codeguard-erlang

Erlang Codeguard Gate

Goal: turn "looks fine" into repeatable tool evidence, and honestly distinguish between passed, failed, unverifiable, and planned.

30-Second Start

1. At the repository root, confirm that rebar.config or the target file exists.
2. Probe tools:elvis --version。
3. Read-only check first:elvis rock。
4. Classify results into: code violations, missing configuration, missing tools, tool internal errors.
5. Only perform safe-to-fix items:erlfmt。
6. Re-run lint, and execute the project's existing test/build gates.

You can directly propose:

• "Check this Erlang project, don't modify anything yet, and give me the lint failure classification."
• "Only fix Erlang formatting issues, list semantic issues first."
• "Verify Erlang lint, test, and build evidence before committing."

Capability Boundaries

✅ Good at handling

1. Based on .erl, .hrl and project markers to identify the Erlang workspace.
2. Execute elvis rock and retain exit codes, scope, and tool versions.
3. Distinguish between formatting, static rules, configuration, dependency, and environment failures.
4. Use erlfmt to handle reversible issues and re-scan.
5. Report local results in layers alongside CI/build/test evidence.

⚠️ Requires conditions

1. The target tool must already be installed and its version compatible with the project constraints.
2. Must be executed from the correct repository or module root directory.
3. If the project has custom configuration, the committed configuration takes precedence.
4. Whether generated code, vendor, and cache directories are scanned must follow repository rules.

❌ Not applicable

1. Do not treat formatter passing as compilation, test, or security audit passing.
2. Do not silently install tools, upgrade dependencies, or modify team rules.
3. Do not use suppress/ignore/raising thresholds to mask real problems.
4. Do not claim "checks passed" when tools or configuration are missing.

When to Use

• The user requests checking or fixing Erlang code standards.
• AI has modified .erl, .hrl, and pre-commit verification is needed.
• CI shows failures related to elvis rock .
• Need to determine whether an issue can be fixed automatically or must be handled manually.

When Not to Use

• When the main task is learning language syntax, framework design, or business modeling, use the corresponding language professional skill instead.
• When the main task is dependency vulnerabilities, security auditing, or license governance, use a dedicated security skill.
• When the user only asks to explain a single error and there is no project context, provide a local explanation first and do not claim the entire repository is green.

Data and Security

This skill does not collect, upload, send, or store user code or credentials. By default, it only reads local repository configuration and runs local tools; it does not install dependencies over the network and does not record tokens, passwords, or private source code. Before any automatic fix, check the diff first; destructive or large-scale modifications must be explicitly confirmed by the user.

Execution Contract

Item	Current Fact
Status	stable(Since Codeguard V0.5)
File Extension	.erl, .hrl
Project Marker	rebar.config
Integration Configuration	elvis.config, elvis.config.js
Tool Preparation	rebar3 plugins / escript
Probe Command	使用命令查找与项目配置检查
lint	elvis rock
format/fix	erlfmt
Project-level gate	elvis rock

Standard Workflow

Step 1: Determine the Real Scope

Confirm the repository root, module roots, generated directories, vendor directories, and user-specified files. For multi-module projects, list the modules to be scanned first; do not guess based on the current directory.

Step 2: Read the Project Contract

Read elvis.config, elvis.config.js and the actual commands in CI. Repository configuration takes precedence over this skill's examples; if the two conflict, report the difference first.

Step 3: Probe Tools and Versions

Run 对应工具 --version. Missing tools, incompatible versions, or failure to load configuration are all recorded as "unable to verify", not as passing.

Step 4: Execute Read-only Checks

Run elvis rock, and record the command, working directory, exit code, tool version, and first actionable error.

Step 5: Failure Classification

Type	Typical Signal	Handling
Formatting	Indentation, whitespace, import order	Allow formatter, then check the diff
Static Rules	unused, complexity, naming, dangerous APIs	Minimal semantic fixes, no batch guessing
Configuration	parser/config/schema not found	Fix integration or report preconditions
Environment	command not found, version conflict	Report installation/version requirements, do not install silently
Internal Tool Error	crash, timeout, parser exception	Preserve raw evidence, narrow the reproduction scope

Step 6: Controlled Fixes

Prefer running erlfmt. Only handle issues that are certain and reversible; dependency upgrades, rule exemptions, generated files, and business semantic changes must be explained separately.

Step 7: Verification Loop

Re-run the same lint command, then run the project's existing tests and build. Only write "pass" when the command, scope, and exit code are all clear; otherwise write "not run" or "unable to verify".

Rules

1. Re-verify with the Same Command: After fixing, you must re-run the original command that triggered the failure.
2. Layered Evidence: Report lint, format, compile, test, and security separately.
3. Minimal Changes: Do not refactor along the way, and do not expand style fixes into business rewrites.
4. Configuration First: Do not override the project's existing ignore, dialect, target, or version constraints.
5. No Fabrication: Tools not run, configurations not seen, and platforms not verified must be clearly marked.

Output Template

Erlang Codeguard 结果
- 范围：<仓库/模块/文件>
- 工具：<名称与版本>
- 命令：<实际命令>
- 状态：PASS / FAIL / UNVERIFIED / PLANNED
- 发现：<按格式/规则/配置/环境分类>
- 修改：<文件与原因；无修改写 none>
- 复验：<命令、退出码>
- 未验证：<测试/构建/平台差异>

Gotchas

1. Missing tools are not a pass — must output UNVERIFIED and a clear preparation method.
2. formatter is not a linter — all-green formatting cannot cover static rules or compilation errors.
3. The root directory determines the result — Running in the wrong module may miss detection or load the wrong configuration.
4. Placeholders are not literal arguments — {file} must be replaced with real, authorized paths.
5. Automatic fixes may enlarge the diff — After fixing, review the diff first, then run the regression gate.
6. Generated and vendor directories require an explicit policy — Do not casually scan or modify third-party content across the whole repository.

Domain pitfalls and fixes

1. Domain pitfalls — Elvis and erlfmt depend on the rebar project context; the OTP version also changes the available syntax.

When information is insufficient

Do not just say "please provide more information". First give a safe read-only inspection plan, and list the specific items that still need to be confirmed:

1. Repository/module root directory;
2. Target tools and versions;
3. Project configuration files;
4. Authoritative commands in CI;
5. Whether automatic fixes are allowed.

FAQ

Q1: If the tool is not installed, can we conclude the code is fine? No. The status must be UNVERIFIED。

Q2: Can ignore or suppression be added automatically? No. Exemptions may only be granted when the user explicitly accepts them and the reason is recorded.

Q3: Why does it still fail after formatting? The formatter only covers formatting; static rules, configuration, compilation, and tests still need to be handled separately.

Q4: Should generated code be scanned? By default, follow the repository configuration; when there are no rules, exclude generated/vendor code first, then explain to the user.

Q5: How can too many changes at once be avoided? Fix in batches by failure category and file first, and rerun the original command and review the diff for each batch.

Q6: If it passes locally, can we say CI will pass? No. The CI's versions, environment variables, operating system, and command scope still need to be aligned.

Load resources on demand

• When encountering exit codes, failure classification, or exemption decisions, read references/rules/gate-rules.md。
• When you need to check this language's registry, toolchain, and project configuration, read references/tooling/toolchain.md。
• When you need copyable task examples, read by scenario examples/, and there is no need to load all of them at once.