Bug 966681: improve robustness of error reporting. r=Unfocused

testing/modules/Assert.jsm

@@ -57,9 +57,21 @@ function truncate(text, newLength = kTruncateLength) {
 }
 
 function getMessage(error) {
-  return truncate(JSON.stringify(error.actual, replacer)) + " " +
-         (error.operator ? error.operator + " " : "") +
-         truncate(JSON.stringify(error.expected, replacer));
+  let actual, expected;
+  // Wrap calls to JSON.stringify in try...catch blocks, as they may throw. If
+  // so, fall back to toString().
+  try {
+    actual = JSON.stringify(error.actual, replacer);
+  } catch (ex) {
+    actual = Object.prototype.toString.call(error.actual);
+  }
+  try {
+    expected = JSON.stringify(error.expected, replacer);
+  } catch (ex) {
+    expected = Object.prototype.toString.call(error.expected);
+  }
+  return truncate(actual) + " " + (error.operator ? error.operator + " " : "") +
+         truncate(expected);
 }
 
 /**

testing/modules/tests/xpcshell/test_assert.js

@@ -288,4 +288,15 @@ function run_test() {
   deepEqual(/a/igm, /a/igm, "deep equal should work on RegExp");
   deepEqual({a: 4, b: "1"}, {b: "1", a: 4}, "deep equal should work on regular Object");
   deepEqual(a1, a2, "deep equal should work on Array with Object properties");
+
+  // Test robustness of reporting:
+  equal(new ns.Assert.AssertionError({
+    actual: {
+      toJSON: function() {
+        throw "bam!";
+      }
+    },
+    expected: "foo",
+    operator: "="
+  }).message, "[object Object] = \"foo\"");
 }