cli: stop --jsx-* flags from switching the automatic JSX runtime to production

[robobun]

What

Passing any --jsx-* CLI flag (--jsx-import-source, --jsx-fragment, --jsx-factory, --jsx-runtime) to bun <file.jsx> silently flipped the automatic JSX runtime from development (jsxDEV / <source>/jsx-dev-runtime) to production (jsx / <source>/jsx-runtime), even when the flag had nothing to do with dev/prod selection. Setting NODE_ENV=development in the environment did not restore it; only an explicit --define process.env.NODE_ENV='"development"' did.

Repro

d=$(mktemp -d); cd $d
mkdir -p node_modules/react/jsx-runtime node_modules/react/jsx-dev-runtime
echo 'exports.jsx=(t)=>({rt:"PROD"});exports.jsxs=exports.jsx' > node_modules/react/jsx-runtime/index.js
echo 'exports.jsxDEV=(t)=>({rt:"DEV"})' > node_modules/react/jsx-dev-runtime/index.js
printf '{"name":"react"}' > node_modules/react/package.json
echo 'console.log(JSON.stringify(<div/>))' > a.jsx

bun a.jsx                                                  # {"rt":"DEV"}   ok
bun --jsx-import-source=react a.jsx                        # {"rt":"PROD"}  dev lost, even though source == default
bun --jsx-fragment=Fragment a.jsx                          # {"rt":"PROD"}  unrelated flag also flips it
NODE_ENV=development bun --jsx-import-source=react a.jsx   # {"rt":"PROD"}  env NODE_ENV ignored

Cause

src/runtime/cli/Arguments.rs constructs an api::Jsx when any --jsx-* flag is present and hardcoded development: false in both the fresh-construct branch and the merge-with-bunfig branch. With no --jsx-* flags, transform.jsx stays None and BundleOptions::from_api keeps Pragma::default(), which has development: true. So the presence of any flag re-derived JSX options without the development default, and nothing downstream on the bun run path restores it unless NODE_ENV reaches the define map (the LoadAllWithoutInlining env behavior used by bun run skips that injection).

Fix

Default development: true to match Pragma::default(), bunfig, and JSBundler. In the bunfig-merge branch, preserve prev.development instead of overwriting it. NODE_ENV=production still switches to the production runtime via set_production() exactly as before.

Verification

New parameterized test in test/bundler/transpiler/jsx-cli-flags.test.ts spawns bun a.jsx with a shim react package whose jsx-runtime and jsx-dev-runtime report which one was imported, across the matrix of --jsx-* flags and NODE_ENV values. 6 of the 12 cases fail before this change (all --jsx-* + dev cases emit PROD); all 12 pass after.

The test lives in its own file rather than jsx-production.test.ts because the existing describe block in that file spawns a heavy fixture (react-dom render + Bun.build + dynamic import) that races the 5s default timeout under debug+ASAN builds, independently of this change.

---

[review] gate passed · iteration 3 · 2 files touched

fails on main (without fix)

ASAN without fix: 9 FAILED
$ BUN_DEBUG_QUIET_LOGS=1 bun scripts/build.ts --profile=debug --quiet test "--reporter=junit" "--reporter-outfile=/tmp/mechgate.xml" test/bundler/transpiler/jsx-cli-flags.test.ts
bun test v1.4.0 (e4812883e)

test/bundler/transpiler/jsx-cli-flags.test.ts:
(pass) jsx: --jsx-* CLI flags preserve development runtime > bun (no flags) NODE_ENV=<unset> [no bunfig] -> DEV [996.95ms]
(pass) jsx: --jsx-* CLI flags preserve development runtime > bun (no flags) NODE_ENV=development [no bunfig] -> DEV [757.11ms]
(pass) jsx: --jsx-* CLI flags preserve development runtime > bun (no flags) NODE_ENV=production [no bunfig] -> PROD [748.38ms]
64 |         stdout: "pipe",
65 |         stderr: "pipe",
66 |       });
67 |       const [stdout, stderr, exitCode] = await Promise.all([proc.stdout.text(), proc.stderr.text(), proc.exited]);
68 |       expect(stderr).toBe("");
69 |       expect(stdout.trim()).toBe(JSON.stringify({ rt: expected }));
                                 ^
error: expect(received).toBe(expected)

Expected: "{"rt":"DEV"}"
Received: "{"rt":"PROD"}"

      at <anonymous> (/workspace/bun/test/bundler/transpiler/jsx-cli-flags.test.ts:69:29)
(fail) jsx: --jsx-* CLI flags pre
... (truncated)

release without fix: 9 FAILED
bun test v1.4.0-canary.1 (1498d7b77)

test/bundler/transpiler/jsx-cli-flags.test.ts:
64 |         stdout: "pipe",
65 |         stderr: "pipe",
66 |       });
67 |       const [stdout, stderr, exitCode] = await Promise.all([proc.stdout.text(), proc.stderr.text(), proc.exited]);
68 |       expect(stderr).toBe("");
69 |       expect(stdout.trim()).toBe(JSON.stringify({ rt: expected }));
                                 ^
error: expect(received).toBe(expected)

Expected: "{"rt":"DEV"}"
Received: "{"rt":"PROD"}"

      at <anonymous> (/workspace/bun/test/bundler/transpiler/jsx-cli-flags.test.ts:69:29)
64 |         stdout: "pipe",
65 |         stderr: "pipe",
66 |       });
67 |       const [stdout, stderr, exitCode] = await Promise.all([proc.stdout.text(), proc.stderr.text(), proc.exited]);
68 |       expect(stderr).toBe("");
69 |       expect(stdout.trim()).toBe(JSON.stringify({ rt: expected }));
                                 ^
error: expect(received).toBe(expected)

Expected: "{"rt":"DEV"}"
Received: "{"rt":"PROD"}"

      at <anonymous> (/workspace/bun/test/bundler/transpiler/jsx-cli-flags.test.ts:69:29)
64 |         stdout: "pipe",
65 |         stderr: "pipe",
66 
... (truncated)

passes on PR (with fix)

ASAN with fix: all passed
$ BUN_DEBUG_QUIET_LOGS=1 bun scripts/build.ts --profile=debug --quiet test "--reporter=junit" "--reporter-outfile=/tmp/mechgate.xml" test/bundler/transpiler/jsx-cli-flags.test.ts
bun test v1.4.0 (e4812883e)

test/bundler/transpiler/jsx-cli-flags.test.ts:
(pass) jsx: --jsx-* CLI flags preserve development runtime > bun (no flags) NODE_ENV=<unset> [no bunfig] -> DEV [1043.19ms]
(pass) jsx: --jsx-* CLI flags preserve development runtime > bun (no flags) NODE_ENV=production [no bunfig] -> PROD [1064.69ms]
(pass) jsx: --jsx-* CLI flags preserve development runtime > bun (no flags) NODE_ENV=development [no bunfig] -> DEV [1198.58ms]
(pass) jsx: --jsx-* CLI flags preserve development runtime > bun --jsx-import-source=react NODE_ENV=<unset> [no bunfig] -> DEV [1190.26ms]
(pass) jsx: --jsx-* CLI flags preserve development runtime > bun --jsx-import-source=react NODE_ENV=production [no bunfig] -> PROD [1054.65ms]
(pass) jsx: --jsx-* CLI flags preserve development runtime > bun --jsx-import-source=react NODE_ENV=development [no bunfig] -> DEV [2363.22ms]
(pass) jsx: --jsx-* CLI flags preserve development runtime > bun --jsx-fragment=Fragment NODE_ENV=development [no bunfig] ->
... (truncated)

release with fix: all passed
$ bun scripts/build.ts --profile=release
[configured] bun-profile → bun (stripped)
  target       linux-x64-gnu
  build type   Release
  build dir    ./build/release
  revision     e4812883e7
  features     baseline

22 deps, 108 codegen, 1171 objects in 9631ms

ninja: Entering directory `/workspace/bun/build/release'
[1/1234] gen bindgenv2
[2/1234] fetch zlib
[zlib] up to date
[3/1234] fetch libjpeg-turbo
[libjpeg-turbo] up to date
[4/1234] fetch tinycc
[tinycc] up to date
[5/1234] fetch picohttpparser
[picohttpparser] up to date
[6/1234] gen ErrorCode+*.h
[7/1234] gen .bind.ts → GeneratedBindings.cpp
[8/1234] gen JSBuffer.lut.h
Generating /workspace/bun/build/release/codegen/JSBuffer.lut.h from /workspace/bun/src/jsc/bindings/JSBuffer.cpp
[9/1234] gen BunProcess.lut.h
Generating /workspace/bun/build/release/codegen/BunProcess.lut.h from /workspace/bun/src/jsc/bindings/BunProcess.cpp
[10/1234] gen ProcessBindingBuffer.lut.h
Generating /workspace/bun/build/release/codegen/ProcessBindingBuffer.lut.h from /workspace/bun/src/jsc/bindings/ProcessBindingBuffer.cpp
[11/1234] gen ProcessBindingConstants.lut.h
Generating /workspace/bun/build/release/codegen/ProcessBindi
... (truncated)

diff hotspot

src/runtime/cli/Arguments.rs                  |  4 +-
 test/bundler/transpiler/jsx-cli-flags.test.ts | 73 +++++++++++++++++++++++++++
 2 files changed, 75 insertions(+), 2 deletions(-)

gate history · 4 passed · 1 rejected · iteration 3

evidence per changed file

file                                           reads  edits  tests
src/runtime/cli/Arguments.rs                       7      3      0
test/bundler/transpiler/jsx-cli-flags.test.ts      1      2      0

[coderabbitai]

Walkthrough

CLI JSX override handling now preserves the JSX development setting instead of resetting it. A concurrent bundler test suite covers flag combinations, environment values, optional bunfig.toml, runtime selection, stderr, and exit status.

Changes

JSX runtime mode

Layer / File(s)	Summary
Preserve development mode through CLI overrides src/runtime/cli/Arguments.rs, test/bundler/transpiler/jsx-cli-flags.test.ts	api::Jsx creation and updates now retain the appropriate development value, while parameterized tests verify DEV/PROD runtime selection across CLI and environment configurations.

Possibly related PRs

• oven-sh/bun#35557: Also addresses preservation of JSX development mode during JSX runtime selection.

Suggested reviewers: jarred-sumner

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Title check	✅ Passed	The title is concise, specific, and matches the main fix in the PR.
Description check	✅ Passed	The description covers the problem, fix, and verification, so it mostly satisfies the template.

---

_{Comment @coderabbitai help to get the list of available commands.}

[robobun]

^{Updated 9:41 PM PT - Jul 28th, 2026}

❌ @robobun, your commit e481288 has 1 failures in Build #84493 (All Failures):

• test/js/bun/http/proxy-stress-protocol.test.ts - code 1 on 🐧 13 x64-asan

---

🧪   To try this PR locally:

bunx bun-pr 36209

That installs a local version of the PR into your bun-36209 executable, so you can run:

bun-36209 --bun

[claude]

LGTM — the two-line default flip is correct and now matches Pragma::default(), bunfig's jsx_dev = true, and JSBundler; NODE_ENV=production still reaches set_production() on the run path. The inline nit about test-file placement is non-blocking.

Extended reasoning...

Overview

Two-line change in src/runtime/cli/Arguments.rs: when any --jsx-* CLI flag is present and an api::Jsx is constructed, development now defaults to true (fresh-construct branch) or preserves prev.development (bunfig-merge branch) instead of hardcoding false. A new 12-case parameterized test in test/bundler/transpiler/jsx-cli-flags.test.ts spawns bun a.jsx against a shim react package that reports which runtime entrypoint was imported, across --jsx-import-source / --jsx-fragment / --jsx-factory / --jsx-runtime × NODE_ENV ∈ {unset, development, production}.

Correctness verification

I traced the claim end-to-end:

• Pragma::default() at src/options_types/jsx.rs:201 sets development: true.
• Pragma::from_api at jsx.rs:329 copies jsx.development verbatim, so the old false here overrode the default only when a flag was present — exactly the reported inconsistency.
• Bunfig's parser (src/bunfig/bunfig.rs:953) defaults jsx_dev = true and only sets false for jsx = "react-jsx"; the merge branch now preserves that via prev.development instead of clobbering it.
• JSBundler at src/runtime/api/JSBundler.rs:191 also defaults development: true.
• NODE_ENV=production still flips to prod via set_production(true) in src/bundler/transpiler.rs:734/786, which the test's production cases cover.

The finder-raised concern that the merge branch still overwrites prev.side_effects was checked and is pre-existing behavior unrelated to this fix.

Security risks

None. This is transpiler-option defaulting; no untrusted input parsing, no auth/crypto/fs surface.

Level of scrutiny

Low-to-moderate. A two-line default change in CLI arg assembly with a well-argued root cause and three independent in-tree precedents for the new value. The test is hermetic (tempDir, shim package, port-free), drains stdout/stderr/exited concurrently, spreads bunEnv, and asserts exact JSON — it follows harness conventions.

Other factors

The only finding is a nit about test-file placement (new jsx-cli-flags.test.ts vs. appending to jsx-production.test.ts, which the PR description still names). That's organizational and was a deliberate follow-up commit; it doesn't affect correctness. The comment-cop bot's earlier note about an explanatory code comment was addressed in d8f05e4.

[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@test/bundler/transpiler/jsx-cli-flags.test.ts`:
- Around line 26-49: Expand the `cases` matrix to add explicit development and
production entries for `--jsx-factory=h`, an explicit development entry for
`--jsx-runtime=automatic`, and separated-argument forms such as
`["--jsx-factory", "h"]` with both relevant environment outcomes. Preserve the
expected DEV/PROD behavior established by the existing cases.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: ASSERTIVE

Plan: Pro

Run ID: eab96ecd-b9ed-4950-912d-9bd0b16d7a77

📥 Commits

Reviewing files that changed from the base of the PR and between e532ad9 and ab00356.

📒 Files selected for processing (2)

• src/runtime/cli/Arguments.rs
• test/bundler/transpiler/jsx-cli-flags.test.ts

[claude]

LGTM — the two-line fix aligns --jsx-* CLI flag handling with Pragma::default(), bunfig, and JSBundler (all default development: true), and NODE_ENV=production still overrides via set_production().

What was reviewed:

• Verified development: true matches Pragma::default() (options_types/jsx.rs:201), bunfig's jsx_dev = true default (bunfig.rs:953), and JSBundler.rs:191.
• Confirmed the bunfig-merge test cases added in c9f4327 exercise line 1467 — bunfig.rs:990-1013 unconditionally populates ctx.args.jsx for any bunfig, and the jsx = "react-jsx" / "react-jsxDEV" cases map correctly to jsx_dev = false/true.
• Checked bun build is unaffected: without --jsx-* flags it already used Pragma::default() (dev), and --production still forces jsx.development = false at build_command.rs:461-464.

Extended reasoning...

Overview

Two-line change in src/runtime/cli/Arguments.rs: when any --jsx-* CLI flag is passed and an api::Jsx struct is constructed, the development field now defaults to true (fresh-construct branch, line 1451) or preserves prev.development from bunfig (merge branch, line 1467), instead of hardcoding false in both. A new 17-case parameterized test in test/bundler/transpiler/jsx-cli-flags.test.ts covers the flag × NODE_ENV × bunfig matrix.

Security risks

None. This is JSX transpilation dev/prod-mode selection — no auth, crypto, filesystem, or network surface involved.

Level of scrutiny

Low-to-medium. The source change is 2 lines and mechanically aligns a default with three existing sources of truth (Pragma::default() at options_types/jsx.rs:201, bunfig.rs:953, JSBundler.rs:191). The behavior change is user-visible but strictly a bugfix: previously, adding an unrelated --jsx-* flag silently flipped dev→prod, which was inconsistent with the no-flag path. NODE_ENV=production continues to override via set_production() in transpiler.rs, so the production path is unaffected. I also confirmed bun build behavior is consistent — it already defaulted to dev JSX without --jsx-* flags (via Pragma::default()), and --production still forces development: false explicitly at build_command.rs:461-464.

Other factors

All three of my earlier review threads are resolved: the test-file-location nit was addressed by updating the PR description with a stated reason for the separate file; the missing bunfig-merge-branch coverage was fixed in c9f4327 (author verified reverting line 1467 alone now fails 3 cases); the pre-existing --jsx-side-effects gate omission was acknowledged and reasonably deferred to a follow-up since it needs a different test shape (bun build output assertion vs. runtime import). CodeRabbit's suggestion to expand the matrix was declined with sound reasoning (all flags share one gate, no per-flag branching) and withdrawn. The test follows harness conventions (tempDir, bunEnv spread, concurrent pipe drain, exit-code asserted last, describe.concurrent), and bunEnv already deletes NODE_ENV so the undefined cases are hermetic.

[claude]

LGTM — the bunfig-merge coverage gap I flagged is now closed (17-case matrix exercises both the fresh-construct and prev.development branches, and both bunfig react-jsx/react-jsxDEV directions), and the separate-file rationale is documented. Two-line fix aligns with Pragma::default() (development: true at src/options_types/jsx.rs:201); NODE_ENV=production cases in the matrix confirm the prod path is unaffected.

Extended reasoning...

Overview

Two-line change in src/runtime/cli/Arguments.rs: when any --jsx-* CLI flag triggers construction of api::Jsx, default development to true (fresh-construct branch, matching Pragma::default() at src/options_types/jsx.rs:201) and preserve prev.development (bunfig-merge branch) instead of hardcoding false. New test file test/bundler/transpiler/jsx-cli-flags.test.ts with a 17-case concurrent matrix over --jsx-* flags × NODE_ENV × bunfig presence/content, asserting which of jsx-runtime/jsx-dev-runtime a shim react package reports.

Security risks

None. This is CLI option-plumbing that only affects which JSX runtime import specifier the transpiler emits; no untrusted-input parsing, auth, crypto, or filesystem semantics change.

Level of scrutiny

Low-to-medium. The source change is two field initializers whose new values are demonstrably the defaults already used everywhere else (Pragma::default(), bunfig, JSBundler). The test proves both that the regression is fixed and that NODE_ENV=production still selects the production runtime on both branches, so no behavior is lost. I verified bunfig.rs:961-966 accepts the exact "react-jsx"/"react-jsxDEV" spellings the test uses and sets jsx_dev accordingly, so the merge-branch cases exercise prev.development in both true and false states.

Other factors

All prior review threads are resolved: the comment-cop note was addressed (comment dropped), my test-organization nit was answered with a concrete debug+ASAN timeout justification now recorded in the PR description, my coverage-gap finding was fixed in c9f4327 (author confirmed reverting either changed line independently now fails tests), and CodeRabbit withdrew its matrix-expansion suggestion. The pre-existing --jsx-side-effects gate omission I noted was explicitly and reasonably deferred as out-of-scope (different test shape, tracked separately). The test follows harness conventions: tempDir, bunEnv spread with NODE_ENV explicitly deleted when unset, concurrent pipe drain, stderr/stdout asserted before exit code, describe.concurrent for independent subprocess spawns.

[robobun]

CI status: the diff is green. test/bundler/transpiler/jsx-cli-flags.test.ts passed on every lane that ran tests in both #84370 and #84493.

Remaining red in #84493 is unrelated to this change:

• test/js/bun/http/proxy-stress-protocol.test.ts ECONNRESET on debian x64-asan (1/102 subtests, HTTP proxy upload stress; reported to main-break triage)
• everything else is parallel-batch flake that passed when re-run alone (spawn-streaming-stdout, fetch-tls-abortsignal-timeout, 28004 MySQL timeout, bun-serve-date, fastutf8stream-reopen, etc.)

Ready for review.