URL path construction incorrectly handles colons in path segments

[knaoe]

When using the / operator to construct URLs with path segments containing colons (e.g., "posts:today"), Flutter Data incorrectly processes the string, resulting in malformed URLs.

Steps to Reproduce

1. Create an adapter with a custom action endpoint that uses colon notation:

@override
String urlForFindAll(Map<String, dynamic> params) {
  final action = params['action'] as String?;
  if (action != null) {
    return '$type:$action'; // e.g., returns "posts:today"
  }
  return super.urlForFindAll(params);
}

2. Call findAll with an action parameter:

await findAll(params: {'action': 'today'});

3. The URL construction in remote_adapter.dart uses:

baseUrl.asUri / urlForFindAll(params) & params

Expected Behavior

When baseUrl.asUri is https://api.example.com/ and urlForFindAll(params) returns "posts:today", the resulting URL should be:

https://api.example.com/posts:today

Actual Behavior

The URL is incorrectly constructed as:

https://api.example.com/today

The part before the colon (posts:) is dropped.

Analysis

The issue appears to be in how the / operator handles strings with colons. It seems to be treating the colon as a special character and only keeping the part after it.

Workaround

Currently, we have to manually construct the URI to avoid this issue:

final pathWithAction = '$type:today';
final uri = baseUrl.asUri.replace(
  path: '${baseUrl.asUri.path}/$pathWithAction',
  queryParameters: queryParams,
);

Proposed Solutions

Fix the / operator: Update the URL path joining logic to properly handle colons in path segments. Colons are valid characters in URL paths when not used as scheme separators.

Environment

• Flutter Data version: 2.0.0
• Flutter version: 3.29.2
• Dart version: 3.7.2

Additional Context

This pattern of using colons in API paths is common in REST API design, particularly following Google's API design guide for custom methods. Many APIs use this pattern (e.g., /posts:publish, /users:verify, etc.), so proper support would be beneficial.

Related Code

The issue is in the URL construction at:
https://github.com/flutterdata/flutter_data/blob/master/lib/src/adapter/remote_adapter.dart

Specifically where it constructs: baseUrl.asUri / urlForFindAll(params) & params