or not.

[majocha]

I suspect there is still a lot that can be optimized w.r.t. graph creation and how Transparent Compiler caches it. But I feel it would be best to do it separately.

[Copilot]

Pull Request Overview

This PR enables parallel compilation features by default after stabilization, including parallel reference resolution, parallel optimizations, parallel ILxGen, and graph-based type checking. The --parallelcompilation- switch can be used to revert to previous behavior. Setting --deterministic also makes compilation sequential except for parallel imports. IL baselines changed due to reordered methods from parallel processing.

Key Changes:

• Enabled parallel compilation by default in configuration and build settings
• Fixed deterministic mode to exclude graph-based type checking
• Improved script handling and signature-to-implementation file mapping in graph checking
• Updated thread safety for type provider disposal

Reviewed Changes

Copilot reviewed 24 out of 24 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
src/FSharp.Build/Microsoft.FSharp.NetSdk.props	Changed ParallelCompilation default to true
src/FSharp.Build/Fsc.fs	Changed ParallelCompilation default from false to true
src/Compiler/Optimize/Optimizer.fs	Changed default processing mode from Sequential to Parallel
src/Compiler/Driver/ParseAndCheckInputs.fs	Added deterministic mode check to exclude graph-based type checking
src/Compiler/Driver/GraphChecking/Types.fsi	Added IsScript property and TryGetWrongOrderSignatureToImplementationIndex method
src/Compiler/Driver/GraphChecking/Types.fs	Improved file pair mapping logic and added script detection
src/Compiler/Driver/GraphChecking/DependencyResolution.fs	Added script compilation handling and wrong-order signature detection
src/Compiler/Driver/CompilerOptions.fs	Updated parallel compilation switch to control reference resolution
src/Compiler/Driver/CompilerImports.fs	Refactored assembly import to be fully async and fixed thread safety
src/Compiler/Driver/CompilerConfig.fs	Changed defaults to enable parallel features
docs/release-notes/.FSharp.Compiler.Service/11.0.0.md	Added release notes entry
tests/fsharp/typecheck/sigs/neg56_a.bsl	Updated baseline with new error
tests/fsharp/typecheck/sigs/neg14.bsl	Updated baseline with reordered errors
tests/fsharp/tests.fs	Removed skipped test
tests/FSharp.Compiler.ComponentTests/Miscellaneous/MigratedTypeCheckTests.fs	Re-enabled previously skipped test
Multiple IL baseline files	Updated baselines reflecting method reordering from parallel compilation

[nojaf]

Great to see another step in the right direction. That said, don’t present this as "everything is now parallel." It needs more transparency and nuance.

[nojaf]

This is quite vague about what is actually changed here. Anyone reading this, will need to scour through the PR to know what is actual up.

[majocha]

@nojaf thanks for the careful review👍 , I'll do a follow up addressing it.