avouch

Review the Python you changed, not the Python you inherited.

Avouch is a lightweight, Git-aware static analysis CLI for Python. It asks Git which files your next commit will touch, parses each changed .py file with the standard ast module, and reports structural problems against limits you configure in avouch.toml.

No daemon. No network. No path lists to maintain. Run it in the seconds before git push, fix what it flags, push.

pip install avouch
cd your-repo
avouch

---

Table of contents

• Why it exists
• Installation
• Quick start
• JSON output
• Quiet mode
• GitHub Actions
• Other CI systems
• Configuration
• Rules
• How it works
• Repository layout
• Adding a rule
• Testing
• Roadmap
• FAQ
• Contributing
• License

---

Why it exists

• The review set is the diff, not the repository. Avouch computes the review set from Git at run time (git diff HEAD --name-only plus untracked files). Every finding is attributable to work you are about to push — never to the legacy you inherited.
• Metrics are exact. Parameter counts, nesting depth, and line spans come from the AST, not regex. If a metric cannot be computed exactly, Avouch does not claim it.
• Errors are data. An unreadable or syntactically broken file becomes an ERROR entry in the report. One broken file never cancels the review of the others.
• Avouch reviews; it does not gate. The exit code signals the outcome — 0 clean, 1 violations found, 2 Avouch error — but enforcement belongs in an opt-in interface, not in a tool you run before every push.
• The runtime is the standard library. Three git subprocess calls and ast/tomllib. No daemon to keep alive; runtime is bounded by the size of your diff, not your repository.

---

Installation

Requires Python 3.10+ (rules use ast.Match; configuration uses tomllib) and Git on PATH.

pip install avouch

or from source:

git clone https://github.com/mukundzha/avouch.git
cd avouch
pip install -e .

Both register the avouch console script (avouch.cli:main).

---

Quick start

The interface is one command with a small set of optional flags:

cd your-repo
# ... make a change ...
avouch            # human report
avouch --json     # one JSON document on stdout
avouch --docs     # built-in documentation; no review performed
avouch --version  # print the version and exit
avouch --verbose  # step-by-step review details on stderr
avouch --quiet    # analyze, print no report; exit code only
avouch --changed  # compact added/deleted view of changed files vs HEAD
avouch --staged   # review only files staged for the next commit
avouch --all-files  # review every eligible Python file, not just the diff
avouch --not-git  # review every eligible .py file on disk; no Git repo needed
avouch --help     # every flag

The review set is defined by Git, so there is nothing to configure at invocation time. With --not-git, Avouch skips the Git requirement and reviews every eligible .py file found by walking the current directory instead (skipping Git, cache, and virtual-environment directories). Avouch reviews:

• tracked files modified vs. HEAD (git diff HEAD --name-only), and
• untracked .py files (git ls-files --others --exclude-standard).

Deleted paths and non-.py files are skipped. Committed, untouched files never appear in the output. Files that look generated (generated.py, *_generated.py, codegen.py, autogen.py, … — see src/avouch/utility/is_generated.py) are skipped too.

The review-scope flags --changed, --staged, and --all-files are mutually exclusive — pick at most one. The output flags --json, --verbose, and --quiet combine freely with any review scope.

A run with findings

$ avouch

AVOUCH · 2 FILES · 4 WARN
────────────────────────────────────────────────────────────────────────────────

bad.py:1: SCR002: Bare except detected. Catch a specific exception instead, e.g. except ValueError:.
  │
1 │ def connect(host, port, user, password, db, timeout):
  │     ^^^^^^^ SCR002
2 │     try:
  │

bad.py:1: SCR014: Too many parameters (6/5). Group related parameters into a data class or dictionary.
  │
1 │ def connect(host, port, user, password, db, timeout):
  │     ^^^^^^^ SCR014
2 │     try:
  │

────────────────────────────────────────────────────────────────────────────────
BY RULE

  SCR002 Bare except          1
  SCR014 Too many parameters  1

────────────────────────────────────────────────────────────────────────────────
PASSED
  ✓ src/util.py

• Header — AVOUCH · N FILES · W WARN · E ERR: file and per-severity counts, followed by the per-file findings.
• Findings — each finding renders compiler-style: a file:line header with the rule id and full message, then the offending code region with dimmed line numbers and a caret ^^^^^ under the flagged name (rule id in blue on a TTY).
• BY RULE summary — findings counted per rule, most common first, with counts aligned on the right. Rendered only when findings exist.
• PASSING grid — compliant files, compressed to a few lines with a [+N more] note when there are many.
• Identical (component, rule) findings are deduplicated per file — the header counts every finding, so with overlapping rule IDs (SCR004 / SCR006 duplicate-branch) the row count can be lower than the header count.

A clean run

$ avouch

All clean.

Edge cases

$ cd /tmp/somewhere-without-git
$ avouch
error: no Git repository found
hint: run Avouch from inside a Git repository, or use --not-git to review files without Git

$ cd ~/fresh-checkout   # e.g. a CI runner
$ avouch
error: nothing to review
hint: nothing changed vs HEAD (CI checkouts are clean); use --all-files for a full review

Colors are ANSI codes emitted only when stdout is a TTY. Piped output is plain, so avouch | tee review.log and CI capture work cleanly. Runtime errors are written to stderr, so stdout stays clean for piping and --json capture. The exit code is 0 when the review is clean, 1 when findings are reported, and 2 when Avouch cannot run.

Built-in documentation

avouch --docs prints terminal documentation derived from this codebase — what Avouch does, the Git-aware workflow, every rule with its scope, every configuration key with its default, both output formats, and realistic examples — then exits 0 without running a review. It works anywhere, even outside a Git repository. In a real terminal it opens as an interactive browser (Help, Go, Main screen, Quit); when stdout is piped it prints the plain text instead.

---

JSON output

For automation and CI, --json prints the review as a single JSON document on stdout, with no human-readable text mixed in:

avouch --json

{
  "version": 1,
  "tool": "avouch",
  "violations": [
    {
      "rule": "SCR014",
      "severity": "WARNING",
      "message": "Too many parameters (6/5). Group related parameters into a data class or dictionary.",
      "file": "buggy.py",
      "name": "extra",
      "kind": "func",
      "line": 4
    }
  ],
  "summary": {
    "total": 1,
    "errors": 0,
    "warnings": 1,
    "files_with_violations": 1
  }
}

Each violation carries the rule id (or a human-readable label when the finding has none), its severity, the message, the file, the component name, its kind (func, class, or file), and the line the finding refers to (null for file-level findings) — the same component and kind shown in the human table. files_with_violations is the number of distinct files containing at least one violation.

The document is a stable, versioned contract for automation: version is the schema version (independent of the Avouch package version), tool identifies the emitter, and the same input always produces the same JSON — no colors, timestamps, or diagnostics leak in. Exit codes behave exactly as in normal mode, so avouch --json can gate CI: parse stdout for the findings and react to the exit status (0 clean, 1 violations, 2 Avouch error).

---

Quiet mode

--quiet runs the exact same analysis but prints no report; only the exit code signals the outcome (0 clean, 1 violations, 2 Avouch error), which makes it fit hooks and scripts that need only the status. Errors are never silenced: messages such as "error: no Git repository found" still print, --json still emits its document, and --verbose diagnostics still go to stderr.

---

GitHub Actions

Avouch can run as a GitHub Actions check on every pull request and push.

Add Avouch to your pipeline

For an existing project, a minimal workflow installs the published package and reviews the whole checkout on every PR and push:

name: Avouch

on:
  pull_request:
  push:

jobs:
  avouch:
    runs-on: ubuntu-latest
    permissions:
      contents: read

    steps:
      - uses: actions/checkout@v6

      - uses: actions/setup-python@v5
        with:
          python-version: "3.12"

      - name: Install Avouch
        run: python -m pip install avouch

      - name: Run Avouch
        run: avouch --all-files --json

• actions/checkout puts the pull request's code in the runner's working tree — Avouch analyzes the files that checkout provided, nothing more.
• actions/setup-python provides a Python runtime; Avouch requires Python 3.10+.
• python -m pip install avouch installs the latest published release. Pin a version (avouch==0.3.1) for reproducible runs.
• avouch --all-files --json reviews every eligible .py file and prints the machine-readable document to the job log. permissions: contents: read is the only permission needed — the workflow makes no API calls.

Why --all-files

The default review set is files changed vs. Git HEAD, so a freshly checked-out working tree — clean by construction — has nothing to review: avouch would print error: nothing to review and exit 2. The same applies to --changed and --staged; they only make sense locally, against your own working tree. Whole-repository review is the mode that works in CI:

Command	Purpose	In CI
avouch	review files changed vs HEAD	empty set; don't use
avouch --changed	diff view of changed files	empty set; don't use
avouch --staged	review staged changes	empty set; don't use
avouch --all-files	review every eligible Python file	the CI mode
avouch --json	machine-readable document on stdout	combine with --all-files
avouch --quiet	suppress report; exit code only	fine for gating

Exit codes and failures

Avouch's exit code behaves in CI exactly as it does locally: 0 is clean, 1 means findings were reported, 2 means Avouch could not run. GitHub Actions fails a job when a step exits non-zero, so --all-files --json fails the check on any finding, and the JSON document in the job log shows why. Nothing is hidden with || true; findings already present in the repository fail the check until they are fixed or excluded with ignore_paths in avouch.toml.

The repository's own workflow

The Avouch repository itself ships .github/workflows/avouch.yml; enable it in the repository's Actions tab and it runs on its own. It installs the repository's own source with pip install -e ., so it tests the code in the pull request rather than a published release, then reviews the whole checked-out repository with --all-files --json.

---

Other CI systems

Avouch is a plain console command with a documented exit code, so any CI system can run it with the same three steps:

1. Install: python -m pip install avouch
2. Run: avouch --all-files --json
3. Treat the exit code as the result: 0 pass, 1 findings, 2 error.

The JSON document on stdout is stable and versioned (see JSON output), so it can be parsed for job annotations, summary comments, or dashboards.

---

Configuration

Configuration is optional, partial, and declarative. Avouch looks for a avouch.toml in the current working directory — no upward search, so configuration is repository-local. Any subset of keys is merged over the built-in defaults; a missing or empty file simply means defaults, with no warning.

[limits]        # numeric thresholds per rule
[rules]         # on/off toggle per rule
ignore_paths = ["tests", "migrations"]   # top-level: paths to skip

The configuration file

• Name and format: avouch.toml in your working directory, plain TOML.
• Scope: the current directory only. Avouch never searches parent directories, so each project configures itself.
• Missing or empty: defaults are used silently — there is no "no configuration found" warning.
• Environment variables: none. Configuration comes only from avouch.toml (the AVOUCH_FONT variable only selects a terminal font).

Changing a threshold

List the limit you want under [limits]; only the keys you name change, everything else stays at its default:

[limits]
max_parameters = 8    # allow up to 8 parameters instead of 5
max_file_lines = 2500 # tolerate larger files

Disabling a rule

Put the rule under [rules] and set it to false:

[rules]
nested_function = false   # stop reporting SCR015

A one-line [rules] section is a complete, valid configuration.

Rule toggles

Key	Default	Rule
async_without_await	true	SCR001
bare_except	true	SCR002
max_boolean_conditions	true	SCR003
detect_duplicateb	true	SCR004
max_large_comprehensions	true	SCR005
empty_except	true	SCR006
max_if_else_chain	true	SCR007
max_lambda_nodes	true	SCR008
max_local_variables	true	SCR009
max_class_lines	true	SCR010
max_file_lines	true	SCR011
max_function_lines	true	SCR012
max_nesting	true	SCR013
max_parameters	true	SCR014
nested_function	true	SCR015
max_return_statements	true	SCR016
mutable_default_args	true	SCR017
max_complexity	true	function/class complexity

Setting a toggle to false disables that rule's findings.

Limits

Key	Default	Rule	Meaning
max_parameters	5	SCR014	Max positional + keyword params
max_nesting	5	SCR013	Max block nesting depth
max_function_lines	300	SCR012	Max function line span
max_class_lines	200	SCR010	Max class line span
max_file_lines	1000	SCR011	Max file line count
max_complexity	40	—	Max cyclomatic complexity
max_boolean_conditions	5	SCR003	Max operands in one chain
max_if_chain	5	SCR007	Max if/elif links in a chain
max_local_variables	30	SCR009	Max distinct assigned names
max_return_statements	6	SCR016	Max returns per function
max_lambda_nodes	10	SCR008	Max AST nodes in a lambda body
max_large_comprehensions	40	SCR005	Max AST nodes in a comprehension

Limits are applied by key. A rule whose limit key is absent from the merged config falls back to the limit hardcoded in its own module, so a partial [limits] never turns a rule off. Every limit key in the table above lives in DEFAULT_LIMITS and can be tuned from avouch.toml.

Ignoring paths

Two mechanisms exclude files, both matching repository-relative paths component-wise — tests skips tests/ and tests/x.py but not tests.py; a bare "." skips the whole repository:

• avouch --ignore-path PATH — repeatable CLI flag, or
• ignore_paths = ["tests", "migrations"] at the top level of avouch.toml (must be a list; anything else raises).

CLI and TOML paths are combined and de-duplicated before analysis. Matching is purely string-based (src/avouch/utility/is_ignored.py) — no filesystem access.

Verifying that your configuration was loaded

Run avouch --verbose: when there is a review set, the first diagnostics line reports the config source and the active ignore-path count:

avouch: config: avouch.toml, 2 ignore path(s)
avouch: ignore paths: tests, migrations

Without a avouch.toml the line reads config: defaults (no avouch.toml), 0 ignore path(s). avouch --docs prints the same limits and rule defaults for reference.

Invalid and unknown configuration

• Malformed TOML (or a non-list ignore_paths) prints error: invalid avouch.toml configuration: ... on stderr and exits 2.
• Unknown keys are accepted and ignored silently — a typo makes the intended setting silently ineffective, and Avouch does not warn (--verbose shows only the file name and the ignore-path count).
• Limit values are not type-checked: a non-numeric value such as max_parameters = "eight" is not rejected and fails at analysis time with an internal error (exit 2).

How configuration interacts with the CLI

• --ignore-path appends to the TOML ignore_paths (combined and de-duplicated); there is no CLI override for [limits] or [rules].
• Configuration applies equally to every review mode — --changed, --staged, and --all-files — and to every output mode: --json, --quiet, and --verbose.
• Severity is not configurable: rule findings are WARNING; ERROR is reserved for files that cannot be read or parsed.
• --docs renders the built-in documentation and exits before any configuration is read, so it is unaffected by avouch.toml.

Example

# avouch.toml — the exact file this repository lives by
ignore_paths = ["tests"]

[limits]
max_parameters = 5
max_nesting = 5
max_function_lines = 300
max_class_lines = 200
max_file_lines = 1000
max_complexity = 40
max_boolean_conditions = 5
max_if_chain = 5
max_local_variables = 30
max_return_statements = 6
max_lambda_nodes = 10
max_large_comprehensions = 40

[rules]
max_parameters = true
max_nesting = true
max_function_lines = true
max_class_lines = true
max_file_lines = true
max_complexity = true
max_boolean_conditions = true
max_local_variables = true
max_return_statements = true
max_lambda_nodes = true
max_large_comprehensions = true
mutable_default_args = true

---

Rules

Avouch ships 17 rule identifiers (SCR001–SCR017) plus two cyclomatic complexity checks on functions and classes sharing the max_complexity limit. Every rule finding is a WARNING; ERROR findings exist only for files that cannot be read or parsed. Rules with a threshold render measured/limit; presence-based rules render detected.

ID	Rule	Limit	Scope	Metric
SCR001	Async without await	—	async funcs	detected
SCR002	Bare except	—	funcs	detected
SCR003	Boolean expression too complex	5	funcs, classes	N/limit
SCR004	Duplicate branch	—	funcs	detected
SCR005	Large comprehension	40	funcs	N/limit
SCR006	Duplicate branch	—	funcs, classes	detected
SCR007	Long if/elif chain	5	funcs, classes	N/limit
SCR008	Lambda too complex	10	funcs	N/limit
SCR009	Too many local variables	30	funcs	N/limit
SCR010	Class too large	200	classes	N/limit
SCR011	File too large	1000	files	N/limit
SCR012	Function too long	300	funcs	N/limit
SCR013	Nesting too deep	5	funcs	N/limit
SCR014	Too many parameters	5	funcs	N/limit
SCR015	Nested function definition	—	funcs	detected
SCR016	Too many return statements	6	funcs	N/limit
SCR017	Mutable default argument	—	funcs	detected
—	Function too complex	40	funcs	N/limit
—	Class too complex	40	classes	N/limit

SCR001 — Async without await

Flags async def functions that never await. An async function without an await runs synchronously while still incurring event-loop overhead. This is the only rule applied to async def functions; the other function rules do not run on them.

# bad
async def fetch_config():
    return json.load(open("config.json"))

# good
def fetch_config():
    return json.load(open("config.json"))

SCR002 — Bare except

Flags except: handlers that catch every exception — including KeyboardInterrupt and SystemExit.

# bad
try:
    return json.loads(raw)
except:
    return None

# good
try:
    return json.loads(raw)
except (ValueError, TypeError):
    return None

SCR003 — Boolean expression too complex

Flags a single and/or chain with too many operands. Nested chains sum their operands, so a and (b or c) scores 3.

# bad — 6 operands
if a and b and c and d and e and f:
    launch()

# good
if is_ready(a, b, c) and has_clearance(d, e, f):
    launch()

SCR004 / SCR006 — Duplicate branch

Flags if/elif branches whose bodies are identical — a copy-paste or a condition that never varies. The trailing else body is excluded from the comparison. Two rule IDs cover the same detection: SCR004 (detect_duplicateb) runs on functions; SCR006 (empty_except) runs on functions and classes. Both emit the same finding, and the report deduplicates identical rows, so one violation renders once.

# bad
if kind == "csv":
    rows = read_csv(path)
elif kind == "json":
    rows = read_csv(path)      # copy-paste

# good
if kind in ("csv", "json"):
    rows = read_csv(path)

SCR005 — Large comprehension

Flags list/set/dict comprehensions and generator expressions whose AST node count exceeds max_large_comprehensions (default 40). Past a few nested clauses a comprehension stops being an expression and becomes a program.

# bad
result = [
    [x * 100 for x in row if x != 0]
    for row in matrix
    if row and any(v > limit for v in row)
]

# good
def scale_row(row, factor):
    return [x * factor for x in row if x != 0]

result = [scale_row(row, 100) for row in matrix if row]

SCR007 — Long if/elif chain

Flags if/elif chains longer than max_if_chain (default 5); the trailing else clause does not add to the chain length.

# bad
if status == "ok":
    ...
elif status == "warn":
    ...
elif status == "error":
    ...
elif status == "fatal":
    ...
elif status == "timeout":
    ...
else:
    ...

# good
status_actions = {"ok": ok_action, "warn": warn_action}
status_actions.get(status, unknown_action)()

SCR008 — Lambda too complex

Flags lambda bodies exceeding max_lambda_nodes (default 10) AST nodes.

# bad
transform = lambda v: v.strip().lower().split(",") if "," in v else [v]

# good
def transform(v):
    return v.strip().lower().split(",") if "," in v else [v]

SCR009 — Too many local variables

Flags functions assigning more than max_local_variables (default 30) distinct names — every new name is cognitive load and a chance for shadowing. The count covers plain x = ... assignment targets only (ast.Assign with ast.Name targets); augmented and unpacked assignments are not counted. Assignments inside nested functions count toward the enclosing function's total. Fix: extract groups of assignments into helpers.

SCR010 — Class too large

Flags classes whose line span exceeds max_class_lines (default 200). A class past ~200 lines is usually several classes; fix by splitting by responsibility.

SCR011 — File too large

Flags files exceeding max_file_lines (default 1000). Fix: split into modules with single concerns.

SCR012 — Function too long

Flags functions whose line span exceeds max_function_lines (default 300). Fix: extract helpers — process_order becomes validate, reserve, and send.

SCR013 — Nesting too deep

Flags maximum nesting depth of block nodes above max_nesting (default 5). Depth counts if, for, while, async for, with, async with, try, and match only. Comprehensions, lambdas, and nested defs do not add depth; sibling blocks do not stack — the metric is maximum depth, not block count.

# bad — 5 deep
with open(path) as f:               # 1
    for row in f:                   # 2
        if row.startswith("#"):     # 3
            try:                    # 4
                parse(row)          # 5

# good — early-return guards flatten it
def line_ready(row):
    if not row:
        return False
    if row.startswith("#"):
        return False
    return True

with open(path) as f:
    for row in f:
        if line_ready(row):
            parse(row)

SCR014 — Too many parameters

Flags functions with more than max_parameters (default 5) positional or keyword parameters. The count is node.args.args, so *args and **kwargs are excluded; self on methods counts as a parameter.

# bad
def connect(host, port, user, password, db, timeout):
    ...

# good
@dataclass
class Connection:
    host: str
    port: int
    user: str
    password: str
    db: str

def connect(cfg: Connection, timeout: int) -> None: ...

SCR015 — Nested function definition

Flags a function defined inside another function. Closures that capture their enclosing scope run once per outer call and defeat unit testing. Only plain def definitions are flagged; a nested async def is not.

# bad
def process_all(data):
    def normalize(value):
        return value.strip().lower()
    return [normalize(x) for x in data]

# good
def normalize(value):
    return value.strip().lower()

def process_all(data):
    return [normalize(x) for x in data]

SCR016 — Too many return statements

Flags functions with more than max_return_statements (default 6) returns — every exit point is a path to maintain. Returns inside nested functions count toward the enclosing function's total.

SCR017 — Mutable default argument

Flags default parameter values that are mutable — list/dict/set literals ([], {}, {1, 2}) or mutable constructor calls (list(), dict(), set(), bytearray(), defaultdict(), OrderedDict()). Defaults are evaluated once at definition time, so the same object is shared across every call that omits the argument — state leaks between unrelated calls.

# bad
def add_item(item, items=[]):
    items.append(item)
    return items

# good
def add_item(item, items=None):
    if items is None:
        items = []
    items.append(item)
    return items

The rule inspects only the function's own defaults — a mutable default on a nested function is reported once, by that function's own finding, never duplicated in the enclosing function's report. Immutable defaults (None, strings, numbers, tuples, frozenset()) are never flagged.

Function / Class too complex — cyclomatic complexity

Flags functions and classes whose McCabe cyclomatic complexity exceeds max_complexity (default 40). Base 1, then +1 for every if, for, async for, while, try, except handler, match, ternary, assert, with, async with, and every and/or chain — an and/or chain counts 1 regardless of how many operands it combines, so a and (b or c) adds 2 (one per chain). The walk covers the whole subtree: a class's complexity is the sum over its entire body, methods included.

---

How it works

The codebase is deliberately small: a CLI orchestrator, four pipeline modules, two config modules, and one rule per file. The governing rule is that cli.py only orchestrates — every function it calls lives in another module, and nothing imports cli.py.

Execution flow — this is the full path of a run (--docs and --version short-circuit before configuration):

flowchart TD
    M["avouch.cli:main()"] --> P["argparse<br/>--json · --quiet · --verbose · --ignore-path ·<br/>--changed · --staged · --all-files · --not-git"]
    P --> PD{"--docs?"}
    PD -- "yes" --> D["utility/docs.py<br/>render_docs()"]
    D --> X0["exit 0"]
    PD -- "no" --> C["config/loader.py<br/>load_config(): avouch.toml merged over defaults"]
    C --> G{"Git repository?"}
    G -- "no · without --not-git" --> EX2A["exit 2<br/>error: no Git repository found"]
    G -- "yes, or --not-git" --> S{"Selection mode"}
    S -- "--not-git" --> F4["git.py: get_all_files_on_disk()<br/>*.py walked from CWD"]
    S -- "--all-files" --> F3["git.py: get_all_files()<br/>git ls-files"]
    S -- "--staged" --> F2["git.py: get_staged_files()<br/>git diff --cached --name-only"]
    S -- "default" --> F1["git.py: get_changed_files()<br/>git diff HEAD --name-only + untracked"]
    F1 --> R["git.py: get_reviewable_files()<br/>existing .py · not generated · not ignored"]
    F2 --> R
    F3 --> R
    F4 --> R
    R -- "none left" --> EX2B["exit 2<br/>error: nothing to review"]
    R -- "files" --> A["analyzer.py: analyze_file()<br/>read file → ast.parse → walk cache → rules"]
    A --> O{"Output mode"}
    O -- "--json" --> J["report.py: render_json()"]
    O -- "--quiet" --> Q["no report"]
    O -- "default + --changed" --> DIF["report.py: render_diff_view()<br/>git diff of the review set"]
    O -- "default" --> H["report.py: generate_report()<br/>terminal report"]
    J --> E{"Any findings?"}
    Q --> E
    DIF --> E
    H --> E
    E -- "no" --> EX0["exit 0"]
    E -- "yes" --> EX1["exit 1"]

Module dependencies — what imports what (each arrow is a real import):

flowchart LR
    CLI["cli.py<br/>orchestration only"] -->|load_config, DEFAULT_RULES| CFG["config/loader.py"]
    CLI -->|DEFAULT_LIMITS| DEF["config/default.py"]
    CLI -->|review-set computation| GIT["git.py"]
    CLI -->|analyze_file| AN["analyzer.py"]
    CLI -->|render_json · render_diff_view<br/>generate_report · vlog| REP["report.py"]
    CLI -->|render_docs| DOC["utility/docs.py"]
    CFG --> DEF
    AN --> RULES["rules/*.py<br/>one analyze(node, limits) per rule"]
    AN --> COM["rules/complexity.py<br/>calculate_complexity"]
    RULES -->|walk| WAL["utility/walk.py<br/>cached ast.walk, reset per file"]
    GIT --> IG["utility/is_generated.py"]
    GIT --> II["utility/is_ignored.py"]
    REP -->|get_file_diff| GIT

Module	Role	Key exports
cli.py	Pipeline wiring	main()
docs.py (in utility/)	Built-in --docs text	DOCS
git.py	Git interaction	is_gitrepo, get_changed_files, get_staged_files, get_reviewable_files
analyzer.py	AST analysis	read_file, analyze_file
rules/*.py	One rule per module	analyze(node, limits)
utility/walk.py	Cached AST traversal	walk, reset_walk_cache
report.py	Terminal + JSON rendering	render_report, generate_report, render_json
config/default.py	Default limits	DEFAULT_LIMITS
config/loader.py	TOML load + merge	load_config, merge_limits, merge_rules, DEFAULT_RULES

Pipeline

1. cli.main() loads config (limits + rules merged over defaults).
2. git.is_gitrepo() — git rev-parse --is-inside-work-tree; exits the run with a message if not a repo.
3. git.get_changed_files() — git diff HEAD --name-only plus untracked files; git.get_staged_files() — git diff --cached --name-only — is used with --staged; get_reviewable_files() keeps existing .py paths that are neither generated (is_generated) nor covered by ignore paths (is_ignored); if none remain, prints a message and exits 2.
4. Per file, analyzer.analyze_file(path, limits, rules):
   • reads UTF-8 (OSError → ERROR report), parses with ast.parse (SyntaxError → ERROR report; the rest of the run continues),
   • resets the walk cache (utility/walk.py), then walks the AST, dispatching FunctionDef, AsyncFunctionDef, and ClassDef nodes to their rules (rule toggles are checked before dispatch, so disabled rules never run),
   • returns (function_reports, file_reports, class_reports).
5. report.render_report(...) groups issues by file in a single pass and renders the AVOUCH header, per-file findings, the BY RULE summary, and the [PASSING] grid.

cli.py with --docs short-circuits before config loading and calls docs.render_docs(), so no Git or analysis code runs. In a TTY that renders an interactive browser over docs.DOCS; piped stdout prints the plain text.

Reporting details

Terminal rendering is hand-rolled ANSI in src/avouch/report.py — the rich dependency declared in pyproject.toml is not imported. Colors are emitted only when stdout is a TTY; piped output is plain. Each finding renders compiler-style: a file:line header with rule id and message, the offending code region with dimmed line numbers, and a caret under the flagged name. Identical (component, rule) findings are deduplicated per file, and the BY RULE summary counts deduplicated findings, sorted most common first. The [PASSING] grid collapses to at most a few lines, with a [+N more] note when it overflows. AVOUCH_FONT=name is an opt-in OSC 50 font switch honored only by capable terminals.

---

Repository layout

avouch/
├── pyproject.toml          # packaging, console script
├── avouch.toml              # limits this repo lives by
├── src/avouch/
│   ├── cli.py              # entry point; orchestration only
│   ├── git.py              # review-set computation
│   ├── analyzer.py         # AST walk, rule dispatch
│   ├── report.py           # terminal report UI
│   ├── rules/              # one module per rule
│   │   ├── complexity.py           # cyclomatic metric (no issues itself)
│   │   ├── max_nesting.py          # get_depth + BLOCK_NODES
│   │   └── ...                     # one analyze(node, limits) per rule
│   ├── utility/
│   │   ├── walk.py         # cached ast.walk + per-file cache reset
│   │   ├── docs.py         # --docs terminal documentation text
│   │   ├── is_generated.py # generated-file patterns
│   │   └── is_ignored.py   # ignore-path matching
│   └── config/
│       ├── default.py      # DEFAULT_LIMITS
│       └── loader.py       # load_config, merge_limits, merge_rules
└── tests/
    └── test_git.py         # 74 tests, incl. a real-git end-to-end run

---

Adding a rule

A rule is a module in src/avouch/rules/ exposing analyze(node, limits) -> list[issue], where an issue is:

{"rule": "SCR017", "severity": "WARNING",
 "message": "Description (value/limit). Remediation guidance."}

Plus a [rules] toggle in DEFAULT_RULES (and a limit in DEFAULT_LIMITS if the rule has a threshold). Wire the dispatch into analyze_file with a toggle guard, then write the tests: one for the violation, one for the boundary. The renderer displays any (severity, message) pair it receives, so no report code changes.

---

Testing

All 74 tests run in a fraction of a second — no network, no package installs:

pip install -e .
python -m pytest tests/

Coverage includes the git helpers, config merging, every nesting block type, every complexity decision point, boolean-chain measurement, rule boundaries, analysis failure paths (unreadable/syntax-error files), report output, the --docs flag (asserted to exit cleanly without touching Git, inside or outside a repository), and an end-to-end run against a real temporary git repository — Git itself is not mocked. Mocking is limited to subprocess.run where a real Git isn't needed.

---

Roadmap

The detailed implementation plan for the next release lives in roadmap.md — v0.3.3 ships eight new capabilities under the theme "first run clean, every run relevant" (avouch init, a findings baseline, parallel review, CI-native output formats, rule man pages, a pre-commit hook, and inline diff annotations).

Beyond v0.3.3, informed by documented limitations, ordered by the pain they remove:

0.4 — Configuration hardening

• Validate avouch.toml values with readable errors (today: a malformed file raises)
• Search upward from the working directory for avouch.toml (today: CWD only)

1.0 — CI-grade interface

• Configurable exit codes, so enforcement thresholds can be tuned without changing avouch's review-only default

New rules must survive the philosophy section — the ceiling is raised deliberately, not by accretion.

---

FAQ

Why only changed files? Pre-existing issues are noise. A whole-repo run buries the few findings you introduced under hundreds you didn't. The review set is the diff, so the output is always relevant to the next push.

Why git diff HEAD and not git diff? Plain git diff covers only unstaged changes. HEAD covers staged plus unstaged — the complete set of files about to be pushed — and avouch adds untracked files on top, so brand-new files are never missed.

Why AST instead of regex? Regex cannot count parentheses across lines, measure nesting, or distinguish a definition from a call. The AST answers structural questions exactly for every valid Python file.

What are the exit codes? Avouch returns 0 when the review is clean, 1 when findings are reported, and 2 when Avouch cannot run. It still reviews rather than gates — enforcement stays in whatever calls it — but CI can now react to the outcome directly.

Does it need a network or a daemon? No. Three git subprocess calls and the standard library. Runtime is bounded by the size of your diff, not your repository.

---

Contributing

• Tests before code. A fix that cannot be expressed as a failing test first is not a fix yet.
• Keep the diff small. A change that touches more than two modules needs a justification in the PR description.
• The standard-library runtime is the contract. No new runtime dependencies without a written case that survives the philosophy section.
• The README is the spec. If the behavior changed, the README changes in the same commit.

Setup:

git clone https://github.com/mukundzha/avouch.git
cd avouch
pip install -e .
python -m pytest tests/

---

License

MIT — see LICENSE.