3817: vscode: highlight syntax tree ro editor r=matklad a=Veetaha
Small textmate grammar declaration to make rust-analyzer syntax tree more easily inspectable:
Btw, if we change the file extension of our `ra_syntax/test_data/**` files to `.rast` they should be highlighted in vscode too.
The colors of the tokens are actually going to be color-theme dependent, or you can customize them via:
```jsonc
{
"editor.tokenColorCustomizations": {
"textMateRules": [ { "scope": "name", "settings": { /* */ } } ]
}
}
```
Related: #3682
Co-authored-by: veetaha <veetaha2@gmail.com>
