FinchDart Dag (VS Code)

Editor support for .dag files, produced by the dag package for Dart (part of FinchDart) — a transpiler that lets you embed Dart in HTML/text, PHP-style.

Features

• Syntax highlighting — .dag files are highlighted as HTML, with every <?dag ... ?> / <?- ... ?> region highlighted as real Dart (via an embedded-language TextMate injection, the same technique VS Code's built-in PHP grammar uses to embed PHP inside HTML). Requires the Dart extension (declared as a dependency, so VS Code installs it automatically) for the source.dart grammar.
• File icon — .dag files get a distinct icon so they stand out from plain .html/.dart files in the Explorer. Since a file-icon theme replaces your current one, it ships as an optional icon theme: run Preferences: File Icon Theme and pick Dag Icons (uproid).
• Dart diagnostics on .dag files — errors and warnings from dart analyze are shown directly on the .dag file, not just on the generated .dart.
• Tag highlighting that always renders — <?dag/<?-/?>/-?> are colored via an editor decoration the extension applies itself (not a theme rule), so they stand out consistently no matter which color theme is active, with no setup required.
• .g.dart nested under its .dag file in the Explorer — the generated sibling (foo.g.dart) is collapsed under foo.dag, the same way VS Code nests file.js under file.ts. Clicking foo.dag opens it directly; expanding the arrow reveals foo.g.dart, still fully viewable/editable on its own. Ships as a default via explorer.fileNesting.patterns, no configuration needed — if you had file nesting turned off entirely, this extension turns it back on.

How diagnostics work

There is no embedded Dart language server here — that's a much bigger project (a full LSP proxy that remaps every request/response, like Vue/Svelte's tooling does for their SFCs). Instead, on open/save and a short debounce after you stop typing, the extension:

1. Runs dart run dag:dag <file>.dag -o <file>.g.dart — the same command the dag CLI/build_runner would run, so the sibling .g.dart is a real, normal generated file.
2. Runs dart analyze --format=machine on that .g.dart file — the real Dart analyzer, so you get the exact diagnostics Dart itself reports.
3. Maps each reported line back to the .dag source line that produced it, using the _dagLine = N; markers the transpiler already emits (the same mechanism DagError uses at runtime — see the main package README), and publishes the result on the .dag document.

This means diagnostics land on save / shortly after you stop typing, not on every keystroke, and the column/range shown is the whole .dag line rather than an exact character span (the generated code doesn't line up character-for-character with the source). Both are deliberate trade-offs to keep this a small, maintainable extension instead of a full LSP proxy.

Requirements: your project's pubspec.yaml must depend on dag (that's what makes .dag files meaningful in the first place), and dart must be on PATH (or set dag.dartSdkPath).

Settings

Development

npm install
npm run compile   # or: npm run watch

Then press F5 in VS Code (with this folder open) to launch an Extension Development Host with the extension loaded.