1 files changed, 97 insertions, 0 deletions
diff --git a/devtools/shared/test-helpers/test-stepper.js b/devtools/shared/test-helpers/test-stepper.js
new file mode 100644
index 0000000000..314a687dbf
--- /dev/null
+++ b/devtools/shared/test-helpers/test-stepper.js
@@ -0,0 +1,97 @@
+/* this source code form is subject to the terms of the mozilla public
+ * license, v. 2.0. if a copy of the mpl was not distributed with this
+ * file, you can obtain one at http://mozilla.org/mpl/2.0/. */
+
+"use strict";
+
+const {
+  startTracing,
+  addTracingListener,
+  stopTracing,
+  removeTracingListener,
+} = require("resource://devtools/server/tracer/tracer.jsm");
+
+let testFileContent;
+
+function traceFrame({ frame }) {
+  const { script } = frame;
+  const { lineNumber, columnNumber } = script.getOffsetMetadata(frame.offset);
+
+  const { url } = script.source;
+  const filename = url.substr(url.lastIndexOf("/") + 1);
+  const line = testFileContent[lineNumber - 1];
+  // Grey out the beginning of the line, before frame's column,
+  // and display an arrow before displaying the rest of the line.
+  const code =
+    "\x1b[2m" +
+    line.substr(0, columnNumber - 1) +
+    "\x1b[0m" +
+    "\u21A6 " +
+    line.substr(columnNumber - 1);
+
+  const position = (lineNumber + ":" + columnNumber).padEnd(7);
+  logStep(`${filename} @ ${position} :: ${code}`);
+
+  // Disable builtin tracer logging
+  return false;
+}
+
+function logStep(message) {
+  dump(` \x1b[2m[STEP]\x1b[0m ${message}\n`);
+}
+
+const tracingListener = {
+  onTracingFrame: traceFrame,
+  onTracingFrameStep: traceFrame,
+};
+
+exports.start = function (testGlobal, testUrl, pause) {
+  const tracerOptions = {
+    global: testGlobal,
+    // Ensure tracing each execution within functions (and not only function calls)
+    traceSteps: true,
+    // Only trace the running test and nothing else
+    filterFrameSourceUrl: testUrl,
+  };
+  testFileContent = readURI(testUrl).split("\n");
+  // Only pause on each step if the passed value is a number,
+  // otherwise we are only going to print each executed line in the test script.
+  if (!isNaN(pause)) {
+    // Delay each step by an amount of milliseconds
+    tracerOptions.pauseOnStep = Number(pause);
+    logStep(`Tracing all test script steps with ${pause}ms pause`);
+    logStep(
+      `/!\\ Be conscious about each pause releasing the event loop and breaking run-to-completion.`
+    );
+  } else {
+    logStep(`Tracing all test script steps`);
+  }
+  logStep(
+    `'\u21A6 ' symbol highlights what precise instruction is being called`
+  );
+  startTracing(tracerOptions);
+  addTracingListener(tracingListener);
+};
+
+exports.stop = function () {
+  stopTracing();
+  removeTracingListener(tracingListener);
+};
+
+function readURI(uri) {
+  const { NetUtil } = ChromeUtils.importESModule(
+    "resource://gre/modules/NetUtil.sys.mjs",
+    { global: "contextual" }
+  );
+  const stream = NetUtil.newChannel({
+    uri: NetUtil.newURI(uri, "UTF-8"),
+    loadUsingSystemPrincipal: true,
+  }).open();
+  const count = stream.available();
+  const data = NetUtil.readInputStreamToString(stream, count, {
+    charset: "UTF-8",
+  });
+
+  stream.close();
+  return data;
+}