Update updating-schema.md (#482)

docs/updating-schema.md

@@ -1,23 +1,6 @@
-HHAST is closely coupled to Hack's syntax tree, so if the schema of `hh_parse`
-changes, HHAST needs updating.
+HHAST is closely coupled to Hack's syntax tree, so if the schema of `hh_parse` changes, HHAST needs updating.
 
-1. Get a github codespace or use vscode devcontainers. If a codespace, pick the biggest one you can for this (in general, the smallest are good enough, but here more power is useful).
-2. Edit `/etc/apt/sources.list` - remove `-4.x` suffix from dl.hhvm.com repository
-3. `apt update; apt remove -y hhvm; apt install -y hhvm-nightly` (or `apt install hhvm` for latest stable release)
-4. `cd /workspaces; git clone --depth 1 https://github.com/facebook/hhvm.git`
-5. `cd hhast`
-6. `bin/update-schema --hhvm-path=/workspaces/hhvm`
-7. wait 5-15 minutes as it parses and analyzes the hack/hhvm unit tests to infer valid node relationships
-8. `git diff codegen/schema.json codegen/inferred_relationships.hack` - are the schema changes going to change how code that is valid on both versions is represented?
-9. Adjust `src/__Private/is_compatible_schema_version.hack`, following the instructions in the code comments
-10. Fix `hh_client`, `bin/hhast-lint`, and `vendor/bin/hacktest tests/` errors
-11. If the changes are not backwards compatible, update the minimum versions in composer.json and .github/workflows/ci.yaml
-12. Create pull request
-13. Once merged and CI is green on main branch, tag a new release, matching the new minimum HHVM version
+There is a [update-schema](https://github.com/hhvm/hhast/blob/27318055fd122777e8279c673ee2d578d32cbc03/.github/workflows/build-and-test.yml#L45) GitHub Action job to create Pull Requests to update the schema. 
 
-* Steps 1-2 could be simplified by https://github.com/hhvm/hhvm-docker/issues/22
-* If some valid node relationships are banned:
-  1. Add a SyntaxExample file to src/__Private/codegen/data/
-  2. `git clean -ffdx codegen/; git checkout codegen/`
-  3. re-run the original steps starting with `bin/update-schema --hhvm-path=/workspaces/hhvm`
-* CI also runs all the test steps; doing it yourself just saves time.
+- It is executed everyday to create pull requests to update schema if it the schema changes. The job does not know whether the change is backward compatible, therefore it creates two pull requests, one for breaking change and one for backward compatible change. The maintainer can review the PRs to merge one of them. For example: https://github.com/hhvm/hhast/pull/481 and https://github.com/hhvm/hhast/pull/480.
+- The job `update-schema` is also executed when pushing a commit to any branch in either this repository or a forked repository. When a commit is pushed and the schema change is detected, the pull requests in that repository are created against that branch.