[clangd][c++20]Check for correct auto location in DeducedTypeVisitor

[massberg]

Summary

In case of a constrained auto the correct location has to chosen.

clang-tools-extra/clangd/AST.cpp

public:
 
   // Handle auto initializers:
   //- auto i = 1;
   //- decltype(auto) i = 1;
   //- auto& i = 1;
   //- auto* i = &a;
   bool VisitDeclaratorDecl(DeclaratorDecl *D) {
     if (!D->getTypeSourceInfo() ||
-        D->getTypeSourceInfo()->getTypeLoc().getBeginLoc() != SearchedLocation)
+        !D->getTypeSourceInfo()->getTypeLoc().getContainedAutoTypeLoc() ||
+        D->getTypeSourceInfo()
+                ->getTypeLoc()
+                .getContainedAutoTypeLoc()
+                .getNameLoc() != SearchedLocation)
       return true;
 
     if (auto *AT = D->getType()->getContainedAutoType()) {
       DeducedType = AT->desugar();
     }
     return true;
   }
 

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

class Foo final {})cpp";
           [[au^to]] x = T{};
         }
         )cpp",
        [](HoverInfo &HI) {
          HI.Name = "auto";
          HI.Kind = index::SymbolKind::TypeAlias;
          HI.Definition = "/* not deduced */";
        }},
+      // constrained auto
+      {R"cpp(
+        template <class T> concept F = true;
+        F [[au^to]] x = 1;
+        )cpp",
+       [](HoverInfo &HI) {
+         HI.Name = "auto";
+         HI.Kind = index::SymbolKind::TypeAlias;
+         HI.Definition = "int";
+       }},
       // auto on lambda
       {R"cpp(
         void foo() {
           [[au^to]] lamb = []{};
         }
         )cpp",
        [](HoverInfo &HI) {
          HI.Name = "auto";

          HI.Padding = 23;
          HI.AccessSpecifier = "public";
        }}};
   for (const auto &Case : Cases) {
     SCOPED_TRACE(Case.Code);
 
     Annotations T(Case.Code);
     TestTU TU = TestTU::withCode(T.code());
-    TU.ExtraArgs.push_back("-std=c++17");
+    TU.ExtraArgs.push_back("-std=c++20");
     // Types might be different depending on the target triplet, we chose a
     // fixed one to make sure tests passes on different platform.
     TU.ExtraArgs.push_back("--target=x86_64-pc-linux-gnu");
     auto AST = TU.build();
     Config Cfg;
     Cfg.Hover.ShowAKA = true;
     WithContextValue WithCfg(Config::Key, std::move(Cfg));