[clang][AST][NFC] Move isSubstitutedDefaultArgument out of TypePrinter into separate component

[Michael137]

Summary

A use-case has come up in DWARF CodeGen where we want to determine
whether a particular template argument matches the default template
parameter declaration.

Re-using this TypePrinter component there allows us to avoid duplicating
most of this code and immediately allows us to cover a wider range
of use-cases than the DWARF CodeGen does today.

[aprantl]

Seems fine to me, I just have one inline comment about the name of the namespace.

clang/include/clang/AST/TemplateUtils.h

19 ↗

(On Diff #482676)

It looks like all the other namespaces in Clang are all lowercase?

[dblaikie]

clang/include/clang/AST/TemplateUtils.h

19 ↗

(On Diff #482676)

Yeah, +1 to the naming.

& maybe not introducing a new "utils" bucket - they can be a bit of a dumping ground. Could this operation belong elsewhere/in some existing type, or maybe doesn't need a namespace wrapper - could be a free function in the clang namespace?)

clang/lib/AST/TemplateUtils.cpp

19 ↗

(On Diff #482676)

The LLVM style is to use static for file-local functions, only using anonymous namespaces for file-local classes ( https://llvm.org/docs/CodingStandards.html#anonymous-namespaces )

144–148 ↗

(On Diff #482676)

Could probably remove these "else after return"s while you're moving this code if you like.

[Michael137]

clang/include/clang/AST/TemplateUtils.h

19 ↗

(On Diff #482676)

I suppose this could just be a static function on clang::TypePrinter. We use it from CGDebugInfo already anyway so it wouldn't be an extra dependency. Wdyt? @aprantl @dblaikie

[aprantl]

clang/include/clang/AST/TemplateUtils.h

19 ↗

(On Diff #482676)

I don't have any strong opinions either way.

[dblaikie]

clang/include/clang/AST/TemplateUtils.h

19 ↗

(On Diff #482676)

Sounds good to me.

[Michael137]

• Don't create separate component. Instead move API into Type.h

[dblaikie]

Looks good, thanks!

[Michael137]

committed in 98afcbab66505661045dccb85ee9acdbf9410047 (https://reviews.llvm.org/rG98afcbab6650)
Missed phab link in commit message

clang/include/clang/AST/Type.h

void printTemplateArgumentList(raw_ostream &OS,
                                const PrintingPolicy &Policy,
                                const TemplateParameterList *TPL = nullptr);
 
 void printTemplateArgumentList(raw_ostream &OS,
                                const TemplateArgumentListInfo &Args,
                                const PrintingPolicy &Policy,
                                const TemplateParameterList *TPL = nullptr);
 
+/// Make a best-effort determination of whether the type T can be produced by
+/// substituting Args into the default argument of Param.
+bool isSubstitutedDefaultArgument(ASTContext &Ctx, TemplateArgument Arg,
+                                  const NamedDecl *Param,
+                                  ArrayRef<TemplateArgument> Args,
+                                  unsigned Depth);
+
 /// The injected class name of a C++ class template or class
 /// template partial specialization.  Used to record that a type was
 /// spelled with a bare identifier rather than as a template-id; the
 /// equivalent for non-templated classes is just RecordType.
 ///
 /// Injected class name types are always dependent.  Template
 /// instantiation turns these into RecordTypes.
 ///

clang/lib/AST/TypePrinter.cpp

if (auto *TTPD = dyn_cast_or_null<TemplateTemplateParmDecl>(PatTD))
              Ctx.getCanonicalTemplateArgument(Args[TTPD->getIndex()])
                  .structurallyEquals(Arg);
   }
 
   // FIXME: Handle more cases.
   return false;
 }
 
-/// Make a best-effort determination of whether the type T can be produced by
-/// substituting Args into the default argument of Param.
-static bool isSubstitutedDefaultArgument(ASTContext &Ctx, TemplateArgument Arg,
+bool clang::isSubstitutedDefaultArgument(ASTContext &Ctx, TemplateArgument Arg,
                                          const NamedDecl *Param,
                                          ArrayRef<TemplateArgument> Args,
                                          unsigned Depth) {
   // An empty pack is equivalent to not providing a pack argument.
   if (Arg.getKind() == TemplateArgument::Pack && Arg.pack_size() == 0)
     return true;
 
   if (auto *TTPD = dyn_cast<TemplateTypeParmDecl>(Param)) {