Description

Fixes #6312.

When flet_code_editor is used with CodeLanguage.JSON, invalid JSON did not produce gutter error markers. The root cause was that JSON mode still relied on the default local analyzer, which does not perform real JSON syntax validation.

This change adds a JSON-specific analyzer in the Flutter extension layer. It validates editor content with dart:convert, converts FormatException into editor Issues, and maps the error to the correct line so the gutter can render the marker. Non-JSON languages keep their existing analyzer behavior.

Test Code

import flet as ft
import flet_code_editor as fce

INVALID_JSON = """{
  "name": "flet"
  "version": 1
}"""

def main(page: ft.Page):
    page.add(
        fce.CodeEditor(
            language=fce.CodeLanguage.JSON,
            value=INVALID_JSON,
            gutter_style=fce.GutterStyle(
                show_errors=True,
                show_line_numbers=True,
                show_folding_handles=False,
                width=80,
            ),
            expand=True,
        )
    )

ft.run(main)

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Checklist

• I signed the CLA.
• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• My changes generate no new warnings
• New and existing tests pass locally with my changes
• I have made corresponding changes to the documentation (if applicable)

Screenshots

Before

After

Additional details

Local validation:

flutter test test/json_gutter_analyzer_test.dart
flutter analyze lib/src/utils/flet_code_controller.dart lib/src/utils/json_analyzer.dart test/json_gutter_analyzer_test.dart

Summary by Sourcery

Add a JSON-specific analyzer for the Flutter code editor to surface JSON syntax errors as gutter issues while preserving existing behavior for other languages.

Bug Fixes:

• Ensure invalid JSON content in the code editor is reported as error issues with correct line mapping in the gutter.

Tests:

• Add unit tests verifying that JSON language uses the JSON analyzer, reports invalid JSON syntax as a single error issue, and leaves valid JSON without issues.