Fix: avoid creating invalid regex in no-warning-comments (fixes #11471)

5018378 changed the codebase to use unicode regexes almost everywhere, with the exception of places where regexes are constructed from user input. However, two issues occurred to cause a bug:

* Due to an oversight, the regular expressions constructed in the `no-warning-comments` rule were changed to be unicode regexes even though those regexes were constructed from user input.
* The `no-warning-comments` rule dynamically creates regexes with unnecessary escape characters, and unnecessary escape characters are invalid in unicode regexes.

This commit fixes the first issue. The second issue isn't a problem on its own, but it will need to be fixed in order to implement #11423.

lib/rules/no-warning-comments.js

@@ -95,15 +95,15 @@ module.exports = {
                  * ^\s*TERM\b.  This checks the word boundary
                  * at the beginning of the comment.
                  */
-                return new RegExp(prefix + escaped + suffix, "iu");
+                return new RegExp(prefix + escaped + suffix, "i"); // eslint-disable-line require-unicode-regexp
             }
 
             /*
              * For location "anywhere" the regex should be
              * \bTERM\b|\bTERM\b, this checks the entire comment
              * for the term.
              */
-            return new RegExp(prefix + escaped + suffix + eitherOrWordBoundary + term + wordBoundary, "iu");
+            return new RegExp(prefix + escaped + suffix + eitherOrWordBoundary + term + wordBoundary, "i"); // eslint-disable-line require-unicode-regexp
         }
 
         const warningRegExps = warningTerms.map(convertToRegExp);

tests/lib/rules/no-warning-comments.js

@@ -36,7 +36,8 @@ ruleTester.run("no-warning-comments", rule, {
         { code: "// comments containing terms as substrings like TodoMVC", options: [{ terms: ["todo"], location: "anywhere" }] },
         { code: "// special regex characters don't cause problems", options: [{ terms: ["[aeiou]"], location: "anywhere" }] },
         "/*eslint no-warning-comments: [2, { \"terms\": [\"todo\", \"fixme\", \"any other term\"], \"location\": \"anywhere\" }]*/\n\nvar x = 10;\n",
-        { code: "/*eslint no-warning-comments: [2, { \"terms\": [\"todo\", \"fixme\", \"any other term\"], \"location\": \"anywhere\" }]*/\n\nvar x = 10;\n", options: [{ location: "anywhere" }] }
+        { code: "/*eslint no-warning-comments: [2, { \"terms\": [\"todo\", \"fixme\", \"any other term\"], \"location\": \"anywhere\" }]*/\n\nvar x = 10;\n", options: [{ location: "anywhere" }] },
+        { code: "foo", options: [{ terms: ["foo-bar"] }] }
     ],
     invalid: [
         { code: "// fixme", errors: [{ message: "Unexpected 'fixme' comment." }] },