msvc: fix passing /Zc:__cplusplus flag

It is mandatory to pass /Zc:__cplusplus when building
with Qt 6.2 and MSVC.

Fixes: QBS-1655
Change-Id: I27d928a568d0ac2075ce3f77f4142e20342be358
Reviewed-by: Christian Kandeler <christian.kandeler@qt.io>

1 files changed, 16 insertions, 0 deletions

diff --git a/share/qbs/modules/cpp/msvc.js b/share/qbs/modules/cpp/msvc.js
index 1ebe5173b..3e528ddee 100644
--- a/share/qbs/modules/cpp/msvc.js
+++ b/share/qbs/modules/cpp/msvc.js
@@ -83,6 +83,19 @@ function hasCxx17Option(input)
             || (input.qbs.toolchain.contains("clang-cl") && input.cpp.compilerVersionMajor >= 7);
 }
 
+function hasZCplusPlusOption(input)
+{
+    // /Zc:__cplusplus is supported starting from Visual Studio 15.7
+    // Looks like closest MSVC version is 14.14.26428 (cl ver 19.14.26433)
+    // At least, this version is tested
+    // https://docs.microsoft.com/en-us/cpp/build/reference/zc-cplusplus
+    // clang-cl supports this option starting around-ish versions 8/9, but it
+    // ignores this option, so this doesn't really matter
+    // https://reviews.llvm.org/D45877
+    return Utilities.versionCompare(input.cpp.compilerVersion, "19.14.26433") >= 0
+            || (input.qbs.toolchain.contains("clang-cl") && input.cpp.compilerVersionMajor >= 9);
+}
+
 function supportsExternalIncludesOption(input) {
     if (input.qbs.toolchain.contains("clang-cl"))
         return false; // Exclude clang-cl.
@@ -240,6 +253,9 @@ function prepareCompiler(project, product, inputs, outputs, input, output, expli
     if (input.cpp.generateCompilerListingFiles)
         args.push("/Fa" + FileInfo.toWindowsSeparators(outputs.lst[0].filePath));
 
+    if (input.cpp.enableCxxLanguageMacro && hasZCplusPlusOption(input))
+        args.push("/Zc:__cplusplus");
+
     var objectMap = outputs.obj || outputs.intermediate_obj
     var objOutput = objectMap ? objectMap[0] : undefined
     args.push('/Fo' + FileInfo.toWindowsSeparators(objOutput.filePath))