Put types defined in prototype into translation unit context

[sepavloff]

Summary

If a type is defined in a function prototype, put it into translation unit
rather than current context. This patch fixes PR19018, in which such type
was placed into class context, but as it did not have access specifier,
assertion violation occurred.

[rsmith]

I think this is the wrong place for this fix; can we check for types being defined in a parameter type sooner, and mark the type invalid in that case? (The assertion will be suppressed for an invalid type.)

We also assert on this test case, for a reason that looks closely related:

struct pr19018 {
  short foo6 (struct bar0 {} bar3); // expected-error{{cannot be defined in a parameter type}}
  bar0 *p;
};

... and I'd really like us to fix this more thoroughly, for all relevant cases.

lib/Sema/SemaDecl.cpp

10743–10748

This looks wrong in C. Given:

void f(enum E { e } *p);

... the enum definition should not be visible outside the function.

[sepavloff]

This revision is superceder by D4145.

lib/Sema/SemaDecl.cpp

if (Name && SS.isNotEmpty()) {
     if (!getLangOpts().CPlusPlus && TUK != TUK_Reference) {
       // FIXME: This makes sure that we ignore the contexts associated
       // with C structs, unions, and enums when looking for a matching
       // tag declaration or definition. See the similar lookup tweak
       // in Sema::LookupName; is there a better way to deal with this?
       while (isa<RecordDecl>(SearchDC) || isa<EnumDecl>(SearchDC))
         SearchDC = SearchDC->getParent();
     }
-  } else if (S->isFunctionPrototypeScope()) {
+  }
+  if (S->isFunctionPrototypeScope() && TUK == TUK_Definition) {
     // If this is an enum declaration in function prototype scope, set its
     // initial context to the translation unit.
     // FIXME: [citation needed]
     SearchDC = Context.getTranslationUnitDecl();
   }
 
   if (Previous.isSingleResult() &&
       Previous.getFoundDecl()->isTemplateParameter()) {
     // Maybe we will complain about the shadowed template parameter.
     DiagnoseTemplateParameterShadow(NameLoc, Previous.getFoundDecl());
     // Just pretend that we didn't see the previous declaration.
     Previous.clear();
   }

test/SemaCXX/type-definition-in-specifier.cpp

void f0() {
   struct S3 { int x; } s3;
 
   (void)static_cast<struct S4 { int x; } *>(0); // expected-error{{cannot be defined}}
 }
 
 struct S5 { int x; } f1() { return S5(); } // expected-error{{result type}}
 
 void f2(struct S6 { int x; } p); // expected-error{{parameter type}}
+
+struct pr19018 {
+  short foo6 (enum bar0 {qq} bar3); // expected-error{{cannot be defined in a parameter type}}
+};
+
+struct pr19018a {
+  void func1(enum t19018 {qq} x); // expected-error{{cannot be defined in a parameter type}}
+  void func2(enum t19018 {qq} x); // expected-error{{cannot be defined in a parameter type}}
+  void func3(enum {qq} x);        // expected-error{{cannot be defined in a parameter type}}
+  void func4(struct t19018 {int qq;} x);  // expected-error{{cannot be defined in a parameter type}}
+  void func5(struct {int qq;} x); // expected-error{{cannot be defined in a parameter type}}
+};
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