assert: align character indicators properly

This makes sure color codes are not taken into account in case
util.inspect's default value was changed.

PR-URL: #31429
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>

lib/internal/assert/assertion_error.js

@@ -13,6 +13,9 @@ const { inspect } = require('internal/util/inspect');
 const { codes: {
   ERR_INVALID_ARG_TYPE
 } } = require('internal/errors');
+const {
+  removeColors,
+} = require('internal/util');
 
 let blue = '';
 let green = '';
@@ -93,7 +96,12 @@ function createErrDiff(actual, expected, operator) {
   // equal, check further special handling.
   if (actualLines.length === 1 && expectedLines.length === 1 &&
     actualLines[0] !== expectedLines[0]) {
-    const inputLength = actualLines[0].length + expectedLines[0].length;
+    // Check for the visible length using the `removeColors()` function, if
+    // appropriate.
+    const c = inspect.defaultOptions.colors;
+    const actualRaw = c ? removeColors(actualLines[0]) : actualLines[0];
+    const expectedRaw = c ? removeColors(expectedLines[0]) : expectedLines[0];
+    const inputLength = actualRaw.length + expectedRaw.length;
     // If the character length of "actual" and "expected" together is less than
     // kMaxShortLength and if neither is an object and at least one of them is
     // not `zero`, use the strict equal comparison to visualize the output.
@@ -110,7 +118,7 @@ function createErrDiff(actual, expected, operator) {
       // not a tty, use a default value of 80 characters.
       const maxLength = process.stderr.isTTY ? process.stderr.columns : 80;
       if (inputLength < maxLength) {
-        while (actualLines[0][i] === expectedLines[0][i]) {
+        while (actualRaw[i] === expectedRaw[i]) {
           i++;
         }
         // Ignore the first characters.

test/parallel/test-assert.js

@@ -1401,3 +1401,16 @@ assert.throws(
   );
   assert.doesNotMatch('I will pass', /different$/);
 }
+
+{
+  const tempColor = inspect.defaultOptions.colors;
+  assert.throws(() => {
+    inspect.defaultOptions.colors = true;
+    // Guarantee the position indicator is placed correctly.
+    assert.strictEqual(111554n, 11111115);
+  }, (err) => {
+    assert.strictEqual(inspect(err).split('\n')[5], '     ^');
+    inspect.defaultOptions.colors = tempColor;
+    return true;
+  });
+}