When a tag is declared in prototype scope in C, if we've decided that it

redeclares an existing tag but are creating a new declaration anyway (because
it has attributes or changes the visibility of the name), don't warn that it
won't be visible outside the current scope. That's not true.

Also narrow down the set of cases where we create these extra declarations when
building modules; previously, all tag declarations but the first in a module
header would get this treatment if -fmodules-local-submodule-visibility. (This
isn't a functional change, but we try to avoid creating these extra
declarations whenever we can.)

llvm-svn: 257403

clang/lib/Sema/SemaDecl.cpp

@@ -12316,7 +12316,8 @@ Decl *Sema::ActOnTag(Scope *S, unsigned TagSpec, TagUseKind TUK,
             } else if (TUK == TUK_Reference &&
                        (PrevTagDecl->getFriendObjectKind() ==
                             Decl::FOK_Undeclared ||
-                        getOwningModule(PrevDecl) !=
+                        PP.getModuleContainingLocation(
+                            PrevDecl->getLocation()) !=
                             PP.getModuleContainingLocation(KWLoc)) &&
                        SS.isEmpty()) {
               // This declaration is a reference to an existing entity, but
@@ -12326,8 +12327,7 @@ Decl *Sema::ActOnTag(Scope *S, unsigned TagSpec, TagUseKind TUK,
               // the declaration would have meant the same thing if no prior
               // declaration were found, that is, if it was found in the same
               // scope where we would have injected a declaration.
-              if (!getTagInjectionContext(CurContext)
-                       ->getRedeclContext()
+              if (!getTagInjectionContext(CurContext)->getRedeclContext()
                        ->Equals(PrevDecl->getDeclContext()->getRedeclContext()))
                 return PrevTagDecl;
               // This is in the injected scope, create a new declaration in
@@ -12634,7 +12634,7 @@ CreateNewDecl:
             << Name;
         Invalid = true;
       }
-    } else {
+    } else if (!PrevDecl) {
       Diag(Loc, diag::warn_decl_in_param_list) << Context.getTagDeclType(New);
     }
     DeclsInPrototypeScope.push_back(New);

clang/test/Modules/tag-injection.c

@@ -0,0 +1,18 @@
+// RUN: rm -rf %t
+// RUN: mkdir %t
+// RUN: echo 'struct a;' > %t/a.h
+// RUN: echo 'struct b {}; void foo(struct b*);' > %t/b.h
+// RUN: echo 'module X { module a { header "a.h" } module b { header "b.h" } }' > %t/x.modulemap
+// RUN: %clang_cc1 -fmodules -fmodules-cache-path=%t -fmodule-map-file=%t/x.modulemap %s -I%t -verify
+
+#include "a.h"
+
+void f(struct a *p);
+
+// FIXME: We should warn that 'b' will not be visible outside of this function,
+// but we merge this 'b' with X.b's 'b' because we don't yet implement C's
+// "compatible types" rule.
+void g(struct b *p);
+
+struct b b; // expected-error {{definition of 'b' must be imported from module 'X.b' before it is required}}
+// expected-note@b.h:1 {{here}}

clang/test/Sema/decl-in-prototype.c

@@ -35,3 +35,6 @@ void f6(struct z {int b;} c) { // expected-warning {{declaration of 'struct z' w
 void pr19018_1 (enum e19018 { qq } x); // expected-warning{{declaration of 'enum e19018' will not be visible outside of this function}}
 enum e19018 qq; //expected-error{{tentative definition has type 'enum e19018' that is never completed}} \
                 //expected-note{{forward declaration of 'enum e19018'}}
+
+// Only warn once, even if we create two declarations.
+void f(struct q *, struct __attribute__((aligned(4))) q *); // expected-warning {{will not be visible outside}}