[dart] fix: explode object query parameters

modules/openapi-generator/src/main/resources/dart2/api.mustache

@@ -67,7 +67,23 @@ class {{{classname}}} {
         {{^required}}
     if ({{{paramName}}} != null) {
           {{/required}}
+        {{#isMap}}
+          {{#isExplode}}
+            {{^isDeepObject}}
+      // form style, explode: one query parameter per entry, keyed by the property name; a collection repeats the key per non-null element
+      {{#isFreeFormObject}}({{{paramName}}} as Map){{/isFreeFormObject}}{{^isFreeFormObject}}{{{paramName}}}{{/isFreeFormObject}}.forEach((entryKey, dynamic entryValue) => queryParams.addAll(_queryParams('multi', entryKey.toString(), entryValue is Iterable ? entryValue.where((e) => e != null).toList() : entryValue)));
+            {{/isDeepObject}}
+            {{#isDeepObject}}
       queryParams.addAll(_queryParams('{{{collectionFormat}}}', '{{{baseName}}}', {{{paramName}}}));
+            {{/isDeepObject}}
+          {{/isExplode}}
+          {{^isExplode}}
+      queryParams.addAll(_queryParams('{{{collectionFormat}}}', '{{{baseName}}}', {{{paramName}}}));
+          {{/isExplode}}
+        {{/isMap}}
+        {{^isMap}}
+      queryParams.addAll(_queryParams('{{{collectionFormat}}}', '{{{baseName}}}', {{{paramName}}}));
+        {{/isMap}}
           {{^required}}
     }
         {{/required}}

modules/openapi-generator/src/test/java/org/openapitools/codegen/dart/DartClientCodegenTest.java

@@ -137,6 +137,34 @@ public void testObjectArrayDoesNotUseListFromJson() throws Exception {
         TestUtils.assertFileContains(modelFile.toPath(), "cast<Object>");
     }
 
+    @Test(description = "Verify a form style, exploded map query parameter goes on the wire one entry per parameter")
+    public void testExplodedObjectQueryParameter() throws Exception {
+        List<File> files = generateDartNativeFromSpec(
+                "src/test/resources/3_0/exploded-object-query-param.yaml");
+
+        File apiFile = files.stream()
+                .filter(f -> f.getName().equals("default_api.dart"))
+                .findFirst()
+                .orElseThrow(() -> new AssertionError("default_api.dart not found in generated files"));
+
+        // form style with explode - the default - puts every entry on the wire under its own
+        // property name. Handing the whole map to _queryParams stringifies it with
+        // Map.toString(), which is what used to happen. A collection value repeats the key per
+        // non-null element ('multi').
+        TestUtils.assertFileContains(apiFile.toPath(),
+                "(filter as Map).forEach((entryKey, dynamic entryValue) => queryParams.addAll(_queryParams('multi', entryKey.toString(), entryValue is Iterable ? entryValue.where((e) => e != null).toList() : entryValue)));");
+        TestUtils.assertFileNotContains(apiFile.toPath(), "_queryParams('', 'filter', filter)");
+
+        // a declared map behaves the same way, and needs no cast
+        TestUtils.assertFileContains(apiFile.toPath(),
+                "typedFilter.forEach((entryKey, dynamic entryValue) => queryParams.addAll(_queryParams('multi', entryKey.toString(), entryValue is Iterable ? entryValue.where((e) => e != null).toList() : entryValue)));");
+
+        // deepObject and form without explode both keep a single parameter
+        TestUtils.assertFileContains(apiFile.toPath(),
+                "_queryParams('', 'deepFilter', deepFilter)",
+                "_queryParams('', 'flatFilter', flatFilter)");
+    }
+
     @Test(description = "Enum properties with defaults should emit enum constructor, not string literal")
     public void testEnumDefaultUsesEnumConstructor() throws Exception {
         List<File> files = generateDartNativeFromSpec(

modules/openapi-generator/src/test/resources/3_0/exploded-object-query-param.yaml

@@ -0,0 +1,49 @@
+openapi: 3.0.3
+info:
+  title: Exploded object query parameters
+  description: >
+    Object typed query parameters under form/explode (as a free-form object and as a typed map), deepObject, and form without explode. The free-form variant matters because it is flagged isMap but not isContainer.
+  version: 1.0.0
+servers:
+  - url: localhost:8080
+paths:
+  /items:
+    get:
+      operationId: listItems
+      parameters:
+        # style and explode both left out, so the form/true defaults apply: every entry
+        # becomes its own parameter, keyed by the property name alone.
+        - in: query
+          name: filter
+          schema:
+            type: object
+        # the same, but declared as a map rather than as a free-form object
+        - in: query
+          name: typedFilter
+          schema:
+            type: object
+            additionalProperties:
+              type: string
+        # deepObject nests each entry under the parameter name: deepFilter[key]=value
+        - in: query
+          name: deepFilter
+          style: deepObject
+          explode: true
+          schema:
+            type: object
+        # form without explode keeps a single parameter carrying the whole object
+        - in: query
+          name: flatFilter
+          style: form
+          explode: false
+          schema:
+            type: object
+      responses:
+        '200':
+          description: a list of items
+          content:
+            application/json:
+              schema:
+                type: array
+                items:
+                  type: string

samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/api/fake_api.dart

@@ -1382,7 +1382,8 @@ class FakeApi {
       queryParams.addAll(_queryParams('csv', 'url', url));
       queryParams.addAll(_queryParams('multi', 'context', context));
     if (language != null) {
-      queryParams.addAll(_queryParams('', 'language', language));
+      // form style, explode: one query parameter per entry, keyed by the property name; a collection repeats the key per non-null element
+      language.forEach((entryKey, dynamic entryValue) => queryParams.addAll(_queryParams('multi', entryKey.toString(), entryValue is Iterable ? entryValue.where((e) => e != null).toList() : entryValue)));
     }
       queryParams.addAll(_queryParams('', 'allowEmpty', allowEmpty));