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CMake: Specify modern Cxx interop flag when building SwiftCompilerSources #72033

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Mar 5, 2024
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CMake: Specify modern Cxx interop flag when building SwiftCompilerSources #72033

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9 changes: 8 additions & 1 deletion SwiftCompilerSources/CMakeLists.txt
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Expand Up @@ -98,10 +98,17 @@ function(add_swift_compiler_modules_library name)
"DEPENDS"
${ARGN})

# Prior to 5.9, we have to use the experimental flag for C++ interop.
if (CMAKE_Swift_COMPILER_VERSION VERSION_LESS 5.9)
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I don't think CMAKE_Swift_COMPILER_VERSION is valid unless we're building with hosttools. Last time I checked it was empty when bootstrapping is enabled since we aren't using CMake's built-in Swift support in that case. @eeckstein knows more about this.

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Perhaps this can be further refined to check something that indicates whether we are bootstrapping and specify -cxx-interoperability-mode=default when we are. Lmk if that sounds reasonable.

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That would make sense to me!

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I wouldn't bother with it. Bootstrapping is on life support and not even checked on the official CI: hosttools are de facto required at this point, with bootstrapping soon to be removed.

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Ok, given that assessment of bootstrapping, the fact that CI passed, and that this approach matches ASTGen I'm inclined to land it as-is. I think the failure case is just that we pass the deprecated flag when bootstrapping?

set(cxx_interop_flag "-enable-experimental-cxx-interop")
else()
set(cxx_interop_flag "-cxx-interoperability-mode=default")
endif()

set(swift_compile_options
"-color-diagnostics"
"-Xfrontend" "-validate-tbd-against-ir=none"
"-Xfrontend" "-enable-experimental-cxx-interop"
"${cxx_interop_flag}"
"-Xfrontend" "-disable-target-os-checking"
"-Xcc" "-std=c++17"
"-Xcc" "-DCOMPILED_WITH_SWIFT" "-Xcc" "-DSWIFT_TARGET"
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