[BUG] [dart-dio] Generated deserialize() for Map<String, anything> targetType throws exception for json_serializable

[rankoz]

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• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• Have you tested with the latest master to confirm the issue still exists?
• Have you searched for related issues/PRs?
• What's the actual output vs expected output?
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Description

Deserializing fails for any type of dictionary return type for 'json_serializable'. Even as simple Map<String, String>.

I/flutter ( 7275): Exception: Cannot deserialize

The problem is here.

openapi-generator version

7.8.0

OpenAPI declaration file content or url

openapi: 3.1.0
info:
  title: Example API
  version: 1.0.0
paths:
  /example:
    get:
      summary: Returns a map of strings
      responses:
        '200':
          description: A map of key-value pairs
          content:
            application/json:
              schema:
                type: object
                additionalProperties:
                  type: string

Generation Details

Steps to reproduce

Related issues/PRs

Suggest a fix

In deserialize.mustache, the regular expression for Map type looks looks like this:

final _regMap = RegExp(r'^Map<String,(.*)>$');

... it will pick up everything after a comma.

Generated code for the above spec will have this snippet:

    Map<String, String>? _responseData;

    try {
final rawData = _response.data;
_responseData = rawData == null ? null : deserialize<Map<String, String>, String>(rawData, 'Map<String, String>', growable: true);
    } catch (error, stackTrace) {

The second parameter passed to deserialize (targetType), "Map<String, String>", contains space after a comma.

if (value is Map && (match = _regMap.firstMatch(targetType)) != null) {
  // targetType resolves to ' String' with a space in front and recursive call below will not find matching type
  targetType = match![1]!; // ignore: parameter_assignments.
  return Map<dynamic, BaseType>.fromIterables(
    value.keys,
    value.values.map((dynamic v) => deserialize<BaseType, BaseType>(v, targetType, growable: growable)),
  ) as ReturnType;
}

Fixing the above by adding .trim() causes a second issue:
Error: type '_Map<dynamic, String>' is not a subtype of type 'Map<String, String>' in type cast

Therefore the correct code for the above snippet, considering that _regMap is looking for Map<String, ...> should be:

if (value is Map && (match = _regMap.firstMatch(targetType)) != null) {
  targetType = match![1]!.trim(); // ignore: parameter_assignments
  return Map<String, BaseType>.fromIterables(
    value.keys as Iterable<String>,
    value.values.map((dynamic v) => deserialize<BaseType, BaseType>(v, targetType, growable: growable)),
  ) as ReturnType;
}

I will do a PR for this in a minute.