ast_edit

Preview and apply structural rewrites over source files via native ast-grep.

Source

• Entry: packages/coding-agent/src/tools/ast-edit.ts
• Model-facing prompt: packages/coding-agent/src/prompts/tools/ast-edit.md
• Key collaborators:
  • crates/pi-natives/src/ast.rs — native rewrite planning and file mutation
  • crates/pi-ast/src/language/mod.rs — language aliases and extension inference used by the native wrapper.
  • packages/coding-agent/src/tools/path-utils.ts — path/glob parsing and multi-path resolution
  • packages/coding-agent/src/tools/resolve.ts — preview/apply queueing
  • packages/coding-agent/src/tools/render-utils.ts — parse-error dedupe and display caps
  • packages/coding-agent/src/utils/file-display-mode.ts — hashline vs line-number diff references
  • packages/hashline/src/format.ts — stable hashline header formatting for preview anchors
  • packages/natives/native/index.d.ts — JS-visible native binding contract

Inputs

Field	Type	Required	Description
ops	{ pat: string; out: string }[]	Yes	One or more rewrite rules. pat must be non-empty. Duplicate pat values fail before native execution. Empty out deletes the matched node.
paths	string[]	Yes	One or more files, directories, globs, or internal URLs with backing files. Empty entries are rejected. Globs are forbidden for internal URLs.

Shared AST pattern grammar and language catalog: see ast_grep.

• ast_edit uses the same $NAME, $_, $$$NAME, and $$$ metavariable semantics.
• The tool prompt adds rewrite-specific constraints:
  • metavariable names must be uppercase and must stand for whole AST nodes,
  • captures from pat are substituted into out,
  • each rewrite is a 1:1 structural substitution; one capture cannot expand into multiple sibling nodes unless the grammar itself permits that expansion at that position.

Outputs

• Single-shot preview result from ast_edit itself.
• Model-facing content is one text block showing proposed edits, grouped by file for directory/multi-file runs.
  • Each change renders as two lines. Hashline mode uses -LINE:before / +LINE:after under a ¶PATH#TAG header; plain mode uses -LINE:COLUMN before / +LINE:COLUMN after.
  • Only the first line of each before/after snippet is shown, truncated to 120 characters in the wrapper.
  • Limit reached; narrow paths. and formatted parse issues are appended when applicable.
• If no rewrites match, text is No replacements made plus formatted parse issues when present.
• details includes aggregate preview metadata:
  • totalReplacements, filesTouched, filesSearched, applied, limitReached
  • optional parseErrors, scopePath, files, fileReplacements, displayContent, meta
• The tool always previews first (applied: false in the direct result). Actual file writes happen only later through resolve(action: "apply", ...).
• When preview produced replacements, ast_edit also queues a pending resolve action. Successful apply returns a separate resolve result, not another ast_edit result.

Flow

1. AstEditTool.execute() validates each op in packages/coding-agent/src/tools/ast-edit.ts:
   • empty pat fails,
   • at least one op is required,
   • duplicate pat values fail,
   • ops are converted to a Record<pattern, replacement>.
2. The wrapper reads PI_MAX_AST_FILES via $envpos(..., 1000) and uses that as the native maxFiles cap for both preview and apply.
3. Path normalization, internal URL handling, missing-path partitioning, and multi-path resolution follow the same path-utils.ts flow as ast_grep.
4. The wrapper stats the resolved base path to decide whether to render grouped directory output.
5. runAstEditOnce(...) always runs native astEdit(...) with dryRun: true and failOnParseError: false on the first pass.
6. Native ast_edit in crates/pi-natives/src/ast.rs:
   • normalizes the rewrite map and sorts rules by pattern string,
   • resolves strictness (smart by default),
   • collects candidate files from a file or gitignore-aware directory scan,
   • infers a single language for the whole call unless lang was supplied,
   • compiles every rewrite pattern for that language,
   • parses each file, skips files with syntax-error trees, collects replace_by(...) edits for every match, enforces replacement and file caps, and returns textual before/after slices plus source ranges.
7. The TS wrapper deduplicates parse errors, groups changes by file, and renders preview diff lines.
8. If preview found replacements and applied is false, queueResolveHandler(...) registers a forced resolve action and injects a resolve-reminder steering message.
9. On resolve(action: "apply"), the queued callback reruns the same rewrite set with dryRun: false, recomputes counts, and returns an error result if the live result no longer matches the preview (stalePreview). The current implementation compares replacement totals and per-file counts after the rerun; if the new run has already written different counts, the result is marked error.
10. On a non-stale apply, the callback returns Applied N replacements in M files.; on discard, resolve returns a discard message without mutating files.

Modes / Variants

• Single file: preview or apply against one file.
• Directory + optional glob: native scan walks the directory, then filters by compiled glob.
• Multiple explicit paths/globs: wrapper unions them into one synthetic scope or runs per-target native calls when paths only meet at root.
• Internal URL inputs: only supported when the router resolves them to a backing file path.
• Preview mode: always the direct ast_edit tool result.
• Apply mode: only reachable through the queued resolve callback after a preview.
• Hashline output mode vs plain line/column mode: controlled by resolveFileDisplayMode().

Side Effects

• Filesystem
  • Preview reads files and scans directories.
  • Apply rewrites files in place with std::fs::write(...), but only when the computed output differs from the original source.
• Session state (transcript, memory, jobs, checkpoints, registries)
  • Queues a one-shot forced resolve tool choice through queueResolveHandler(...).
  • Adds a resolve-reminder steering message.
• User-visible prompts / interactive UI
  • Direct ast_edit results are previews.
  • Follow-up apply/discard is exposed through the hidden resolve tool.
• Background work / cancellation
  • Native preview/apply work runs on a blocking worker via task::blocking(...).
  • Cancellation and optional native timeout are cooperative through CancelToken::heartbeat().

Limits & Caps

• File cap exposed by the wrapper: PI_MAX_AST_FILES, default 1000, in packages/coding-agent/src/tools/ast-edit.ts.
• Native maxFiles and maxReplacements are both clamped to at least 1 when provided in crates/pi-natives/src/ast.rs.
• The wrapper never sets maxReplacements; native behavior therefore defaults to effectively unbounded replacements for a run.
• Parse issues are rendered with at most PARSE_ERRORS_LIMIT = 20 lines in packages/coding-agent/src/tools/render-utils.ts; details.parseErrors is deduplicated but not capped.
• Directory scans use include_hidden: true, use_gitignore: true, and skip node_modules unless the glob text explicitly mentions node_modules in crates/pi-natives/src/ast.rs.
• No separate glob-expansion count cap exists. Candidate count is whatever the resolved path/glob expands to after gitignore filtering, then native maxFiles stops mutations after the configured number of touched files.
• Preview text truncates each rendered before and after first line to 120 characters in packages/coding-agent/src/tools/ast-edit.ts.

Errors

• TS wrapper throws ToolError for empty patterns, duplicate rewrite patterns, empty path entries, unsupported internal-URL globs, internal URLs without sourcePath, and missing paths.
• Native code returns hard errors for:
  • inability to infer one language across all candidates when lang is absent,
  • unsupported explicit lang,
  • bad glob compilation or unreadable search roots,
  • overlapping computed edits (Overlapping replacements detected; refine pattern to avoid ambiguous edits),
  • out-of-bounds edit ranges or non-UTF-8 replacement text,
  • write failures during apply,
  • cancellation or timeout.
• With failOnParseError: false (the wrapper always uses this), pattern compile failures and file parse failures become parseErrors instead of aborting the whole run.
• If every rewrite pattern fails to compile, native ast_edit returns a successful zero-replacement result with parseErrors populated.
• Files containing tree-sitter error nodes are skipped for rewriting; they do not get partial edits.
• Apply can fail after a successful preview if the preview becomes stale. The resolve callback compares replacement totals and per-file counts and returns an error result rather than silently reporting success for a mismatched preview.

Notes

• ast_edit does not expose the native lang, strictness, selector, maxReplacements, failOnParseError, or timeoutMs fields to the model. The runtime fixes the call shape to a preview-first, smart-strictness, best-effort parse mode.
• Because the wrapper does not expose lang, mixed-language rewrites only succeed when every candidate infers to the same canonical language. This is stricter than ast_grep.
• Idempotency is not enforced syntactically. A rewrite like foo($A) -> foo($A) previews zero changes because output equals input; a rewrite that keeps matching its own output may still produce replacements on repeated calls.
• Rewrites are accumulated per file, then applied from the end of the file backward after an overlap check. Independent matches can coexist; overlapping matches abort the run.
• Native rewrite rule order is by pattern-string sort, not by the original ops array order, because normalize_rewrite_map(...) sorts the (pattern, rewrite) pairs.
• Preview/apply parity is validated by totals and per-file counts after the apply rerun, not by a byte-for-byte diff of every replacement payload.