Give Type::getDesugaredType a "for-display" mode that can apply more

heuristics to determine when it's useful to desugar a type for display
to the user. Introduce two C++-specific heuristics:

  - For a qualified type (like "foo::bar"), only produce a new
    desugred type if desugaring the qualified type ("bar", in this
    case) produces something interesting. For example, if "foo::bar"
    refers to a class named "bar", don't desugar. However, if
    "foo::bar" refers to a typedef of something else, desugar to that
    something else. This gives some useful desugaring such as
    "foo::bar (aka 'int')".
  - Don't desugar class template specialization types like
    "basic_string<char>" down to their underlying "class
    basic_string<char, char_traits<char>, allocator<char>>, etc.";
    it's better just to leave such types alone. 

Update diagnostics.html with some discussion and examples of type
preservation in C++, showing qualified names and class template
specialization types.

llvm-svn: 68207

1 files changed, 1 insertions, 1 deletions

diff --git a/clang/lib/Sema/Sema.cpp b/clang/lib/Sema/Sema.cpp
index 7e72a8453b6..f11ce2043a8 100644
--- a/clang/lib/Sema/Sema.cpp
+++ b/clang/lib/Sema/Sema.cpp
@@ -40,7 +40,7 @@ static void ConvertArgToStringFn(Diagnostic::ArgumentKind Kind, intptr_t Val,
     
     // If this is a sugared type (like a typedef, typeof, etc), then unwrap one
     // level of the sugar so that the type is more obvious to the user.
-    QualType DesugaredTy = Ty->getDesugaredType();
+    QualType DesugaredTy = Ty->getDesugaredType(true);
     DesugaredTy.setCVRQualifiers(DesugaredTy.getCVRQualifiers() |
                                  Ty.getCVRQualifiers());