[clangd] Handle DeducedTemplateSpecializationType in TargetFinder

[nridge]

Summary

This is mostly a workaround for
https://bugs.llvm.org/show_bug.cgi?id=42914. Once that is fixed, the
handling in VisitDeducedTyped() should be sufficient.

Fixes https://github.com/clangd/clangd/issues/242

[merge_guards_bot]

Unit tests: unknown.

clang-tidy: unknown.

clang-format: unknown.

Build artifacts: diff.json, console-log.txt

[kadircet]

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

499

could you rather add this test into FindTargetTests.cpp ?

[ilya-biryukov]

Please add a test for findExplicitReferences too

[sammccall]

Thanks!

clang-tools-extra/clangd/FindTarget.cpp

318

This needs a comment referencing the bug, and describing the consequence (we're going to miss the instantiation even when it's in principle known)

[nridge]

Address review comments

[nridge]

Remove no longer used flag from XRefTests.cpp

[merge_guards_bot]

Unit tests: pass. 61301 tests passed, 0 failed and 736 were skipped.

clang-tidy: fail. Please fix clang-tidy findings.

clang-format: pass.

Build artifacts: diff.json, clang-tidy.txt, clang-format.patch, CMakeCache.txt, console-log.txt, test-results.xml

[merge_guards_bot]

Unit tests: pass. 61301 tests passed, 0 failed and 736 were skipped.

clang-tidy: fail. Please fix clang-tidy findings.

clang-format: pass.

Build artifacts: diff.json, clang-tidy.txt, clang-format.patch, CMakeCache.txt, console-log.txt, test-results.xml

[ilya-biryukov]

LGTM

clang-tools-extra/clangd/FindTarget.cpp

327

NIT: remove braces

[ilya-biryukov]

I'm also looking into fixing this in clang, this shouldn't be too hard.
But please land the workaround for now.

[ilya-biryukov]

Here's my attempt at storing the deduced type in TypeLocs: D72442.
It almost worked, but still needs an update to fix some test failures.

The change proves it's possible to do this in principle, although it does require a few hacky tweaks to type and decl printing to make sure we produce the same output in diagnostics and other places that need it.

clang-tools-extra/clangd/FindTarget.cpp

struct Visitor : public TypeVisitor<Visitor> {
       void VisitDecltypeType(const DecltypeType *DTT) {
         Outer.add(DTT->getUnderlyingType(), Flags | Rel::Underlying);
       }
       void VisitDeducedType(const DeducedType *DT) {
         // FIXME: In practice this doesn't work: the AutoType you find inside
         // TypeLoc never has a deduced type. https://llvm.org/PR42914
         Outer.add(DT->getDeducedType(), Flags | Rel::Underlying);
       }
+      void VisitDeducedTemplateSpecializationType(
+          const DeducedTemplateSpecializationType *DTST) {
+        if (auto *TD = DTST->getTemplateName().getAsTemplateDecl()) {
+          Outer.add(TD->getTemplatedDecl(), Flags | Rel::TemplatePattern);
+        }
+      }
       void VisitTypedefType(const TypedefType *TT) {
         Outer.add(TT->getDecl(), Flags);
       }
       void
       VisitTemplateSpecializationType(const TemplateSpecializationType *TST) {
         // Have to handle these case-by-case.
 
         // templated type aliases: there's no specialized/instantiated using
         // decl to point to. So try to find a decl for the underlying type
         // (after substitution), and failing that point to the (templated) using
         // decl.
         if (TST->isTypeAlias()) {

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

const char *Tests[] = {
         template <typename> struct S { void foo(); };
         template <typename T> struct unique_ptr {
           T* operator->();
         };
         template <typename T>
         void test(unique_ptr<S<T>>& V) {
           V->fo^o();
         }
+      )cpp",
+
+      R"cpp(// Class template argument deduction
+        template <typename T>
+        struct [[Test]] {
+          Test(T);
+        };
+        void foo() {
+          T^est a(5);
+        }
       )cpp"};
   for (const char *Test : Tests) {
     Annotations T(Test);
     llvm::Optional<Range> WantDecl;
     llvm::Optional<Range> WantDef;
     if (!T.ranges().empty())
       WantDecl = WantDef = T.range();
     if (!T.ranges("decl").empty())
       WantDecl = T.range("decl");
     if (!T.ranges("def").empty())
       WantDef = T.range("def");
 
     TestTU TU;
     TU.Code = T.code();
 
     // FIXME: Auto-completion in a template requires disabling delayed template
     // parsing.
     TU.ExtraArgs.push_back("-fno-delayed-template-parsing");
+    TU.ExtraArgs.push_back("-std=c++17");
 
     auto AST = TU.build();
     ASSERT_TRUE(AST.getDiagnostics().empty())
         << AST.getDiagnostics().begin()->Message << Test;
 
     auto Results = locateSymbolAt(AST, T.point());
 
     if (!WantDecl) {