[compiler] Summaries of the compiler passes to assist agents in development #35595
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This was referenced Jan 22, 2026
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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. --- [//]: # (BEGIN SAPLING FOOTER) Stack created with [Sapling](https://sapling-scm.com). Best reviewed with [ReviewStack](https://reviewstack.dev/facebook/react/pull/35523). * #35607 * #35298 * #35596 * #35573 * #35595 * #35539 * #35537 * __->__ #35523
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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.
---
[//]: # (BEGIN SAPLING FOOTER)
Stack created with [Sapling](https://sapling-scm.com). Best reviewed
with [ReviewStack](https://reviewstack.dev/facebook/react/pull/35537).
* #35607
* #35298
* #35596
* #35573
* #35595
* #35539
* __->__ #35537
* #35523
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)
…opment Autogenerated summaries of each of the compiler passes which allow agents to get the key ideas of a compiler pass, including key input/output invariants, without having to reprocess the file each time. In the subsequent diff this seemed to help.
josephsavona
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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) --- [//]: # (BEGIN SAPLING FOOTER) Stack created with [Sapling](https://sapling-scm.com). Best reviewed with [ReviewStack](https://reviewstack.dev/facebook/react/pull/35539). * #35607 * #35298 * #35596 * #35573 * #35595 * __->__ #35539
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Autogenerated summaries of each of the compiler passes which allow agents to get the key ideas of a compiler pass, including key input/output invariants, without having to reprocess the file each time. In the subsequent diff this seemed to help.
Stack created with Sapling. Best reviewed with ReviewStack.
finallyclauses #35607