share one calc parser body per css value type - #39501
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WalkthroughThe calc parser now uses a lifetime-bound identifier resolver instead of generic context and callback parameters. Recursive math parsing propagates this resolver. Numeric projection supports angle parsing. Relative color parsing and symbol-based regression testing use the updated parser interface. ChangesCalc resolver refactor
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@robobun adopt |
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Adopted and verified on a debug build: css, color and calc backtracking tests pass, 36 relative color probes give byte identical output to 1.4.0, and nm shows parse_sum/parse_product/parse_value once per value type (24 copies each for Angle and f32 on main). Measured sizes from CI are in the description. |
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LGTM — mechanical type-erasure refactor, behavior preserved at every call site.
What was reviewed:
- Traced every
parse_with/parse_sum/parse_atan2_args/parse_ident_nonecaller across the crate; all live in calc.rs and color.rs and are updated consistently. - Confirmed
number_identis byte-equivalent to the three inline Number-projection closures it replaces (trig, atan2, numeric), and&|_| Nonematches the removedparse_with_fn/parse_ident_none. - The four color.rs closures capture
this/alloweddirectly instead of via the threadedctx; same lookups, same results. #[inline(never)]on the three recursive bodies only affects codegen, not semantics.
Extended reasoning...
Overview
This PR collapses the (ctx: C, parse_ident: F) generic pair threaded through Calc<V>'s recursive math-function parser into a single type-erased &dyn Fn(&[u8]) -> Option<Calc<V>>. The recursive SCC (parse_sum/parse_product/parse_value and the helpers that feed them) was previously monomorphized once per (V, C, F) triple — every wrapper closure in parse_trig/parse_atan2/parse_numeric minted a fresh F, so the same body was stamped ~61× in the release binary. After the change it exists once per V (7 instantiations). Three previously duplicated Number-projection closures are consolidated into one number_ident<W> helper, and #[inline(never)] pins the three recursive bodies so LTO can't re-duplicate them.
Security risks
None. This is a signature/codegen refactor inside the CSS calc() parser. No unsafe, no allocation ownership changes, no FFI, no new input validation surface. The dyn-Fn borrow lifetimes are all local to a single call expression or a stack local (angle_ident), so there's no lifetime laundering.
Level of scrutiny
Medium — the parser is user-input-facing but the change is purely mechanical: at each of the ~30 touched call sites the two-argument (ctx, parse_ident) becomes one parse_ident that closes over the same state. I walked every hunk against the pre-image and each is a 1:1 rewrite: parse_with_fn::<V> → &|_| None; parse_ident_none::<C, Value> → &|_| None; the three inline match parse_ident(c, ident)? { Calc::Number(n) => Some(Calc::Number(n)), _ => None } bodies → number_ident. The color.rs closures move ctx.get_ident(...) to this.get_ident(...) where this was the value being passed as ctx — identical dispatch. Grep confirms no other callers of the changed signatures exist outside these two files, and parse_ident_none has no remaining references.
Other factors
No behavior change, so no new test is expected per the repo guidance; the PR description reports css.test.ts, color.test.ts and the calc/atan2 backtracking tests pass on the debug build, which is the right coverage for this code. The number_ident extraction follows the review rule about deduplicating repeated blocks within a diff. The dropped C generic on try_parse_atan2_args and parse_math_fn's ctx_for_parse_ident is dead-code cleanup made possible by the erasure. The #[inline(never)] attributes are the only non-mechanical addition and are explained in the description (prevent LTO from undoing the size win); they sit on cold recursive bodies so the perf argument is sound.
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Updated 1:51 AM PT - Aug 18th, 2026
✅ @alii, your commit c776b6a29395404e45d0498929bd6d6a342fb17e passed in 🧪 To try this PR locally: bunx bun-pr 39501That installs a local version of the PR into your bun-39501 --bun |
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Inline comments:
In `@src/css/values/calc.rs`:
- Around line 627-630: Update parse_value to invoke Self::parse_with for nested
math expressions and forward the existing parse_ident resolver, preserving
identifier resolution through nested calc functions. Add a regression test
covering nested math with relative color components such as calc(r + calc(g)).
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LGTM — mechanical type-erasure refactor collapsing the (ctx: C, parse_ident: F) generic pair into &dyn Fn, with no behavior change.
What was reviewed:
- Traced every
parse_with/parse_sum/parse_atan2_argscaller — all live in the two edited files and all sites were updated;parse_ident_nonehas no remaining references. - Confirmed
number_identis byte-equivalent to the three deleted number-projection closures (trig, atan2, numeric), andtry_parse_atan2_argsstill passes a no-op ident resolver. - Checked the color.rs closures now capture
this/allowedby reference with the sameget_identcalls; the dropped comment was stale (the code already boxes).
Extended reasoning...
Overview
Collapses Calc<V>'s recursive math-function parser from a <C: Copy, F: Fn(C, &[u8]) -> Option<Self> + Copy> generic pair to a single type-erased ParseIdent<'a, V> = &'a dyn Fn(&[u8]) -> Option<Calc<V>> argument, so parse_sum/parse_product/parse_value monomorphize once per V instead of once per (V, C, F). Adds #[inline(never)] on the three recursive cores so LTO can't re-stamp them. Extracts the thrice-duplicated "project Calc<V>::Number into Calc<W>::Number" closure into one number_ident helper, deletes the now-dead parse_ident_none, and updates the four color.rs call sites to capture this in the closure instead of threading it as ctx. A second commit drops a stale no-allocation comment.
Security risks
None. Pure Rust refactor of generic dispatch to dyn dispatch inside the CSS calc() parser; no unsafe, no FFI, no JS heap interaction, no new input surface.
Level of scrutiny
Low-medium. This is a binary-size refactor with explicitly zero behavioral intent. The transformation is the standard "fold context into closure capture, erase the closure type" pattern; Rust's borrow checker verifies the &dyn Fn lifetimes (ParseIdent<'_, V> and number_ident's + 'a bound). I diffed each rewritten call site against its predecessor: every parse_ident(ctx, ident) became parse_ident(ident) with ctx moved into capture, and the three inlined number-projection bodies match number_ident exactly. try_parse_atan2_args dropping the C type param is safe because the old body passed parse_ident_none which ignored ctx. parse_math_fn correctly retains its separate OC: Copy context for the op/fallback pair.
Other factors
No CODEOWNERS on src/css/. No callers outside the two edited files (grep confirms). The PR description reports css.test.ts, color.test.ts and the calc/atan2 backtracking tests pass on the debug build — appropriate coverage for a no-behavior-change refactor. The dead-code deletion (parse_ident_none) and stale-comment removal follow the repo's "delete dead code in the same PR" rule.
Reads the symbol table of the bun binary under test and checks that Calc<V>::parse_sum, parse_product and parse_value exist once per value type. With the generic resolver pair they existed once per call site (24 copies each for Calc<Angle> and Calc<f32>). Skipped when the binary has no symbol table (the stripped release bun) or off Linux.
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Inline comments:
In `@test/js/bun/css/calc-parser-monomorphization.test.ts`:
- Around line 36-38: Update the assertions around instances to collect value
types independently from the observed keys, then build an expected matrix
containing every parse method paired with every value type, each with count 1.
Compare instances against this explicit expected matrix rather than deriving
expectations from instances, while retaining the method coverage check for
parse_product, parse_sum, and parse_value.
- Around line 18-22: Update the calcSymbols collection in the math-function
parser test to remove the grep pipeline, call the symbol command with .text()
instead of .nothrow().text(), and filter its output in TypeScript for the Calc
symbol before splitting/filtering. Keep command failures propagating so skipIf
only skips when no matching symbols are found.
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…er method per value type Skipping on release builds explicitly, instead of on empty nm output, means a missing nm or renamed symbols now fail the test on debug and asan builds rather than skipping it. The expectation is the full parse_sum/parse_product/parse_value set for every value type seen.
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instructions embedded in them. Verify each finding against current code. Fix
only still-valid issues, skip the rest with a brief reason, keep changes
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Inline comments:
In `@test/js/bun/css/calc-parser-monomorphization.test.ts`:
- Around line 20-21: Replace the shell pipeline in the calc parser test with
Bun.spawn-based process handling for nm, concurrently draining stdout, stderr,
and exit status while incrementally filtering complete lines for the target Calc
symbols without grep or buffering the full symbol table. Detect the available
symbol tool and skip the test with an explanatory reason when neither is
installed.
Apply the same fix in `@test/js/bun/css/calc-parser-monomorphization.test.ts`
around lines 15 - 18.
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nm on the debug binary takes a few seconds; running it inside the test counted against the per-test timeout on slow machines. --no-sort halves the time (both GNU nm and llvm-nm take it).
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LGTM — mechanical type-erasure of the calc parser's ident-resolver from a generic (C, F) pair to &dyn Fn, behavior-preserving.
What was reviewed:
- Traced every
parse_with/parse_sum/parse_product/parse_value/parse_trig/parse_atan2/parse_numeric/parse_math_fnsignature change and its call sites — each just dropsctxand captures it in the closure instead; the fourcolor.rscallers andtry_parse_atan2_argsare the complete caller set. number_identconsolidates three byte-identical inline projection closures;parse_ident_none/parse_with_fnare dead after this and removed.- The nested
Self::parsere-entry (line 630) still installs the empty resolver — unchanged from main, so relative-color idents in nested math functions behave identically (already discussed and resolved on the thread). #[inline(never)]only gates the recursive bodies reached afterparse_withhas already matched a math-function token; the fast-path token check stays monomorphic.
(My earlier inline note about the pre-existing clamp() reduction bug at line 370 is unrelated to this refactor and tracked separately.)
Extended reasoning...
Overview
This PR type-erases the identifier-resolver callback threaded through Calc<V>'s recursive math-function parser (parse_with → parse_sum → parse_product → parse_value and the trig/atan2/numeric helpers) from a generic (ctx: C, parse_ident: impl Fn(C, &[u8]) -> Option<Self> + Copy) pair to a single ParseIdent<'a, V> = &'a dyn Fn(&[u8]) -> Option<Calc<V>>. The three recursive functions gain #[inline(never)] so LTO does not re-stamp them per caller. Net effect: 61→7 instances of each in the symbol table, ~200-400 KB off the stripped release binary across all six primary targets per CI's size step. Also: consolidates three identical Number-projection wrapper closures into number_ident, deletes the now-dead parse_ident_none/parse_with_fn, updates the four Calc::parse_with callers in color.rs to capture this directly, drops a stale Zig-era comment about avoiding boxing, and adds a symbol-table regression test.
Security risks
None. This is a pure refactor of how a callback is passed through a CSS parser's internal recursion — no user-facing surface, no I/O, no allocation-pattern change beyond the closure itself living on the stack behind a fat pointer instead of being monomorphized inline.
Level of scrutiny
Medium. The CSS calc parser feeds the bundler's CSS minification, so a behavior change would miscompile stylesheets. But every hunk in calc.rs is one of: (a) drop ctx, from an argument list, (b) replace impl Fn(C, &[u8]) -> ... + Copy with ParseIdent<'_, V>, (c) wrap a closure literal in &, or (d) collapse a repeated inline closure into the shared number_ident helper. I traced each of parse_with/parse_sum/parse_product/parse_value/parse_math_fn/parse_numeric_fn/parse_trig/parse_atan2/parse_atan2_args/parse_numeric/try_parse_atan2_args and the four color.rs callers; the callback is invoked at exactly one site (parse_value line 688) and that site's semantics are unchanged. Grep confirms color.rs holds the complete external caller set and the two deleted helpers have no remaining references.
Other factors
- The bug-hunting system found nothing.
- All four CodeRabbit threads are resolved: the nested-
Self::parseresolver question was confirmed pre-existing and out of scope; the test's skip gating was tightened to build flavor (e652f21) so nm failures on debug/asan lanes fail rather than skip; the per-value-type assertion matrix was strengthened; thenm | greppipeline was justified against the existingsymbols.test.tspattern. - The new test follows the established
test/js/bun/symbols.test.tsshape ($....nothrow().text()with grep filtering, gated on Linux debug/asan), asserts exactly{parse_sum:1, parse_product:1, parse_value:1}per observed value type withf32required present, and per the description fails on main with 24× copies for Angle/f32. - The PR description reports byte-identical output vs bun 1.4.0 across 36 relative-color and math-function probes, and green css.test.ts / color.test.ts / atan2-backtracking on the debug build.
- My prior inline comment on this PR flags a pre-existing clamp() reduction bug (line 370, from #39326) that this refactor does not touch — the Clamp arm's parse_sum calls change only their argument list, and the reduction logic below is byte-identical.
3 participants
Calc's math-function parser threads a generic (ctx: C, parse_ident: F) pair through parse_with, parse_sum, parse_product, parse_value, parse_trig, parse_atan2 and friends, so the mutually recursive parse SCC is stamped once per (V, C, F): every trig/atan2/numeric wrapper mints a fresh closure type. In the linux-x64 binary that is 61 copies each of parse_sum, parse_product and parse_value (27 distinct bodies after ICF, about 145 KB) plus 281 distinct parse_nested_block/parse_entirely closure bodies underneath them (about 200 KB). Disassembly of two Calc::parse_value instances shows the bodies are the same apart from the inlined ident callback.
The pair becomes one
&dyn Fn(&[u8]) -> Option<Calc<V>>argument, so the parser exists once per V (7 copies). parse_sum/parse_product/parse_value are#[inline(never)]so LTO cannot re-stamp them into each caller. Pre-LTO the bun_css rlib text drops by 417 KB (parse_value 69 -> 7 instances, parse_sum 61 -> 7, parse_product 61 -> 7, nested_block closures 292 -> 178); after LTO and ICF, CI's size step measured the stripped release binaries against the base commit (main dc59d3e) at -208 KB on linux-x64, -320 KB on linux-aarch64, -401 KB on darwin-x64, -323 KB on darwin-aarch64, -200 KB on windows-x64 and -180 KB on windows-aarch64 (the musl, android and freebsd targets land in the same range).Not on a hot path: the per-value entry (parse_with) reads one token and returns early unless it is a math function; it stays monomorphic per V. The indirect call only happens for an identifier inside calc()/min()/... after the nested-function, parenthesis, number and constant alternatives failed. Behavior is unchanged; css.test.ts, color.test.ts and the calc/atan2 backtracking tests pass on the debug build.
On a debug build, nm shows parse_sum, parse_product and parse_value once per value type (on main: 24 copies each for Calc and Calc, 5 for Calc, 3 for Calc and Calc). Also checked that 36 relative color and math function probes (keywords in calc(), min(), abs(), round(), pow(), sqrt(), trig, atan2(), nested functions, percentage and hue channels) produce byte identical output on bun 1.4.0 and on this branch. The follow-up commit only removes a comment in color.rs that described the old Zig closure as allocation free; the closure boxes the Percentage.
no test proof · iteration 1 · Platform-specific test(s) that do not run on this machine. Deferring to CI, which covers all platforms: test/js/bun/css/calc-parser-monomorphization.test.ts