PR #37018 - oven-sh/bun

TOML.parse returned all four TOML date/time types as strings of their source text. They now map 1:1 and losslessly onto Temporal, which is enabled by default on main:

TOML	JS
offset date-time (`1979-05-27T00:32:00-07:00`)	`Temporal.Instant`
local date-time (`1979-05-27T07:32:00`, 1.1's `1979-05-27 07:32`)	`Temporal.PlainDateTime`
local date (`1979-05-27`)	`Temporal.PlainDate`
local time (`07:32:00`, `07:32`)	`Temporal.PlainTime`

Per the spec an offset date-time "specifies an instant", so it is Temporal.Instant and the written offset normalizes to UTC. Sub-second digits are preserved (Temporal carries nanoseconds; fractional seconds beyond 9 digits are truncated as the TOML spec directs, since Temporal rejects them). Leap-second :60 clamps to :59 through Temporal's own ISO parsing.

const doc = Bun.TOML.parse("d = 1979-05-27T00:32:00-07:00");
doc.d instanceof Temporal.Instant; // true
doc.d.toString(); // "1979-05-27T07:32:00Z"
Bun.TOML.stringify(doc); // "d = 1979-05-27T07:32:00Z\n" (unquoted date-time literal)

How

The TOML parser tags the E::String it produces with the date/time kind (toml_datetime on EString); the lexer already distinguished the four kinds. The TOML AST never enters the JS visit/transform passes, so only the TOML sinks check the tag.
All three sinks of the TOML AST stay consistent:
- Bun.TOML.parse and import/require of .toml construct the object through the same JSC code paths Temporal.*.from(string) uses (new bindings in bindings.cpp).
- The bundler lowers the node to a Temporal.*.from("...") call over a real unbound Temporal symbol, so the chunk renamer renames a user binding named Temporal instead of letting it capture the reference, and the calls are pure-annotated so unused exports tree-shake.
- bun build --no-bundle of a .toml file (which prints the data AST directly, without a symbol table) prints the tagged string as a bare Temporal.*.from("...") call. That path turns each top-level key into a module-scope var, so a document with both a date/time and a top-level key literally named Temporal fails at evaluation with a TypeError; renaming without a symbol table was tried and dropped as open-ended.
TOML.stringify emits Temporal.Instant/PlainDateTime/PlainDate/PlainTime as unquoted TOML literals, so stringify(parse(doc)) round-trips date/times. Temporal.ZonedDateTime is also accepted and emits the offset at that instant, dropping the [Time/Zone] annotation (TOML has no zone syntax); non-ISO [u-ca=...] calendar annotations are dropped the same way (the stored ISO fields are emitted). PlainYearMonth/PlainMonthDay/Duration have no TOML form and throw. Values TOML's 4-digit years cannot spell throw like Date already did, with one refinement for instants: an offset date-time at a year edge (0000-01-01T00:00:00+01:00 is valid TOML but its UTC year is -1) is emitted with the nearest offset whose local year fits, so everything parse accepts also stringifies; only instants a day or more outside 0000..9999 throw. Date output now trims trailing fraction zeros (Z rather than .000Z) so Date and Instant spell the same instant identically; otherwise Date handling is unchanged.
With BUN_JSC_useTemporal=0, a date/time value throws a TypeError ("Date/time values require Temporal, which is disabled in this process"); the module-import path previously would have panicked on any conversion error and now fails the load with the pending exception.
bunfig.toml uses no date values, so config parsing is unaffected.

Everything else about parse/stringify (error messages, layout, numbers) is byte-for-byte unchanged.

Tests

Regenerated toml-test-suite.test.ts (708 cases) from the same pinned toml-test commit: datetime expectations construct the Temporal value and compare with plain toEqual (deepEquals learned Temporal objects in #37024). All pass, including the parse(stringify(parse(input))) lap each valid case asserts.
Hand-written coverage in toml.test.ts: the four mappings, instant semantics, TOML spellings Temporal does not print (space separator, lowercase t/z, omitted seconds, leap second), fraction truncation, nesting, both useTemporal=0 behaviors, stringify of all eight Temporal types, year bounds, calendar/zone annotation dropping, array layout.
Import fixtures (test/js/bun/resolve/toml) extended with a [dates] table; bundler tests assert the emitted Temporal.*.from modules run and that a user var Temporal in the same bundle is renamed instead of captured.

Types and docs updated (bun.d.ts JSDoc, docs/runtime/toml.mdx).

[review] gate passed · iteration 3 · 25 files touched

fails on main (without fix)

ASAN without fix: 53 FAILED
$ BUN_DEBUG_QUIET_LOGS=1 bun scripts/build.ts --profile=debug --quiet test "--reporter=junit" "--reporter-outfile=/tmp/mechgate.xml" test/bundler/bundler_loader.test.ts test/js/bun/resolve/toml/toml.test.js test/js/bun/toml/toml-test-suite.test.ts test/js/bun/toml/toml.test.ts
bun test v1.4.0 (48b6af953)

test/bundler/bundler_loader.test.ts:
(pass) bundler > bun loader > bun/loader-yaml-file [1013.43ms]
(pass) bundler > bun loader > bun/loader-text-file [412.02ms]
(pass) bundler > bun loader > bun/loader-json-file [489.14ms]
(pass) bundler > bun loader > bun/loader-toml-file [429.12ms]
(pass) bundler > bun loader > bun/loader-toml-datetime-shadowed-temporal-global [413.44ms]
runtime failed file: /tmp/bun-build-tests/bun-avOXit/bun/loader-toml-datetime-imported-temporal-binding/out.js
stdout output:
polyfill false 1979-05-27
---
expected stdout:
polyfill true 1979-05-27
---
1843 |               console.log(`---`);
1844 |               console.log(`expected ${name}:`);
1845 |               console.log(expected);
1846 |               console.log(`---`);
1847 |             }
1848 |             expect(result).toBe(expected);
                                  ^
error: exp
... (truncated)

release without fix: 53 FAILED
bun test v1.4.0-canary.1 (b7a043103)

test/bundler/bundler_loader.test.ts:
(pass) bundler > bun loader > bun/loader-yaml-file [31.84ms]
(pass) bundler > bun loader > bun/loader-text-file [14.09ms]
(pass) bundler > bun loader > bun/loader-json-file [18.21ms]
(pass) bundler > bun loader > bun/loader-toml-file [13.89ms]
(pass) bundler > bun loader > bun/loader-toml-datetime-shadowed-temporal-global [22.56ms]
runtime failed file: /tmp/bun-build-tests/bun-Rboeq6/bun/loader-toml-datetime-imported-temporal-binding/out.js
stdout output:
polyfill false 1979-05-27
---
expected stdout:
polyfill true 1979-05-27
---
1843 |               console.log(`---`);
1844 |               console.log(`expected ${name}:`);
1845 |               console.log(expected);
1846 |               console.log(`---`);
1847 |             }
1848 |             expect(result).toBe(expected);
                                  ^
error: expect(received).toBe(expected)

Expected: "polyfill true 1979-05-27"
Received: "polyfill false 1979-05-27"

      at <anonymous> (/workspace/bun/test/bundler/expectBundled.ts:1848:28)
(fail) bundler > bun loader > bun/loader-toml-datetime-imported-temporal-binding [18.93ms]
93
... (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/bundler_loader.test.ts test/js/bun/resolve/toml/toml.test.js test/js/bun/toml/toml-test-suite.test.ts test/js/bun/toml/toml.test.ts
bun test v1.4.0 (48b6af953)

test/bundler/bundler_loader.test.ts:
(pass) bundler > bun loader > bun/loader-yaml-file [1011.62ms]
(pass) bundler > bun loader > bun/loader-text-file [508.58ms]
(pass) bundler > bun loader > bun/loader-json-file [360.53ms]
(pass) bundler > bun loader > bun/loader-toml-file [381.91ms]
(pass) bundler > bun loader > bun/loader-toml-datetime-shadowed-temporal-global [387.83ms]
(pass) bundler > bun loader > bun/loader-toml-datetime-imported-temporal-binding [377.21ms]
(pass) bundler > bun loader > bun/loader-toml-datetime-no-bundle [464.49ms]
(pass) bundler > bun loader > bun/loader-toml-datetime [433.16ms]
(pass) bundler > bun loader > bun/loader-text-file [398.02ms]
(pass) bundler > bun loader > bun/loader-xml-file [432.77ms]
(pass) bundler > node loader > bun/loader-yaml-file [427.98ms]
(pass) bundler > node loader > bun/loader-text-file [385.65ms]
(pass) bundler > 
... (truncated)

release with fix: all passed
$ bun scripts/build.ts --profile=release
[configured] bun-profile → bun (stripped) in 652ms (unchanged)
ninja: Entering directory `/workspace/bun/build/release'
[1/23] gen generated_host_exports.rs
generated_host_exports.rs: 92 exports (host=3, lazy=10, generic=79, rust=0); 240 extern-C blocks audited
[2/23] gen cpp.rs (cppbind)
[3/23] gen JS modules (bundle-modules)
Preprocess modules (8539ms)
Bundle modules (64ms)
Postprocesss modules (324ms)
Bundle Functions (858ms)
Generate Code (29ms)

[9.83s] Bundled "src/js" for production
  2632 kb
  197 internal modules
  13 native modules
  91 internal functions across 17 files
[3/8] cargo bun_bin → libbun_rust.a (--target x86_64-unknown-linux-gnu)

  nightly-2026-07-20-x86_64-unknown-linux-gnu unchanged - rustc 1.99.0-nightly (9f36de775 2026-07-19)

[1m[92m   Compiling[0m bun_ast v0.0.0 (/workspace/bun/src/ast)
[1m[92m   Compiling[0m bun_install_types v0.0.0 (/workspace/bun/src/install_types)
[1m[92m   Compiling[0m bun_parsers v0.0.0 (/workspace/bun/src/parsers)
[1m[92m   Compiling[0m bun_react_compiler v0.0.0 (/workspace/bun/src/react_compiler)
[1m[92m   Compiling[0m bun_css v0.0.0 (/workspace/bun/src/
... (truncated)

diff hotspot

docs/runtime/toml.mdx                          |  38 +-
 packages/bun-types/bun.d.ts                    |  20 +-
 src/ast/e.rs                                   |  45 ++
 src/ast/expr.rs                                |   1 +
 src/bundler/ParseTask.rs                       |  30 +-
 src/bundler/bundle_v2.rs                       |   2 +-
 src/bundler/transpiler.rs                      |   1 +
 src/codegen/cppbind.ts                         |   1 +
 src/js_parser/parse/parse_entry.rs             | 117 +++
 src/js_parser_jsc/expr_jsc.rs                  |  26 +-
 src/js_parser_jsc/lib.rs                       |   3 +-
 src/js_printer/lib.rs                          |  21 +
 src/jsc/JSValue.rs                             |  19 +
 src/jsc/bindings/bindings.cpp                  | 155 ++++
 src/jsc/lib.rs                                 |   1 +
 src/parsers/toml.rs                            | 129 ++--
 src/runtime/api.rs                             |  63 +-
 src/runtime/api/TOMLObject.rs                  | 150 +++-
 test/bundler/bundler_loader.test.ts            |  67 ++
 test/js/bun/resolve/toml/toml-fixture.toml     |   6 +
 test/js/bun/resolve/toml/toml-fixture.toml.txt |   6 +
 test/js/bun/resolve/toml/toml.test.js          |   9 +
 test/js/bun/toml/generate_toml_test_suite.ts   |  93 +--
 test/js/bun/toml/toml-test-suite.test.ts       | 951 ++++++++++++-------------
 test/js/bun/toml/toml.test.ts                  | 297 ++++++--
 25 files changed, 1494 insertions(+), 757 deletions(-)

gate history · 7 passed · 0 rejected · iteration 3

evidence per changed file

file                                reads  edits  tests
docs/runtime/toml.mdx                   1      1      0
packages/bun-types/bun.d.ts             1      1      0
src/ast/e.rs                            6      8      0
src/ast/expr.rs                         5      6      0
src/bundler/ParseTask.rs                2      1      0
src/bundler/bundle_v2.rs                1      1      0
src/bundler/transpiler.rs               5      7      0
src/codegen/cppbind.ts                  0      0      0
src/js_parser/parse/parse_entry.rs      4     10      0
src/js_parser_jsc/expr_jsc.rs           4      7      0
src/js_parser_jsc/lib.rs                1      2      0
src/js_printer/lib.rs                   3      7      0
src/jsc/JSValue.rs                      2      4      0
src/jsc/bindings/bindings.cpp           7     11      0
src/jsc/lib.rs                          0      0      0
src/parsers/toml.rs                     5      7      0
(+ 9 more files)

#37018 TOML: map date/time values to Temporal, round-trip them through stringify

How

Tests

TOML: map date/time values to Temporal, round-trip them through stringify