Repository navigation
Conversation
…s the later one AlignHandler and FlexHandler hold a declaration until the block ends, so a later declaration of a property replaced the earlier one. When a browser target lacks the later value (dvh, cqw, round()) and every target supports the held one, the held declaration is the fallback for that target. It is now written first, as it already is for width and margin. This covers row-gap, column-gap, gap, flex-basis, flex and -ms-flex-preferred-size. A shorthand takes one decision for the longhands it sets. A held value that a target lacks is not written early: flush would fold it with the values around it into one declaration that the target drops.
Contributor
|
Warning Review limit reachedYou've used all free OSS reviews for now. Wait for the free limit to reset to keep reviewing this public repository. Next included review available in 6 minutes. View limit details
Thanks for using CodeRabbit! It's free for OSS, and your support helps us grow. If you like it, consider giving us a shout-out. Comment |
Collaborator
Author
|
Updated 6:27 AM PT - Oct 24th, 2026
❌ @robobun, your commit 9d89efb has some failures in 🧪 To try this PR locally: bunx bun-pr 46694That installs a local version of the PR into your bun-46694 --bun |
Collaborator
Author
|
Status
|
![claude[bot]](https://avatars.githubusercontent.com/in/1236702?s=60&v=4){kind=small}
Contributor
There was a problem hiding this comment.
Nothing blocking. The comments below are optional suggestions. There is no need to push a fix for them before merging.
Beyond the inline findings, I also checked whether the new flush in the Flex arm could print a duplicate generated -webkit-box-flex line for a fallback pair — the arm clears box_flex/flex_positive/flex_negative/preferred_size before the is_fallback check whenever browser targets are set, so the flush emits none of them. The Option<GapValue> arguments to Targets::supports resolve to the existing IsCompatible for Option<T> impl in src/css/generics.rs:991, which treats an unset gap as supported, so an empty row_gap/column_gap does not block the early write.
Extended reasoning...
The change adds an early flush to the gap and flex-basis handlers in src/css/properties/align.rs and src/css/properties/flex.rs plus a Targets::supports helper in src/css/targets.rs, with new test cases in test/js/bun/css/css.test.ts; it touches no security-sensitive surface. Five confirmed inline findings (a cascade regression around all: unset, a duplicate -ms-flex-preferred-size line, a dropped middle value in three-step chains, and two smaller points) are posted separately and are enough that a human should look before merge.
PropertyHandlerContext::is_fallback holds the check that AlignHandler and FlexHandler each had a copy of. -ms-flex-preferred-size is left as it was. Next to a held flex-basis, its early write printed the -ms-flex-preferred-size line of that flex-basis a second time for IE 10.
![github-actions[bot]](https://avatars.githubusercontent.com/in/15368?s=60&v=4){kind=small}
Contributor
There was a problem hiding this comment.
I re-reviewed after a19946c and found no new bugs; the second commit addresses the duplicated predicate and the -ms-flex-preferred-size double print raised earlier. Because this changes user-visible minifier output and deliberately diverges from lightningcss (which collapses these pairs), a human look at the design trade-off is still worthwhile.
What was reviewed:
- The
holds_gap_fallback/is_fallbackconsolidation intoPropertyHandlerContext::is_fallback— checked it is behavior-preserving: the derivedIsCompatibleforGapANDs both fields, and the[T; N]/Option/&Timpls makegaps()equivalent to the old per-field checks. - The
Flexarm with only grow/shrink held:heldisNone, sosupports(&None)is true and the flush fires as the tests expect. - The
tempDirimport added to css.test.ts is used by the newbun buildsubprocess test, which drains stdout/stderr/exited concurrently.
Extended reasoning...
The diff adds a Targets::supports helper and a PropertyHandlerContext::is_fallback predicate, an IsCompatible impl for fixed-size arrays, IsCompatible derives on GapValue/Gap, and early-flush gates in the RowGap/ColumnGap/Gap arms of AlignHandler and the FlexBasis/Flex arms of FlexHandler, plus ~160 lines of tests. No security-sensitive surface is touched; it is CSS minifier output. The second commit removed the separate FlexPreferredSize check and the duplicated helper, both of which an earlier run flagged. Deferral rather than approval because the change alters emitted CSS for existing users with browser targets, intentionally diverges from the lightningcss reference, and the author's own description lists ordering side effects (e.g. all: unset between the pair) that a maintainer should weigh.
Still open from earlier reviews (3):
- Unresolved: 3 minor or pre-existing.
This was referenced Oct 24, 2026
Jarred-Sumner
added a commit
that referenced
this pull request
Oct 27, 2026
### What does this PR do? Consolidates the open pull requests on the CSS parser (`src/css`: parsing, minifying, lowering, printing, CSS modules) into one. 179 open pull requests were in scope. Each was judged by one rule: **the output must mean to a browser what the input meant.** Every claim was run through a build of `main`, a build with the change, lightningcss 1.33 and Chromium 156 (CSSOM, computed values, painted pixels for colors and gradients), and counted against 10,116 real stylesheets: the published CSS of about 190 popular npm packages, plus stylesheets from open source repositories. 107 land here, whole or in part, most of them cut down. The source diff is net negative. Of the 10,116, 9,509 are stylesheets that someone ships. The rest are test fixtures of other tools (521), Tailwind v4 source that needs its plugin (59) and SCSS, PostCSS or template source (27). | 9,509 shipped stylesheets | `main` | this branch | |---|---|---| | fail to build | 71 | 35 | | ... of those, valid CSS that Bun rejects | | 0 | | minified output reads differently in Chromium than the input | 552 | 2 | | CSS modules with a name that is referenced but not defined, or exported but not defined | 166 | 0 | | all 10,116 | `main` | this branch | |---|---|---| | fail to build | 192 | 141 | | minified output reads differently in Chromium than the input | 593 | 15 | | build on `main`, fail here | | 0 | | right on `main`, wrong here (minified, and at the default targets) | | 0 | | size of the minified output, no targets | 162.32 MB | 162.47 MB (+0.093%) | | size of the output at the default targets | 224.1 MB | 210.2 MB (-6.2%) | A syntax error is a build error, with one exception: the IE star hack `*zoom: 1` is skipped, because tachyons and handsontable ship it. The 35 shipped stylesheets that fail are invalid CSS: 28 have a selector that Chromium drops (semantic-ui-css, swiper, @ionic/core, Adobe Spectrum, xp.css), 2 an `@import` after other rules, and one each `@supports not X and Y`, a nested `@keyframes`, a stray comma, a selector list in `::slotted()`, `@media screen\0` (govuk-frontend). The 2 that read differently fold a `color-mix()` inside a gradient (see the known gaps). The growth of the minified output is rules and declarations that `main` deleted by mistake: 87 KB of rules, 45 KB of prefixed declarations that only browser targets can rule out. #### Popular CSS that `main` breaks today - normalize.css, modern-normalize, sanitize.css: `font-family: monospace, monospace` is collapsed to `monospace`, which changes the font size from 16px to 13px (#46662). - CKEditor 5, Tabler, Carbon, VitePress, Ionic, PatternFly, Excalidraw: a rule of custom properties is deleted as a "duplicate" of a later rule with the same selector and other custom properties. 37 stylesheets lose 1,681 custom properties (#33684). - Material Components, daisyUI, DocSearch, plyr: a `var()` size loses to its own fallback (#42101). - nextra, daisyUI, CKEditor: declarations written after a nested rule are moved above it (#45462). - antd 4, purecss, govuk-frontend: browser hacks in selector lists start to apply everywhere (#42100). - foundation-sites, flatpickr, 98.css, blueprintjs, scalar, react-datepicker: the build fails on valid CSS (#46756, #38552, #38534). tachyons, handsontable: it fails on the IE star hack (#46751). - nodejs.org, Mantine: a CSS module exports classes that no rule defines, because the `@apply` or `@mixin` in them is moved out of the rule (#46759). - hint.css and 42 more: `z-index: 1000001` and `1000000` become the same number (#46715). - Adobe Spectrum: `--version: 5.0.1` prints as `5.1`. - A quarter of all stylesheets: minified output has a stray space in `align-items: center` (#41993). #### Behavior changes to look at first 1. **`light-dark()` is kept as written at the default browser targets** (#42009). The lowered form `var(--buncss-light, a) var(--buncss-dark, b)` is invalid unless a compiled `color-scheme` covers the element: 184 of the 215 real stylesheets that get it never define the variable, so every browser drops the declaration. The docs section on the polyfill is removed. 2. **`border` is not built from longhands** (#42072): `border-width:0;border-style:solid;border-color:red` stays three declarations, because `border` also resets `border-image`. 305 real stylesheets grow by 30 KB in total; `bootstrap.min.css` by 113 bytes, 5 gzipped. No real stylesheet was found where the old merge shows, so this is the one to drop if size matters more. 14 existing expectations change. 3. **A CSS module no longer exports names that only occur inside `:global(...)`** (#45487). 73 real modules lose 202 export keys, all of them names that no rule has. `import { g }` or `composes: g` of such a name becomes a build error. 4. **Container names and `@counter-style` names stay global in a CSS module** (#45247 by @mikamikasuki). `main` hashes the `@container` name but not `container-name`, so a named query never matches. postcss-modules (Vite, css-loader, Next.js) keeps them global; lightningcss and esbuild hash both. Global keeps a container that is queried from another file or from JS working. 5. **Syntax errors are build errors, also two that `main` lets through**: a media query that stops short (`@media screen and {`, `@media not {`, `@import "a.css" screen and;`) and `@media (width <) foo {`. No stylesheet of the 10,116 has either. A condition that is valid by the grammar though no browser knows it, `( ... )` or `fn( ... )`, is kept as written (#46756): `(min-width:0\0)`, `(not(hover))`. 6. **Declarations after a nested rule stay where they were written**, as a nested declarations rule (#45462). Changes the output of 199 real stylesheets; in a fuzz of 2,850 nested programs compared by computed style, `main` was wrong in 1,056 and the pull request's code, before it was trimmed here, in none. 7. **`Bun.color`**: `color()` inputs are converted instead of returned as a string (`Bun.color("color(srgb 1 0 0)", "hex")` was `"color(srgb 1 0 0)"`); `currentColor`, system colors and `light-dark()` give `null` in the converting formats instead of the keyword as a string; a relative color or `color-mix()` outside sRGB is clipped, not gamut-mapped (`hsl(from oklch(100% .399 336.3) h s l)` is `#ff5bff`, was `#fff`). 8. The `:-moz-any()` and `:-webkit-any()` copies of rules with `:is()` are gone at the default targets (#45945, #42029). The `:-webkit-any()` copy outranked the original rule: `.title{color:blue} :is(h1,h2,h3){color:red}` painted red. 5.8% of all default-target output was the `:-moz-any()` copies. 9. `Property` grows from 216 to 224 bytes: `Url` stores its text as a slice so that two `url()` values can be compared (#46895). The pull request packed a pointer and a `u32` behind `unsafe` to avoid that. #### Not in this PR, needs a decision - **Raise the default browser targets (#40369) and add a `cssTarget` option (#40368).** Today: Chrome 80, Edge 80, Firefox 78, Safari 14, Opera 67, and no public way to change them. At Vite 8's floor the output of the 9,924 stylesheets is 15.3% smaller (3.9% gzipped). About a dozen fixes here only matter at today's floor, and code for older targets is unreachable without the option. - Vendor prefixes for `user-select`, `appearance`, `hyphens` and five more (#45814): 1,116 real stylesheets lack a prefix they need at the default targets. And for `backdrop-filter` (#44648): 173. - Clip instead of gamut-map in the sRGB fallback of a plain wide-gamut color: deletes about 90 lines, changes every pinned fallback hex. If the mapping stays, #44647 by @oddharsh makes it closer to what browsers paint (colors off by 2/255 or more: 168 to 110 of 3,170 real ones). #### Changes **Rules: duplicates, merging, nesting, fallbacks** - The `:-moz-any()` copy of every rule with `:is()` or `:not(a, b)` is gone: Firefox 78 has `:is()` (#45945). 1,164 real stylesheets - Keep declarations written after a nested rule in place with a nested declarations rule (#45462). 379 real stylesheets - With nesting compiled away, an unknown at-rule inside a style rule was moved out of it: `.wrapper{@apply flex}` printed a bare `@apply flex;` and the rule was gone, so a CSS module exported a class that no rule defines. It now stays in a block under the compiled selector. 72 real modules with Tailwind's `@apply`, 25 with Mantine's `@mixin` (#46759). 316 real stylesheets - Keep !important in the rules generated for logical properties and color-scheme (#38597). 311 real stylesheets - With browser targets, remove an earlier duplicate rule only when its declaration block is equal (#46861). 171 real stylesheets - Compare custom property names in `PropertyId` equality and importance in duplicate-rule detection (#33684). 40 real stylesheets - Keep same-condition @supports rules and empty named @layer blocks (#46733). 31 real stylesheets - Keep target-added vendor prefix passes on cloned and re-minified rules, and never print a bare `:full-screen` (#43339). 12 real stylesheets - Keep the selectors on rules added for color fallbacks and logical properties (#43240). 3 real stylesheets - A later declaration of a property drops the `@supports` color copies of the earlier one, which printed after the rule and won (#45560). 2 real stylesheets - Do not merge style rules in a stylesheet that holds `revert-rule` (#46953). 1 real stylesheets - `@import ... supports(-webkit-mask: none)` kept its prefix (#38589) **Properties and shorthands** - Print align-items:center without a stray space when no safe/unsafe keyword is given (#41993). 3,317 real stylesheets - Emit the physical longhands instead of the inset shorthand for targets without it (#38583). 1,452 real stylesheets - Keep the stops of an upward gradient as written, and drop a `50%` hint only at the midpoint (#46790). 104 real stylesheets - Emit unparsed border-block-* declarations when compiling logical borders (#38582). 89 real stylesheets - Keep repeated font families and dedupe only the inserted system-ui fallbacks (#46662). 88 real stylesheets - A `width` / `height` / `min-*` / `max-*` with `var()` or `env()` was printed before the plain fallback written above it, so the fallback won (#42101). 26 real stylesheets - Keep box-orient and box-direction when flex-direction or flex-flow follows (#45672). 16 real stylesheets - Write held prefixed background declarations at every flush (#46882). 6 real stylesheets - Derive equality for Size2D and BorderRadius, and keep every prefix in the border-radius handler (#45665). 2 real stylesheets - Print `none` instead of an empty border-image, mask-border or mask-box-image value (#45143). 2 real stylesheets - Keep font/transition sub-properties on the side of the shorthand they were written on (#41990). 2 real stylesheets - CSS-wide keywords are not names: `font:12px Arial;font-family:inherit` printed `font:12px inherit`, `color-scheme:inherit` and `color-scheme:auto` printed `normal`, `transition-property:unset` was folded into `transition` (#42022). 2 real stylesheets - Only fold font longhands into `font` when the rule declared a `font` (#45459) - Keep a font family name quoted when its identifiers do not read back as the same name (#46606) - Stop rewriting valid positions into ones browsers reject (#45197) - `border` is no longer built from longhands unless the rule also sets what `border` resets (`border-image`), and an author's `border-image` reset is no longer dropped. `transition` is likewise only written where the rule wrote one, because it resets `transition-behavior` (#42072) - `border; border-image: <gradient>; border-image-slice: 1` lost the gradient in every default build (#42018) - A prefixed `linear-gradient` keeps its direction, written or generated: the prefixed syntax names the starting side and measures angles differently (#46697) **At-rules** - Print @font-face format() keywords as strings (#37979). 439 real stylesheets - Print @supports `not` conditions without a leading space (#38559). 88 real stylesheets - Reset after the number token of a unicode-range (#45835). 33 real stylesheets - Keep `<general-enclosed>` media and container conditions as written (#46756). 24 real stylesheets - A strict range such as `(width < 768px)` lowered for old targets still matched at exactly 768px. The step is now `.02px`. The `not all and` form for other units is not taken (#46806). 18 real stylesheets - Keep scanning an @supports condition after a nested block (#38552). 9 real stylesheets - Every `@counter-style name` printed as `@counter-stylename`, which browsers drop (also #46692). In a CSS module the name now stays global, like the `list-style` that refers to it (#33679). 9 real stylesheets - Keep a keyframe whose block has an invalid item (#46288). 2 real stylesheets - Read an @Property initial-value on the stylesheet's parser, keep an unmatched value as written (#45806). 2 real stylesheets - `@media {}` is `all`. A media query that stops after `and`, `or` or `not` (`@media screen and {`) is a build error; `main` printed `not all` or dropped the condition, silently. The `@layer` and type selector parts are not taken (#46869). 2 real stylesheets - Accept a name-only `@container` and a `style()` feature with no value (#46689). 1 real stylesheets - Parse `<timeline-range-name> <percentage>` keyframe selectors (#45652) - Allow `or` inside parentheses after a media type (#45088) - Print the `=` comparison in media and container queries as `=` (#45071) - Parse the @font-palette-values font-family descriptor as a list of family names (#45484) **Selectors** - Never wrap a selector list in :is() (#46787). 414 real stylesheets - Stop emitting :-webkit-any() copies of :is() that outrank the original rule (#42029). 373 real stylesheets - With browser targets, a selector list with a vendor-prefixed member was split, which revives hacks that rely on other engines dropping the whole list: `.s *::-ms-backdrop,.s{flex:auto}` applied everywhere. Rewritten; the list is printed as written (#42100). 42 real stylesheets - Print the vendor prefix on downleveled :any-link, :read-only, :read-write, :placeholder-shown and :autofill (#42131). 12 real stylesheets - Fix nesting lowering of a `&` that does not lead its selector (#43047). 8 real stylesheets - `@scope`: `&` and implicit selectors compile to `:where(:scope)`, relative selectors and bare declarations parse (#43165). 7 real stylesheets - Only reject bare :global / :local pseudo-classes in CSS modules (#38534). 5 real stylesheets - Stop truncating `@scope to (...)` and stop replacing `&` in the scope-end selector (#43146). 2 real stylesheets - `[xl|href$=".pdf"]` lost its namespace prefix (#45159). 2 real stylesheets - Match An+B keywords exactly and take only `+` as the leading sign (#42953). 1 real stylesheets - Parse ::details-content and ::picker() like ::part() (#45504). 1 real stylesheets - Parse :window-inactive as an ordinary pseudo-class, and accept it after ::selection (#45815) - Print :nth-col(1) and :nth-last-col(1) in functional form (#41575) - `li::before::marker` failed the build (#45810) - `&` inside `:nth-child(... of S)` is resolved when nesting is compiled away. The second selector serializer (326 lines) is deleted (#43024) **Colors and `Bun.color`** - Keep light-dark() as written under the default browser targets (#42009). 227 real stylesheets - Number and percentage channels parse in `lab()`, `lch()`, `oklab()`, `oklch()`, `hsl()` and `hwb()`; the hue of `lch` / `oklch` is no longer scaled by alpha (#45084). 130 real stylesheets - `Bun.color` returns `null` for `currentColor`, system colors and `light-dark()` in the converting formats, instead of the CSS keyword as a string (#33047). 130 real stylesheets - Relative colors: channel keywords are on the scale of their function (`rgb(from #369 calc(r + 10) g b)`), the origin's alpha is kept, a relative color kept as written gets no `@supports` copies, and a result outside sRGB is not folded (#45362). 31 real stylesheets - Keep rotate: 0deg out of none, and keep the origin alpha in relative colors (#38486). 13 real stylesheets - Compute the D50 reference white in f32 so greys convert to lab(l 0 0) like lightningcss (#38535). 7 real stylesheets - Return a missing hue for a grey from conversions into lch, oklch, hsl and hwb (#45201). 5 real stylesheets - Fix color(a98-rgb), srgb-linear relative colors and color-mix(in xyz-d50) (#38487). 4 real stylesheets - Match named colors without regard to ASCII case (#45092). 3 real stylesheets - Fold min(), max() and clamp() over plain numbers (#39515) - `calc(l - .08)` in a percentage channel of a relative color became NaN and printed `#000` (also #45970) (#45971) - Bun.color: convert color() inputs instead of returning them as a CSS string (#38488) - A `color-mix(in srgb, ...)` result outside sRGB prints `color(srgb ...)` instead of a gamut-mapped hex (#39269) **`calc()` and numbers** - Rounding to 6 significant digits ate into the integer part: `z-index:2147483647` became `2147480000`, `max-width:9999999px` became `10000000px`, `--x:1234567.5` became `1234570`. It now only cuts a fraction short: a value kept as tokens prints its source text, a typed value prints every integer digit and at least one digit of the fraction (#46715). 43 real stylesheets - A number without a unit is no longer repaired into `px` (`height:1.5715` is dropped by a standards-mode browser, so it prints as written), `calc(-1 * 0)` is not a length, and on a property of the range [0,∞] (sizes, border radii, padding, border and outline widths, gap, `flex-basis`, `font-size`) a `calc()` that folds below zero prints `0` instead of an invalid negative literal, and a negative literal no longer replaces the valid declaration before it (`width:10px;width:-5px` printed `width:-5px`) (#42104). 24 real stylesheets - Print numbers from the f32's shortest digits, not its f64 expansion (#38565). 17 real stylesheets - Print negative numbers below 1 with a single minus sign (#38516) - Keep math functions over two different length units as written (#38489) - Fold rem() with a truncated quotient, so it keeps the sign of the dividend (#32286) - A one-argument `min()` / `max()` around a sum printed without any function (`width:100% - 20px`) (#46145) - `round()` breaks ties upward and handles a negative step as browsers do (#45249) **CSS modules** - A CSS module exports its `@keyframes` names (`styles.spin`). Hashing is unchanged (#46720). 145 real stylesheets - A name inside `:global(...)` prints plain but was exported as `name_<hash>`, a class no rule has (also #38573) (#45487). 90 real stylesheets - Keep container names global in CSS modules (#45247). 6 real stylesheets - Tag the keyframes name when an `animation` value falls back to raw tokens (#46034). 6 real stylesheets - In a plain stylesheet `composes: a from "./b.css"` was treated as an import: the file was inlined and an absolute path printed (#45961). 4 real stylesheets - Drop a rejected composes instead of failing the file at print time (#38538). 1 real stylesheets - Keep every rule's custom properties for the composes conflict check (#38523) - Keep composes working after a nested rule in the same block (#38520) - `IdentOrRef::hash` read 2 of 16 bytes, so in release builds every class of a module hashed alike (#30784) **Tokens, `url()`, diagnostics** - The block skip stack no longer allocates on every block exit (#39533) - Report the diagnostic's line without its line breaks in position.lineText (#38342). 192 real stylesheets - Compare `url()` values by their text (#46895). 26 real stylesheets - Values kept as tokens keep the blanks they were written with instead of having them re-invented at print time: `attr(x type(<number>))` printed `type(< number> )`, which browsers drop. Minified output still drops the blanks that cannot matter (#45577). 19 real stylesheets - The IE star hack (`*zoom:1`) failed the whole build. The declaration is skipped, as every browser does. It is the one syntax error that builds: tachyons, handsontable and jasmine ship it (#46751). 8 real stylesheets - The path of a copied asset spliced into `url()` is always quoted, so a file name with a space or a parenthesis cannot end the `url()` (#41557). 7 real stylesheets - Move the skip loop of parse_until_before out of the generic body (#39520) - Remove dead code from bun_css: the unused `impl Default for Property` (#45618) - Default the at-rule and qualified-rule parser traits, drop the url_to_css shim (#31999) **Speed** Four inputs that took quadratic or exponential time, or produced output out of proportion, are now linear, with no new limit and no extra pass (#31639, #42243, #38531, #43421). **Tests only** - `css-fuzz.test.ts` never ran in CI and timed out on debug builds; it is a deterministic table now (#38500) - `nth-anplusb-ident.test.ts` counts heaps in a child process (#46331) - `color.test.ts` checks the ansi-16 sweep with one `expect()` (#42824) - Not CSS, but it failed this PR's CI and fails on `main` too: `ws-proxy.test.ts` on Windows, "a message sent during a TLS renegotiation arrives after it". The helper server now renegotiates from the callback of the frame's write (#46170) **No pull request covered these** - `--v: 5.0.1` printed as `5.1`, `--w: 1.0.0` as `10`, `--x: 1+2` as `12`, `2n+1` as `2n1`: a number token that touches another keeps its source text. - `color-scheme: auto` printed as `normal`, and `color-scheme: dark light` as `light dark`. - A bare `:global` or `:local` in a CSS module sets the scope of the names after it, up to the end of the selector, as in css-loader. It was a build error. - The scrollbar states (`a:horizontal`, `::-webkit-scrollbar{&:horizontal{}}`) are valid in a plain compound, as in WebKit and Blink. - Without browser targets, `-webkit-box-align`, `-ms-flex-align` and the like were dropped next to their standard form (flatpickr, foundation-sites, materialize-css: 28 stylesheets), and `-webkit-fill-available` before `-moz-available` (beercss). - `(-o-min-device-pixel-ratio: 2/1)` printed as `2`. - `sin()`, `cos()` and `tan()` are exact at multiples of 90deg: `calc(100px * cos(90deg))` printed `-.00000437114px`. - A `display-p3` color at targets that have P3 but not the other `color()` spaces (Safari 10.1 to 14) got itself as a fallback. - `width: rem(-18px, 5px)` folds to a negative literal once `rem()` is right; it prints `0`. - Consecutive nested declarations rules, which arise when same-query `@media` blocks in one rule merge, are folded into one and count against the existing selector expansion limit as the `&{}` rules they replace did. #### Known and not fixed here - Four longhands are still folded into a `transition` the author did not write where the targets add a prefixed copy of a property (`mask-image` at Chrome 80): only the shorthand gives the copy its own times. - A later `background`, `box-shadow` or `border-*` declaration still loses to the `@supports` copy of an earlier `var()` value of the same property with a wide-gamut color. Same on `main`; #45560 is taken for the properties of the fallback handler and for unparsed values only. - A merged rule prints the unprefixed name in the passes of the rule it absorbed: `.d::-webkit-input-placeholder{}.d::-moz-placeholder{}` prints `::placeholder` for the second (#42106, not taken: it breaks the merge of prefix-equivalent rules). - The `border`, `outline` and `font` shorthands, `line-height`, `scroll-padding`, `background-size` and a few more still print a `calc()` that folds below zero as a negative literal. No real stylesheet has one. - `all` is not a property Bun knows, so `a{margin-top:1px;all:unset}` prints `all` first. Same on `main`. - A selector kept as raw tokens loses the blank before `*` when minified: `--sel: .dark *` prints `.dark*`. Same on `main`. - `width:calc(0% + 12px)` folds to `12px`, which lays out differently in a table cell. Same on `main`. - The `:dir()` / `:lang()` rules of a lowered logical property print before the nested rules of their rule, so a logical declaration written after a nested rule of equal specificity still loses to it. Same on `main`. - A fraction is still rounded to 6 significant digits (`12345.678` prints `12345.7`, `33.3333333333%` prints `33.3333%`). Keeping every digit would add up to 282 KB over the corpus. - `@keyframes "quoted"` is hashed in a module but not exported. - In a module, a keyframes name inside a `var()` fallback is not hashed: `animation: var(--enter, fade 1s)`. Same on `main`. - A `color-mix()` or relative color folded to a hex inside a gradient changes the interpolation from Oklab to sRGB (VS Code, clawhub). Printing `color(srgb ..)` instead needs a fallback for `mask-image`, `list-style-image` and custom properties at the default targets, which have none. - A comma list in `@container` still fails the build. - After a bare `:global`, names that are hashed at print time (`::view-transition-old(foo)`) are still hashed; inside `:global(...)` they are not. #### Pull requests in scope that do not land here - Duplicates of a pull request that lands here: #36961 (of #37979), #38478 (of #46662), #38480 (of #46733), #38482 (of #46715), #38491 (of #38500), #38508 (of #45201), #38513 (of #45362), #38573 (of #45487), #38640 (of #38500), #45525 (of #45247), #45589 (of #46756), #45970 (of #45971) - Already fixed on `main`: #38674 - Right, but for input nobody writes (0 of 10,116 stylesheets, and not new syntax): #31916, #38526, #38592, #39349, #41139, #41801, #42042, #42484, #43078, #45604, #45908, #46086, #46221, #46224, #46273, #46694, #46707, #46737, #46755, #46816, #46870, #46934 - Right or harmless, but not worth their code, their bigger output or the behavior they change: #30905, #31924, #33332, #34426, #36225, #38006, #38512, #38547, #38551, #38561, #38572, #38576, #38607, #38623, #38667, #38692, #42106, #42912, #42918, #43407, #43434, #44700, #45442, #45546, #45747, #45759, #45825, #45946, #46061, #46127, #46206 - Need a decision (see above), stay open: #40368, #40369, #44647, #44648, #45814 - Stays open: #45787 Out of scope: CSS linking and chunking in the bundler, the dev server, docs-only pull requests, and repository-wide sweeps that touch `src/css` in passing. Thanks to @mikamikasuki (#45247), @alii (#39520, #31999) and @oddharsh, whose measurements on #40369 and #41990 were used. Fixes #16727. Fixes #24770. Fixes #30772. Fixes #44704. Fixes #45089. Fixes #45237. Fixes #46872. ### How did you verify your code works? - The 35 CSS test files pass on a debug build, also with `FORCE_COLOR=1`. 600+ of the tests in this branch fail on a build of `main`. An earlier head of this branch passed all 179 CI jobs that ran. - The reproduction of each issue listed above was run on `main` (wrong) and on this branch (right). - Differential run over the 10,116 stylesheets, `main` against this branch, minified without targets and through `Bun.build` at the default targets: no stylesheet that builds on `main` fails; Chromium 156 compares the output with the input rule by rule (CSSOM, then computed values on a sized element in a standards-mode document, colors as painted pixels in sRGB and P3). The comparison has 195 control pairs that must read equal or different. For stylesheets that read differently on both builds, mostly because of lowering, the sets of differences were compared; the three new ones are two minifier fixtures that are wrong on both and one comparison artifact. - CSS modules are checked for consistency instead, since hashed names defeat the comparison: every reference points at a name the output defines, every export exists. - `Bun.color`: 59 inputs in 13 formats on both builds; every changed cell was read.
Collaborator
Collaborator
Author
|
Understood. The corpus check of this PR agrees with that: 0 of 17,464 builds of 4,574 npm stylesheets differ from main. The branch stays at |
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.This suggestion is invalid because no changes were made to the code.Suggestions cannot be applied while the pull request is closed.Suggestions cannot be applied while viewing a subset of changes.Only one suggestion per line can be applied in a batch.Add this suggestion to a batch that can be applied as a single commit.Applying suggestions on deleted lines is not supported.You must change the existing code in this line in order to create a valid suggestion.Outdated suggestions cannot be applied.This suggestion has been applied or marked resolved.Suggestions cannot be applied from pending reviews.Suggestions cannot be applied on multi-line comments.Suggestions cannot be applied while the pull request is queued to merge.Suggestion cannot be applied right now. Please check back later.
Problem
bun buildprints only the later line ofgap: 15px; gap: round(1em, 5px). No default target hasround(), so those browsers get no gap.row-gap,column-gap,flex-basisandflexlose the line too.widthkeeps it.AlignHandler(align.rs:1284) andFlexHandler(flex.rs:607) replace the value they hold with no target check.Fix
test/js/bun/css/css.test.ts(98 new tests, 51 fail on main). Alsotest/js/bun/css,test/bundler/css,test/bundler/esbuild/css.test.ts.Background
DeclarationBlock::minifyholds its declarations until the block ends, so a later declaration replaces an earlier one.DeclarationHandler::handle_property: it runs for every declaration and cannot see the held value.Downsides
gap: A; all: unset; gap: BprintsAafterall: unsetwhen a target lacksB, aswidthdoes (css: make theallshorthand reset the declarations before it #42042).row-gap: 8px; gap: 1dvh; row-gap: normal, a browser withoutdvhkeeps8px. Main is right by accident (Notes)..textgrows 1,536 bytes. A firstgaporflexdeclaration costs 0 to 11 more instructions, a second one 52 to 65.Notes
Reproduce
5c6d4e24cd) and 1.4.2:.g{gap:round(1em,5px)}.f{flex:100dvh}.w{width:15px;width:round(1em,5px)}.g{gap:15px;gap:round(1em,5px)}.f{flex:100vh;flex:100dvh}.w{width:15px;width:round(1em,5px)}No issue reports this. A sweep of declaration pairs found it. lightningcss collapses these pairs too.
What an arm does
row-gap,column-gap,gap,flex-basisandflex. All five callPropertyHandlerContext::is_fallback(held, later).flex-basisandflexrun the check after they clear the legacy properties that they replace, so no-webkit-box-flexor-ms-flex-preferred-sizeline is written in front of them.-ms-flex-preferred-sizeis left as on main. Only IE 10 reads it. Next to a heldflex-basis, an early write prints the-ms-flex-preferred-sizeline of thatflex-basisa second time.Targets::supportsis byte for byte the function that css: keep an earlier transform or translate declaration when a target does not support the later one #45908 adds. The two PRs merge in either order.Other designs
DeclarationHandler::handle_propertycannot see the held value, so it cannot tell an equal declaration from another one.align-items: center; gap: clamp(8px, 2vw, 16px); justify-items: centerno longer folds intoplace-items.flex: 1 1 100vh; flex-basis: 100dvhwould lose grow and shrink in a browser withoutdvh.color,displayand custom properties go straight to the output, sogap: 15px; color: red; gap: round(1em, 5px)would lose the fallback.Known results of the early write
A; B; C, where a target lacksBand every target supportsC, printsA; C.widthdoes the same on main.A; B; C, where a target lacksBandC, printsA; C. A browser that hasBand notCgetsA.widthprints all three lines. Here an arm writes early only a declaration that every target reads, so it does not have to know whatflushfolds.-webkit-flex-direction: row; flex-basis: 100vh; flex-basis: 100dvh; flex-direction: rowkeeps the-webkit-flex-directionline, andorder: 1; flex-basis: 100vh; flex-basis: 100dvh; order: 2keepsorder: 1. The cascade is the same..a { gap: 1vh; gap: 1dvh }with one selector are merged and print N + 1 declarations, aswidthdoes on main. A second pass prints 2.alland unknown properties go straight to the output. Sogap: A; all: unset; gap: Bandgap: A; grid-gap: X; gap: BprintAafter the declaration in the middle. Main has that order for the plain case:gap: 15px; all: unsetprintsall: unset; gap: 15px, andgap: 1px; grid-gap: 2pxprintsgrid-gap: 2px; gap: 1px. css: make theallshorthand reset the declarations before it #42042 drops whatallresets, and css: resolve legacy aliases in the name table and keep them after the property they alias #45825 writes the held gaps before an alias of them.Not in this PR (the same loss, by owner)
transform,translate: css: keep an earlier transform or translate declaration when a target does not support the later one #45908.border-image: css: keep border-image andborderin source cascade order within a rule #42018.borderand the physical side shorthands: part of css: keep later physical declarations ahead of compiled logical ones #38623. The logical side shorthands have no PR.background-position,background-size,background: no PR. A first cut was removed from this branch. Its early write stopped the color fallbacks thatflushgenerates for a laterbackground: lab(...).rex,rch,rcap,ric, read as supported by every target. They wait for css: keep border-image andborderin source cascade order within a rule #42018: its inverted check keeps thoseborder-imagepairs today.flush. A longhand next to a value that a target lacks goes into onegaporflexwith it:column-gap: 8px; row-gap: 1dvhandrow-gap: 1dvh; column-gap: 8pxboth printgap: 1dvh 8px, androw-gap: 2vh; row-gap: 2dvh; column-gap: 8pxprintsrow-gap: 2vh; gap: 2dvh 8px. A browser withoutdvhloses the column gap.row-gap: 8px; gap: 1dvh; row-gap: normalprintsgap: normal 1dvhon main androw-gap: 8px; gap: normal 1dvhhere. A browser withoutdvhdrops thegapline. On main it then has the initial value, which is what the source gives it. Here it has8px. Forflex:flex: 2 1 auto; flex: 2 1 100dvh; flex-grow: 0printsflex: 0 100dvhon main andflex: 2 auto; flex: 0 100dvhhere.margin,padding,border-widthandfont:margin-top: 2px; margin: 1px 1dvhprints one line.text-shadowwithround(): css: parse math functions in text-shadow lengths #45546..a{width:100vh}.b{color:red}.a{width:100dvh}drops the first rule, for every property (rules/mod.rs:847).--target bun,--no-bundle) keep no fallback: bun build --no-bundle: minify css with the build target's browser targets #38544.Targets
dvh,cqworclamp()then collapse, because every target has them. Pairs withround(),mod(),lh,rlhorcapstill need this check. Thebun buildtest usesround()for that reason.Self-review items that are not done
Measurements (release builds, main
5c6d4e24cdand this PR)size -A:.text82,231,705 to 82,233,241 bytes,.rodataunchanged.DeclarationHandler::handle_propertycall (gdb single-step, with the targets chrome 87, edge 88, firefox 78, safari 14).row-gap162 to 166,column-gap162 to 168,gap181 to 192,flex-basis186 to 186,flex215 to 223.align-items,justify-content,place-items,flex-direction,flex-wrap,flex-grow,flex-shrink,order,-ms-flex-preferred-size,width,margin,color,display. Two properties with no source change compile to 2 more instructions:background(644 to 646, a loop inBackgroundHandler) and a second-ms-flex-preferred-size(227 to 229).gap181 to 245,row-gapandcolumn-gap162 to 226,flex-basis233 to 287,flex305 to 357,flexafterflex-grow222 to 287.gap181 to 358,flex-basis233 to 415.flush):gap181 to 831,flex-basis233 to 730,flex315 to 884.StyleSheet::minify(gdb breakpoints on the mimalloc entry points): the same counts for 20 one-declaration rules and for 12 two-declaration rules.test/js/bun/css/filesdiffer (default,--minify,--target bun, both). 0 of 17,464 builds of 4,574 CSS files from 111 npm packages differ (832 fail on both with the same exit code).16px,8px,1dvh,2cqw), for 4 browsers (neither unit,dvhonly,cqwonly, both). Blocks where each browser computes what the source gives it: 22,271 on main, 40,298 here. Right on main and wrong here: 0. Withnormalin place of16px: 31,893 on main, 43,806 here, and 508 that are right on main and wrong here.is_fallback, the gate of each arm and each part of it, each held value, and the order after the legacy clears. Each time at least one test failed.Suites (debug build)
test/js/bun/css/css.test.ts: 1,413 pass, 0 fail. With a build of main: 51 fail, all in the new block or the newbun buildtest.test/js/bun/cssexceptcss-fuzz.test.ts: 1,203 pass, 0 fail.nested-selector-expansion.test.tsran on its own: in the debug build two of its tests take 3.4 to 5 s, and their timeout is 5 s.test/bundler/cssandtest/bundler/esbuild/css.test.ts: 241 pass, 0 fail.