[clangd] Hover: resolve forwarding parameters for CalleeArgInfo

[tom-anders]

Summary

This uses the logic added in D124690

[nridge]

Makes sense, thanks!

clang-tools-extra/clangd/Hover.cpp

void maybeAddCalleeArgInfo(const SelectionTree::Node *N, HoverInfo &HI,
   // to not support that.
   // Both variadic functions and operator() (especially relevant for lambdas)
   // should be supported in the future.
   if (!FD || FD->isOverloadedOperator() || FD->isVariadic())
     return;
 
   HoverInfo::PassType PassType;
 
+  auto Parameters = resolveForwardingParameters(FD);
+
   // Find argument index for N.
-  for (unsigned I = 0; I < CE->getNumArgs() && I < FD->getNumParams(); ++I) {
+  for (unsigned I = 0; I < CE->getNumArgs() && I < Parameters.size(); ++I) {
     if (CE->getArg(I) != OuterNode.ASTNode.get<Expr>())
       continue;
 
     // Extract matching argument from function declaration.
-    if (const ParmVarDecl *PVD = FD->getParamDecl(I)) {
+    if (const ParmVarDecl *PVD = Parameters[I]) {
       HI.CalleeArgInfo.emplace(toHoverInfoParam(PVD, PP));
       if (N == &OuterNode)
         PassType.PassBy = getPassMode(PVD->getType());
     }
     break;
   }
   if (!HI.CalleeArgInfo)
     return;

clang-tools-extra/clangd/unittests/HoverTests.cpp

class Foo final {})cpp";
          HI.LocalScope = "code::";
          HI.Value = "2";
          HI.Type = "int";
          HI.CalleeArgInfo.emplace();
          HI.CalleeArgInfo->Name = "arg_b";
          HI.CalleeArgInfo->Type = "int &";
          HI.CallPassType = HoverInfo::PassType{PassMode::Ref, false};
        }},
+      {// make_unique-like function call
+       R"cpp(
+          struct Foo {
+            explicit Foo(int arg_a) {}
+          };
+          template<class T, class... Args>
+          T make(Args&&... args)
+          {
+              return T(args...);
+          }
+
+          void code() {
+            int a = 1;
+            auto foo = make<Foo>([[^a]]);
+          }
+          )cpp",
+       [](HoverInfo &HI) {
+         HI.Name = "a";
+         HI.Kind = index::SymbolKind::Variable;
+         HI.NamespaceScope = "";
+         HI.Definition = "int a = 1";
+         HI.LocalScope = "code::";
+         HI.Value = "1";
+         HI.Type = "int";
+         HI.CalleeArgInfo.emplace();
+         HI.CalleeArgInfo->Name = "arg_a";
+         HI.CalleeArgInfo->Type = "int";
+         HI.CallPassType = HoverInfo::PassType{PassMode::Value, false};
+       }},
       {
           R"cpp(
           void foobar(const float &arg);
           int main() {
             int a = 0;
             foobar([[^a]]);
           }
           )cpp",