[libc] Update libc namespace clang-tidy checks (#98424)

This patch updates the clang-tidy checks for llvm-libc to ensure that
the namespace macro used to declare the libc namespace is updated from
LIBC_NAMESPACE to LIBC_NAMESPACE_DECL which by default has hidden
visibility.

Co-authored-by: Prabhu Rajesakeran <prabhukr@google.com>

Author: ilovepi

clang-tools-extra/clang-tidy/llvmlibc/CalleeNamespaceCheck.cpp

@@ -51,7 +51,7 @@ void CalleeNamespaceCheck::check(const MatchFinder::MatchResult &Result) {
   // __llvm_libc, we're good.
   const auto *NS = dyn_cast<NamespaceDecl>(getOutermostNamespace(FuncDecl));
   if (NS && Result.SourceManager->isMacroBodyExpansion(NS->getLocation()) &&
-      NS->getName().starts_with(RequiredNamespaceStart))
+      NS->getName().starts_with(RequiredNamespaceRefStart))
     return;
 
   const DeclarationName &Name = FuncDecl->getDeclName();
@@ -62,7 +62,7 @@ void CalleeNamespaceCheck::check(const MatchFinder::MatchResult &Result) {
   diag(UsageSiteExpr->getBeginLoc(),
        "%0 must resolve to a function declared "
        "within the namespace defined by the '%1' macro")
-      << FuncDecl << RequiredNamespaceMacroName;
+      << FuncDecl << RequiredNamespaceRefMacroName;
 
   diag(FuncDecl->getLocation(), "resolves to this declaration",
        clang::DiagnosticIDs::Note);

clang-tools-extra/clang-tidy/llvmlibc/ImplementationInNamespaceCheck.cpp

@@ -30,20 +30,35 @@ void ImplementationInNamespaceCheck::check(
   const auto *MatchedDecl =
       Result.Nodes.getNodeAs<Decl>("child_of_translation_unit");
   const auto *NS = dyn_cast<NamespaceDecl>(MatchedDecl);
+
+  // LLVM libc declarations should be inside of a non-anonymous namespace.
   if (NS == nullptr || NS->isAnonymousNamespace()) {
     diag(MatchedDecl->getLocation(),
          "declaration must be enclosed within the '%0' namespace")
-        << RequiredNamespaceMacroName;
+        << RequiredNamespaceDeclMacroName;
     return;
   }
+
+  // Enforce that the namespace is the result of macro expansion
   if (Result.SourceManager->isMacroBodyExpansion(NS->getLocation()) == false) {
     diag(NS->getLocation(), "the outermost namespace should be the '%0' macro")
-        << RequiredNamespaceMacroName;
+        << RequiredNamespaceDeclMacroName;
     return;
   }
-  if (NS->getName().starts_with(RequiredNamespaceStart) == false) {
+
+  // We want the macro to have [[gnu::visibility("hidden")]] as a prefix, but
+  // visibility is just an attribute in the AST construct, so we check that
+  // instead.
+  if (NS->getVisibility() != Visibility::HiddenVisibility) {
     diag(NS->getLocation(), "the '%0' macro should start with '%1'")
-        << RequiredNamespaceMacroName << RequiredNamespaceStart;
+        << RequiredNamespaceDeclMacroName << RequiredNamespaceDeclStart;
+    return;
+  }
+
+  // Lastly, make sure the namespace name actually has the __llvm_libc prefix
+  if (NS->getName().starts_with(RequiredNamespaceRefStart) == false) {
+    diag(NS->getLocation(), "the '%0' macro expansion should start with '%1'")
+        << RequiredNamespaceDeclMacroName << RequiredNamespaceRefStart;
     return;
   }
 }

clang-tools-extra/clang-tidy/llvmlibc/NamespaceConstants.h

@@ -10,7 +10,11 @@
 
 namespace clang::tidy::llvm_libc {
 
-const static llvm::StringRef RequiredNamespaceStart = "__llvm_libc";
-const static llvm::StringRef RequiredNamespaceMacroName = "LIBC_NAMESPACE";
+const static llvm::StringRef RequiredNamespaceRefStart = "__llvm_libc";
+const static llvm::StringRef RequiredNamespaceRefMacroName = "LIBC_NAMESPACE";
+const static llvm::StringRef RequiredNamespaceDeclStart =
+    "[[gnu::visibility(\"hidden\")]] __llvm_libc";
+const static llvm::StringRef RequiredNamespaceDeclMacroName =
+    "LIBC_NAMESPACE_DECL";
 
 } // namespace clang::tidy::llvm_libc

clang-tools-extra/docs/clang-tidy/checks/llvmlibc/implementation-in-namespace.rst

@@ -8,30 +8,30 @@ correct namespace.
 
 .. code-block:: c++
 
-    // Implementation inside the LIBC_NAMESPACE namespace.
+    // Implementation inside the LIBC_NAMESPACE_DECL namespace.
     // Correct if:
-    // - LIBC_NAMESPACE is a macro
-    // - LIBC_NAMESPACE expansion starts with `__llvm_libc`
-    namespace LIBC_NAMESPACE {
+    // - LIBC_NAMESPACE_DECL is a macro
+    // - LIBC_NAMESPACE_DECL expansion starts with `[[gnu::visibility("hidden")]] __llvm_libc`
+    namespace LIBC_NAMESPACE_DECL {
         void LLVM_LIBC_ENTRYPOINT(strcpy)(char *dest, const char *src) {}
-        // Namespaces within LIBC_NAMESPACE namespace are allowed.
+        // Namespaces within LIBC_NAMESPACE_DECL namespace are allowed.
         namespace inner {
             int localVar = 0;
         }
         // Functions with C linkage are allowed.
         extern "C" void str_fuzz() {}
     }
 
-    // Incorrect: implementation not in the LIBC_NAMESPACE namespace.
+    // Incorrect: implementation not in the LIBC_NAMESPACE_DECL namespace.
     void LLVM_LIBC_ENTRYPOINT(strcpy)(char *dest, const char *src) {}
 
-    // Incorrect: outer most namespace is not the LIBC_NAMESPACE macro.
+    // Incorrect: outer most namespace is not the LIBC_NAMESPACE_DECL macro.
     namespace something_else {
         void LLVM_LIBC_ENTRYPOINT(strcpy)(char *dest, const char *src) {}
     }
 
-    // Incorrect: outer most namespace expansion does not start with `__llvm_libc`.
-    #define LIBC_NAMESPACE custom_namespace
-    namespace LIBC_NAMESPACE {
+    // Incorrect: outer most namespace expansion does not start with `[[gnu::visibility("hidden")]] __llvm_libc`.
+    #define LIBC_NAMESPACE_DECL custom_namespace
+    namespace LIBC_NAMESPACE_DECL {
         void LLVM_LIBC_ENTRYPOINT(strcpy)(char *dest, const char *src) {}
     }

clang-tools-extra/test/clang-tidy/checkers/llvmlibc/implementation-in-namespace.cpp

@@ -3,60 +3,61 @@
 #define MACRO_A "defining macros outside namespace is valid"
 
 class ClassB;
-// CHECK-MESSAGES: :[[@LINE-1]]:7: warning: declaration must be enclosed within the 'LIBC_NAMESPACE' namespace
+// CHECK-MESSAGES: :[[@LINE-1]]:7: warning: declaration must be enclosed within the 'LIBC_NAMESPACE_DECL' namespace
 struct StructC {};
-// CHECK-MESSAGES: :[[@LINE-1]]:8: warning: declaration must be enclosed within the 'LIBC_NAMESPACE' namespace
-char *VarD = MACRO_A;
-// CHECK-MESSAGES: :[[@LINE-1]]:7: warning: declaration must be enclosed within the 'LIBC_NAMESPACE' namespace
+// CHECK-MESSAGES: :[[@LINE-1]]:8: warning: declaration must be enclosed within the 'LIBC_NAMESPACE_DECL' namespace
+const char *VarD = MACRO_A;
+// CHECK-MESSAGES: :[[@LINE-1]]:13: warning: declaration must be enclosed within the 'LIBC_NAMESPACE_DECL' namespace
 typedef int typeE;
-// CHECK-MESSAGES: :[[@LINE-1]]:13: warning: declaration must be enclosed within the 'LIBC_NAMESPACE' namespace
+// CHECK-MESSAGES: :[[@LINE-1]]:13: warning: declaration must be enclosed within the 'LIBC_NAMESPACE_DECL' namespace
 void funcF() {}
-// CHECK-MESSAGES: :[[@LINE-1]]:6: warning: declaration must be enclosed within the 'LIBC_NAMESPACE' namespace
+// CHECK-MESSAGES: :[[@LINE-1]]:6: warning: declaration must be enclosed within the 'LIBC_NAMESPACE_DECL' namespace
 
 namespace outer_most {
-// CHECK-MESSAGES: :[[@LINE-1]]:11: warning: the outermost namespace should be the 'LIBC_NAMESPACE' macro
+// CHECK-MESSAGES: :[[@LINE-1]]:11: warning: the outermost namespace should be the 'LIBC_NAMESPACE_DECL' macro
  class A {};
 }
 
 // Wrapped in anonymous namespace.
 namespace {
-// CHECK-MESSAGES: :[[@LINE-1]]:11: warning: declaration must be enclosed within the 'LIBC_NAMESPACE' namespace
+// CHECK-MESSAGES: :[[@LINE-1]]:11: warning: declaration must be enclosed within the 'LIBC_NAMESPACE_DECL' namespace
  class A {};
 }
 
 namespace namespaceG {
-// CHECK-MESSAGES: :[[@LINE-1]]:11: warning: the outermost namespace should be the 'LIBC_NAMESPACE' macro
+// CHECK-MESSAGES: :[[@LINE-1]]:11: warning: the outermost namespace should be the 'LIBC_NAMESPACE_DECL' macro
 namespace __llvm_libc {
 namespace namespaceH {
 class ClassB;
 } // namespace namespaceH
 struct StructC {};
 } // namespace __llvm_libc
-char *VarD = MACRO_A;
+const char *VarD = MACRO_A;
 typedef int typeE;
 void funcF() {}
 } // namespace namespaceG
 
 // Wrapped in macro namespace but with an incorrect name
-#define LIBC_NAMESPACE custom_namespace
-namespace LIBC_NAMESPACE {
-// CHECK-MESSAGES: :[[@LINE-1]]:11: warning: the 'LIBC_NAMESPACE' macro should start with '__llvm_libc'
+#define LIBC_NAMESPACE_DECL [[gnu::visibility("hidden")]] custom_namespace
+namespace LIBC_NAMESPACE_DECL {
+// CHECK-MESSAGES: :[[@LINE-1]]:11: warning: the 'LIBC_NAMESPACE_DECL' macro expansion should start with '__llvm_libc'
+
 namespace namespaceH {
 class ClassB;
 } // namespace namespaceH
-} // namespace LIBC_NAMESPACE
+} // namespace LIBC_NAMESPACE_DECL
 
 
-// Wrapped in macro namespace with a valid name, LIBC_NAMESPACE starts with '__llvm_libc'
-#undef LIBC_NAMESPACE
-#define LIBC_NAMESPACE __llvm_libc_xyz
-namespace LIBC_NAMESPACE {
+// Wrapped in macro namespace with a valid name, LIBC_NAMESPACE_DECL starts with '__llvm_libc'
+#undef LIBC_NAMESPACE_DECL
+#define LIBC_NAMESPACE_DECL [[gnu::visibility("hidden")]] __llvm_libc_xyz
+namespace LIBC_NAMESPACE_DECL {
 namespace namespaceI {
 class ClassB;
 } // namespace namespaceI
 struct StructC {};
-char *VarD = MACRO_A;
+const char *VarD = MACRO_A;
 typedef int typeE;
 void funcF() {}
 extern "C" void extern_funcJ() {}
-} // namespace LIBC_NAMESPACE
+} // namespace LIBC_NAMESPACE_DECL