[lldb-dap] add debugAdapterExecutable property to launch configuration (llvm#126803)

The Swift extension for VS Code requires that the `lldb-dap` executable
come from the Swift toolchain which may or may not be configured in
`PATH`. At the moment, this can be configured via LLDB DAP's extension
settings, but experience has shown that modifying other extensions'
settings on behalf of the user (especially those subject to change
whenever a new toolchain is selected) causes issues. Instead, it would
be easier to have this configurable in the launch configuration and let
the Swift extension (or any other extension that wanted to, really)
configure the path to `lldb-dap` that way. This allows the Swift
extension to have its own launch configuration type that delegates to
the LLDB DAP extension in order to provide a more seamless debugging
experience for Swift executables.

This PR adds a new property to the launch configuration object called
`debugAdapterExecutable` which allows overriding the `lldb-dap`
executable path for a specific debug session.

Author: matthewbastien

lldb/tools/lldb-dap/package.json

@@ -86,7 +86,7 @@
           "default": {},
           "description": "The environment of the lldb-dap process.",
           "additionalProperties": {
-             "type": "string"
+            "type": "string"
           }
         }
       }
@@ -152,6 +152,10 @@
               "program"
             ],
             "properties": {
+              "debugAdapterExecutable": {
+                "type": "string",
+                "markdownDescription": "The absolute path to the LLDB debug adapter executable to use."
+              },
               "program": {
                 "type": "string",
                 "description": "Path to the program to debug."
@@ -338,6 +342,10 @@
           },
           "attach": {
             "properties": {
+              "debugAdapterExecutable": {
+                "type": "string",
+                "markdownDescription": "The absolute path to the LLDB debug adapter executable to use."
+              },
               "program": {
                 "type": "string",
                 "description": "Path to the program to attach to."

lldb/tools/lldb-dap/src-ts/debug-adapter-factory.ts

@@ -67,12 +67,17 @@ async function findDAPExecutable(): Promise<string | undefined> {
 async function getDAPExecutable(
   session: vscode.DebugSession,
 ): Promise<string | undefined> {
+  // Check if the executable was provided in the launch configuration.
+  const launchConfigPath = session.configuration["debugAdapterExecutable"];
+  if (typeof launchConfigPath === "string" && launchConfigPath.length !== 0) {
+    return launchConfigPath;
+  }
+
+  // Check if the executable was provided in the extension's configuration.
   const config = vscode.workspace.getConfiguration(
     "lldb-dap",
     session.workspaceFolder,
   );
-
-  // Prefer the explicitly specified path in the extension's configuration.
   const configPath = config.get<string>("executable-path");
   if (configPath && configPath.length !== 0) {
     return configPath;