[clangd] Add unittests for D51917

[ilya-biryukov]

LGTM

unittests/clangd/CodeCompleteTests.cpp

TEST(CompletionTest, DeprecatedResults) {
   )cpp";
 
   EXPECT_THAT(
       completions(Body + "int main() { TestClang^ }").Completions,
       UnorderedElementsAre(AllOf(Named("TestClangd"), Not(Deprecated())),
                            AllOf(Named("TestClangc"), Deprecated())));
 }
 
+TEST(SignatureHelpTest, ConstructorInitializeFields) {
+  {
+    const auto Results = signatures(R"cpp(
+      struct A {
+        A(int);
+      };
+      struct B {
+        B() : a_elem(^) {}
+        A a_elem;
+      };
+    )cpp");
+    EXPECT_THAT(Results.signatures, UnorderedElementsAre(
+            Sig("A(int)", {"int"}),
+            Sig("A(A &&)", {"A &&"}),
+            Sig("A(const A &)", {"const A &"})
+        ));
+  }
+  {
+    const auto Results = signatures(R"cpp(
+      struct A {
+        A(int);
+      };
+      struct C {
+        C(int);
+        C(A);
+      };
+      struct B {
+        B() : c_elem(A(1^)) {}
+        C c_elem;
+      };
+    )cpp");
+    EXPECT_THAT(Results.signatures, UnorderedElementsAre(
+            Sig("A(int)", {"int"}),
+            Sig("A(A &&)", {"A &&"}),
+            Sig("A(const A &)", {"const A &"})
+        ));
+  }
+}
+
 } // namespace
 } // namespace clangd
 } // namespace clang