[clang] [clang-tools-extra] [clangd] CodeCompletion consistent parameter names (PR #206716)

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<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clangd

Author: timon-ul

<details>
<summary>Changes</summary>

Resolves issue https://github.com/clangd/clangd/issues/2651

---
Full diff: https://github.com/llvm/llvm-project/pull/206716.diff


3 Files Affected:

- (modified) clang-tools-extra/clangd/unittests/CodeCompleteTests.cpp (+18) 
- (modified) clang-tools-extra/clangd/unittests/IndexActionTests.cpp (+25) 
- (modified) clang/lib/Sema/SemaCodeComplete.cpp (+7) 


``````````diff
diff --git a/clang-tools-extra/clangd/unittests/CodeCompleteTests.cpp b/clang-tools-extra/clangd/unittests/CodeCompleteTests.cpp
index 5808b2145965f..037983a80300d 100644
--- a/clang-tools-extra/clangd/unittests/CodeCompleteTests.cpp
+++ b/clang-tools-extra/clangd/unittests/CodeCompleteTests.cpp
@@ -698,6 +698,24 @@ TEST(CompletionTest, PrivateMemberDefinition) {
                              snippetSuffix("(int a, int b)"))));
 }
 
+TEST(CompletionTest, DeclParamName) {
+  // This is 1/2 regression tests to make sure signatures
+  // 1) have consistent variable names between header and source file
+  // 2) find variable names in other declarations
+  clangd::CodeCompleteOptions Opts;
+  Opts.EnableSnippets = true;
+  auto FuncFromSource = completions(R"cpp(
+      void sun(int);
+      void sun(int day);
+      void sun(int);
+      void position() {
+        sun^;
+      }
+      )cpp",
+                                    {}, Opts);
+  EXPECT_THAT(FuncFromSource.Completions, Contains(signature("(int day)")));
+}
+
 TEST(CompletionTest, DefaultArgsWithValues) {
   clangd::CodeCompleteOptions Opts;
   Opts.EnableSnippets = true;
diff --git a/clang-tools-extra/clangd/unittests/IndexActionTests.cpp b/clang-tools-extra/clangd/unittests/IndexActionTests.cpp
index 025027fdcee5d..5b8029654a73d 100644
--- a/clang-tools-extra/clangd/unittests/IndexActionTests.cpp
+++ b/clang-tools-extra/clangd/unittests/IndexActionTests.cpp
@@ -11,6 +11,7 @@
 #include "URI.h"
 #include "index/IndexAction.h"
 #include "index/Serialization.h"
+#include "index/Symbol.h"
 #include "clang/Basic/SourceLocation.h"
 #include "clang/Basic/SourceManager.h"
 #include "clang/Tooling/Tooling.h"
@@ -38,6 +39,8 @@ MATCHER_P(hasDigest, Digest, "") { return arg.Digest == Digest; }
 
 MATCHER_P(hasName, Name, "") { return arg.Name == Name; }
 
+MATCHER_P(hasSignature, Signature, "") { return arg.Signature == Signature; }
+
 MATCHER(hasSameURI, "") {
   llvm::StringRef URI = ::testing::get<0>(arg);
   const std::string &Path = ::testing::get<1>(arg);
@@ -258,6 +261,28 @@ TEST_F(IndexActionTest, NoWarnings) {
   EXPECT_THAT(*IndexFile.Symbols, ElementsAre(hasName("foo"), hasName("bar")));
 }
 
+TEST_F(IndexActionTest, DeclParamName) {
+  // This is 2/2 regression tests to make sure signatures
+  // 1) have consistent variable names between header and source file
+  // 2) find variable names in other declarations
+  std::string MainFilePath = testPath("main.cpp");
+  std::string MainCode = R"cpp( #include "zenith.hpp" )cpp";
+  std::string HeaderPath = testPath("zenith.hpp");
+  std::string HeaderCode = R"cpp(
+      void moon(int, int);
+      void moon(int month, int day);
+      void moon(int, int);
+      )cpp";
+
+  addFile(MainFilePath, MainCode);
+  addFile(HeaderPath, HeaderCode);
+
+  IndexFileIn IndexFile = runIndexingAction(MainFilePath);
+
+  EXPECT_THAT(*IndexFile.Symbols,
+              ElementsAre(hasSignature("(int month, int day)")));
+}
+
 TEST_F(IndexActionTest, SkipFiles) {
   std::string MainFilePath = testPath("main.cpp");
   addFile(MainFilePath, R"cpp(
diff --git a/clang/lib/Sema/SemaCodeComplete.cpp b/clang/lib/Sema/SemaCodeComplete.cpp
index bef5eea9ed442..f724fb44f184e 100644
--- a/clang/lib/Sema/SemaCodeComplete.cpp
+++ b/clang/lib/Sema/SemaCodeComplete.cpp
@@ -3320,6 +3320,13 @@ static void AddFunctionParameterChunks(
 
   for (unsigned P = Start, N = Function->getNumParams(); P != N; ++P) {
     const ParmVarDecl *Param = Function->getParamDecl(P);
+    // Select a parameter with identifier if possible for better signature
+    if (!Param->getIdentifier()) {
+      for (auto *Redecl : Function->redecls()) {
+        if (auto *RParam = Redecl->getParamDecl(P); RParam->getIdentifier())
+          Param = RParam;
+      }
+    }
 
     if (Param->hasDefaultArg() && !InOptional && !IsInDeclarationContext &&
         !AsInformativeChunk) {

``````````

</details>


https://github.com/llvm/llvm-project/pull/206716