# issue-11-compiler-len-zero-fix: Fix len_zero Clippy Warning in compiler.rs

## Description
Replace idiomatic `params.len() > 0` with `!params.is_empty()` on compiler.rs line 453 to eliminate the len_zero clippy warning. This single-line transformation preserves exact semantics while following Rust idioms for empty collection checking.

## Architecture Reference
Read architecture.md Section "Component 4: Clippy Warning Fix - compiler.rs len_zero" (lines 294-328) for:
- Exact line location and context (line 453)
- Before/after transformation pattern
- Verification commands for clippy warning elimination

## Interface Contracts
- Implements: Single expression transformation
```rust
// Before: if params.len() > 0 { ... } else { ... }
// After:  if !params.is_empty() { ... } else { ... }
```
- Exports: compiler.rs with len_zero warning eliminated, idiomatic Rust empty check pattern
- Consumes: compiler.rs after dead code removal (issue-02)
- Consumed by: issue-13-final-validation (clippy warnings AC2)

## Isolation Context
- Available: Compiler struct with unused `functions` field removed (issue-02 completed)
- NOT available: Other clippy fixes (sibling issues 05, 06, 07 in same phase)
- Source of truth: architecture.md Component 4 for exact line numbers and patterns

## Files
- **Modify**: `src/compiler.rs` (line 453: replace `params.len() > 0` with `!params.is_empty()`)

## Dependencies
- issue-02-compiler-dead-code-removal (provides: compiler.rs without functions field, avoiding file conflicts)

## Provides
- compiler.rs with len_zero warning eliminated
- Idiomatic Rust empty check pattern

## Acceptance Criteria
- [ ] `cargo clippy --lib -- -D warnings 2>&1 | grep -c 'len_zero'` outputs 0
- [ ] `cargo build --lib 2>&1` exits with code 0 (compilation succeeds)
- [ ] Line 453 contains `!params.is_empty()` instead of `params.len() > 0`

## Testing Strategy

### Test Files
- No new test files (transformation preserves semantics)
- Existing tests: `tests/test_*.rs` verify compiler behavior unchanged

### Test Categories
- **Unit tests**: Existing compiler tests verify register allocation logic
- **Functional tests**: Integration tests confirm function compilation works correctly
- **Edge cases**: Zero-parameter functions (`params.len() == 0` case preserved)

### Run Command
`cargo test --lib -- compiler::tests`

## Verification Commands
- Build: `cargo build --lib 2>&1`
- Clippy: `cargo clippy --lib -- -D warnings 2>&1 | grep len_zero`
- Check: `grep -n "is_empty()" src/compiler.rs | grep -q "453"`
