fix(ignore-generator): dedupe anchored .gitignore patterns against defaults and skip negation patterns in suggestions

[tirth8205]

Problem

generateStarterIgnoreFile produces a starter .understandignore whose "From .gitignore (uncomment to exclude)" section is supposed to list only patterns not already handled by the built-in DEFAULT_IGNORE_PATTERNS. Two bugs defeat that:

1. Anchored patterns are not deduped against defaults. isCoveredByDefaults()'s normalize() only strips trailing slashes, not the leading / anchor that is extremely common in real .gitignore files (Create React App, Vite, many JS templates use /node_modules, /dist, /build, /coverage). So /node_modules normalizes to /node_modules, never equals the default's normalized node_modules, and the directory is re-suggested even though node_modules/, dist/, etc. are already in the defaults — defeating the whole purpose of the section.

2. Negation (!) lines are emitted under "uncomment to exclude". parseGitignorePatterns() keeps every non-comment, non-blank line, including re-include lines like !build/keep.txt. These get dumped verbatim under # --- From .gitignore (uncomment to exclude) ---, which is semantically inverted: a !-pattern force-includes a file, it does not exclude it, and the path is only meaningful relative to the project's own .gitignore (which understand-anything does not apply). So the suggestion is misleading noise.

Fix

• isCoveredByDefaults(): strip a leading root anchor as well as trailing slashes in normalize() (p.replace(/^\//, "").replace(/\/+$/, "")), so /node_modules and /dist/ normalize to node_modules/dist and correctly match the defaults node_modules//dist/.
• parseGitignorePatterns(): drop !-prefixed lines when collecting suggestable patterns, since they cannot meaningfully be presented as "uncomment to exclude".

Both are minimal, single-file changes in understand-anything-plugin/packages/core/src/ignore-generator.ts.

Testing

Added two tests to ignore-generator.test.ts under the .gitignore integration block:

• treats anchored .gitignore patterns as covered by defaults — feeds /node_modules\n/dist\n.env and asserts the suggestion section omits the anchored defaults while keeping .env.
• does not suggest .gitignore negation (!) patterns — feeds build/\n!build/keep.txt\n.env and asserts !build/keep.txt is not emitted while .env is.

Both tests fail before the fix (the anchored patterns are re-suggested; the !-line is emitted) and pass after. The full core Vitest suite is green (694 tests, 34 files) with no regressions, and tsc --noEmit and eslint on the changed files both exit 0.

🤖 Generated with Claude Code

[thejesh23]

1. Dropping ! patterns silently discards user signal that belongs under the header's own ! guidance.
The file header explicitly tells users "Use ! prefix to force-include something excluded by defaults," but parseGitignorePatterns now filters !-lines out at parse time, so a project's !build/keep.txt is invisible rather than surfaced (commented) as a candidate re-include. A more faithful fix would route negations into a separate "From .gitignore (force-include)" section instead of dropping them.

2. normalize() still misses common anchor variants beyond a single leading /.
**/node_modules, **/node_modules/, and ./node_modules/ are all routinely written in real .gitignore files (and CRA/Vite/Next templates) and none of them strip down to the defaults' node_modules. The regex only handles ^\/, so the dedup section will still re-suggest these. Consider p.replace(/^\.?\/+/, "").replace(/^\*\*\/+/, "").replace(/\/+$/, "") or document the limitation.

3. First new test is brittle when the section is fully deduped.
headerIdx = lines.findIndex(...includes("From .gitignore")) returns -1 if every pattern is covered; lines.slice(headerIdx + 1, ...) then becomes slice(0, ...) and silently scans the header, which would mask a future regression where the section is emitted with no patterns. Assert headerIdx >= 0 (or expect(content).toContain("From .gitignore")) before slicing.

Nit: isCoveredByDefaults doc still says "Normalizes trailing slashes" in the one-line summary; the expanded sentence updates it but the lead is now stale.

[tirth8205]

Addressed all points.

2. normalize() anchor variants — Fixed. normalize() now strips ./, a root /, and a leading globstar (p.replace(/^\.?\/+/, "").replace(/^\*\*\/+/, "").replace(/\/+$/, "")), so **/node_modules, **/node_modules/, ./node_modules/, **/build/, and ./dist/ all dedupe against the built-in defaults. Added a test (treats **/ and ./ anchor variants as covered by defaults) feeding **/node_modules, **/build/, ./dist/, and asserting a non-default (.env) survives. Broadened the isCoveredByDefaults JSDoc accordingly.

3. Brittle test when the section is fully deduped — Fixed. Added expect(headerIdx).toBeGreaterThanOrEqual(0) before the slice in the anchored-patterns test (and in the new anchor-variants test), so the section silently disappearing now fails loudly instead of scanning the header.

1. Dropping ! patterns — Kept as a drop, now documented in parseGitignorePatterns. The reason it isn't routed to a "force-include" section: a !pattern re-includes a path relative to git's own ignore stack, which understand-anything does not apply. Presenting it under "uncomment to exclude" inverts its meaning, and surfacing it as an understandignore force-include would itself be misleading since the path it re-includes isn't excluded by our defaults in the first place. The file header still documents the general ! mechanism for users who want to author one by hand. The added comment explains this intent so it's no longer a silent discard.

Nit (JSDoc lead) — The standalone "Normalizes trailing slashes" lead was already replaced on this branch; the expanded version is now broadened to cover the ./ and globstar anchors too. (Note: the globstar is described in prose rather than the literal **/ token, because that sequence closes a JSDoc block comment.)

Core suite: 695 passed. tsc --noEmit clean.