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fix(@formatjs/intl-durationformat): use BigDecimal for sub-second rollups (#6466)
## Summary Sub-second units that roll up into a numeric parent (`milliseconds: 'numeric'`, etc.) were combined with float arithmetic. `1 + 473/1e3` lands on `1.4729999999999998650`, and `roundingMode: 'trunc'` truncated that to `1.472999999s` instead of `1.473s`. Carry the value as `BigDecimal` end-to-end and pass its decimal string to `NumberFormat`. NumberFormat (V3, ES2023) parses the string as a Mathematical Value, sidestepping the IEEE 754 round-trip entirely. Also adds `ES2023.Intl` to `BASE_TSCONFIG.lib` so `formatToParts` accepts the `${number}` string overload at type-check time. Fixes #6462 ## Test plan - [x] New regression test covers the seconds/milliseconds/microseconds rollup cases - [x] `bazel test //packages/intl-durationformat/...` — all 7 tests pass - [x] `bazel test //packages/...` — full suite (374 tests) passes; the `ES2023.Intl` lib addition didn't break any other package's typecheck - [ ] CI green 🤖 Generated with [Claude Code](https://claude.com/claude-code) --------- Co-authored-by: Claude Opus 4.7 (1M context) <[email protected]>
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4 files changed

Lines changed: 62 additions & 10 deletions

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‎packages/ecma402-abstract/utils.ts‎

Lines changed: 15 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -1,3 +1,4 @@
1+
import type {BigDecimal} from '@formatjs/bigdecimal'
12
import {memoize, strategies} from '@formatjs/fast-memoize'
23

34
export function repeat(s: string, times: number): string {
@@ -142,11 +143,23 @@ export function invariant(
142143
}
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}
144145

146+
// Native NumberFormat coerces non-primitive inputs via ToPrimitive (calling
147+
// `toString()`) before feeding them to ToIntlMathematicalValue, so a
148+
// `BigDecimal` passed to `format`/`formatToParts` is parsed as an exact
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// StringNumericLiteral. The widened return type lets call sites carry
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// BigDecimal end-to-end without lossy intermediate `.toString()` casts.
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type NumberFormatLike = Omit<Intl.NumberFormat, 'format' | 'formatToParts'> & {
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format(value: number | bigint | string | BigDecimal | undefined): string
153+
formatToParts(
154+
value: number | bigint | string | BigDecimal | undefined
155+
): Intl.NumberFormatPart[]
156+
}
157+
145158
export const createMemoizedNumberFormat: (
146159
...args: ConstructorParameters<typeof Intl.NumberFormat>
147-
) => Intl.NumberFormat = memoize(
160+
) => NumberFormatLike = memoize(
148161
(...args: ConstructorParameters<typeof Intl.NumberFormat>) =>
149-
new Intl.NumberFormat(...args),
162+
new Intl.NumberFormat(...args) as NumberFormatLike,
150163
{
151164
strategy: strategies.variadic,
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}

‎packages/intl-durationformat/BUILD.bazel‎

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Original file line numberDiff line numberDiff line change
@@ -35,6 +35,7 @@ formatjs_library(
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types = True,
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visibility = ["//visibility:public"],
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deps = [
38+
"//:node_modules/@formatjs/bigdecimal",
3839
"//:node_modules/@formatjs/intl-localematcher",
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"//:node_modules/@formatjs_generated/cldr.number",
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"//packages/ecma262-abstract",
@@ -49,6 +50,7 @@ formatjs_test(
4950
data = [
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"tests/index.test.ts",
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":intl-durationformat",
53+
"//:node_modules/@formatjs/bigdecimal",
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"//:node_modules/@formatjs/intl-localematcher",
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"//:node_modules/@formatjs_generated/cldr.number",
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"//:node_modules/vitest",

‎packages/intl-durationformat/abstract/PartitionDurationFormatPattern.ts‎

Lines changed: 19 additions & 8 deletions
Original file line numberDiff line numberDiff line change
@@ -1,3 +1,4 @@
1+
import {BigDecimal} from '@formatjs/bigdecimal'
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import type {NumberFormatOptions} from '#packages/ecma402-abstract/types/number.js'
23
import {
34
createMemoizedListFormat,
@@ -30,7 +31,11 @@ export function PartitionDurationFormatPattern(
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3132
for (let i = 0; i < TABLE_2.length && !done; i++) {
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const row = TABLE_2[i]
33-
let value = duration[row.valueField]
34+
// Carry the value as BigDecimal end-to-end so sub-second rollups stay
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// exact. Float arithmetic like `1 + 473/1e3` lands on
36+
// `1.4729999999999998650`, which `roundingMode: 'trunc'` truncates to
37+
// `1.472999999` instead of `1.473` (#6462).
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let value = new BigDecimal(duration[row.valueField])
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const style = internalSlots[row.styleSlot]
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const display = internalSlots[row.displaySlot]
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const {unit, numberFormatUnit} = row
@@ -51,14 +56,16 @@ export function PartitionDurationFormatPattern(
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}
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if (nextStyle === 'numeric') {
5358
if (unit === 'seconds') {
54-
value +=
55-
duration.milliseconds / 1e3 +
56-
duration.microseconds / 1e6 +
57-
duration.nanoseconds / 1e9
59+
value = value
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.plus(new BigDecimal(duration.milliseconds).div(1000))
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.plus(new BigDecimal(duration.microseconds).div(1_000_000))
62+
.plus(new BigDecimal(duration.nanoseconds).div(1_000_000_000))
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} else if (unit === 'milliseconds') {
59-
value += duration.microseconds / 1e3 + duration.nanoseconds / 1e6
64+
value = value
65+
.plus(new BigDecimal(duration.microseconds).div(1000))
66+
.plus(new BigDecimal(duration.nanoseconds).div(1_000_000))
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} else {
61-
value += duration.nanoseconds / 1e3
68+
value = value.plus(new BigDecimal(duration.nanoseconds).div(1000))
6269
}
6370
if (internalSlots.fractionalDigits === undefined) {
6471
nfOpts.maximumFractionDigits = 9
@@ -71,7 +78,7 @@ export function PartitionDurationFormatPattern(
7178
done = true
7279
}
7380
}
74-
if (value !== 0 || display !== 'auto') {
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if (!value.isZero() || display !== 'auto') {
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nfOpts.numberingSystem = internalSlots.numberingSystem
7683
if (style === '2-digit') {
7784
nfOpts.minimumIntegerDigits = 2
@@ -95,6 +102,10 @@ export function PartitionDurationFormatPattern(
95102
value: separator,
96103
})
97104
}
105+
// Pass the BigDecimal straight through. NumberFormat (V3) parses it
106+
// as an exact Mathematical Value via ToPrimitive → BigDecimal.toString,
107+
// which sidesteps the IEEE 754 round-trip that breaks
108+
// `roundingMode: 'trunc'` on values like `1 + 473/1e3` (#6462).
98109
let parts = nf.formatToParts(value)
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parts.forEach(({type, value}) => {
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list.push({

‎packages/intl-durationformat/tests/index.test.ts‎

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Original file line numberDiff line numberDiff line change
@@ -78,6 +78,32 @@ test('Intl.DurationFormat format digital', function () {
7878
)
7979
})
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81+
test('Intl.DurationFormat sub-second rollup is exact (#6462)', function () {
82+
// 1s + 473ms is exactly 1.473s. Float arithmetic — `1 + 473/1e3` —
83+
// lands on `1.4729999999999998650`, which `roundingMode: 'trunc'`
84+
// truncated to `1.472999999s` before the BigDecimal rewrite.
85+
expect(
86+
new DurationFormat('en', {
87+
milliseconds: 'numeric',
88+
style: 'narrow',
89+
}).format({milliseconds: 473, seconds: 1})
90+
).toBe('1.473s')
91+
// Same kind of failure modes for milliseconds → microseconds and
92+
// microseconds → nanoseconds rollups.
93+
expect(
94+
new DurationFormat('en', {
95+
microseconds: 'numeric',
96+
style: 'narrow',
97+
}).format({milliseconds: 1, microseconds: 473})
98+
).toBe('1.473ms')
99+
expect(
100+
new DurationFormat('en', {
101+
nanoseconds: 'numeric',
102+
style: 'narrow',
103+
}).format({microseconds: 1, nanoseconds: 473})
104+
).toBe('1.473μs')
105+
})
106+
81107
test('Intl.DurationFormat hours with 2-digit', function () {
82108
expect(
83109
new DurationFormat('en', {

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