Stream CLI server command stderr instead of buffering

extensions/ql-vscode/src/codeql-cli/cli.ts

@@ -362,6 +362,8 @@ export class CodeQLCliServer implements Disposable {
     silent?: boolean,
   ): Promise<string> {
     const stderrBuffers: Buffer[] = [];
+    // The array of fragments of stderr of this line. To be used for logging.
+    let currentLineStderrBuffers: Buffer[] = [];
     if (this.commandInProcess) {
       throw new Error("runCodeQlCliInternal called while cli was running");
     }
@@ -419,6 +421,32 @@ export class CodeQLCliServer implements Disposable {
           // Listen to stderr
           process.stderr.addListener("data", (newData: Buffer) => {
             stderrBuffers.push(newData);
+
+            if (!silent) {
+              currentLineStderrBuffers.push(newData);
+
+              // Print the stderr to the logger as it comes in. We need to ensure that
+              // we don't split messages on the same line, so we buffer the stderr and
+              // split it on EOLs.
+              let currentLineBuffer = Buffer.concat(currentLineStderrBuffers);
+              const eolBuffer = Buffer.from(EOL);
+              if (currentLineBuffer.includes(eolBuffer)) {
+                while (currentLineBuffer.includes(eolBuffer)) {
+                  const line = currentLineBuffer.subarray(
+                    0,
+                    currentLineBuffer.indexOf(eolBuffer),
+                  );
+
+                  void this.logger.log(line.toString("utf-8"));
+
+                  currentLineBuffer = currentLineBuffer.subarray(
+                    currentLineBuffer.indexOf(eolBuffer) + eolBuffer.length,
+                  );
+                }
+
+                currentLineStderrBuffers = [currentLineBuffer];
+              }
+            }
           });
           // Listen for process exit.
           process.addListener("close", (code) =>
@@ -433,6 +461,10 @@ export class CodeQLCliServer implements Disposable {
         // Make sure we remove the terminator;
         const data = fullBuffer.toString("utf8", 0, fullBuffer.length - 1);
         if (!silent) {
+          void this.logger.log(
+            Buffer.concat(currentLineStderrBuffers).toString("utf8"),
+          );
+          currentLineStderrBuffers = [];
           void this.logger.log("CLI command succeeded.");
         }
         return data;
@@ -452,8 +484,10 @@ export class CodeQLCliServer implements Disposable {
         cliError.stack += getErrorStack(err);
         throw cliError;
       } finally {
-        if (!silent) {
+        if (!silent && currentLineStderrBuffers.length > 0) {
-          void this.logger.log(Buffer.concat(stderrBuffers).toString("utf8"));
+          void this.logger.log(
+            Buffer.concat(currentLineStderrBuffers).toString("utf8"),
+          );
         }
         // Remove the listeners we set up.
         process.stdout.removeAllListeners("data");