# Root Cause

> glob.py had a usegitignore parameter that did nothing. The function _loadgitignorepatterns() was called, populated a global _gitignorepatterns, but that global was never read.

- Skill: `tools-only/root-cause-12` (Agent Skill, multi-file: 3 files)
- Install (CLI): `npx skillmds@latest add tools-only/root-cause-12`
- Raw SKILL.md: https://api.skillmd.com/api/skills/tools-only/root-cause-12/raw
- Safety review: pending (external: skill-scanner PASS, skillspector PASS)
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: tools-only (https://skillmd.com/u/tools-only)
- Updated: 2026-09-29
- Page: https://skillmd.com/skills/tools-only/root-cause-12

---


## 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:

```bash
# 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)