Support multithreaded MSBuild in F# build tasks - #20506

Draft

T-Gro wants to merge 36 commits into

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T-Gro:t-gro-msbuild-task-multithreading

Commits on Sep 8, 2026

Add FSharp.Build task environment test helpers
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Fix shared FSharp.Build test logger

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Mark pure FSharp.Build tasks multithreadable
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Make FSharp.Build output tasks multithread-safe
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Harden multithreaded task tests
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Make FSharp resource generators multithread-safe
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Preserve relative resource task diagnostics
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Avoid duplicate resource task errors

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Make SubstituteText multithread-safe
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Make FSharp compiler tasks multithread-safe
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Compact multithreaded task tests

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Fix remaining multithreaded task path handling
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Handle multithreaded task path edge cases

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Exercise multithreaded MSBuild in Linux PR builds

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Keep multithreaded MSBuild canary informational

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Preserve partially qualified diagnostic paths

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cb2bc45
Compact multithreaded task migration

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c745bd3
Compact multithreaded task test matrix

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Deduplicate concurrent task assertions

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Simplify multithreaded path scenarios

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NoBloat multithreaded task migration pass 1

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NoBloat multithreaded task migration pass 2

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CodeCompaction MT tasks pass 1

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CodeCompaction MT tasks pass 2

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7abe423
Make multithreaded task paths more idiomatic

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7ec06b8
Refine multithreaded task functional style
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Refine multithreaded task test style
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Preserve ILLink task diagnostic paths

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Preserve MSBuild exception logging semantics
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Apply rebased multithreaded task compaction

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Refine rebased multithreaded task helpers

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Commits on Sep 9, 2026

Harden multithreaded task diagnostics and regression coverage

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Embed linker substitutions before resource compilation

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Exercise concurrent SDK builds on Linux and Windows

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Enable multithreaded MSBuild in existing SDK CI jobs

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1b16326

Commits on Sep 10, 2026

Link multithreaded task release notes to the draft PR

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