1 files changed, 90 insertions, 0 deletions
diff --git a/tools/code-coverage/PerTestCoverageUtils.sys.mjs b/tools/code-coverage/PerTestCoverageUtils.sys.mjs
new file mode 100644
index 0000000000..1ae0887a07
--- /dev/null
+++ b/tools/code-coverage/PerTestCoverageUtils.sys.mjs
@@ -0,0 +1,90 @@
+/* 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/. */
+
+/* exported PerTestCoverageUtils */
+
+// This is the directory where gcov is emitting the gcda files.
+const gcovPrefixPath = Services.env.get("GCOV_PREFIX");
+// This is the directory where codecoverage.py is expecting to see the gcda files.
+const gcovResultsPath = Services.env.get("GCOV_RESULTS_DIR");
+// This is the directory where the JS engine is emitting the lcov files.
+const jsvmPrefixPath = Services.env.get("JS_CODE_COVERAGE_OUTPUT_DIR");
+// This is the directory where codecoverage.py is expecting to see the lcov files.
+const jsvmResultsPath = Services.env.get("JSVM_RESULTS_DIR");
+
+function awaitPromise(promise) {
+  let ret;
+  let complete = false;
+  let error = null;
+  promise
+    .catch(e => (error = e))
+    .then(v => {
+      ret = v;
+      complete = true;
+    });
+  Services.tm.spinEventLoopUntil(
+    "PerTestCoverageUtils.sys.mjs:awaitPromise",
+    () => complete
+  );
+  if (error) {
+    throw new Error(error);
+  }
+  return ret;
+}
+
+export var PerTestCoverageUtils = class PerTestCoverageUtilsClass {
+  // Resets the counters to 0.
+  static async beforeTest() {
+    if (!PerTestCoverageUtils.enabled) {
+      return;
+    }
+
+    // Flush the counters.
+    let codeCoverageService = Cc[
+      "@mozilla.org/tools/code-coverage;1"
+    ].getService(Ci.nsICodeCoverage);
+    await codeCoverageService.flushCounters();
+
+    // Remove coverage files created by the flush, and those that might have been created between the end of a previous test and the beginning of the next one (e.g. some tests can create a new content process for every sub-test).
+    await IOUtils.remove(gcovPrefixPath, {
+      recursive: true,
+      ignoreAbsent: true,
+    });
+    await IOUtils.remove(jsvmPrefixPath, {
+      recursive: true,
+      ignoreAbsent: true,
+    });
+
+    // Move coverage files from the GCOV_RESULTS_DIR and JSVM_RESULTS_DIR directories, so we can accumulate the counters.
+    await IOUtils.move(gcovResultsPath, gcovPrefixPath);
+    await IOUtils.move(jsvmResultsPath, jsvmPrefixPath);
+  }
+
+  static beforeTestSync() {
+    awaitPromise(this.beforeTest());
+  }
+
+  // Dumps counters and moves the gcda files in the directory expected by codecoverage.py.
+  static async afterTest() {
+    if (!PerTestCoverageUtils.enabled) {
+      return;
+    }
+
+    // Flush the counters.
+    let codeCoverageService = Cc[
+      "@mozilla.org/tools/code-coverage;1"
+    ].getService(Ci.nsICodeCoverage);
+    await codeCoverageService.flushCounters();
+
+    // Move the coverage files in GCOV_RESULTS_DIR and JSVM_RESULTS_DIR, so that the execution from now to shutdown (or next test) is not counted.
+    await IOUtils.move(gcovPrefixPath, gcovResultsPath);
+    await IOUtils.move(jsvmPrefixPath, jsvmResultsPath);
+  }
+
+  static afterTestSync() {
+    awaitPromise(this.afterTest());
+  }
+};
+
+PerTestCoverageUtils.enabled = !!gcovResultsPath;