Assessing Impact skill

Assessing Impact

Cheap, ad-hoc impact analysis for a single target. Not a graph database — a focused walk over an AST cache plus a complementary text scan, clustered into a report that's easy to summarize.

Use this when you're about to refactor / rename / delete a symbol in a repo you don't work in daily, and you want a single artifact that says: "these N files will need to change, in these M packages, with these tests likely affected."

Don't use this for deep ongoing impact analysis on your own codebase — stand up GitNexus, SourceGraph, or your IDE's index. This skill is for the one-shot case.

Setup

uv venv /home/claude/.venv 2>/dev/null
uv pip install --python /home/claude/.venv/bin/python tree-sitter
export PYTHON=/home/claude/.venv/bin/python
export IMPACT=/mnt/skills/user/assessing-impact/scripts/impact.py

The script depends on the tree-sitting skill — it imports engine.py directly. The bundled grammars live with tree-sitting; no separate language-pack install needed.

Workflow

1. Run the report

$PYTHON $IMPACT /path/to/repo SYMBOL_NAME

Or target a whole file:

$PYTHON $IMPACT /path/to/repo path/to/module.py

2. Read the data, write the summary

The script prints a structured markdown report. Treat it as input for your final summary, not the deliverable. It deliberately doesn't assign a "high/medium/low" risk label — that's your job, after weighing:

• Refs concentrated in one package (low blast) vs. fanned across many (high)
• Test refs present (good — the change has a verification surface) vs. absent
• Doc mentions (renames need to update docs too)
• Caveats listed at the bottom (what the script can't see)

3. Drill if needed

If a particular package looks suspicious, follow up with tree-sitting to read the actual call sites:

TREESIT=/mnt/skills/user/tree-sitting/scripts/treesit.py
$PYTHON $TREESIT /path/to/repo --no-tree 'source:caller_function'

Options

Flag	Default	Purpose
--features PATH	_FEATURES.md	Root _FEATURES.md — when present, refs get clustered by feature in addition to by package.
--skip DIRS	(defaults from tree-sitting)	Extra comma-separated dirs to skip.
--limit-per-name N	500	Cap refs per symbol name. Bump if you suspect truncation.
--json	off	Emit JSON instead of markdown — for downstream tooling.

Output Sections

# Impact Report: <target>

## Target
  Kind, definition sites with line ranges.

## Direct & Textual References (N total)
  Top-line counts, then refs grouped by:
  - Code references by package
  - Test references
  - Documentation mentions

## Affected Features (from _FEATURES.md)        ← only if file present
  Feature name → ref count + file count.

## Suggested Test Surfaces
  Test files that already reference the target, plus tests neighboring
  the definition. Likely the regression net for the change.

## Caveats
  What the scan can't see (dynamic dispatch, cross-language, cross-repo).

Composition with Other Skills

• Run after exploring-codebases if the repo also has a freshly generated _FEATURES.md — the impact report will cluster refs by feature, which makes the blast radius story much more legible than raw package directories.
• Use tree-sitting to drill specific call sites once impact has identified them.
• Use searching-codebases when you want regex/AST search over the same corpus rather than impact analysis on a known target.

Honest Limits

• Text-based ref discovery. Refs are matched by symbol name, not by type-resolved call edges. Common names (run, init, handler) will pick up unrelated symbols. Prefer running this on distinctive names; otherwise expect noise and read the snippets.
• No type/MRO resolution. Dynamic dispatch (getattr, duck-typed method calls, virtual dispatch in C++) is missed or over-matched.
• No cross-language tracing. A TS frontend calling a Python backend handler over HTTP appears as zero refs — they're not in the same AST.
• No cross-repo tracing. Consumers in separate repos (downstream packages, sibling services) are invisible. For multi-repo impact, reach for GitNexus / SourceGraph.
• No persistent index. Each run re-scans. Fine for single-shot use; acceptable cost (~700ms scan + sub-ms queries) for a few hundred files.
• Diff input not yet supported. v0.1 takes a symbol or file path. Diff → affected-symbols extraction is a planned follow-up.

Files

• scripts/impact.py — Single-entry CLI. Resolves target → walks AST refs → augments with text scan → clusters by package and (optionally) by feature → renders markdown or JSON.