[clang] Improves -print-library-module-manifest-path. (#85943)

This adds a libc++ to modules.json as is currently used by libc++. When
libc++.so is not found the function will search for libc++.a as
fallback.

Author: mordante

clang/lib/Driver/Driver.cpp

@@ -6203,28 +6203,35 @@ std::string Driver::GetStdModuleManifestPath(const Compilation &C,
 
   switch (TC.GetCXXStdlibType(C.getArgs())) {
   case ToolChain::CST_Libcxx: {
-    std::string lib = GetFilePath("libc++.so", TC);
-
-    // Note when there are multiple flavours of libc++ the module json needs to
-    // look at the command-line arguments for the proper json.
-    // These flavours do not exist at the moment, but there are plans to
-    // provide a variant that is built with sanitizer instrumentation enabled.
-
-    // For example
-    //  StringRef modules = [&] {
-    //    const SanitizerArgs &Sanitize = TC.getSanitizerArgs(C.getArgs());
-    //    if (Sanitize.needsAsanRt())
-    //      return "modules-asan.json";
-    //    return "modules.json";
-    //  }();
-
-    SmallString<128> path(lib.begin(), lib.end());
-    llvm::sys::path::remove_filename(path);
-    llvm::sys::path::append(path, "modules.json");
-    if (TC.getVFS().exists(path))
-      return static_cast<std::string>(path);
+    auto evaluate = [&](const char *library) -> std::optional<std::string> {
+      std::string lib = GetFilePath(library, TC);
+
+      // Note when there are multiple flavours of libc++ the module json needs
+      // to look at the command-line arguments for the proper json. These
+      // flavours do not exist at the moment, but there are plans to provide a
+      // variant that is built with sanitizer instrumentation enabled.
+
+      // For example
+      //  StringRef modules = [&] {
+      //    const SanitizerArgs &Sanitize = TC.getSanitizerArgs(C.getArgs());
+      //    if (Sanitize.needsAsanRt())
+      //      return "libc++.modules-asan.json";
+      //    return "libc++.modules.json";
+      //  }();
+
+      SmallString<128> path(lib.begin(), lib.end());
+      llvm::sys::path::remove_filename(path);
+      llvm::sys::path::append(path, "libc++.modules.json");
+      if (TC.getVFS().exists(path))
+        return static_cast<std::string>(path);
+
+      return {};
+    };
 
-    return error;
+    if (std::optional<std::string> result = evaluate("libc++.so"); result)
+      return *result;
+
+    return evaluate("libc++.a").value_or(error);
   }
 
   case ToolChain::CST_Libstdcxx:

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

@@ -3,20 +3,29 @@
 // RUN: rm -rf %t && split-file %s %t && cd %t
 // RUN: mkdir -p %t/Inputs/usr/lib/x86_64-linux-gnu
 // RUN: touch %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 \
 // RUN:     -stdlib=libc++ \
 // RUN:     -resource-dir=%t/Inputs/usr/lib/x86_64-linux-gnu \
 // RUN:     --target=x86_64-linux-gnu 2>&1 \
 // RUN:   | FileCheck libcxx-no-module-json.cpp
 
-// RUN: touch %t/Inputs/usr/lib/x86_64-linux-gnu/modules.json
+// RUN: touch %t/Inputs/usr/lib/x86_64-linux-gnu/libc++.modules.json
 // RUN: %clang -print-library-module-manifest-path \
 // RUN:     -stdlib=libc++ \
 // RUN:     -resource-dir=%t/Inputs/usr/lib/x86_64-linux-gnu \
 // RUN:     --target=x86_64-linux-gnu 2>&1 \
 // RUN:   | FileCheck libcxx.cpp
 
+// 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 \
+// RUN:     -stdlib=libc++ \
+// RUN:     -resource-dir=%t/Inputs/usr/lib/x86_64-linux-gnu \
+// RUN:     --target=x86_64-linux-gnu 2>&1 \
+// RUN:   | FileCheck libcxx-no-shared-lib.cpp
+
 // RUN: %clang -print-library-module-manifest-path \
 // RUN:     -stdlib=libstdc++ \
 // RUN:     -resource-dir=%t/Inputs/usr/lib/x86_64-linux-gnu \
@@ -29,7 +38,13 @@
 
 //--- libcxx.cpp
 
-// CHECK: {{.*}}/Inputs/usr/lib/x86_64-linux-gnu{{/|\\}}modules.json
+// CHECK: {{.*}}/Inputs/usr/lib/x86_64-linux-gnu{{/|\\}}libc++.modules.json
+
+//--- libcxx-no-shared-lib.cpp
+
+// Note this might find a different path depending whether search path
+// contains a different libc++.so.
+// CHECK: {{.*}}libc++.modules.json
 
 //--- libstdcxx.cpp