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orca/docs/reference/xterm-patch-regeneration.md

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xterm Patch Regeneration

Scope

Orca ships @xterm/xterm with four source changes it needs and upstream has not taken: the IME composition hooks, the xterm-composition-* custom events they raise, the ITerminal surface those events widen, and a SortedList fix. pnpm applies them through config/patches/@xterm__xterm@<version>.patch.

That patch touches eight files. Four are hand-authored source (src/browser/CoreBrowserTerminal.ts, src/browser/Types.ts, src/browser/input/CompositionHelper.ts, src/common/SortedList.ts) and four are the build output those sources produce (lib/xterm.js, lib/xterm.mjs, and both sourcemaps). The bundle half is 7.3 MB of minified code. It is generated, and this document exists so nobody edits it by hand.

The source patch carries a fifth file, src/browser/TestUtils.test.ts, which the shipped patch does not and cannot; see The Source Patch Is a Superset.

config/patches/xterm-src/@xterm__xterm@<version>.src.patch is the source of truth. Everything else is derived from it by config/scripts/regenerate-xterm-patches.mjs, which is pinned to the exact upstream commit the published tarball was built from.

This policy covers @xterm/xterm only. The addon patches (@xterm/addon-webgl, @xterm/addon-serialize) are still hand-edited bundles and are tracked separately; see Known Gaps.

Rules

  1. Never edit config/patches/@xterm__xterm@<version>.patch. Edit the source patch and regenerate.
  2. Never edit lib/ inside a patched node_modules tree and re-run pnpm patch-commit. That is how bundle hunks stop matching their sources.
  3. Every source change must land together with the regenerated bundle hunks and the pnpm-lock.yaml hash bump, in one commit.
  4. The upstream commit lives in config/patches/xterm-upstream.json, not in a comment. A version bump that leaves it stale fails the generator, it does not silently patch the wrong tree.
  5. Sourcemaps are deleted, not patched and not silently omitted. The patch moves the bundle, so a retained map would have to move with it; dropping only the map hunks ships offsets that point at the wrong code. Deletion is the honest form of that saving, and sourcemaps.policy in the manifest controls it.
  6. --check is the authority on the lockfile, not pnpm install. pnpm writes the patch hash in two places — patchedDependencies and every resolution key that depends on the patched package — and on a warm store it will leave the resolution keys at their previous value while reporting success. That installs locally and drifts on CI's cold store. Always finish on step 4, and if it reports a stale hash after an install, rerun --write.

Workflow

# 1. Edit the source hunks.
$EDITOR config/patches/xterm-src/@xterm__xterm@6.1.0-beta.287.src.patch

# 2. Rebuild the bundle hunks, the full patch, and the lockfile hash.
node config/scripts/regenerate-xterm-patches.mjs --write

# 3. Reinstall so node_modules picks up the new patch hash.
pnpm install

# 4. Confirm the tree is self-consistent.
node config/scripts/regenerate-xterm-patches.mjs --check

Editing a patch file by hand is awkward for anything larger than a one-liner. For a substantial change, work in the generator's own checkout instead — after any run it is left at the pinned commit with the source patch applied:

node config/scripts/regenerate-xterm-patches.mjs --check --work-dir=/tmp/xterm
$EDITOR /tmp/xterm/upstream/src/browser/input/CompositionHelper.ts
git -C /tmp/xterm/upstream diff -- src/ > config/patches/xterm-src/@xterm__xterm@6.1.0-beta.287.src.patch
node config/scripts/regenerate-xterm-patches.mjs --write --work-dir=/tmp/xterm

--write rewrites the source patch into the canonical form it would emit on a re-diff, so a hand-produced git diff gets normalized on the first run rather than fighting --check forever.

Run the checkout outside this repository. A build tree underneath it makes tsgo walk up into Orca's own node_modules and fail with TS2300: Duplicate identifier, which is a symptom of where the tree sits and not of the patch.

How the Commit Is Known

Upstream bin/publish.js sets packageJson.commit before npm publish, so each published tarball names the commit that built it. The generator asserts that stamp against xterm-upstream.json and then compares the tarball's src/ against the checkout file by file. Only src/common/Version.ts may differ, because publish.js rewrites the version immediately before packaging; the generator applies the same stamp.

That pair of checks is what makes the rebuild trustworthy. Without them a wrong commit would still produce a plausible-looking 7 MB patch.

The Source Patch Is a Superset

Patching ICompositionHelper widens an interface, so every implementor has to follow — including MockCompositionHelper in upstream's src/browser/TestUtils.test.ts. Without that hunk the patched checkout does not type-check and npm run package never reaches webpack, so the generator cannot build the patched bundles at all.

Upstream's .npmignore strips *.test.ts, so that file is not in the published tarball. The shipped patch is a diff against the published tarball, and it therefore cannot name the file — correctly, since pnpm has nothing there to patch.

That is why the source patch is derived from the upstream checkout (git diff -- src/) and not from the emitted patch. Deriving it from the emitted patch is the trap: --write would filter the hunk out through the published file set and delete it, so the fix that makes the build work would erase itself on the first run that used it.

The two derivations are still cross-checked. assertSourceDerivationsAgree requires them to be byte-identical on every file the tarball publishes, so the carve-out stays confined to files upstream does not ship rather than becoming a place where the source patch and the shipped patch can quietly disagree. The checkout diff uses pnpm's own formatting flags minus --no-index, which is what makes that byte comparison meaningful.

Build Order

Upstream's publish path is npm ci → stamp Version.ts → npm run package. npm run package runs webpack for lib/xterm.js and then, via postpackage, bin/esbuild_all.mjs --prod for lib/xterm.mjs.

Do not run npm run setup after the packaging build. setup is the development esbuild pass with minify: false. Running it afterwards overwrites lib/xterm.mjs with an unminified bundle and a map that no longer matches, and the resulting patch is silently wrong — the failure mode is a .mjs that is 50% larger than the published one, which is easy to miss inside a 7 MB diff. forbiddenBuildScripts in the manifest encodes this and the generator refuses to run a build step that names one of those scripts.

The generator also builds the unmodified commit first and asserts that it reproduces the published lib/ byte for byte before it emits anything. A toolchain or build-order problem therefore surfaces as an explicit "did not reproduce the published bundles" error rather than as 7 MB of mystery diff.

The Lockfile Moves With the Patch

pnpm derives the patchedDependencies hash in pnpm-lock.yaml — and the .pnpm/@xterm+xterm@<version>_patch_hash=<hash>/ store directory name — from the sha256 of the patch file itself. A regenerated patch without the lockfile bump fails pnpm install --frozen-lockfile on every machine except the author's. --write makes that edit; --check fails if it is missing.

config/scripts/regenerate-xterm-patches.test.mjs asserts the same thing without a network or a build, so the ordinary test job catches lockfile drift in milliseconds even though the full rebuild runs in its own CI lane.

Toolchain Pin

toolchain in the manifest records what upstream's package-lock.json resolves at the pinned commit, and the generator fails if npm ci produces something else. The entry that matters is @typescript/native-preview (tsgo), which upstream pins to a dated development build — 7.0.0-dev.20260521.1 at the time of writing. It is a real published version and npm does not prune old releases, but it is the one dependency of this scheme that is not a stable release.

If that version ever becomes unresolvable the generator fails with a toolchain error naming it. Recovery is to move the pin to the next upstream commit whose package-lock.json resolves, re-verify that the rebuild still reproduces the published bundles, and regenerate. The committed patch keeps working the whole time — only regeneration is blocked, so this is never an outage.

Version Bumps

Bumping @xterm/xterm is:

  1. Update the version in package.json and run pnpm install.
  2. Rename both patch files to the new version and update patch, sourcePatch, and version in xterm-upstream.json.
  3. Update upstream.commit to the commit field of the new tarball's package.json, and toolchain to whatever the new package-lock.json resolves.
  4. node config/scripts/regenerate-xterm-patches.mjs --write.

Step 4 is where a real upstream conflict shows up: git apply of the source patch fails against the new tree. Resolve it in the checkout, re-diff, and rerun. The bundle hunks need no attention at any point.

Why Not Vendor a Fork

A vendored @xterm/xterm fork removes the patch entirely, but it moves Orca off the published package, so every upstream beta becomes a merge rather than a version bump, and Orca inherits responsibility for building and publishing a package it does not own. The patch is four small source hunks against a commit that reproduces byte for byte; a fork is a much larger standing cost for the same result.

Why Not Handle Composition at Runtime

CompositionHelper hooks four private call sites upstream of onData, and SortedList has no public surface at all. There is no supported extension point that reaches either, so a runtime shim would mean reaching into _core internals that upstream renames freely between betas. The patch is the smaller risk.

CI Contract

xterm_patch_sync in .github/workflows/pr.yml runs regenerate-xterm-patches.mjs --check on every PR and is part of the verify aggregate. It clones the pinned commit, installs upstream's toolchain, builds twice, and byte-compares the result against the committed patch. A warm run is about eight seconds of work around the clone and install.

config/scripts/regenerate-xterm-patches.test.mjs covers the pure pieces — pnpm's diff flags and normalization, hunk splitting, round-trip stability, the commit and build-order assertions, and lockfile coupling — with no network and no build, so they run in the ordinary test shards.

Known Gaps

@xterm/addon-webgl and @xterm/addon-serialize are still hand-edited minified bundles. Their patches carry a literal /* PATCH(orca): ... */ comment inside minified code and parser round-trip artifacts, and neither patch touches its .map file, so both addons currently ship sourcemaps whose offsets do not match the shipped bundle — the defect sourcemaps.policy now avoids for @xterm/xterm and which folding them into this manifest would also fix. Both addons build from the same pinned commit and reproduce byte for byte, so they can be folded into this manifest as additional packages entries; that change needs e2e sign-off because, unlike @xterm/xterm, it will not be a byte-for-byte no-op.