[clang-tools-extra] 487ba79 - [clangd] Handle template template parameters in TargetFinder::VisitDeducedTemplateSpecializationType (#228601)

[via cfe-commits]

Author: Nathan Ridge
Date: 2026-10-05T06:02:38Z
New Revision: 487ba792d817afc4807c27a446d15c4c0669897f

URL: https://github.com/llvm/llvm-project/commit/487ba792d817afc4807c27a446d15c4c0669897f
DIFF: https://github.com/llvm/llvm-project/commit/487ba792d817afc4807c27a446d15c4c0669897f.diff

LOG: [clangd] Handle template template parameters in TargetFinder::VisitDeducedTemplateSpecializationType (#228601)

Fixes https://github.com/clangd/clangd/issues/1870

Added: 
    

Modified: 
    clang-tools-extra/clangd/FindTarget.cpp
    clang-tools-extra/clangd/unittests/FindTargetTests.cpp

Removed: 
    


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diff  --git a/clang-tools-extra/clangd/FindTarget.cpp b/clang-tools-extra/clangd/FindTarget.cpp
index 142776d0dfaa7..a3379d1337d62 100644
--- a/clang-tools-extra/clangd/FindTarget.cpp
+++ b/clang-tools-extra/clangd/FindTarget.cpp
@@ -397,14 +397,20 @@ struct TargetFinder {
         if (const auto *USD = DTST->getTemplateName().getAsUsingShadowDecl())
           Outer.add(USD, Flags);
 
-        // FIXME: This is a workaround for https://llvm.org/PR42914,
-        // which is causing DTST->getDeducedType() to be empty. We
-        // fall back to the template pattern and miss the instantiation
-        // even when it's known in principle. Once that bug is fixed,
-        // the following code can be removed (the existing handling in
-        // VisitDeducedType() is sufficient).
-        if (auto *TD = DTST->getTemplateName().getAsTemplateDecl())
+        // Template template parameters have no templated decl, so they must
+        // refer to the parameter itself.
+        if (const auto *Parm =
+                DTST->getTemplateName().getAsTemplateTemplateParmDecl()) {
+          Outer.add(Parm, Flags);
+        } else if (auto *TD = DTST->getTemplateName().getAsTemplateDecl()) {
+          // FIXME: This is a workaround for https://llvm.org/PR42914,
+          // which is causing DTST->getDeducedType() to be empty. We
+          // fall back to the template pattern and miss the instantiation
+          // even when it's known in principle. Once that bug is fixed,
+          // the following code can be removed (the existing handling in
+          // VisitDeducedType() is sufficient).
           Outer.add(TD->getTemplatedDecl(), Flags | Rel::TemplatePattern);
+        }
       }
       void VisitDependentNameType(const DependentNameType *DNT) {
         if (Outer.Resolver) {

diff  --git a/clang-tools-extra/clangd/unittests/FindTargetTests.cpp b/clang-tools-extra/clangd/unittests/FindTargetTests.cpp
index 0c0ef1262141f..94837803cd64c 100644
--- a/clang-tools-extra/clangd/unittests/FindTargetTests.cpp
+++ b/clang-tools-extra/clangd/unittests/FindTargetTests.cpp
@@ -593,6 +593,16 @@ TEST_F(TargetDeclTest, ClassTemplate) {
   EXPECT_DECLS("DeducedTemplateSpecializationTypeLoc",
                {"struct Test", Rel::TemplatePattern});
 
+  Code = R"cpp(
+    // Deduced specialization of a template template parameter
+    template <template<typename> class X>
+    void foo() {
+      [[X]] a;
+    }
+  )cpp";
+  EXPECT_DECLS("DeducedTemplateSpecializationTypeLoc",
+               "template <typename> class X");
+
   Code = R"cpp(
     // Deduction guide
     template <typename T>
@@ -604,6 +614,18 @@ TEST_F(TargetDeclTest, ClassTemplate) {
     [[Test]](I, I) -> Test<typename I::type>;
   )cpp";
   EXPECT_DECLS("CXXDeductionGuideDecl", {"template <typename T> struct Test"});
+
+  Flags.push_back("-std=c++26"); // for pack indexing
+
+  Code = R"cpp(
+    // Deduced specialization of an indexed template template parameter pack
+    template <template <typename> class... X>
+    void foo() {
+      [[X]]...[0] a(1);
+    }
+  )cpp";
+  EXPECT_DECLS("DeducedTemplateSpecializationTypeLoc",
+               "template <typename> class ...X");
 }
 
 TEST_F(TargetDeclTest, Concept) {