[clang] [C++20] [Modules] [Driver] Don't enable -fdelayed-template-parsing by default on windows with C++20 modules (PR #69431)

[David Blaikie via cfe-commits]

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@@ -6870,8 +6852,38 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
 
   Args.AddLastArg(CmdArgs, options::OPT_finline_max_stacksize_EQ);
 
+  // FIXME: Find a better way to determine whether we are in C++20.
+  bool HaveCxx20 =
+      Std &&
+      (Std->containsValue("c++2a") || Std->containsValue("gnu++2a") ||
+       Std->containsValue("c++20") || Std->containsValue("gnu++20") ||
+       Std->containsValue("c++2b") || Std->containsValue("gnu++2b") ||
+       Std->containsValue("c++23") || Std->containsValue("gnu++23") ||
+       Std->containsValue("c++2c") || Std->containsValue("gnu++2c") ||
+       Std->containsValue("c++26") || Std->containsValue("gnu++26") ||
+       Std->containsValue("c++latest") || Std->containsValue("gnu++latest"));
   bool HaveModules =
-      RenderModulesOptions(C, D, Args, Input, Output, Std, CmdArgs);
+      RenderModulesOptions(C, D, Args, Input, Output, HaveCxx20, CmdArgs);
+
+  // -fno-delayed-template-parsing is default, except when targeting MSVC.
+  // Many old Windows SDK versions require this to parse.
+  //
+  // According to
+  // https://learn.microsoft.com/en-us/cpp/build/reference/permissive-standards-conformance?view=msvc-170,
+  // the MSVC actually defaults to -fno-delayed-template-parsing (/Zc:twoPhase-
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dwblaikie wrote:

"the" can be removed here, 

https://github.com/llvm/llvm-project/pull/69431