Do not pass /shared to compilers that cannot reach a compiler server - #3943
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The dotnet-hosted Roslyn 2.10 build cannot start its VBCSCompiler server under a current dotnet host, so with /shared every test compilation first waited out the client's full 20-second new-server connection timeout before falling back to a sub-second in-process compile. Since the 2.10 configurations were enabled on non-Windows (#3914), that added ~29 minutes to the Linux CI job and ~43 minutes on macOS: ~340 affected tests at ~21s each, versus ~0.2s for the toolsets whose server works. Assisted-by: Claude:claude-fable-5:Claude Code
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Since #3914 enabled the Roslyn 1.x/2.x configurations on non-Windows, the Linux decompiler-tests CI step went from ~2 to ~31 minutes (and the macOS job from ~10 to ~53 minutes total).
The TRX artifacts show where the time goes: the ~340
UseRoslyn2_10_0test cases average 20.7 s each, while every other toolset averages 0.2 s. The compile itself is not slow -- invoking the same 2.10csc.dllby hand takes 0.7 s. The cost is the/sharedswitch the test harness passes to every Roslyn invocation: the dotnet-hosted Roslyn 2.x client cannot start its VBCSCompiler server under a currentdotnethost (the--roll-forwardonly applies to csc/vbc itself, not to the server process the client spawns), so each invocation waits out the client's full 20-second new-server connection timeout and then falls back to a sub-second in-process compile. Measured with the same trivial compile: 0.7 s without/shared, 20.8 s with it (of which only ~1 s is CPU time).This gates
/sharedon Windows-or-Roslyn-3.0+, keeping the compiler server where it works and dropping it for the dotnet-hosted 2.x and Mono-hosted 1.x builds. Locally theInlineAssignmentTestmatrix drops from 25 s to 6 s, with the 2.10 cases going from 21.5 s to 2.5 s; the full VBPretty suite passes.This should also make it feasible to re-enable the decompiler tests on macOS (skipped in #3941's follow-up commit for being the slowest job) if desired.
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