Add 'source-root' input to init action

This input is exposed in the CodeQL CLI as the flag --source-root, allowing
users of the CLI to set --source-root different from --working-dir. However,
in codeql-action, these two paths are conflated and it poses problems for
users with complicated build environments, in which a source root may be
a child of the working directory.

Most users should not notice this, as the default value is
${{ github.workspace }}, as it is implied now (`path.resolve()`).

src/init-action.ts

@@ -201,7 +201,11 @@ async function run() {
     const codeqlRam = process.env["CODEQL_RAM"] || "6500";
     core.exportVariable("CODEQL_RAM", codeqlRam);
 
-    const tracerConfig = await runInit(codeql, config);
+    const tracerConfig = await runInit(
+      codeql,
+      config,
+      getRequiredInput("source-root")
+    );
     if (tracerConfig !== undefined) {
       for (const [key, value] of Object.entries(tracerConfig.env)) {
         core.exportVariable(key, value);

src/init.ts

@@ -73,10 +73,9 @@ export async function initConfig(
 
 export async function runInit(
   codeql: CodeQL,
-  config: configUtils.Config
+  config: configUtils.Config,
+  sourceRoot: string
 ): Promise<TracerConfig | undefined> {
-  const sourceRoot = path.resolve();
-
   fs.mkdirSync(config.dbLocation, { recursive: true });
 
   // TODO: replace this code once CodeQL supports multi-language tracing

src/runner.ts

@@ -171,6 +171,7 @@ program
     try {
       const tempDir = getTempDir(cmd.tempDir);
       const toolsDir = getToolsDir(cmd.toolsDir);
+      const checkoutPath = cmd.checkoutPath || process.cwd();
 
       // Wipe the temp dir
       logger.info(`Cleaning temp directory ${tempDir}`);
@@ -218,13 +219,13 @@ program
         tempDir,
         toolsDir,
         codeql,
-        cmd.checkoutPath || process.cwd(),
+        checkoutPath,
         gitHubVersion,
         apiDetails,
         logger
       );
 
-      const tracerConfig = await runInit(codeql, config);
+      const tracerConfig = await runInit(codeql, config, checkoutPath);
       if (tracerConfig === undefined) {
         return;
       }