[CodeCompletion][clangd] Clean __uglified parameter names in completion & hover

Underscore-uglified identifiers are used in standard library implementations to
guard against collisions with macros, and they hurt readability considerably.
(Consider `push_back(Tp_ &&__value)` vs `push_back(Tp value)`.
When we're describing an interface, the exact names of parameters are not
critical so we can drop these prefixes.

This patch adds a new PrintingPolicy flag that can applies this stripping
when recursively printing pieces of AST.
We set it in code completion/signature help, and in clangd's hover display.
All three features also do a bit of manual poking at names, so fix up those too.

Fixes https://github.com/clangd/clangd/issues/736

Differential Revision: https://reviews.llvm.org/D116387

1 files changed, 8 insertions, 0 deletions

diff --git a/clang/lib/Basic/IdentifierTable.cpp b/clang/lib/Basic/IdentifierTable.cpp
index d811aeec..b86cb7a 100644
--- a/clang/lib/Basic/IdentifierTable.cpp
+++ b/clang/lib/Basic/IdentifierTable.cpp
@@ -309,6 +309,14 @@ IdentifierInfo::isReserved(const LangOptions &LangOpts) const {
   return ReservedIdentifierStatus::NotReserved;
 }
 
+StringRef IdentifierInfo::deuglifiedName() const {
+  StringRef Name = getName();
+  if (Name.size() >= 2 && Name.front() == '_' &&
+      (Name[1] == '_' || (Name[1] >= 'A' && Name[1] <= 'Z')))
+    return Name.ltrim('_');
+  return Name;
+}
+
 tok::PPKeywordKind IdentifierInfo::getPPKeywordID() const {
   // We use a perfect hash function here involving the length of the keyword,
   // the first and third character.  For preprocessor ID's there are no