[Sema][Comments] Add support for TypeAliasTemplate

[bruno]

Summary

Emit proper diagnostics when -Wdocumentation is used with constructs such as:

template<typename T>
using fn = int(T aaa, int ccc);

Previously clang wouldn't recognize the function and complain with
'comment that is not attached to a function declaration'.

[gribozavr]

LGTM with two more tests.

test/Sema/warn-documentation.cpp

433

For consistency with the rest of the file, could you use '11' instead of 'A'?

Could you also add these two tests:

/// <please-add-some-comment>
template<typename T>
using test_function_like_using10 = int (*)(T aaa, int ccc);

/// <please-add-some-comment>
template<typename T>
using test_function_like_using12 = foo::function_wrapper<int (T aaa, int ccc)> *;

[bruno]

Applied your suggestions and committed r279754. Thanks!

lib/AST/Comment.cpp

case Decl::Typedef: {
     }
     break;
   }
   case Decl::TypeAliasTemplate: {
     const TypeAliasTemplateDecl *TAT = cast<TypeAliasTemplateDecl>(CommentDecl);
     Kind = TypedefKind;
     TemplateKind = Template;
     TemplateParameters = TAT->getTemplateParameters();
+    TypeAliasDecl *TAD = TAT->getTemplatedDecl();
+    if (!TAD)
+      break;
+
+    const TypeSourceInfo *TSI = TAD->getTypeSourceInfo();
+    if (!TSI)
+      break;
+    TypeLoc TL = TSI->getTypeLoc().getUnqualifiedLoc();
+    FunctionTypeLoc FTL;
+    if (getFunctionTypeLoc(TL, FTL)) {
+      Kind = FunctionKind;
+      ParamVars = FTL.getParams();
+      ReturnType = FTL.getReturnLoc().getType();
+    }
     break;
   }
   case Decl::Enum:
     Kind = EnumKind;
     break;
   }
 
   IsFilled = true;

test/Sema/warn-documentation.cpp

 using test_function_like_using7 = foo::function_wrapper<int (int aaa, int ccc)> &;
 
 // expected-warning@+2 {{parameter 'bbb' not found in the function declaration}} expected-note@+2 {{did you mean 'ccc'?}}
 /// \param aaa Meow.
 /// \param bbb Bbb.
 /// \returns aaa.
 using test_function_like_using8 = foo::function_wrapper<int (int aaa, int ccc)> &&;
 
+// expected-warning@+4 {{template parameter 'U' not found in the template declaration}} expected-note@+4 {{did you mean 'T'?}}
+// expected-warning@+2 {{parameter 'bbb' not found in the function declaration}} expected-note@+2 {{did you mean 'ccc'?}}
+/// \param aaa Meow.
+/// \param bbb Bbb.
+/// \tparam U Uuu.
+template<typename T>
+using test_function_like_using9 = int(T aaa, int ccc);
+
+// expected-warning@+4 {{template parameter 'U' not found in the template declaration}} expected-note@+4 {{did you mean 'T'?}}
+// expected-warning@+2 {{parameter 'bbb' not found in the function declaration}} expected-note@+2 {{did you mean 'ccc'?}}
+/// \param aaa Meow.
+/// \param bbb Bbb.
+/// \tparam U Uuu.
+template<typename T>
+using test_function_like_usingA = foo::function_wrapper<int (T aaa, int ccc)>;
+
 using test_not_function_like_using1 = int (*)(int aaa);
 
 // expected-warning@+1 {{'\param' command used in a comment that is not attached to a function declaration}}
 /// \param aaa Meow.
 using test_not_function_like_using2 = test_not_function_like_using1;
 
 // Check that the diagnostic uses the same command marker as the comment.
 // expected-warning@+1 {{'@param' command used in a comment that is not attached to a function declaration}}