[clang-tools-extra] [clangd] Clangd running with `--experimental-modules-support` crashes when the compilation database is unavailable (PR #153802)

[via cfe-commits]

https://github.com/slavek-kucera updated https://github.com/llvm/llvm-project/pull/153802

>From f0931962ffaa23cfea14ed97640c0c18f9f91ae7 Mon Sep 17 00:00:00 2001
From: Slavomir Kucera <slavomir.kucera at broadcom.com>
Date: Fri, 15 Aug 2025 14:43:46 +0200
Subject: [PATCH] [clangd] Clangd running with `--experimental-modules-support`
 crashes when the compilation database is unavailable

fixes llvm/llvm-project#132413
---
 .../clangd/GlobalCompilationDatabase.cpp      |  4 ++
 .../clangd/test/modules_no_cdb.test           | 66 +++++++++++++++++++
 2 files changed, 70 insertions(+)
 create mode 100644 clang-tools-extra/clangd/test/modules_no_cdb.test

diff --git a/clang-tools-extra/clangd/GlobalCompilationDatabase.cpp b/clang-tools-extra/clangd/GlobalCompilationDatabase.cpp
index 7c0eb9651feaa..c6afd0bc07cbd 100644
--- a/clang-tools-extra/clangd/GlobalCompilationDatabase.cpp
+++ b/clang-tools-extra/clangd/GlobalCompilationDatabase.cpp
@@ -833,6 +833,10 @@ bool OverlayCDB::setCompileCommand(PathRef File,
 std::unique_ptr<ProjectModules>
 OverlayCDB::getProjectModules(PathRef File) const {
   auto MDB = DelegatingCDB::getProjectModules(File);
+  if (!MDB) {
+    log("Failed to get compilation Database for {0}", File);
+    return {};
+  }
   MDB->setCommandMangler([&Mangler = Mangler](tooling::CompileCommand &Command,
                                               PathRef CommandPath) {
     Mangler(Command, CommandPath);
diff --git a/clang-tools-extra/clangd/test/modules_no_cdb.test b/clang-tools-extra/clangd/test/modules_no_cdb.test
new file mode 100644
index 0000000000000..8f92be2c7b3f3
--- /dev/null
+++ b/clang-tools-extra/clangd/test/modules_no_cdb.test
@@ -0,0 +1,66 @@
+# A smoke test to check that clangd works without compilation database
+#
+# Windows have different escaping modes.
+# FIXME: We should add one for windows.
+# UNSUPPORTED: system-windows
+#
+# RUN: rm -fr %t
+# RUN: mkdir -p %t
+# RUN: split-file %s %t
+#
+# RUN: sed -e "s|DIR|%/t|g" %t/definition.jsonrpc.tmpl > %t/definition.jsonrpc
+#
+# RUN: clangd -experimental-modules-support -lit-test < %t/definition.jsonrpc \
+# RUN:      | FileCheck -strict-whitespace %t/definition.jsonrpc
+
+#--- A.h
+void printA();
+
+#--- Use.cpp
+#include "A.h"
+void foo() {
+    print
+}
+
+#--- definition.jsonrpc.tmpl
+{
+  "jsonrpc": "2.0",
+  "id": 0,
+  "method": "initialize",
+  "params": {
+    "processId": 123,
+    "rootPath": "clangd",
+    "capabilities": {
+      "textDocument": {
+        "completion": {
+          "completionItem": {
+            "snippetSupport": true
+          }
+        }
+      }
+    },
+    "trace": "off"
+  }
+}
+---
+{
+  "jsonrpc": "2.0",
+  "method": "textDocument/didOpen",
+  "params": {
+    "textDocument": {
+      "uri": "file://DIR/Use.cpp",
+      "languageId": "cpp",
+      "version": 1,
+      "text": "#include \"A.h\"\nvoid foo() {\n    print\n}\n"
+    }
+  }
+}
+
+# CHECK: "message"{{.*}}printA{{.*}}(fix available)
+
+---
+{"jsonrpc":"2.0","id":1,"method":"textDocument/completion","params":{"textDocument":{"uri":"file://DIR/Use.cpp"},"context":{"triggerKind":1},"position":{"line":2,"character":6}}}
+---
+{"jsonrpc":"2.0","id":2,"method":"shutdown"}
+---
+{"jsonrpc":"2.0","method":"exit"}