1 files changed, 82 insertions, 0 deletions
diff --git a/toolkit/modules/Deprecated.sys.mjs b/toolkit/modules/Deprecated.sys.mjs
new file mode 100644
index 0000000000..5c3a0dae18
--- /dev/null
+++ b/toolkit/modules/Deprecated.sys.mjs
@@ -0,0 +1,82 @@
+/* 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/. */
+
+const PREF_DEPRECATION_WARNINGS = "devtools.errorconsole.deprecation_warnings";
+
+// A flag that indicates whether deprecation warnings should be logged.
+var logWarnings = Services.prefs.getBoolPref(PREF_DEPRECATION_WARNINGS);
+
+Services.prefs.addObserver(PREF_DEPRECATION_WARNINGS, function(
+  aSubject,
+  aTopic,
+  aData
+) {
+  logWarnings = Services.prefs.getBoolPref(PREF_DEPRECATION_WARNINGS);
+});
+
+/**
+ * Build a callstack log message.
+ *
+ * @param nsIStackFrame aStack
+ *        A callstack to be converted into a string log message.
+ */
+function stringifyCallstack(aStack) {
+  // If aStack is invalid, use Components.stack (ignoring the last frame).
+  if (!aStack || !(aStack instanceof Ci.nsIStackFrame)) {
+    aStack = Components.stack.caller;
+  }
+
+  let frame = aStack.caller;
+  let msg = "";
+  // Get every frame in the callstack.
+  while (frame) {
+    if (frame.filename || frame.lineNumber || frame.name) {
+      msg += frame.filename + " " + frame.lineNumber + " " + frame.name + "\n";
+    }
+    frame = frame.caller;
+  }
+  return msg;
+}
+
+export var Deprecated = {
+  /**
+   * Log a deprecation warning.
+   *
+   * @param string aText
+   *        Deprecation warning text.
+   * @param string aUrl
+   *        A URL pointing to documentation describing deprecation
+   *        and the way to address it.
+   * @param nsIStackFrame aStack
+   *        An optional callstack. If it is not provided a
+   *        snapshot of the current JavaScript callstack will be
+   *        logged.
+   */
+  warning(aText, aUrl, aStack) {
+    if (!logWarnings) {
+      return;
+    }
+
+    // If URL is not provided, report an error.
+    if (!aUrl) {
+      console.error(
+        "Error in Deprecated.warning: warnings must " +
+          "provide a URL documenting this deprecation."
+      );
+      return;
+    }
+
+    let textMessage =
+      "DEPRECATION WARNING: " +
+      aText +
+      "\nYou may find more details about this deprecation at: " +
+      aUrl +
+      "\n" +
+      // Append a callstack part to the deprecation message.
+      stringifyCallstack(aStack);
+
+    // Report deprecation warning.
+    console.error(textMessage);
+  },
+};