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/test/SemaTemplate/qualified-names-diag.cpp b/clang/test/SemaTemplate/qualified-names-diag.cpp
index bf4ae118769..4bc8bdfc9a8 100644
--- a/clang/test/SemaTemplate/qualified-names-diag.cpp
+++ b/clang/test/SemaTemplate/qualified-names-diag.cpp
@@ -12,5 +12,5 @@ void test() {
 
   std::vector<INT> v1;
   vector<Real> v2;
-  v1 = v2; // expected-error{{incompatible type assigning 'vector<Real>' (aka 'class std::vector<float>'), expected 'std::vector<INT>' (aka 'class std::vector<int>')}}
+  v1 = v2; // expected-error{{incompatible type assigning 'vector<Real>', expected 'std::vector<INT>'}}
 }