Http-parser: Make CaseInsensitiveMap be extension type.

[lrhn]

Avoids extending a class unnecessarily, which may pave the way for package:collection making the class final.

(Nothing uses that CaseInsensitiveMap is a type at all, the constructors could all just be functions returning Map.)

Change is not breaking, the type is not publicly visible.

[github-actions]

Package publishing

Package	Version	Status	Publish tag (post-merge)
package:cronet_http	1.3.3-wip	WIP (no publish necessary)
package:cupertino_http	2.0.3-wip	WIP (no publish necessary)
package:http	1.4.0-wip	WIP (no publish necessary)
package:http2	2.3.2-wip	WIP (no publish necessary)
package:http_multi_server	3.2.2	already published at pub.dev
package:http_parser	4.1.3	ready to publish	http_parser-v4.1.3
package:http_profile	0.1.1-wip	WIP (no publish necessary)
package:ok_http	0.1.1-wip	WIP (no publish necessary)
package:web_socket	0.1.6	already published at pub.dev
package:web_socket_channel	3.0.2	already published at pub.dev

Documentation at https://github.com/dart-lang/ecosystem/wiki/Publishing-automation.

[github-actions]

PR Health

Changelog Entry ✔️

Package	Changed Files

Changes to files need to be accounted for in their respective changelogs.

Coverage ✔️

File	Coverage
pkgs/http_parser/lib/src/case_insensitive_map.dart	💚 100 %

This check for test coverage is informational (issues shown here will not fail the PR).

API leaks ✔️

The following packages contain symbols visible in the public API, but not exported by the library. Export these symbols or remove them from your publicly visible API.

Package	Leaked API symbols

License Headers ✔️

// Copyright (c) 2025, the Dart project authors. Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

Files
no missing headers

All source files should start with a license header.

Unrelated files missing license headers

Files
pkgs/http/example/main.dart
pkgs/http_client_conformance_tests/example/client_test.dart
pkgs/http_client_conformance_tests/lib/src/dummy_isolate.dart
pkgs/http_parser/test/example_test.dart
pkgs/http_profile/lib/http_profile.dart
pkgs/web_socket/example/web_socket_example.dart
pkgs/web_socket/lib/testing.dart
pkgs/web_socket_conformance_tests/example/client_test.dart

[brianquinlan]

That's neat! My first introduction to extension types.

[kevmoo]

Hold a sec. Strictly, this is breaking right? Folks might implement/extend this?

Maybe we say that's okay, but we should at least discuss.

[brianquinlan]

Hold a sec. Strictly, this is breaking right? Folks might implement/extend this?

Maybe we say that's okay, but we should at least discuss.

Good point!

@lrhn said that this type is not publicly visible but it seems to be

The only instances of extends CaseInsensitiveMap/implements CaseInsensitiveMap that I found on github are false positives.