[clang] [clang][modules-driver] Add support for C++ named modules and `import std` (PR #193312)

[Naveen Seth Hanig via cfe-commits]

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@@ -1506,6 +1518,80 @@ static void createAndConnectRoot(CompilationGraph &Graph) {
   }
 }
 
+/// Creates a temporary output path for \p ModuleName.
+static std::string createModuleOutputPath(const Compilation &C,
+                                          StringRef ModuleName) {
+  // Sanitize the ':' included in parition names. It is illegal for filenames on
+  // Windows.
+  SmallString<32> SanitizedModuleName(ModuleName);
+  llvm::replace(SanitizedModuleName, ':', '_');
+  auto ModuleOutputPath = C.getDriver().GetTemporaryPath(
+      SanitizedModuleName, types::getTypeTempSuffix(types::TY_ModuleFile));
+  return ModuleOutputPath;
+}
+
+/// Adds arguments to output the module produced by \p Node at \p OutputPath.
+static void configureNamedModuleOutputArgs(Compilation &C,
+                                           NamedModuleJobNode &Node,
+                                           StringRef ModuleOutputPath) {
+  auto &Job = *Node.Job;
+  const auto &TCArgs = getToolChainArgs(C, Job);
+  auto JobArgs = Job.getArguments();
+
+  JobArgs.push_back(
+      TCArgs.MakeArgString("-fmodule-output=" + ModuleOutputPath));
+  // Ensure that this job will emit a module. If the main input for this job
+  // is not of types::CXXModule, we need to explicitly add this.
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naveen-seth wrote:

Do you mean we should not support exporting modules from `.cpp` files, and instead only allow exports from `.cppm` files?
I would strongly prefer that as well, since supporting exports from `.cpp` would make future support for `-fno-modules-reduced-bmi` much harder and also makes maintenance more complex overall.

https://github.com/llvm/llvm-project/pull/193312