[clang] [clang-tools-extra] [clang] skip explicit obj param in code complete (PR #146258)

[via cfe-commits]

https://github.com/MythreyaK updated https://github.com/llvm/llvm-project/pull/146258

>From a839ba01fc05750ca880ac430a70f7df766f7694 Mon Sep 17 00:00:00 2001
From: Mythreya Kuricheti <git at mythreya.dev>
Date: Sat, 28 Jun 2025 19:06:06 -0700
Subject: [PATCH] [clang] skip explicit obj param in code complete

Skips the first explicit object parameter
when generating autocomplete suggestion string
---
 .../clangd/unittests/CodeCompleteTests.cpp    | 29 +++++++++++++++++++
 clang/lib/Sema/SemaCodeComplete.cpp           |  7 +++++
 2 files changed, 36 insertions(+)

diff --git a/clang-tools-extra/clangd/unittests/CodeCompleteTests.cpp b/clang-tools-extra/clangd/unittests/CodeCompleteTests.cpp
index 311f0d98904ad..34cab8a957a19 100644
--- a/clang-tools-extra/clangd/unittests/CodeCompleteTests.cpp
+++ b/clang-tools-extra/clangd/unittests/CodeCompleteTests.cpp
@@ -4363,6 +4363,35 @@ TEST(CompletionTest, PreambleFromDifferentTarget) {
   EXPECT_THAT(Result.Completions, Not(testing::IsEmpty()));
   EXPECT_THAT(Signatures.signatures, Not(testing::IsEmpty()));
 }
+
+TEST(CompletionTest, DeducingThisIgnoreSelf) {
+  Annotations Test(R"cpp(
+    struct A {
+      void f(this auto&& self, int arg); 
+    };
+
+    int main() {
+      A a {};
+      a.^
+    }
+  )cpp");
+
+  auto TU = TestTU::withCode(Test.code());
+  TU.ExtraArgs = {"-std=c++23"};
+
+  auto Preamble = TU.preamble();
+  ASSERT_TRUE(Preamble);
+
+  CodeCompleteOptions Opts{};
+
+  MockFS FS;
+  auto Inputs = TU.inputs(FS);
+  auto Result = codeComplete(testPath(TU.Filename), Test.point(),
+                             Preamble.get(), Inputs, Opts);
+
+  EXPECT_THAT(Result.Completions,
+              ElementsAre(AllOf(named("f"), snippetSuffix("(${1:int arg})"))));
+}
 } // namespace
 } // namespace clangd
 } // namespace clang
diff --git a/clang/lib/Sema/SemaCodeComplete.cpp b/clang/lib/Sema/SemaCodeComplete.cpp
index 78d4586e45978..b5d4a94da83df 100644
--- a/clang/lib/Sema/SemaCodeComplete.cpp
+++ b/clang/lib/Sema/SemaCodeComplete.cpp
@@ -3260,6 +3260,13 @@ static void AddFunctionParameterChunks(Preprocessor &PP,
       break;
     }
 
+    // C++23 introduces an explicit object parameter, a.k.a. "deducing this"
+    // Skip it for autocomplete and treat the next parameter as the first
+    // parameter
+    if (FirstParameter && Param->isExplicitObjectParameter()) {
+      continue;
+    }
+
     if (FirstParameter)
       FirstParameter = false;
     else