[clang-tools-extra] 540859c - [clangd] Fix crash on completion with out-of-range position (#196112)

[via cfe-commits]

Author: Krzysztof Jędruczyk
Date: 2026-05-07T16:18:13+03:00
New Revision: 540859c2d45b935e6f055663f0d243d2ecc68233

URL: https://github.com/llvm/llvm-project/commit/540859c2d45b935e6f055663f0d243d2ecc68233
DIFF: https://github.com/llvm/llvm-project/commit/540859c2d45b935e6f055663f0d243d2ecc68233.diff

LOG: [clangd] Fix crash on completion with out-of-range position (#196112)

shouldRunCompletion() checked the Expected<> from positionToOffset() via
operator!() but never consumed the error with takeError(). This caused
an assertion failure when a TriggerCharacter completion request had a
position beyond the document bounds.

LLM was used to generate the unit test.

Fixes: #196072

Added: 
    

Modified: 
    clang-tools-extra/clangd/ClangdLSPServer.cpp
    clang-tools-extra/clangd/unittests/ClangdLSPServerTests.cpp

Removed: 
    


################################################################################
diff  --git a/clang-tools-extra/clangd/ClangdLSPServer.cpp b/clang-tools-extra/clangd/ClangdLSPServer.cpp
index 245419dda9151..6e40a5278502c 100644
--- a/clang-tools-extra/clangd/ClangdLSPServer.cpp
+++ b/clang-tools-extra/clangd/ClangdLSPServer.cpp
@@ -1797,9 +1797,9 @@ bool ClangdLSPServer::shouldRunCompletion(
   auto Offset = positionToOffset(*Code, Params.position,
                                  /*AllowColumnsBeyondLineLength=*/false);
   if (!Offset) {
-    vlog("could not convert position '{0}' to offset for file '{1}'",
-         Params.position, Params.textDocument.uri.file());
-    return true;
+    elog("could not convert position '{0}' to offset for file '{1}': {2}",
+         Params.position, Params.textDocument.uri.file(), Offset.takeError());
+    return false;
   }
   return allowImplicitCompletion(*Code, *Offset);
 }

diff  --git a/clang-tools-extra/clangd/unittests/ClangdLSPServerTests.cpp b/clang-tools-extra/clangd/unittests/ClangdLSPServerTests.cpp
index 95bf5e54fc792..0aca1433614dc 100644
--- a/clang-tools-extra/clangd/unittests/ClangdLSPServerTests.cpp
+++ b/clang-tools-extra/clangd/unittests/ClangdLSPServerTests.cpp
@@ -492,6 +492,26 @@ TEST_F(LSPTest, DiagModuleTest) {
   EXPECT_THAT(Client.diagnostics("foo.cpp"),
               llvm::ValueIs(testing::ElementsAre(diagMessage(DiagMsg))));
 }
+
+// Regression test for https://github.com/llvm/llvm-project/issues/196072.
+TEST_F(LSPTest, CompletionOutOfRangePosition) {
+  auto &Client = start();
+  Client.didOpen("foo.cpp", "int x;");
+  auto &Reply = Client.call(
+      "textDocument/completion",
+      llvm::json::Object{
+          {"textDocument", Client.documentID("foo.cpp")},
+          {"position", llvm::json::Object{{"line", 97}, {"character", 0}}},
+          {"context",
+           llvm::json::Object{
+               {"triggerKind", 2},
+               {"triggerCharacter", ">"},
+           }},
+      });
+  auto Result = Reply.take();
+  ASSERT_TRUE(!!Result) << "Expected a response, not a server crash";
+}
+
 } // namespace
 } // namespace clangd
 } // namespace clang