Fix panic in Pattern.Matches with zero StarIndex

[abelcha]

This PR fixes a panic that occurs in the Pattern.Matches method when StarIndex is 0 and Text is empty or too short. The panic was caused by attempting to slice Text with invalid bounds [1:0].

The fix adds special handling for edge cases:

• Empty Text
• StarIndex at the beginning of Text
• StarIndex at or beyond the end of Text

Added tests to verify the fix:

• Unit tests in internal/core/pattern_test.go
• Integration test in internal/module/circular_reference_test.go
• Compiler test case in testdata/tests/cases/compiler/circularModuleReference.ts

Fixes the issue with circular module references in eslint.config.js files.

[abelcha]

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[Copilot]

Pull Request Overview

This PR addresses a panic in Pattern.Matches when StarIndex is 0 and Text is empty or too short, and adds tests to prevent regressions in module resolution with circular references.

• Add edge‐case handling in Pattern.Matches for empty text, star at start, and star beyond end
• Introduce unit and integration tests for zero‐star and circular module imports
• Include a compiler test case for circular eslint.config.js references

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
internal/core/pattern.go	Added branches to safely handle empty text, StarIndex == 0, and out‐of‐range stars
internal/core/pattern_test.go	New unit tests for zero‐star matching and circular pattern scenarios
internal/module/circular_reference_test.go	Integration test to verify no panic during circular module resolution
testdata/tests/cases/compiler/circularModuleReference.ts	TS compiler test case reproducing circular import panic

Comments suppressed due to low confidence (3)

internal/core/pattern.go:41

• There’s no existing test for a pattern where StarIndex exceeds len(Text). Add a unit test for StarIndex > len(Text) to ensure the new branch handles it safely.

if p.StarIndex >= len(p.Text) {

internal/module/circular_reference_test.go:18

• [nitpick] The variable name fs shadows the imported fs package (io/fs). Consider renaming to vfs or fileSystem to avoid confusion.

fs := vfstest.FromMap(map[string]string{

internal/module/circular_reference_test.go:31

• [nitpick] This line and its preceding comment aren't indented to match the surrounding block. Align the indentation for readability.

pattern := core.Pattern{

[Copilot]

Slicing p.Text[:p.StarIndex] will panic if StarIndex > len(p.Text). Clamp the slice index to len(p.Text) or explicitly handle the > case so it never exceeds the text length.

Suggested change

	// If StarIndex is at or beyond the end, we only need to check the prefix
	return strings.HasPrefix(candidate, p.Text[:p.StarIndex])
	// If StarIndex is at or beyond the end, clamp it to len(p.Text) for safe slicing
	return strings.HasPrefix(candidate, p.Text[:len(p.Text)])

[DanielRosenwasser]

I think this was attempting to fix #870 but #875 already did that. Any details on what else this might have fixed?

[DanielRosenwasser]

This should never happen - the empty string is an exact match (StarIndex == -1).

[jakebailey]

I think #875 fixed this