feat(tools): apply_patch — git-style unified-diff edit tool - #39
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Adds a targeted edit tool so agents stop reading+rewriting whole files to change a few lines. - UnifiedDiff: Foundation-only parser + applier. Applies each hunk by matching its context (the @@ line numbers are hints, not authority), with nearest-hint selection and cumulative offset across hunks. All-or-nothing: any hunk that doesn't match leaves the file untouched. Preserves trailing-newline state. - PatchFileTool (apply_patch): reads an existing file, applies a unified diff, writes atomically. requiresConfirmation (the diff shows in the approval sheet). Clear errors name the first unmatched hunk so the model can re-read and regenerate. Robustness: wrong @@ numbers still apply via context (the property that makes LLM-generated diffs usable). Tests cover offset drift, nearest-hint, context not found → unchanged, trailing-newline preservation, insertion/removal. Full suite: 155 green. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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What
Adds
apply_patch(path, patch)— a targeted edit tool. Agents can change a few lines by emitting a unified diff instead of reading the whole file and rewriting it withwrite_file(the cause of the read/rewrite storm on multi-file edits).How
UnifiedDiff(pure, Foundation-only) — parses a git/diff -upatch and applies each hunk by matching its context; the@@line numbers are treated as hints (nearest-hint selection + cumulative offset across hunks). All-or-nothing: any hunk that doesn't match leaves the file untouched. Trailing-newline state preserved.PatchFileTool(apply_patch) — reads an existing file, applies the diff, writes atomically.requiresConfirmation(diff shows in the approval sheet). Errors name the first unmatched hunk so the model can re-read and regenerate.Why context-matching (not strict git apply)
LLMs frequently get
@@line numbers wrong; strictgit applythen rejects the whole patch. Matching on context (like Aider / Codexapply_patch/patch -F) makes LLM-generated diffs reliable — a test asserts a patch with deliberately wrong line numbers still applies.Scope (v1)
Single existing file per call; text hunks only (no binary/rename/create — creation stays
write_file). Pure-Swift, no shelling togit/patch(keeps SwiftAgentKitTools Foundation-only + cross-platform).Testing
✅ Full suite 155 green, incl.
UnifiedDiffTests(wrong line numbers, offset drift, nearest-hint, context-not-found→unchanged, trailing-newline, insert/remove-only) andapply_patchtool cases (in-place edit, missing file, non-matching hunk leaves file unchanged, requiresConfirmation).Consumed by Naseem next (register the tool + prompt nudge) after an alpha bump. Spec in the Naseem repo:
docs/superpowers/specs/2026-08-04-apply-patch-tool-design.md.🤖 Generated with Claude Code