[compiler] Improve snap workflow for debugging errors #35539
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This was referenced Jan 16, 2026
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This was referenced Jan 22, 2026
Initializes CLAUDE.md and a settings file for the compiler/ directory to help use claude with the compiler. Note that some of the commands here depend on changes to snap from the next PR.
A whole bunch of changes to snap aimed at making it more usable for humans and agents. Here's the new CLI interface:
```
node dist/main.js --help
Options:
--version Show version number [boolean]
--sync Run compiler in main thread (instead of using worker
threads or subprocesses). Defaults to false.
[boolean] [default: false]
--worker-threads Run compiler in worker threads (instead of
subprocesses). Defaults to true.
[boolean] [default: true]
--help Show help [boolean]
-w, --watch Run compiler in watch mode, re-running after changes
[boolean]
-u, --update Update fixtures [boolean]
-p, --pattern Optional glob pattern to filter fixtures (e.g.,
"error.*", "use-memo") [string]
-d, --debug Enable debug logging to print HIR for each pass[boolean]
```
Key changes:
* Added abbreviations for common arguments
* No more testfilter.txt! Filtering/debugging works more like Jest, see below.
* The `--debug` flag (`-d`) controls whether to emit debug information. In watch mode, this flag sets the initial debug value, and it can be toggled by pressing the 'd' key while watching.
* The `--pattern` flag (`-p`) sets a filter pattern. In watch mode, this flag sets the initial filter. It can be changed by pressing 'p' and typing a new pattern, or pressing 'a' to switch to running all tests.
* As before, we only actually enable debugging if debug mode is enabled _and_ there is only one test selected.
Much nicer workflow for working through errors in the compiler: * Run `yarn snap -w`, oops there are are errors * Hit 'p' to select a fixture => the suggestions populate with recent failures, sorted alphabetically. No need to copy/paste the name of the fixture you want to focus on! * tab/shift-tab to pick one, hit enter to select that one * ...Focus on fixing that test... * 'p' to re-enter the picker. Snap tracks the last state of each fixture and continues to show all tests that failed on their last run, so you can easily move on to the next one. The currently selected test is highlighted, making it easy to move to the next one. * 'a' at any time to run all tests * 'd' at any time to toggle debug output on/off (while focusing on a single test)
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Much nicer workflow for working through errors in the compiler:
yarn snap -w, oops there are are errorsStack created with Sapling. Best reviewed with ReviewStack.
finallyclauses #35607