Fix the lldb-dap error when empty source map is specified

[jeffreytan81]

We have some lldb-dap clients that are specifying an empty source map during launching, we noticed that, even empty source map is specified, lldb-dap still tries to run it without any arguments which shows as following error in VSCode:

Setting source map:
(lldb) settings set target.source-map 
error: 'settings set' takes more arguments

This PR fixes the regression by detecting the mapping is empty and do not run the command. A test is added which fails before but passes with this PR.

[llvmbot]

@llvm/pr-subscribers-lldb

Author: None (jeffreytan81)

Changes

We have some lldb-dap clients that are specifying an empty source map during launching, we noticed that, even empty source map is specified, lldb-dap still tries to run it without any arguments which shows as following error in VSCode:

Setting source map:
(lldb) settings set target.source-map 
error: 'settings set' takes more arguments

This PR fixes the regression by detecting the mapping is empty and do not run the command. A test is added which fails before but passes with this PR.

---

Full diff: https://github.com/llvm/llvm-project/pull/137722.diff

3 Files Affected:

• (modified) lldb/packages/Python/lldbsuite/test/tools/lldb-dap/dap_server.py (+1-1)
• (modified) lldb/test/API/tools/lldb-dap/launch/TestDAP_launch.py (+17)
• (modified) lldb/tools/lldb-dap/Handler/RequestHandler.cpp (+5-4)

diff --git a/lldb/packages/Python/lldbsuite/test/tools/lldb-dap/dap_server.py b/lldb/packages/Python/lldbsuite/test/tools/lldb-dap/dap_server.py
index a9915ba2f6de6..921bbc9b7200b 100644
--- a/lldb/packages/Python/lldbsuite/test/tools/lldb-dap/dap_server.py
+++ b/lldb/packages/Python/lldbsuite/test/tools/lldb-dap/dap_server.py
@@ -845,7 +845,7 @@ def request_launch(
             args_dict["debuggerRoot"] = debuggerRoot
         if launchCommands:
             args_dict["launchCommands"] = launchCommands
-        if sourceMap:
+        if sourceMap is not None: # sourceMap can be empty array.
             args_dict["sourceMap"] = sourceMap
         if runInTerminal:
             args_dict["runInTerminal"] = runInTerminal
diff --git a/lldb/test/API/tools/lldb-dap/launch/TestDAP_launch.py b/lldb/test/API/tools/lldb-dap/launch/TestDAP_launch.py
index 1599ee5de7075..30a14caebb565 100644
--- a/lldb/test/API/tools/lldb-dap/launch/TestDAP_launch.py
+++ b/lldb/test/API/tools/lldb-dap/launch/TestDAP_launch.py
@@ -65,6 +65,23 @@ def test_stopOnEntry(self):
                         reason, "breakpoint", 'verify stop isn\'t "main" breakpoint'
                     )
 
+    def test_empty_sourceMap(self):
+        """
+        Tests the launch with empty source map should not issue source map command.
+        """
+        program = self.getBuildArtifact("a.out")
+        self.build_and_create_debug_adapter()
+        empty_source_map = []
+        self.launch(program, sourceMap=empty_source_map)
+        self.continue_to_exit()
+
+        # Now get the console output and verify no source map command was issued for empty source map.
+        console_output = self.get_console()
+        self.assertTrue(
+            console_output and len(console_output) > 0, "expect some console output"
+        )
+        self.assertNotIn("Setting source map:", console_output)
+
     def test_cwd(self):
         """
         Tests the default launch of a simple program with a current working
diff --git a/lldb/tools/lldb-dap/Handler/RequestHandler.cpp b/lldb/tools/lldb-dap/Handler/RequestHandler.cpp
index 3520dc2c71a55..266146363b17c 100644
--- a/lldb/tools/lldb-dap/Handler/RequestHandler.cpp
+++ b/lldb/tools/lldb-dap/Handler/RequestHandler.cpp
@@ -56,9 +56,8 @@ void BaseRequestHandler::SetSourceMapFromArguments(
       "source must be be an array of two-element arrays, "
       "each containing a source and replacement path string.\n";
 
-  std::string sourceMapCommand;
-  llvm::raw_string_ostream strm(sourceMapCommand);
-  strm << "settings set target.source-map ";
+  std::string sourceMapCommandMappings;
+  llvm::raw_string_ostream strm(sourceMapCommandMappings);
   const auto sourcePath = GetString(arguments, "sourcePath").value_or("");
 
   // sourceMap is the new, more general form of sourcePath and overrides it.
@@ -93,7 +92,9 @@ void BaseRequestHandler::SetSourceMapFromArguments(
     // Do any source remapping needed before we create our targets
     strm << "\".\" \"" << sourcePath << "\"";
   }
-  if (!sourceMapCommand.empty()) {
+  if (!sourceMapCommandMappings.empty()) {
+    std::string sourceMapCommand = "settings set target.source-map ";
+    sourceMapCommand += sourceMapCommandMappings;
     dap.RunLLDBCommands("Setting source map:", {sourceMapCommand});
   }
 }

[github-actions]

⚠️ Python code formatter, darker found issues in your code. ⚠️

You can test this locally with the following command:

darker --check --diff -r HEAD~1...HEAD lldb/packages/Python/lldbsuite/test/tools/lldb-dap/dap_server.py lldb/test/API/tools/lldb-dap/launch/TestDAP_launch.py

View the diff from darker here.

--- packages/Python/lldbsuite/test/tools/lldb-dap/dap_server.py	2025-04-28 22:26:27.000000 +0000
+++ packages/Python/lldbsuite/test/tools/lldb-dap/dap_server.py	2025-04-28 22:28:46.790461 +0000
@@ -849,11 +849,11 @@
             args_dict["sourcePath"] = sourcePath
         if debuggerRoot:
             args_dict["debuggerRoot"] = debuggerRoot
         if launchCommands:
             args_dict["launchCommands"] = launchCommands
-        if sourceMap is not None: # sourceMap can be empty array.
+        if sourceMap is not None:  # sourceMap can be empty array.
             args_dict["sourceMap"] = sourceMap
         if runInTerminal:
             args_dict["runInTerminal"] = runInTerminal
         if postRunCommands:
             args_dict["postRunCommands"] = postRunCommands

[ashgti]

Should we also add a test for the attach request as well?

[ashgti]

Just FYI, the launch command has been updated and is going through

llvm-project/lldb/tools/lldb-dap/DAP.cpp

Line 1194 in d913ea3

void DAP::ConfigureSourceMaps() {

for setting the target.source-map value. I've been working on migrating the requests to not use raw json objects but I haven't updated the attach handler yet.

The test, as currently written, is not actually going to run this code. Its still good to have and check though.

[JDevlieghere]

LGMT modulo nits

[JDevlieghere]

Suggested change

	std::string sourceMapCommandMappings;
	llvm::raw_string_ostream strm(sourceMapCommandMappings);
	std::string source_map_command_mappings;
	llvm::raw_string_ostream strm(source_map_command_mappings);

[JDevlieghere]

Suggested change

	if (!sourceMapCommandMappings.empty()) {
	std::string sourceMapCommand = "settings set target.source-map ";
	sourceMapCommand += sourceMapCommandMappings;
	if (!sourceMapCommandMappings.empty()) {
	dap.RunLLDBCommands("Setting source map:", llvm::formatv("settings set target.source-map {0}", source_map_command_mappings));