Add support for namespaces on #pragma clang attribute

Namespaces are introduced by adding an "identifier." before a
push/pop directive. Pop directives with namespaces can only pop a
attribute group that was pushed with the same namespace. Push and pop
directives that don't opt into namespaces have the same semantics.

This is necessary to prevent a pitfall of using multiple #pragma
clang attribute directives spread out in a large file, particularly
when macros are involved. It isn't easy to see which pop corripsonds
to which push, so its easy to inadvertently pop the wrong group.

Differential revision: https://reviews.llvm.org/D55628

llvm-svn: 349845

clang/docs/LanguageExtensions.rst

@@ -2697,6 +2697,36 @@ The ``__declspec`` style syntax is also supported:
 A single push directive accepts only one attribute regardless of the syntax
 used.
 
+Because multiple push directives can be nested, if you're writing a macro that
+expands to ``_Pragma("clang attribute")`` it's good hygiene (though not
+required) to add a namespace to your push/pop directives. A pop directive with a
+namespace will pop the innermost push that has that same namespace. This will
+ensure that another macro's ``pop`` won't inadvertently pop your attribute. Note
+that an ``pop`` without a namespace will pop the innermost ``push`` without a
+namespace. ``push``es with a namespace can only be popped by ``pop`` with the
+same namespace. For instance:
+
+.. code-block:: c++
+
+   #define ASSUME_NORETURN_BEGIN _Pragma("clang attribute AssumeNoreturn.push ([[noreturn]], apply_to = function)")
+   #define ASSUME_NORETURN_END   _Pragma("clang attribute AssumeNoreturn.pop")
+
+   #define ASSUME_UNAVAILABLE_BEGIN _Pragma("clang attribute Unavailable.push (__attribute__((unavailable)), apply_to=function)")
+   #define ASSUME_UNAVAILABLE_END   _Pragma("clang attribute Unavailable.pop")
+
+
+   ASSUME_NORETURN_BEGIN
+   ASSUME_UNAVAILABLE_BEGIN
+   void function(); // function has [[noreturn]] and __attribute__((unavailable))
+   ASSUME_NORETURN_END
+   void other_function(); // function has __attribute__((unavailable))
+   ASSUME_UNAVAILABLE_END
+
+Without the namespaces on the macros, ``other_function`` will be annotated with
+``[[noreturn]]`` instead of ``__attribute__((unavailable))``. This may seem like
+a contrived example, but its very possible for this kind of situation to appear
+in real code if the pragmas are spread out accross a large file.
+
 Subject Match Rules
 -------------------
 

clang/include/clang/Basic/DiagnosticParseKinds.td

@@ -1100,6 +1100,13 @@ def err_pragma_attribute_unknown_subject_sub_rule : Error<
   "sub-rules: %3}2">;
 def err_pragma_attribute_duplicate_subject : Error<
   "duplicate attribute subject matcher '%0'">;
+def err_pragma_attribute_expected_period : Error<
+  "expected '.' after pragma attribute namespace %0">;
+def err_pragma_attribute_namespace_on_attribute : Error<
+  "namespace can only apply to 'push' or 'pop' directives">;
+def note_pragma_attribute_namespace_on_attribute : Note<
+  "omit the namespace to add attributes to the most-recently"
+  " pushed attribute group">;
 
 def err_opencl_unroll_hint_on_non_loop : Error<
   "OpenCL only supports 'opencl_unroll_hint' attribute on for, while, and do statements">;

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -815,7 +815,8 @@ def err_pragma_attribute_matcher_negated_subrule_contradicts_subrule : Error<
 def err_pragma_attribute_invalid_matchers : Error<
   "attribute %0 can't be applied to %1">;
 def err_pragma_attribute_stack_mismatch : Error<
-  "'#pragma clang attribute pop' with no matching '#pragma clang attribute push'">;
+  "'#pragma clang attribute %select{%1.|}0pop' with no matching"
+  " '#pragma clang attribute %select{%1.|}0push'">;
 def warn_pragma_attribute_unused : Warning<
   "unused attribute %0 in '#pragma clang attribute push' region">,
   InGroup<PragmaClangAttribute>;

clang/include/clang/Sema/Sema.h

@@ -503,6 +503,8 @@ public:
   struct PragmaAttributeGroup {
     /// The location of the push attribute.
     SourceLocation Loc;
+    /// The namespace of this push group.
+    const IdentifierInfo *Namespace;
     SmallVector<PragmaAttributeEntry, 2> Entries;
   };
 
@@ -8494,10 +8496,12 @@ public:
   void ActOnPragmaAttributeAttribute(ParsedAttr &Attribute,
                                      SourceLocation PragmaLoc,
                                      attr::ParsedSubjectMatchRuleSet Rules);
-  void ActOnPragmaAttributeEmptyPush(SourceLocation PragmaLoc);
+  void ActOnPragmaAttributeEmptyPush(SourceLocation PragmaLoc,
+                                     const IdentifierInfo *Namespace);
 
   /// Called on well-formed '\#pragma clang attribute pop'.
-  void ActOnPragmaAttributePop(SourceLocation PragmaLoc);
+  void ActOnPragmaAttributePop(SourceLocation PragmaLoc,
+                               const IdentifierInfo *Namespace);
 
   /// Adds the attributes that have been specified using the
   /// '\#pragma clang attribute push' directives to the given declaration.

clang/lib/Parse/ParsePragma.cpp

@@ -1139,6 +1139,7 @@ struct PragmaAttributeInfo {
   enum ActionType { Push, Pop, Attribute };
   ParsedAttributes &Attributes;
   ActionType Action;
+  const IdentifierInfo *Namespace = nullptr;
   ArrayRef<Token> Tokens;
 
   PragmaAttributeInfo(ParsedAttributes &Attributes) : Attributes(Attributes) {}
@@ -1393,7 +1394,7 @@ void Parser::HandlePragmaAttribute() {
   auto *Info = static_cast<PragmaAttributeInfo *>(Tok.getAnnotationValue());
   if (Info->Action == PragmaAttributeInfo::Pop) {
     ConsumeAnnotationToken();
-    Actions.ActOnPragmaAttributePop(PragmaLoc);
+    Actions.ActOnPragmaAttributePop(PragmaLoc, Info->Namespace);
     return;
   }
   // Parse the actual attribute with its arguments.
@@ -1403,7 +1404,7 @@ void Parser::HandlePragmaAttribute() {
 
   if (Info->Action == PragmaAttributeInfo::Push && Info->Tokens.empty()) {
     ConsumeAnnotationToken();
-    Actions.ActOnPragmaAttributeEmptyPush(PragmaLoc);
+    Actions.ActOnPragmaAttributeEmptyPush(PragmaLoc, Info->Namespace);
     return;
   }
 
@@ -1555,7 +1556,7 @@ void Parser::HandlePragmaAttribute() {
 
   // Handle a mixed push/attribute by desurging to a push, then an attribute.
   if (Info->Action == PragmaAttributeInfo::Push)
-    Actions.ActOnPragmaAttributeEmptyPush(PragmaLoc);
+    Actions.ActOnPragmaAttributeEmptyPush(PragmaLoc, Info->Namespace);
 
   Actions.ActOnPragmaAttributeAttribute(Attribute, PragmaLoc,
                                         std::move(SubjectMatchRules));
@@ -3118,12 +3119,22 @@ void PragmaForceCUDAHostDeviceHandler::HandlePragma(
 ///
 /// The syntax is:
 /// \code
-///  #pragma clang attribute push(attribute, subject-set)
+///  #pragma clang attribute push (attribute, subject-set)
 ///  #pragma clang attribute push
 ///  #pragma clang attribute (attribute, subject-set)
 ///  #pragma clang attribute pop
 /// \endcode
 ///
+/// There are also 'namespace' variants of push and pop directives. The bare
+/// '#pragma clang attribute (attribute, subject-set)' version doesn't require a
+/// namespace, since it always applies attributes to the most recently pushed
+/// group, regardless of namespace.
+/// \code
+///  #pragma clang attribute namespace.push (attribute, subject-set)
+///  #pragma clang attribute namespace.push
+///  #pragma clang attribute namespace.pop
+/// \endcode
+///
 /// The subject-set clause defines the set of declarations which receive the
 /// attribute. Its exact syntax is described in the LanguageExtensions document
 /// in Clang's documentation.
@@ -3139,6 +3150,22 @@ void PragmaAttributeHandler::HandlePragma(Preprocessor &PP,
   auto *Info = new (PP.getPreprocessorAllocator())
       PragmaAttributeInfo(AttributesForPragmaAttribute);
 
+  // Parse the optional namespace followed by a period.
+  if (Tok.is(tok::identifier)) {
+    IdentifierInfo *II = Tok.getIdentifierInfo();
+    if (!II->isStr("push") && !II->isStr("pop")) {
+      Info->Namespace = II;
+      PP.Lex(Tok);
+
+      if (!Tok.is(tok::period)) {
+        PP.Diag(Tok.getLocation(), diag::err_pragma_attribute_expected_period)
+            << II;
+        return;
+      }
+      PP.Lex(Tok);
+    }
+  }
+
   if (!Tok.isOneOf(tok::identifier, tok::l_paren)) {
     PP.Diag(Tok.getLocation(),
             diag::err_pragma_attribute_expected_push_pop_paren);
@@ -3146,9 +3173,16 @@ void PragmaAttributeHandler::HandlePragma(Preprocessor &PP,
   }
 
   // Determine what action this pragma clang attribute represents.
-  if (Tok.is(tok::l_paren))
+  if (Tok.is(tok::l_paren)) {
+    if (Info->Namespace) {
+      PP.Diag(Tok.getLocation(),
+              diag::err_pragma_attribute_namespace_on_attribute);
+      PP.Diag(Tok.getLocation(),
+              diag::note_pragma_attribute_namespace_on_attribute);
+      return;
+    }
     Info->Action = PragmaAttributeInfo::Attribute;
-  else {
+  } else {
     const IdentifierInfo *II = Tok.getIdentifierInfo();
     if (II->isStr("push"))
       Info->Action = PragmaAttributeInfo::Push;

clang/lib/Sema/SemaAttr.cpp

@@ -631,28 +631,46 @@ void Sema::ActOnPragmaAttributeAttribute(
       {PragmaLoc, &Attribute, std::move(SubjectMatchRules), /*IsUsed=*/false});
 }
 
-void Sema::ActOnPragmaAttributeEmptyPush(SourceLocation PragmaLoc) {
+void Sema::ActOnPragmaAttributeEmptyPush(SourceLocation PragmaLoc,
+                                         const IdentifierInfo *Namespace) {
   PragmaAttributeStack.emplace_back();
   PragmaAttributeStack.back().Loc = PragmaLoc;
+  PragmaAttributeStack.back().Namespace = Namespace;
 }
 
-void Sema::ActOnPragmaAttributePop(SourceLocation PragmaLoc) {
+void Sema::ActOnPragmaAttributePop(SourceLocation PragmaLoc,
+                                   const IdentifierInfo *Namespace) {
   if (PragmaAttributeStack.empty()) {
-    Diag(PragmaLoc, diag::err_pragma_attribute_stack_mismatch);
+    Diag(PragmaLoc, diag::err_pragma_attribute_stack_mismatch) << 1;
     return;
   }
 
-  for (const PragmaAttributeEntry &Entry :
-       PragmaAttributeStack.back().Entries) {
-    if (!Entry.IsUsed) {
-      assert(Entry.Attribute && "Expected an attribute");
-      Diag(Entry.Attribute->getLoc(), diag::warn_pragma_attribute_unused)
-          << Entry.Attribute->getName();
-      Diag(PragmaLoc, diag::note_pragma_attribute_region_ends_here);
+  // Dig back through the stack trying to find the most recently pushed group
+  // that in Namespace. Note that this works fine if no namespace is present,
+  // think of push/pops without namespaces as having an implicit "nullptr"
+  // namespace.
+  for (size_t Index = PragmaAttributeStack.size(); Index;) {
+    --Index;
+    if (PragmaAttributeStack[Index].Namespace == Namespace) {
+      for (const PragmaAttributeEntry &Entry :
+           PragmaAttributeStack[Index].Entries) {
+        if (!Entry.IsUsed) {
+          assert(Entry.Attribute && "Expected an attribute");
+          Diag(Entry.Attribute->getLoc(), diag::warn_pragma_attribute_unused)
+              << *Entry.Attribute;
+          Diag(PragmaLoc, diag::note_pragma_attribute_region_ends_here);
+        }
+      }
+      PragmaAttributeStack.erase(PragmaAttributeStack.begin() + Index);
+      return;
     }
   }
 
-  PragmaAttributeStack.pop_back();
+  if (Namespace)
+    Diag(PragmaLoc, diag::err_pragma_attribute_stack_mismatch)
+        << 0 << Namespace->getName();
+  else
+    Diag(PragmaLoc, diag::err_pragma_attribute_stack_mismatch) << 1;
 }
 
 void Sema::AddPragmaAttributes(Scope *S, Decl *D) {

clang/test/Parser/pragma-attribute.cpp

@@ -102,7 +102,7 @@ void function();
 
 #pragma clang attribute // expected-error {{expected 'push', 'pop', or '(' after '#pragma clang attribute'}}
 #pragma clang attribute 42 // expected-error {{expected 'push', 'pop', or '(' after '#pragma clang attribute'}}
-#pragma clang attribute pushpop // expected-error {{unexpected argument 'pushpop' to '#pragma clang attribute'; expected 'push' or 'pop'}}
+#pragma clang attribute pushpop // expected-error {{expected '.' after pragma attribute namespace 'pushpop'}}
 
 #pragma clang attribute push
 #pragma clang attribute pop

clang/test/Sema/pragma-attribute-namespace.c

@@ -0,0 +1,37 @@
+// RUN: %clang_cc1 -fsyntax-only -verify %s
+
+#pragma clang attribute MyNamespace.push (__attribute__((annotate)), apply_to=function) // expected-error 2 {{'annotate' attribute}}
+
+int some_func(); // expected-note{{when applied to this declaration}}
+
+#pragma clang attribute pop // expected-error{{'#pragma clang attribute pop' with no matching '#pragma clang attribute push'}}
+#pragma clang attribute NotMyNamespace.pop // expected-error{{'#pragma clang attribute NotMyNamespace.pop' with no matching '#pragma clang attribute NotMyNamespace.push'}}
+
+#pragma clang attribute MyOtherNamespace.push (__attribute__((annotate)), apply_to=function) // expected-error 2 {{'annotate' attribute}}
+
+int some_other_func(); // expected-note 2 {{when applied to this declaration}}
+
+// Out of order!
+#pragma clang attribute MyNamespace.pop
+
+int some_other_other_func(); // expected-note 1 {{when applied to this declaration}}
+
+#pragma clang attribute MyOtherNamespace.pop
+
+#pragma clang attribute Misc. () // expected-error{{namespace can only apply to 'push' or 'pop' directives}} expected-note {{omit the namespace to add attributes to the most-recently pushed attribute group}}
+
+#pragma clang attribute Misc push // expected-error{{expected '.' after pragma attribute namespace 'Misc'}}
+
+// Test how pushes with namespaces interact with pushes without namespaces.
+
+#pragma clang attribute Merp.push (__attribute__((annotate)), apply_to=function) // expected-error{{'annotate' attribute}}
+#pragma clang attribute push (__attribute__((annotate)), apply_to=function) // expected-warning {{unused attribute}}
+#pragma clang attribute pop // expected-note{{ends here}}
+int test(); // expected-note{{when applied to this declaration}}
+#pragma clang attribute Merp.pop
+
+#pragma clang attribute push (__attribute__((annotate)), apply_to=function) // expected-warning {{unused attribute}}
+#pragma clang attribute Merp.push (__attribute__((annotate)), apply_to=function) // expected-error{{'annotate' attribute}}
+#pragma clang attribute pop // expected-note{{ends here}}
+int test2(); // expected-note{{when applied to this declaration}}
+#pragma clang attribute Merp.pop