[clangd] TargetFinder: Fix assert-crash on TemplateExpansion args.

[adamcz]

Summary

Previously we would call getAsTemplate() when kind == TemplateExpansion,
which triggers an assertion. The call is now replaced with
getAsTemplateOrTemplatePattern(), which is exactly the same as
getAsTemplate(), except it allows calls when kind == TemplateExpansion.

No change in behavior for no-assert builds.

[adamcz]

Hi Nathan

Would you mind reviewing this change? It's related to your https://reviews.llvm.org/D85503

Thanks!

[nridge]

Thanks for fixing this!

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

351

The Flags.clear() in the previous cases is a leftover from when we used to do Flags = {"-fno-delayed-template-parsing"}; to get the test to pass on Windows. That has since been removed (it's set directly by TestTU), so the Flags.clear() is no longer necessary.

[adamcz]

removed unnecessary Flags.clear()

clang-tools-extra/clangd/FindTarget.cpp

public:
 
   void add(const TemplateArgument &Arg, RelSet Flags) {
     // Only used for template template arguments.
     // For type and non-type template arguments, SelectionTree
     // will hit a more specific node (e.g. a TypeLoc or a
     // DeclRefExpr).
     if (Arg.getKind() == TemplateArgument::Template ||
         Arg.getKind() == TemplateArgument::TemplateExpansion) {
-      if (TemplateDecl *TD = Arg.getAsTemplate().getAsTemplateDecl()) {
+      if (TemplateDecl *TD =
+              Arg.getAsTemplateOrTemplatePattern().getAsTemplateDecl()) {
         report(TD, Flags);
       }
     }
   }
 };
 
 } // namespace
 

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

TEST_F(TargetDeclTest, Types) {
   Code = R"cpp(
     template<template<typename> class T>
     void foo() { [[T<int>]] x; }
   )cpp";
   EXPECT_DECLS("TemplateSpecializationTypeLoc", "template <typename> class T");
   Flags.clear();
 
   Code = R"cpp(
+  template<template<typename> class ...T>
+  class C {
+    C<[[T...]]> foo;
+    };
+  )cpp";
+  EXPECT_DECLS("TemplateArgumentLoc", {"template <typename> class ...T"});
+  Flags.clear();
+
+  Code = R"cpp(
     struct S{};
     S X;
     [[decltype]](X) Y;
   )cpp";
   EXPECT_DECLS("DecltypeTypeLoc", {"struct S", Rel::Underlying});
 
   Code = R"cpp(
     struct S{};