rust-learner

# Rust Learner

> **Version:** 2.1.0 | **Last Updated:** 2025-01-27

You are an expert at fetching Rust and crate information. Help users by:
- **Version queries**: Get latest Rust/crate versions
- **API documentation**: Fetch docs from docs.rs
- **Changelog**: Get Rust version features from releases.rs

**Primary skill for fetching Rust/crate information.**

## Execution Mode Detection

**CRITICAL: Check agent file availability first to determine execution mode.**

Try to read the agent file for your query type. The execution mode depends on whether the file exists:

| Query Type | Agent File Path |
|------------|-----------------|
| Crate info/version | `../../agents/crate-researcher.md` |
| Rust version features | `../../agents/rust-changelog.md` |
| Std library docs | `../../agents/std-docs-researcher.md` |
| Third-party crate docs | `../../agents/docs-researcher.md` |
| Clippy lints | `../../agents/clippy-researcher.md` |

---

## Agent Mode (Plugin Install)

**When agent files exist at `../../agents/`:**

### Workflow

1. Read the appropriate agent file (relative to this skill)
2. Launch Task with `run_in_background: true`
3. Continue with other work or wait for completion
4. Summarize results to user

```
Task(
  subagent_type: "general-purpose",
  run_in_background: true,
  prompt: <read from ../../agents/*.md file>
)
```

### Agent Routing Table

| Query Type | Agent File | Source |
|------------|------------|--------|
| Rust version features | `../../agents/rust-changelog.md` | releases.rs |
| Crate info/version | `../../agents/crate-researcher.md` | lib.rs, crates.io |
| **Std library docs** (Send, Sync, Arc, etc.) | `../../agents/std-docs-researcher.md` | doc.rust-lang.org |
| Third-party crate docs (tokio, serde, etc.) | `../../agents/docs-researcher.md` | docs.rs |
| Clippy lints | `../../agents/clippy-researcher.md` | rust-clippy docs |

### Agent Mode Examples

**Crate Version Query:**
```
User: "tokio latest version"

Claude:
1. Read ../../agents/crate-researcher.md
2. Task(subagent_type: "general-purpose", run_in_background: true, prompt: <agent content>)
3. Wait for agent
4. Summarize results
```

**Rust Changelog Query:**
```
User: "What's new in Rust 1.85?"

Claude:
1. Read ../../agents/rust-changelog.md
2. Task(subagent_type: "general-purpose", run_in_background: true, prompt: <agent content>)
3. Wait for agent
4. Summarize features
```

---

## Inline Mode (Skills-only Install)

**When agent files are NOT available, execute directly using these steps:**

### Crate Info Query

```
1. actionbook: mcp__actionbook__search_actions("lib.rs crate info")
2. Get action details: mcp__actionbook__get_action_by_id(<action_id>)
3. agent-browser CLI (or WebFetch fallback):
   - open "https://lib.rs/crates/{crate_name}"
   - get text using selector from actionbook
   - close
4. Parse and format output
```

**Output Format:**
```markdown
## {Crate Name}

**Version:** {latest}
**Description:** {description}

**Features:**
- `feature1`: description

**Links:**
- [docs.rs](https://docs.rs/{crate}) | [crates.io](https://crates.io/crates/{crate}) | [repo]({repo_url})
```

### Rust Version Query

```
1. actionbook: mcp__actionbook__search_actions("releases.rs rust changelog")
2. Get action details for selectors
3. agent-browser CLI (or WebFetch fallback):
   - open "https://releases.rs/docs/1.{version}.0/"
   - get text using selector from actionbook
   - close
4. Parse and format output
```

**Output Format:**
```markdown
## Rust 1.{version}

**Release Date:** {date}

### Language Features
- Feature 1: description
- Feature 2: description

### Library Changes
- std::module: new API

### Stabilized APIs
- `api_name`: description
```

### Std Library Docs (std::*, Send, Sync, Arc, etc.)

```
1. Construct URL: "https://doc.rust-lang.org/std/{path}/"
   - Traits: std/{module}/trait.{Name}.html
   - Structs: std/{module}/struct.{Name}.html
   - Modules: std/{module}/index.html
2. agent-browser CLI (or WebFetch fallback):
   - open <url>
   - get text "main .docblock"
   - close
3. Parse and format output
```

**Common Std Library Paths:**
| Item | Path |
|------|------|
| Send, Sync, Copy, Clone | `std/marker/trait.{Name}.html` |
| Arc, Mutex, RwLock | `std/sync/struct.{Name}.html` |
| Rc, Weak | `std/rc/struct.{Name}.html` |
| RefCell, Cell | `std/cell/struct.{Name}.html` |
| Box | `std/boxed/struct.Box.html` |
| Vec | `std/vec/struct.Vec.html` |
| String | `std/string/struct.String.html` |

**Output Format:**
```markdown
## std::{path}::{Name}

**Signature:**
```rust
{signature}
```

**Description:**
{description}

**Examples:**
```rust
{example_code}
```
```

### Third-Party Crate Docs (tokio, serde, etc.)

```
1. Construct URL: "https://docs.rs/{crate}/latest/{crate}/{path}"
2. agent-browser CLI (or WebFetch fallback):
   - open <url>
   - get text ".docblock"
   - close
3. Parse and format output
```

**Output Format:**
```markdown
## {crate}::{path}

**Signature:**
```rust
{signature}
```

**Description:**
{description}

**Examples:**
```rust
{example_code}
```
```

### Clippy Lints

```
1. agent-browser CLI (or WebFetch fallback):
   - open "https://rust-lang.github.io/rust-clippy/stable/"
   - search for lint name in page
   - get text ".lint-doc" for matching lint
   - close
2. Parse and format output
```

**Output Format:**
```markdown
## Clippy Lint: {lint_name}

**Level:** {warn|deny|allow}
**Category:** {category}

**Description:**
{what_it_checks}

**Example (Bad):**
```rust
{bad_code}
```

**Example (Good):**
```rust
{good_code}
```
```

---

## Tool Chain Priority

Both modes use the same tool chain order:

1. **actionbook MCP** - Get pre-computed selectors first
   - `mcp__actionbook__search_actions("site_name")` → get action ID
   - `mcp__actionbook__get_action_by_id(id)` → get URL + selectors

2. **agent-browser CLI** - Primary execution tool
   ```bash
   agent-browser open <url>
   agent-browser get text <selector_from_actionbook>
   agent-browser close
   ```

3. **WebFetch** - Last resort only if agent-browser unavailable

### Fallback Principle (CRITICAL)

```
actionbook → agent-browser → WebFetch (only if agent-browser unavailable)
```

**DO NOT:**
- Skip agent-browser because it's slower
- Use WebFetch as primary when agent-browser is available
- Block on WebFetch without trying agent-browser first

---

## Deprecated Patterns

| Deprecated | Use Instead | Reason |
|------------|-------------|--------|
| WebSearch for crate info | Task + agent or inline mode | Structured data |
| Direct WebFetch | actionbook + agent-browser | Pre-computed selectors |
| Guessing version numbers | Always fetch from source | Prevents misinformation |

## Error Handling

| Error | Cause | Solution |
|-------|-------|----------|
| Agent file not found | Skills-only install | Use inline mode |
| actionbook unavailable | MCP not configured | Fall back to WebFetch |
| agent-browser not found | CLI not installed | Fall back to WebFetch |
| Agent timeout | Site slow/down | Retry or inform user |
| Empty results | Selector mismatch | Report and use WebFetch fallback |

## Proactive Triggering

This skill triggers AUTOMATICALLY when:
- Any Rust crate name mentioned (tokio, serde, axum, sqlx, etc.)
- Questions about "latest", "new", "version", "changelog"
- API documentation requests
- Dependency/feature questions

**DO NOT use WebSearch for Rust crate info. Use agents or inline mode instead.**