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Do not pass /shared to compilers that cannot reach a compiler server #3943

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Merged
siegfriedpammer merged 1 commit into from
Jul 31, 2026
+23 −6
Merged

Do not pass /shared to compilers that cannot reach a compiler server #3943

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5 changes: 2 additions & 3 deletions ICSharpCode.Decompiler.Tests/Helpers/Tester.VB.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -135,9 +135,8 @@ public static async Task<CompilerResults> CompileVB(string sourceFileName, Compi
}
}

// note: the /shared switch is undocumented. It allows us to use the VBCSCompiler.exe compiler
// server to speed up testing
if (roslynVersion != "legacy")
// See UseCompilerServer for why /shared is not passed to every compiler.
if (roslynVersion != "legacy" && UseCompilerServer(roslynVersion))
{
otherOptions += "/shared ";
}
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24 changes: 21 additions & 3 deletions ICSharpCode.Decompiler.Tests/Helpers/Tester.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -231,6 +231,23 @@ public static CompilerOptions[] SupportedOnCurrentPlatform(CompilerOptions[] con
&& !(executesCompiledOutput && c.HasFlag(CompilerOptions.TargetNet40))).ToArray();
}

/// <summary>
/// Whether to pass the undocumented /shared switch, which makes the compiler use the
/// VBCSCompiler compiler server and so avoids paying compiler startup per invocation.
/// The dotnet-hosted Roslyn 2.x build cannot start its compiler server under a current
/// 'dotnet' host (the roll-forward in WrapCompiler applies to csc/vbc itself, not to
/// the server process the client tries to spawn), so with /shared every invocation
/// first waits out the client's full 20-second new-server connection timeout before
/// falling back to a sub-second in-process compile. Only the dotnet-hosted Roslyn 3.0+
/// builds get the switch on non-Windows platforms; the Mono-hosted 1.x compilers skip
/// it too rather than rely on the server protocol working under Mono.
/// </summary>
static bool UseCompilerServer(string roslynVersion)
{
return OperatingSystem.IsWindows()
|| Version.Parse(RoslynToolset.SanitizeVersion(roslynVersion)).Major > 2;
}

/// <summary>
/// Wraps an external compiler invocation. The .NET Framework builds of the Roslyn
/// compilers (csc.exe/vbc.exe) are directly executable on Windows and are hosted by
Expand Down Expand Up @@ -717,11 +734,12 @@ public static async Task<CompilerResults> CompileCSharp(string sourceFileName, C

HashSet<string> noWarn = new HashSet<string>(StringComparer.OrdinalIgnoreCase);

// note: the /shared switch is undocumented. It allows us to use the VBCSCompiler.exe compiler
// server to speed up testing
if (roslynVersion != "legacy")
{
otherOptions += "/shared ";
if (UseCompilerServer(roslynVersion))
{
otherOptions += "/shared ";
}
var version = Version.Parse(RoslynToolset.SanitizeVersion(roslynVersion));
if (!targetNet40 && version.Major > 2)
{
Expand Down
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