Accept wrangler.json(c) as a config by ry · Pull Request #8051 · cloudflare/workerd

ry · 2026-10-27T23:14:42Z

Lets workerd take a wrangler.json/wrangler.jsonc directly instead of a config.capnp. This is a developer-experience change: existing Workers projects run under workerd unchanged.

Supported fields: name, main, compatibility_date, compatibility_flags, vars, durable_objects.bindings, migrations (new, sqlite, renamed and deleted classes) and no_bundle. Any other field is rejected by deny_unknown_fields, so a config never silently half-works.
Bundling: shells out to esbuild with wrangler-like flags: ESM output, workerd conditions, node/cloudflare builtins external, and a require banner for CJS dependencies. If esbuild is missing, the error says how to fix it.
Defaults: listens on *:8787. DO storage goes in .wrangler/state/workerd, matching wrangler's layout.
--watch: reloads on the config file and on the inputs listed in esbuild's metafile. After a failed build it watches the project's sources, so fixing the error reloads.
Tests: unit tests cover JSONC, plain modules, DOs, migrations, unsupported fields and missing esbuild.

Does not support: KV, R2, D1, service bindings, define and rules.

`workerd serve wrangler.jsonc` translates a wrangler config into a Config: name, main, compatibility_date/flags, vars, durable_objects and migrations. main is bundled with esbuild the way wrangler does it (WORKERD_ESBUILD, else node_modules/.bin/esbuild, else PATH), or scanned as plain modules under "no_bundle". DO storage goes in .wrangler/state/workerd. --watch reloads on changes to the config or to any bundled input. Unsupported fields are an error.

clanky-the-clanker · 2026-10-27T23:17:53Z

💬 Approved with comments — The earlier WARNING about the default bind address is fixed: it is now localhost:8787. Only two INFO notes remain, one about watch scope after a failed build and one about README defaults.

Findings: 2 info

Not opened by the correctness review: 6 changed files it was meant to read

samples/BUILD.bazel
samples/wrangler/.gitignore
samples/wrangler/src/index.ts
samples/wrangler/wrangler.jsonc
src/workerd/server/BUILD.bazel
src/workerd/server/cli/args.rs

_{The decision is advisory: this comment never approves, blocks or requests changes on the pull request.}

⚡ Performance: 💬 1 info

One earlier INFO is still open: per-file watches after a failed build under --watch.

Recommendation: 💬 Optional Nits

[INFO] After a failed esbuild build under --watch, every source file under the project root gets its own watch, including files in dist/ and build/. A large project can hit the inotify limit. This affects only development. (src/workerd/server/cli/wrangler.rs:353)

View full review

src/workerd/server/cli/wrangler.rs:353-362: after a failed build, the code calls files(root) and watches every source file it returns. files() skips only node_modules and dot-directories, so it also walks output directories such as dist/ and build/.

Impact:

A large project can run out of inotify watches.
Writes into output directories can trigger reloads nobody asked for.
This affects only development with --watch, and only after a failed build.

Fix: skip common output directories, or watch directories instead of single files.

📝 Documentation: 💬 1 info

The README's wrangler section still does not give the listen address or the Durable Object state directory.

Recommendation: 💬 Optional Nits

[INFO] Give the defaults for a wrangler config in the README: the listen address (localhost:8787) and the Durable Object state directory (.wrangler/state/workerd/). (README.md:111)

View full review

README.md:111-115 introduces wrangler config support but does not say:

that the server listens on localhost:8787 by default;
that Durable Object state is stored under .wrangler/state/workerd/.

Adding both tells users where the server is reachable and where persistent state is written.

✅ All other checks passed

🔒 Security: ✅ LGTM

The previous WARNING is resolved:

DEFAULT_ADDRESS is now localhost:8787 (src/workerd/server/cli/wrangler.rs:32).
The module doc says the same and notes that --socket-addr overrides it.
A test asserts the address (wrangler-test.rs:99).

Checked and fine:

esbuild is spawned from an argument list, with no shell.
Bundles are written to .wrangler/tmp inside the project.
files() does not follow symlinks.
Unknown config fields are rejected.

📖 AGENTS.md: ✅ LGTM

The root AGENTS.md and src/workerd/server/AGENTS.md both say that wrangler.json(c) configs are accepted.

📋 Code Quality: ✅ LGTM

The only code changed since the last review is the default listen address, now localhost:8787 (src/workerd/server/cli/wrangler.rs:32). The module doc (wrangler.rs:17), wrangler-test.rs:99 and samples/wrangler/README.md all match it.

_{Reviewed commit: 976e5474}

ask-bonk · 2026-10-27T23:20:21Z

Since last review: 2 resolved, 0 still open, 0 new.
LGTM!

_{Reviewed commit: 976e5474 · github run}

- Bundle into .wrangler/tmp in the project, not a predictable path in the shared temp dir. - Key a Durable Object's storage by the name it was created under, so renamed_classes keeps its data. - files() no longer follows symlinks, so a cycle cannot recurse. - Test bundling, success and failure, against a stub esbuild. - Mention wrangler configs in the README.

codecov-commenter · 2026-10-27T23:40:58Z

Codecov Report

❌ Patch coverage is 2.04082% with 336 lines in your changes missing coverage. Please review.
✅ Project coverage is 69.25%. Comparing base (47cde3f) to head (976e547).
⚠️ Report is 8 commits behind head on main.

Files with missing lines	Patch %	Lines
src/workerd/server/cli/wrangler.rs	1.21%	325 Missing ⚠️
src/workerd/server/cli/lib.rs	21.42%	11 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #8051      +/-   ##
==========================================
- Coverage   69.38%   69.25%   -0.13%     
==========================================
  Files         696      697       +1     
  Lines      181864   182210     +346     
  Branches    29213    29215       +2     
==========================================
+ Hits       126185   126191       +6     
- Misses      38612    38950     +338     
- Partials    17067    17069       +2

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

Within a migration, apply deleted_classes, then renamed_classes, then new classes, as wrangler does, so a class can be deleted and re-created in one migration. Reject deleting or renaming a class that does not exist, and creating one that already does.

ryanking13 · 2026-10-28T04:50:58Z

I guess one thing we need to think about is that wrangler will be replaced by cf cli and it uses a .ts configuration file.

- Never reuse a Durable Object storage key: a class created under a name an earlier class was keyed by (deleted, or renamed away) gets <name>~<n> and starts empty, as in production. Previously a renamed class and a new class under its old name shared storage. - Name the DO disk service after the worker, so a worker named wrangler-do-storage no longer collides with it. - Watch main before bundling, so creating a missing main reloads. - Serialize the tests that spawn processes, so the stub esbuild cannot fail with ETXTBSY. - Test the DO binding, the uniqueKey a renamed class keeps, and that deletes apply before renames. - List $schema among the README's supported fields.

github-actions · 2026-10-28T13:25:48Z

The generated output of @cloudflare/workers-types matches the snapshot in types/generated-snapshot 🎉

- Reject renaming a Durable Object class onto a name that exists. - Test that bundling watches inputs only the metafile names. - Module doc: name storage directories by key and list $schema; the root AGENTS.md mentions wrangler configs.

ry · 2026-10-28T14:50:37Z

@ryanking13 good point

I guess one thing we need to think about is that wrangler will be replaced by [cf cli (https://blog.cloudflare.com/cloudflare-cf-cli-launch/) and it uses a .ts configuration file.

This out of scope for this PR, as it would need Node.js execution - something workerd cannot provide now. That said, we shouldn't let that block DX improvements to workerd.

jasnell

LGTM but having at least one sample that uses wrangler.jsonc instead of the capnp would be helpful.

A TypeScript Worker with a SQLite-backed Durable Object, bundled with esbuild. A unit test parses its config, so it cannot drift from what the loader accepts.

A missing wrangler config was reported as a config error, so --watch waited for it to change but never watched it. Report it as a usage error, as for a missing .capnp config.

A wrangler config's server listened on every interface (*:8787). wrangler dev listens on localhost; do the same, so a dev server is not reachable from the network unless --socket-addr says so.

ry requested review from a team as code owners October 27, 2026 23:14

ask-bonk Bot reviewed Oct 27, 2026

View reviewed changes

Comment thread src/workerd/server/cli/wrangler.rs Outdated

Comment thread src/workerd/server/cli/wrangler.rs

Comment thread src/workerd/server/cli/wrangler.rs Outdated

Comment thread src/workerd/server/cli/wrangler-test.rs Outdated

ask-bonk Bot reviewed Oct 27, 2026

View reviewed changes

Comment thread src/workerd/server/cli/wrangler.rs

ask-bonk Bot reviewed Oct 28, 2026

View reviewed changes

Comment thread src/workerd/server/cli/wrangler.rs Outdated

Comment thread src/workerd/server/cli/wrangler-test.rs

bartlomieju mentioned this pull request Oct 28, 2026

server: workerd run, workerd check, and Wrangler configs for serve #8065

Draft

ask-bonk Bot reviewed Oct 28, 2026

View reviewed changes

Comment thread src/workerd/server/cli/wrangler-test.rs Outdated

ry added 3 commits October 28, 2026 06:26

Add the license header to the new Rust files

f6808fd

Merge main into ry/wrangler-json

cc9b4f5

Merge main into ry/wrangler-json

c38ecab

jasnell approved these changes Oct 28, 2026

View reviewed changes

Add a sample configured with wrangler.jsonc

f8c22ad

A TypeScript Worker with a SQLite-backed Durable Object, bundled with esbuild. A unit test parses its config, so it cannot drift from what the loader accepts.

ask-bonk Bot reviewed Oct 28, 2026

View reviewed changes

Comment thread samples/wrangler/src/index.ts

Merge main into ry/wrangler-json

6a9d123

ry enabled auto-merge (squash) October 28, 2026 21:12

Fail at once on a missing wrangler config

ef05e63

A missing wrangler config was reported as a config error, so --watch waited for it to change but never watched it. Report it as a usage error, as for a missing .capnp config.

ask-bonk Bot reviewed Oct 28, 2026

View reviewed changes

Comment thread src/workerd/server/cli/lib.rs

Listen on localhost:8787 by default, as wrangler dev does

976e547

A wrangler config's server listened on every interface (*:8787). wrangler dev listens on localhost; do the same, so a dev server is not reachable from the network unless --socket-addr says so.

ry merged commit 82872d3 into main Oct 28, 2026
50 of 51 checks passed

ry deleted the ry/wrangler-json branch October 28, 2026 22:53

Conversation

ry commented Oct 27, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

clanky-the-clanker Bot commented Oct 27, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

⚡ Performance: 💬 1 info

📝 Documentation: 💬 1 info

🔒 Security: ✅ LGTM

📖 AGENTS.md: ✅ LGTM

📋 Code Quality: ✅ LGTM

Uh oh!

ask-bonk Bot commented Oct 27, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

codecov-commenter commented Oct 27, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Codecov Report

Uh oh!

Uh oh!

Uh oh!

ryanking13 commented Oct 28, 2026

Uh oh!

Uh oh!

github-actions Bot commented Oct 28, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

ry commented Oct 28, 2026

Uh oh!

jasnell left a comment

Choose a reason for hiding this comment

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Reviewers

Uh oh!

Assignees

Labels

Projects

Milestone

Development

Uh oh!

4 participants

ry commented Oct 27, 2026 •

edited

Loading

clanky-the-clanker Bot commented Oct 27, 2026 •

edited

Loading

ask-bonk Bot commented Oct 27, 2026 •

edited

Loading

codecov-commenter commented Oct 27, 2026 •

edited

Loading

github-actions Bot commented Oct 28, 2026 •

edited

Loading