Fix spelling suggestions involving Unicode characters

[ahejlsberg]

Fixes #4223.

[Copilot]

Pull request overview

This PR adds a regression test for issue #4223 and adjusts the compiler’s spelling-suggestion heuristic so “Did you mean …” suggestions behave correctly when the misspelled identifier contains non-ASCII characters.

Changes:

• Added a new compiler regression test covering Unicode identifiers that previously produced divergent TS1435 “Did you mean …” suggestions.
• Updated GetSpellingSuggestion heuristics to base length thresholds on Unicode-aware length for the input name.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
internal/core/core.go	Adjusts spelling-suggestion length heuristics to use a Unicode-aware length for the target name.
testdata/tests/cases/compiler/unicodeSpellingSuggestions.ts	Adds a regression test for Unicode spelling suggestions (issue #4223).
testdata/baselines/reference/compiler/unicodeSpellingSuggestions.errors.txt	Captures expected diagnostic output for the new test.
testdata/baselines/reference/compiler/unicodeSpellingSuggestions.types	Captures expected type baseline output for the new test.
testdata/baselines/reference/compiler/unicodeSpellingSuggestions.symbols	Captures expected symbol baseline output for the new test.

Comments suppressed due to low confidence (1)

internal/core/core.go:580

• GetSpellingSuggestion now computes maximumLengthDifference/bestDistance using rune count for name, but the candidate-length filter still uses len(candidateName) (byte count). For candidates containing non-ASCII characters this mixes units and can incorrectly skip valid suggestions. It also redundantly converts candidateName to []rune for Levenshtein.

	runeName := []rune(name)
	maximumLengthDifference := max(2, int(float64(len(runeName))*0.34))
	bestDistance := math.Floor(float64(len(runeName))*0.4) + 0.9 // If the best result is worse than this, don't bother.
	buffers := levenshteinBuffersPool.Get().(*levenshteinBuffers)
	defer levenshteinBuffersPool.Put(buffers)
	var bestCandidate T
	hasBest := false
	for candidate := range candidates {
		candidateName := getName(candidate)
		maxLen := max(len(candidateName), len(runeName))
		minLen := min(len(candidateName), len(runeName))
		if candidateName != "" && maxLen-minLen <= maximumLengthDifference {
			if candidateName == name {
				continue
			}
			// Only consider candidates less than 3 characters long when they differ by case.
			// Otherwise, don't bother, since a user would usually notice differences of a 2-character name.
			if len(candidateName) < 3 && !strings.EqualFold(candidateName, name) {
				continue
			}
			distance := levenshteinWithMax(buffers, runeName, []rune(candidateName), bestDistance)