Skip system headers in Clang generator

When not requesting any particular function, `sapi_library()` will try and
make available _all_ functions it finds. In this case, system headers should
be skipped to avoid inflating the API surface. Standard library functions
can still be manually requested by adding them to the `functions` (Bazel)/
`FUNCTIONS` (CMake) argument.

PiperOrigin-RevId: 472272506
Change-Id: I8f8d79796d3044e598eebb7f87ce4cf464b47ed7

sandboxed_api/tools/clang_generator/emitter_test.cc

@@ -52,7 +52,7 @@ TEST_F(EmitterTest, BasicFunctionality) {
 
   EmitterForTesting emitter;
   RunFrontendAction(R"(extern "C" void ExposedFunction() {})",
-                    absl::make_unique<GeneratorAction>(emitter, options));
+                    std::make_unique<GeneratorAction>(emitter, options));
 
   EXPECT_THAT(emitter.functions_, SizeIs(1));
 
@@ -80,7 +80,7 @@ TEST_F(EmitterTest, RelatedTypes) {
     typedef struct { int member; } MyStruct;
     extern "C" void Structize(MyStruct* s);
         )",
-      absl::make_unique<GeneratorAction>(emitter, GeneratorOptions()));
+      std::make_unique<GeneratorAction>(emitter, GeneratorOptions()));
 
   // Types from "std" should be skipped
   EXPECT_THAT(emitter.rendered_types_["std"], IsEmpty());
@@ -106,7 +106,7 @@ TEST_F(EmitterTest, NestedStruct) {
     };
     extern "C" void Structize(A* s);
         )",
-      absl::make_unique<GeneratorAction>(emitter, GeneratorOptions()));
+      std::make_unique<GeneratorAction>(emitter, GeneratorOptions()));
 
   EXPECT_THAT(UglifyAll(emitter.rendered_types_[""]),
               ElementsAre("struct A {"
@@ -125,7 +125,7 @@ TEST_F(EmitterTest, NestedAnonymousStruct) {
     };
     extern "C" void Structize(A* s);
         )",
-      absl::make_unique<GeneratorAction>(emitter, GeneratorOptions()));
+      std::make_unique<GeneratorAction>(emitter, GeneratorOptions()));
 
   EXPECT_THAT(UglifyAll(emitter.rendered_types_[""]),
               ElementsAre("struct A {"
@@ -144,7 +144,7 @@ TEST_F(EmitterTest, ParentNotCollected) {
     };
     extern "C" void Structize(A::B* s);
         )",
-      absl::make_unique<GeneratorAction>(emitter, GeneratorOptions()));
+      std::make_unique<GeneratorAction>(emitter, GeneratorOptions()));
 
   EXPECT_THAT(UglifyAll(emitter.rendered_types_[""]),
               ElementsAre("struct A {"
@@ -160,7 +160,7 @@ TEST_F(EmitterTest, RemoveQualifiers) {
     struct A { int data; };
     extern "C" void Structize(const A* in, A* out);
         )",
-      absl::make_unique<GeneratorAction>(emitter, GeneratorOptions()));
+      std::make_unique<GeneratorAction>(emitter, GeneratorOptions()));
 
   EXPECT_THAT(UglifyAll(emitter.rendered_types_[""]),
               ElementsAre("struct A { int data; }"));

sandboxed_api/tools/clang_generator/generator.cc

@@ -48,12 +48,25 @@ std::string GetOutputFilename(absl::string_view source_file) {
 }
 
 bool GeneratorASTVisitor::VisitFunctionDecl(clang::FunctionDecl* decl) {
-  if (!decl->isCXXClassMember() &&  // Skip classes
-      decl->isExternC() &&          // Skip non external functions
-      !decl->isTemplated() &&       // Skip function templates
-      // Process either all function or just the requested ones
-      (options_.function_names.empty() ||
-       options_.function_names.count(ToStringView(decl->getName())) > 0)) {
+  if (decl->isCXXClassMember() ||  // Skip classes
+      !decl->isExternC() ||        // Skip non external functions
+      decl->isTemplated()          // Skip function templates
+  ) {
+    return true;
+  }
+
+  // Process either all function or just the requested ones
+  if (bool all_functions = options_.function_names.empty();
+      all_functions ||
+      options_.function_names.count(ToStringView(decl->getName())) > 0) {
+    // Skip functions from system headers when all functions are requested.
+    // This allows to still specify standard library functions explicitly.
+    if (all_functions &&
+        decl->getASTContext().getSourceManager().isInSystemHeader(
+            decl->getBeginLoc())) {
+      return true;
+    }
+
     functions_.push_back(decl);
 
     collector_.CollectRelatedTypes(decl->getDeclaredReturnType());

sandboxed_api/tools/clang_generator/generator.h

@@ -97,8 +97,8 @@ class GeneratorAction : public clang::ASTFrontendAction {
  private:
   std::unique_ptr<clang::ASTConsumer> CreateASTConsumer(
       clang::CompilerInstance&, llvm::StringRef in_file) override {
-    return absl::make_unique<GeneratorASTConsumer>(std::string(in_file),
-                                                   emitter_, options_);
+    return std::make_unique<GeneratorASTConsumer>(std::string(in_file),
+                                                  emitter_, options_);
   }
 
   bool hasCodeCompletionSupport() const override { return false; }
@@ -116,7 +116,7 @@ class GeneratorFactory : public clang::tooling::FrontendActionFactory {
  private:
 #if LLVM_VERSION_MAJOR >= 10
   std::unique_ptr<clang::FrontendAction> create() override {
-    return absl::make_unique<GeneratorAction>(emitter_, options_);
+    return std::make_unique<GeneratorAction>(emitter_, options_);
   }
 #else
   clang::FrontendAction* create() override {

sandboxed_api/tools/clang_generator/generator_tool.cc

@@ -136,7 +136,7 @@ absl::Status GeneratorMain(int argc, char* argv[]) {
   }
 
   if (int result = tool.run(
-          absl::make_unique<sapi::GeneratorFactory>(emitter, options).get());
+          std::make_unique<sapi::GeneratorFactory>(emitter, options).get());
       result != 0) {
     return absl::UnknownError("header generation failed");
   }