# issue-12-lexer-vm-clippy-fixes: Fix Clippy Warnings in lexer.rs and vm.rs

## Description
Eliminate redundant_pattern_matching clippy warning in lexer.rs by replacing `if let Err(_) = ` with `.is_err()` idiom, and clone_on_copy warning in vm.rs by removing unnecessary `.clone()` on Copy type Value. These idiomatic transformations improve code clarity without changing behavior.

## Architecture Reference
Read `/Users/santoshkumarradha/Documents/agentfield/code/int-agentfield-examples/af-swe/example-pyrust/.artifacts/plan/architecture.md` Section "Component 5: Clippy Warning Fixes - lexer.rs and vm.rs" for:
- Pre-verification check confirming Value derives Copy trait
- Exact line numbers and transformation patterns
- Fallback strategy if Copy trait assumption is invalid

## Interface Contracts
- **Implements**:
  ```rust
  // lexer.rs line 131 transformation
  // Before: if let Err(_) = text.parse::<i64>()
  // After:  if text.parse::<i64>().is_err()

  // vm.rs line 483 transformation
  // Before: Ok(self.result.clone())
  // After:  Ok(self.result)  // Value is Copy
  ```
- **Exports**: Idiomatic Rust error checking and Copy type handling patterns
- **Consumes**: Clean vm.rs from issue-03-vm-dead-code-removal (no file conflicts)
- **Consumed by**: issue-14-final-validation (verifies AC2 clippy requirements)

## Isolation Context
- **Available**: vm.rs with body_len and clear_register_valid removed (issue-03)
- **NOT available**: Code from sibling Phase 2 issues (issue-04)
- **Source of truth**: Architecture document Component 5 for transformation rules

## Files
- **Modify**: `src/lexer.rs` (line 131: error checking pattern)
- **Modify**: `src/vm.rs` (line 483: remove .clone() on Copy type)

## Dependencies
- issue-03-vm-dead-code-removal (both modify vm.rs, must avoid conflict)

## Provides
- lexer.rs with redundant_pattern_matching warning eliminated
- vm.rs with clone_on_copy warning eliminated
- Idiomatic error checking and Copy type handling

## Acceptance Criteria
- [ ] `cargo clippy --lib -- -D warnings 2>&1 | grep -c 'redundant_pattern_matching'` outputs 0
- [ ] `cargo clippy --lib -- -D warnings 2>&1 | grep -c 'clone_on_copy'` outputs 0
- [ ] `cargo build --lib 2>&1` exits with code 0 (compilation succeeds)
- [ ] `grep -E '(derive|impl).*Copy' src/value.rs` confirms Value is Copy

## Testing Strategy

### Test Files
- `tests/*.rs`: Integration tests verify no behavioral changes
- Unit tests embedded in lexer.rs and vm.rs remain passing

### Test Categories
- **Pre-verification**: Grep check confirms Value enum derives Copy trait (line 14 of value.rs)
- **Functional tests**: `cargo test --lib` verifies lexer integer parsing and VM result handling unchanged
- **Clippy validation**: `cargo clippy --lib -- -D warnings` confirms both warnings eliminated

### Run Command
```bash
# Pre-check Value is Copy
grep -E '(derive|impl).*Copy' src/value.rs

# Apply transformations, then validate
cargo clippy --lib -- -D warnings 2>&1 | grep -E '(redundant_pattern_matching|clone_on_copy)'
cargo build --lib && cargo test --lib
```

## Verification Commands
- Build: `cargo build --lib 2>&1 && echo "SUCCESS" || echo "FAILED"`
- Test: `cargo test --lib 2>&1 | grep "test result:"`
- Check: `cargo clippy --lib -- -D warnings 2>&1 && echo "AC2: PASS" || echo "AC2: FAIL"`
