Fix print module manifest file for macos (#122370)

This commit fixes -print-library-module-manifest-path on macos.
Currently, this only works on linux systems. This is because on macos
systems the library and header files are installed in a different
location. The module manifest is next to the libraries and the search
function was not looking in both places. There is also a test included.

(cherry picked from commit acbd822)

Author: billhoffman

clang/lib/Driver/Driver.cpp

@@ -6189,6 +6189,11 @@ std::string Driver::GetFilePath(StringRef Name, const ToolChain &TC) const {
   if (auto P = SearchPaths(TC.getFilePaths()))
     return *P;
 
+  SmallString<128> R2(ResourceDir);
+  llvm::sys::path::append(R2, "..", "..", Name);
+  if (llvm::sys::fs::exists(Twine(R2)))
+    return std::string(R2);
+
   return std::string(Name);
 }
 

clang/test/Driver/modules-print-library-module-manifest-path.cpp

@@ -18,6 +18,28 @@
 // RUN:     --target=x86_64-linux-gnu 2>&1 \
 // RUN:   | FileCheck libcxx.cpp
 
+// for macos there is a different directory structure
+// where the library and libc++.modules.json file are in lib
+// directly but headers are in clang/ver directory which
+// is the resource directory
+// RUN: mkdir -p %t/Inputs/usr/lib/clang/20
+// RUN: touch %t/Inputs/usr/lib/libc++.so
+// RUN: touch %t/Inputs/usr/lib/libc++.modules.json
+// RUN: %clang -print-library-module-manifest-path \
+// RUN:     -stdlib=libc++ \
+// RUN:     -resource-dir=%t/Inputs/usr/lib/clang/20 \
+// RUN:     --target=arm64-apple-darwin24.1.0 2>&1 \
+// RUN:   | FileCheck libcxx.cpp.macos
+
+// RUN: rm %t/Inputs/usr/lib/libc++.so
+// RUN: touch %t/Inputs/usr/lib/libc++.a
+// RUN: touch %t/Inputs/usr/lib/libc++.modules.json
+// RUN: %clang -print-library-module-manifest-path \
+// RUN:     -stdlib=libc++ \
+// RUN:     -resource-dir=%t/Inputs/usr/lib/clang/20 \
+// RUN:     --target=arm64-apple-darwin24.1.0 2>&1 \
+// RUN:   | FileCheck libcxx.cpp.macos
+
 // RUN: rm %t/Inputs/usr/lib/x86_64-linux-gnu/libc++.so
 // RUN: touch %t/Inputs/usr/lib/x86_64-linux-gnu/libc++.a
 // RUN: %clang -print-library-module-manifest-path \
@@ -40,6 +62,10 @@
 
 // CHECK: {{.*}}/Inputs/usr/lib/x86_64-linux-gnu{{/|\\}}libc++.modules.json
 
+//--- libcxx.cpp.macos
+
+// CHECK: {{.*}}libc++.modules.json
+
 //--- libcxx-no-shared-lib.cpp
 
 // Note this might find a different path depending whether search path