Support for negative lookbehind regex in app.yaml

I am trying to exclude all source map files, i.e files ending with .map from being uploaded to app engine. Here's a snippet of the config in app.yaml file.

handlers:
- url: /(.*\\..+(?\<!map))$
  static_files: \\1
  upload: /(.*\\..+(?\<!map))$
  secure: always

However, when deploying, this is the error that I get.

content <{
  "error": {
    "code": 400,
    "message": "The request is invalid.",
    "status": "INVALID_ARGUMENT",
    "details": [
      {
        "@type": "type.googleapis.com/google.rpc.BadRequest",
        "fieldViolations": [
          {
            "field": "version.handlers[0].url_regex",
            "description": "Value \"/(.*\\..+(?\\\u003c!map))$\" must be a valid regular expression. Details: invalid or unsupported Perl syntax."
          },
          {
            "field": "version.handlers[0].static_files.upload_path_regex",
            "description": "Value \"/(.*\\..+(?\\\u003c!map))$\" must be a valid regular expression. Details: invalid or unsupported Perl syntax."
          }
        ]
      }

In the app.yaml reference documentation, it implies that it supports POSIX extended regular expression syntax.

Might anyone advice on what should be done to fix this.

You can use

^(.*([^.].{3}|.[^m].{2}|.{2}[^a].|.{3}[^p])|.{0,3})$

See the regex demo. Details:

• ^ - start of string
• (.*([^.].{3}|.[^m].{2}|.{2}[^a].|.{3}[^p])|.{0,3}) - Group 1 matching:
  • .*([^.].{3}|.[^m].{2}|.{2}[^a].|.{3}[^p]) - any text, and then any of
    • [^.].{3}| - a char other than a . and then any 3 chars, or
    • .[^m].{2}| - any char, a char other than m, and then any two chars, or
    • .{2}[^a].| - any two chars, any char other than a, and then any one char
    • .{3}[^p] - any three chars, and then a char other than p
  • | - or
  • .{0,3} - any zero, one, two or three chars.
• $ - end of string.