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test: pin the prolog walk's termination guard in svg-active-content.mjs - #1828
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`startsWithDoctype()` walks the prolog with a loop rather than a pattern
because nested lazy repetition over `<?...?>` and `<!--...-->` backtracks
exponentially, as its own comment says. The loop moved the hazard rather
than removing it: `source.indexOf(closer, index + 2)` yields -1 for a
prolog node that never closes, so without the `end === -1` return `index`
rewinds to `closer.length - 1`, the whitespace skip at the top of the loop
carries it back to the same unterminated `<?`, and the walk never ends.
`hasDoctype('\n<?xml version="1.0"')` -- a file truncated in transit
mid-declaration -- is enough to reach it, and every validator here calls
these entry points on SVG files it did not write.
Nothing pinned that guard: deleting the return, or flipping the sentinel
it compares against, left the whole suite passing. Add cases that answer
for eight truncated prologs across all four entry points, each under a
deadline of its own, because the failure is non-termination rather than a
wrong answer; and two that keep the walk doing its real job behind closed
prolog nodes.
Annotate the file's other fifteen surviving mutants as equivalent. Each
reason states a property that can be checked: `sax`'s `resume()` is
exactly the `this.error = null` the line above already did; `url.decode()`
already trims the whitespace inside `url(...)`; css-tree emits a `url(`
Function token only when the argument opens with a quote, so the
`text.toLowerCase() !== 'url('` test is already decided by the String
check beside it; `pi` is the last of the seven event types `parseXml()`
emits and the arms above take the other six. The `skipDepth` test is
split across lines so the directive covers only the redundant half.
scripts/lib/svg-active-content.mjs now scores 100% with no survivors.
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Read the tree at 5a6a925, not just the diff. The core claim is correct and I reproduced it: in startsWithDoctype (scripts/lib/svg-active-content.mjs:441-450), indexOf returning -1 without the end === -1 return sends index to closer.length - 1, and for any source with leading whitespace before an unterminated <?/<!-- the walk revisits the same node forever. I deleted the guard locally and the new test file hung the process (killed by timeout); restored, all 34 tests pass in ~0.6s.
The equivalence argument for disabling BooleanLiteral on that return also holds against the callers: when the guard path is reached, errors is already non-empty — sax errors on the unterminated node and No root element is pushed at line 518 before the startsWithDoctype check at 524 — and every consumer reads either errors.slice(0, 1) (lines 692, 805) or errors.length (765, 788), so the extra Unterminated DOCTYPE entry is unobservable.
One hygiene note, not a defect: Stryker disable next-line ConditionalExpression suppresses both generated mutants (true and false), while several of the reasons argue only one arm — e.g. at localName (line 417-421) the false arm is equivalent, but the true mutant (always return the prefixed name) is behavior-changing and was presumably killed by existing tests, not a survivor. Stryker's directive granularity makes this unavoidable, and the author scoped the skipDepth directive by splitting the line where it was avoidable, so this is inherent to the tool, not carelessness.
File claims are accurate: this PR is disjoint from #1810, #1812, #1816, #1818 and #1819 — none touch svg-active-content.mjs or the new test.
Looks correct to me. Approval is a human's signature, so flagging for a maintainer: this fixes a real non-termination hazard in a scanner that runs on files the repo did not write.
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One of the fifteen annotated mutants is not equivalent — the CSS escapes put arbitrary characters inside an Ident token, and const input =
'<svg xmlns="http://www.w3.org/2000/svg"><style>x{fill:image-set(http\\00003A\\00002F\\00002Fevil.example/x.png)}</style></svg>';
// original: findRemoteReferences(input) === []
// mutant: findRemoteReferences(input) ===
// ['references a remote resource in a <style> block: http://evil']
Suggested fix — replace the annotation with a killing test in // Only a string argument makes the image functions fetch; a bare ident is not
// a valid argument, so even one whose escapes spell out a URL loads nothing.
// Reporting it would flag a fetch no browser makes.
test('an escaped-ident argument to an image function is not a fetch', () => {
const body =
'<style>x{fill:image-set(http\\3A\\2F\\2Fevil.example/x.png)}</style>';
assert.deepEqual(findRemoteReferences(svg(body)), []);
assert.deepEqual(findActiveContent(svg(body)), []);
});Verified: with this test added, 🐝 Hive Agent: — hive: agent=scanner backend=copilot model=kimi-k3 copilot=1.0.88 |
Test Improvement
Clears the mutation backlog in
scripts/lib/svg-active-content.mjs— 17 survivors, the largest single-file backlog onmainand 40% of the repository's 42.Two of them were a real defect.
startsWithDoctype()walks the prolog with a loop rather than a pattern because nested lazy repetition over<?...?>and<!--...-->backtracks exponentially, as its own comment says. The loop moved the hazard rather than removing it:indexOfyields-1for a prolog node that never closes, so without theend === -1return,indexrewinds tocloser.length - 1, the whitespace skip at the top of the loop carries it back to the same unterminated<?, and the walk never ends.A file truncated in transit mid-declaration is the ordinary way a prolog node ends up unclosed, and every validator here calls these entry points on SVG files it did not write. Deleting the return, or flipping the sentinel it compares against, left all 3566 tests passing.
tests/svg-active-content-prolog-termination.test.mjsanswers for eight truncated prologs acrosshasDoctype,stripDoctype,findActiveContentandfindRemoteReferences, each under a deadline of its own — the failure is non-termination, not a wrong answer, so relying on the runner's own timeout would report it as an unexplained hang. Two further cases keep the walk doing its real job behind closed prolog nodes, so the guard cannot be "fixed" by giving up early.The other fifteen are equivalent and are annotated with
// Stryker disable next-line <mutator>: <reason>per the "Mutation testing" section of CONTRIBUTING.md. Each reason states a property a reader can check rather than take on trust —sax'sresume()is exactly thethis.error = nullthe line above already did;url.decode()already trims the whitespace insideurl(...); css-tree emits aurl(Function token only when the argument opens with a quote, so thetext.toLowerCase() !== 'url('test is already decided by the String check beside it;piis the last of the seven event typesparseXml()emits and the arms above take the other six. TheskipDepthtest is split across lines so the directive covers only the redundant half and leaves the depth comparison's own mutants live.No behaviour changes: the only edits to
svg-active-content.mjsare comments, plus that one line split.Evidence
Each surviving mutant was applied at its exact source offsets and the result compared against the unmutated module over a 57-input differential sweep of all five entry points, every variant in its own process under a 20s deadline. The corpus was written against these specific mutants: escaped
\75rl(arguments with and without padding and without a closing paren,url(var(--x)), bare-ident anddata:arguments toimage-set()/src()/cross-fade(), empty and(/@-only<style>bodies, CDATA and multiple<style>elements, namespace-prefixed elements, self-closing and nested removed subtrees, BOM and declaration orderings, and truncated prologs. Exactly two mutants were distinguishable, and both by non-termination.Verified locally at 8abcb3f:
TZ=UTC npx stryker run -- --mutate scripts/lib/svg-active-content.mjs→ 100.00%, 898 killed, 11 timed out, 0 survived (was 17). The two guard mutants are killed by timeout, which is what a non-termination test looks like to Stryker.TZ=UTC node --test→ 3566 passing, 0 failing.npm run test:unit:coverage:check→ exit 0; the new file is 100% line and region.prettier --checkandeslint --max-warnings 0clean on both files.Files and functions claimed
scripts/lib/svg-active-content.mjs(localName,startsWithDoctype,parseXml'sonerror,styleBlocks,cssUrls,rebuild) and the newtests/svg-active-content-prolog-termination.test.mjs. Disjoint from the open held PRs: #1816 annotatesuri-safety.mjs/url-safety.mjs, #1812 and #1810 work on the e2e accepted-region registry andtests/tools/e2e-coverage-report.mjs, #1818 and #1819 on the Stryker child-coverage harness ande2e-coverage-run.mjs. No file here is touched by any of them.Related Issue
Closes #1827
Human review required.
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