m06-error-handling
CRITICAL: Use for error handling. Triggers: Result, Option, Error, ?, unwrap, expect, panic, anyhow, thiserror, when to panic vs return Result, custom error, error propagation, 错误处理, Result 用法, 什么时候用 panic
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Install
Works with every agent the skills CLI supports.
npx skills add https://github.com/actionbook/rust-skills --skill m06-error-handling- 01
Install
Run the command in your project. The CLI asks which agents to install for.
- 02
Describe the task
Ask your agent for something this skill covers. It loads m06-error-handling automatically when relevant.
- 03
Review the result
The agent follows the SKILL.md steps, scripts and references bundled with the skill.
SKILL.md
The instructions your agent reads when the skill is triggered.
Error Handling
Layer 1: Language Mechanics
Core Question
Is this failure expected or a bug?
Before choosing error handling strategy:
- Can this fail in normal operation?
- Who should handle this failure?
- What context does the caller need?
Error → Design Question
| Pattern | Don't Just Say | Ask Instead |
|---|---|---|
| unwrap panics | "Use ?" | Is None/Err actually possible here? |
| Type mismatch on ? | "Use anyhow" | Are error types designed correctly? |
| Lost error context | "Add .context()" | What does the caller need to know? |
| Too many error variants | "Use Box<dyn Error>" | Is error granularity right? |
Thinking Prompt
Before handling an error:
-
What kind of failure is this?
- Expected → Result<T, E>
- Absence normal → Option<T>
- Bug/invariant → panic!
- Unrecoverable → panic!
-
Who handles this?
- Caller → propagate with ?
- Current function → match/if-let
- User → friendly error message
- Programmer → panic with message
-
What context is needed?
- Type of error → thiserror variants
- Call chain → anyhow::Context
- Debug info → anyhow or tracing
Trace Up ↑
When error strategy is unclear:
"Should I return Result or Option?"
↑ Ask: Is absence/failure normal or exceptional?
↑ Check: m09-domain (what does domain say?)
↑ Check: domain-* (error handling requirements)
| Situation | Trace To | Question |
|---|---|---|
| Too many unwraps | m09-domain | Is the data model right? |
| Error context design | m13-domain-error | What recovery is needed? |
| Library vs app errors | m11-ecosystem | Who are the consumers? |
Trace Down ↓
From design to implementation:
"Expected failure, library code"
↓ Use: thiserror for typed errors
"Expected failure, application code"
↓ Use: anyhow for ergonomic errors
"Absence is normal (find, get, lookup)"
↓ Use: Option<T>
"Bug or invariant violation"
↓ Use: panic!, assert!, unreachable!
"Need to propagate with context"
↓ Use: .context("what was happening")
Quick Reference
| Pattern | When | Example |
|---|---|---|
Result<T, E> | Recoverable error | fn read() -> Result<String, io::Error> |
Option<T> | Absence is normal | fn find() -> Option<&Item> |
? | Propagate error | let data = file.read()?; |
unwrap() | Dev/test only | config.get("key").unwrap() |
expect() | Invariant holds | env.get("HOME").expect("HOME set") |
panic! | Unrecoverable | panic!("critical failure") |
Library vs Application
| Context | Error Crate | Why |
|---|---|---|
| Library | thiserror | Typed errors for consumers |
| Application | anyhow | Ergonomic error handling |
| Mixed | Both | thiserror at boundaries, anyhow internally |
Decision Flowchart
Is failure expected?
├─ Yes → Is absence the only "failure"?
│ ├─ Yes → Option<T>
│ └─ No → Result<T, E>
│ ├─ Library → thiserror
│ └─ Application → anyhow
└─ No → Is it a bug?
├─ Yes → panic!, assert!
└─ No → Consider if really unrecoverable
Use ? → Need context?
├─ Yes → .context("message")
└─ No → Plain ?
Common Errors
| Error | Cause | Fix |
|---|---|---|
unwrap() panic | Unhandled None/Err | Use ? or match |
| Type mismatch | Different error types | Use anyhow or From |
| Lost context | ? without context | Add .context() |
cannot use ? | Missing Result return | Return Result<(), E> |
Anti-Patterns
| Anti-Pattern | Why Bad | Better |
|---|---|---|
.unwrap() everywhere | Panics in production | .expect("reason") or ? |
| Ignore errors silently | Bugs hidden | Handle or propagate |
panic! for expected errors | Bad UX, no recovery | Result |
| Box<dyn Error> everywhere | Lost type info | thiserror |
Related Skills
| When | See |
|---|---|
| Domain error strategy | m13-domain-error |
| Crate boundaries | m11-ecosystem |
| Type-safe errors | m05-type-driven |
| Mental models | m14-mental-model |
FAQ
What does the m06-error-handling skill do?
CRITICAL: Use for error handling. Triggers: Result, Option, Error, ?, unwrap, expect, panic, anyhow, thiserror, when to panic vs return Result, custom error, error propagation, 错误处理, Result 用法, 什么时候用 panic
How do I install m06-error-handling?
Run npx skills add https://github.com/actionbook/rust-skills --skill m06-error-handling in your project. The skills CLI detects the agents you use and copies the skill into the right folder. For Claude Code you can also place the skill folder at ~/.claude/skills/m06-error-handling/ (personal) or .claude/skills/m06-error-handling/ (project).
Which AI agents can use m06-error-handling?
Any agent that supports the open Agent Skills format (a folder with a SKILL.md file), including Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, Windsurf, Cline, OpenCode and more.
Is m06-error-handling safe to install?
No partner security audit is available yet. Skills can run commands and scripts, so read the SKILL.md and any bundled files before installing.
Who maintains m06-error-handling?
It is published by actionbook in actionbook/rust-skills. It has 3,499 recorded installs.
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