fix(canonicalize): prevent collapse cache pollution across calls (#19675)

## Summary

fixes
https://github.com/schoero/eslint-plugin-better-tailwindcss/issues/321

This PR fixes an order-sensitive canonicalization bug. This bug caused
issues when running eslint-plugin-better-tailwindcss as the order in
which files are linted in is not consistent. This caused, in some
scenarios, `canonicalizeCandidates(..., { collapse: true,
logicalToPhysical: true, rem: 16 })` to stop collapsing valid
combinations (for example `h-4 + w-4 -> size-4`) after unrelated prior
calls.

To reproduce this issue:
```
# checkout this branch
$ git checkout c/fix-canonicalizeCandidates
# Revert the fix to the current `main` branch
$ git checkout main ./packages/tailwindcss/src/canonicalize-candidates.ts
# Run the tests
$ pnpm run test
```

This should produce a failure like so:

```

 FAIL   tailwindcss  src/canonicalize-candidates.test.ts > regressions > collapse canonicalization is not affected by previous calls
AssertionError: expected [ 'underline', 'h-4', 'w-4' ] to deeply equal [ 'underline', 'size-4' ]

- Expected
+ Received

  [
    "underline",
-   "size-4",
+   "h-4",
+   "w-4",
  ]

 ❯ src/canonicalize-candidates.test.ts:1167:66
    1165|     designSystem.canonicalizeCandidates(['underline', 'mb-4'], options)
    1166| 
    1167|     expect(designSystem.canonicalizeCandidates(target, options)).toEqual(['underline', 'size-4'])
       |                                                                  ^
    1168|   })
    1169| })
```

```
# reset all changes on this branch
git reset --hard
# run the tests again (they should now pass)
pnpm run test
```

The cause of this bug is that the canonicalization caches used
`DefaultMap` in places where lookups were expected to be read-only.
`DefaultMap.get` inserts missing entried, which mutated shared cache
state during intermediate lookups and made later canonicalization
results depend on prior calls.

By replacing the use of `DefaultMap` with a plain `Map`, it avoids
inserting into the map on lookup paths. I've polyfilled
[`Map#getOrInsert`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map/getOrInsert)
as it is not widely available yet, and used that where appropriate.


## Test plan

I wrote a test that fails on `main` branch, I then fixed the issue, and
validated that the test now passes.

---------

Co-authored-by: Robin Malfait <malfait.robin@gmail.com>

CHANGELOG.md

@@ -32,6 +32,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Improve performance Oxide scanner in bigger projects ([#19632](https://github.com/tailwindlabs/tailwindcss/pull/19632))
 - Ensure import aliases in Astro v5 work without crashing ([#19677](https://github.com/tailwindlabs/tailwindcss/issues/19677))
 - Allow escape characters in `@utility` names to improve support with formatters such as Biome ([#19626](https://github.com/tailwindlabs/tailwindcss/pull/19626))
+- Fix invalid cache during subsequent canonicalization calls ([#19675](https://github.com/tailwindlabs/tailwindcss/pull/19675))
 
 ### Deprecated
 

packages/tailwindcss/src/canonicalize-candidates.test.ts

@@ -1163,3 +1163,46 @@ describe('options', () => {
     expect(designSystem.canonicalizeCandidates(['m-[16px]'])).toEqual(['m-[16px]']) // Ensure options don't influence shared state
   })
 })
+
+// https://github.com/schoero/eslint-plugin-better-tailwindcss/issues/321
+test('a subset of classes should be canonicalizable', { timeout }, async () => {
+  let designSystem = await designSystems.get(__dirname).get(css`
+    @import 'tailwindcss';
+  `)
+
+  let options: CanonicalizeOptions = {
+    collapse: true,
+    logicalToPhysical: true,
+    rem: 16,
+  }
+
+  expect(
+    designSystem.canonicalizeCandidates(['underline', 'h-4', 'w-4', 'text-sm'], options),
+  ).toEqual(['underline', 'text-sm', 'size-4'])
+})
+
+test('collapse canonicalization is not affected by previous calls', { timeout }, async () => {
+  let designSystem = await designSystems.get(__dirname).get(css`
+    @import 'tailwindcss';
+  `)
+
+  let options: CanonicalizeOptions = {
+    collapse: true,
+    logicalToPhysical: true,
+    rem: 16,
+  }
+
+  let target = ['underline', 'h-4', 'w-4']
+
+  expect(designSystem.canonicalizeCandidates(target, options)).toEqual(['underline', 'size-4'])
+
+  designSystem.canonicalizeCandidates(['mb-4', 'text-sm'], options)
+  designSystem.canonicalizeCandidates(['underline', 'mb-4'], options)
+
+  expect(designSystem.canonicalizeCandidates(target, options)).toEqual(['underline', 'size-4'])
+  expect(designSystem.canonicalizeCandidates(target.concat('text-sm'), options)).toEqual([
+    'underline',
+    'text-sm',
+    'size-4',
+  ])
+})

packages/tailwindcss/src/canonicalize-candidates.ts

@@ -267,6 +267,8 @@ function collapseCandidates(options: InternalCanonicalizeOptions, candidates: st
         let interestingLineHeights = new Set<string | number>()
         let seenLineHeights = new Set<string>()
         for (let pairs of candidatePropertiesValues) {
+          if (!pairs.has('line-height')) continue
+
           for (let lineHeight of pairs.get('line-height')) {
             if (seenLineHeights.has(lineHeight)) continue
             seenLineHeights.add(lineHeight)
@@ -292,6 +294,8 @@ function collapseCandidates(options: InternalCanonicalizeOptions, candidates: st
 
         let seenFontSizes = new Set<string>()
         for (let pairs of candidatePropertiesValues) {
+          if (!pairs.has('font-size')) continue
+
           for (let fontSize of pairs.get('font-size')) {
             if (seenFontSizes.has(fontSize)) continue
             seenFontSizes.add(fontSize)