Root Cause

Problem

glob.py had a use_gitignore parameter that did nothing. The function _load_gitignore_patterns() was called, populated a global _gitignore_patterns, but that global was never read. The actual filtering used DEFAULT_EXCLUDE_DIRS instead.

Static analysis tools (Vulture) reported "no dead code" because the function WAS called and the variable WAS assigned.

Root Cause

Syntactic vs semantic dead code. Static analyzers check "is this symbol referenced?" not "is the result consumed?"

The code path was:

use_gitignore=True
  -> _load_gitignore_patterns() called
    -> _gitignore_patterns populated
      -> NEVER READ ANYWHERE

All 7 references to _gitignore_patterns were writes, zero reads.

Why It Matters

1. Wasted I/O - Reading .gitignore files on every glob call for nothing
2. API lie - use_gitignore parameter implied functionality that didn't exist
3. Global state pollution - Module-level mutable state with no consumer
4. Race condition - Cache init had check-then-act bug (moot since never used)

Detection Method

Static analysis fails. Manual review required:

# Find all references
grep -n "_gitignore_patterns" src/tunacode/tools/glob.py

# Check for READS (not just assignments)
# Writes: =, .add(), .update()
# Reads: in, if X, for x in X, return X, func(X)

If all references are writes, it's dead.

Prevention

Before shipping code that "loads X":

1. Grep for reads of X - Not just references, actual consumption
2. Trace parameter data flow - If use_foo controls behavior, prove it changes output
3. Question unused returns - If a function populates state but nothing reads it, why?

The Fix

Removed 37 lines:

• _gitignore_patterns global
• _load_gitignore_patterns() function
• use_gitignore parameter
• The call site

Also fixed deprecated asyncio.get_event_loop() -> asyncio.to_thread().

Related

• memory-bank/research/2026-01-14_12-27-29_glob-tool-bottlenecks.md - Original research
• .claude/skills/dead-code-detector/ - Vulture-based detection (syntactic only)