[CodeCompletion] Signature help for template argument lists

Provide signature while typing template arguments: Foo< ^here >
Here the parameters are e.g. "typename x", and the result type is e.g.
"struct" (class template) or "int" (variable template) or "bool (std::string)"
(function template).

Multiple overloads are possible when a template name is used for several
overloaded function templates.

Fixes https://github.com/clangd/clangd/issues/299

Differential Revision: https://reviews.llvm.org/D116352

1 files changed, 11 insertions, 0 deletions

diff --git a/clang/lib/Sema/CodeCompleteConsumer.cpp b/clang/lib/Sema/CodeCompleteConsumer.cpp
index 0a2ca54..f0968ed 100644
--- a/clang/lib/Sema/CodeCompleteConsumer.cpp
+++ b/clang/lib/Sema/CodeCompleteConsumer.cpp
@@ -506,11 +506,22 @@ CodeCompleteConsumer::OverloadCandidate::getFunctionType() const {
 
   case CK_FunctionType:
     return Type;
+
+  case CK_Template:
+    return nullptr;
   }
 
   llvm_unreachable("Invalid CandidateKind!");
 }
 
+unsigned CodeCompleteConsumer::OverloadCandidate::getNumParams() const {
+  if (Kind == CK_Template)
+    return Template->getTemplateParameters()->size();
+  if (const auto *FPT = dyn_cast_or_null<FunctionProtoType>(getFunctionType()))
+    return FPT->getNumParams();
+  return 0;
+}
+
 //===----------------------------------------------------------------------===//
 // Code completion consumer implementation
 //===----------------------------------------------------------------------===//