Fix empty source map error from upstream

Summary:
While testing against latest Beta release using fdb, I noticed that VSCode console always emits following failure:

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

Turns out fdb is sending empty source map settings to lldb, which lldb has a recent regression to setting empty mapping which causes error.

This diff fixes the regression by detecting the mapping is empty and do not run the command.

This internal patch aims to fix and unblock release immediately, will upstream this later.

Test Plan:
The mentioned error does not show up.
The added test in this diff failed before but pass with the change.

Reviewers: gclayton, peix, #lldb_team, zynli

Reviewed By: zynli

Subscribers: #lldb_team

Differential Revision: https://phabricator.intern.facebook.com/D73478506

Author: Jeffrey Tan

lldb/packages/Python/lldbsuite/test/tools/lldb-dap/dap_server.py

@@ -975,7 +975,7 @@ 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

lldb/test/API/tools/lldb-dap/launch/TestDAP_launch.py

@@ -5,11 +5,12 @@
 import dap_server
 from lldbsuite.test.decorators import *
 from lldbsuite.test.lldbtest import *
-from lldbsuite.test import lldbutil
-import lldbdap_testcase
-import time
 import os
 import re
+import time
+
+import lldbdap_testcase
+from lldbsuite.test import lldbutil
 
 # Many tests are skipped on Windows because get_stdout() returns None there.
 # Despite the test program printing correctly. See
@@ -100,6 +101,23 @@ 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)
+
     @skipIfWindows
     def test_cwd(self):
         """
@@ -575,25 +593,28 @@ def test_version(self):
 
     def test_session_id_update(self):
         program = self.getBuildArtifact("a.out")
-        postRunCommands = ["script print('Actual_Session_ID: ' + str(os.getenv('VSCODE_DEBUG_SESSION_ID')))"]
+        postRunCommands = [
+            "script print('Actual_Session_ID: ' + str(os.getenv('VSCODE_DEBUG_SESSION_ID')))"
+        ]
         self.build_and_launch(
-            program, 
-            vscode_session_id="test_session_id", 
+            program,
+            vscode_session_id="test_session_id",
             postRunCommands=postRunCommands,
-        )  
-        output = self.get_console() 
+        )
+        output = self.get_console()
         self.continue_to_exit()
-        lines = filter(lambda x: 'Actual_Session_ID' in x, output.splitlines())  
+        lines = filter(lambda x: "Actual_Session_ID" in x, output.splitlines())
         self.assertTrue(
-            any("test_session_id" in l for l in lines), "expect session id in console output"
+            any("test_session_id" in l for l in lines),
+            "expect session id in console output",
         )
-    
-    def test_session_id_update_empty(self): 
+
+    def test_session_id_update_empty(self):
         program = self.getBuildArtifact("a.out")
-        self.build_and_launch(program)  
-        output = self.get_console() 
+        self.build_and_launch(program)
+        output = self.get_console()
         self.continue_to_exit()
         self.assertTrue(
-            all("VSCODE_DEBUG_SESSION_ID" not in l for l in output.splitlines()), 
-            "expect NO session id update command"
+            all("VSCODE_DEBUG_SESSION_ID" not in l for l in output.splitlines()),
+            "expect NO session id update command",
         )

lldb/tools/lldb-dap/DAP.cpp

@@ -1112,9 +1112,8 @@ void DAP::ConfigureSourceMaps() {
   if (configuration.sourceMap.empty() && configuration.sourcePath.empty())
     return;
 
-  std::string sourceMapCommand;
-  llvm::raw_string_ostream strm(sourceMapCommand);
-  strm << "settings set target.source-map ";
+  std::string sourceMapCommandMappings;
+  llvm::raw_string_ostream strm(sourceMapCommandMappings);
 
   if (!configuration.sourceMap.empty()) {
     for (const auto &kv : configuration.sourceMap) {
@@ -1124,7 +1123,11 @@ void DAP::ConfigureSourceMaps() {
     strm << "\".\" \"" << configuration.sourcePath << "\"";
   }
 
-  RunLLDBCommands("Setting source map:", {sourceMapCommand});
+  if (!sourceMapCommandMappings.empty()) {
+    std::string sourceMapCommand = "settings set target.source-map ";
+    sourceMapCommand += sourceMapCommandMappings;
+    RunLLDBCommands("Setting source map:", {sourceMapCommand});
+  }
 }
 
 void DAP::SetConfiguration(const protocol::Configuration &config,