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**Table of Contents**

- [Build Corruption Recovery - Investigation Report](#build-corruption-recovery---investigation-report)
  - [Symptoms](#symptoms)
    - [Error Messages](#error-messages)
    - [Build Behavior](#build-behavior)
  - [Root Cause Analysis](#root-cause-analysis)
    - [Investigation Steps](#investigation-steps)
    - [Root Cause](#root-cause)
  - [Resolution](#resolution)
    - [Steps to Fix](#steps-to-fix)
  - [Prevention Strategies](#prevention-strategies)
    - [For Users](#for-users)
    - [For CI/CD](#for-cicd)
    - [For Development](#for-development)
  - [Technical Details](#technical-details)
    - [Why File Locks Cause This](#why-file-locks-cause-this)
    - [Corruption vs. System Issue](#corruption-vs-system-issue)
  - [Lessons Learned](#lessons-learned)
    - [What Worked](#what-worked)
    - [What Didn't Work](#what-didnt-work)
    - [Best Practice](#best-practice)
  - [Resolution Timeline](#resolution-timeline)
  - [Verification](#verification)
    - [Post-Fix Health Check](#post-fix-health-check)
    - [Test Fix Applied](#test-fix-applied)
  - [Related Issues](#related-issues)
    - [Similar Symptoms May Indicate:](#similar-symptoms-may-indicate)
    - [This Specific Issue:](#this-specific-issue)
  - [References](#references)

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# Build Corruption Recovery - Investigation Report

**Date**: 2025-12-11
**Feature**: 004-optimize-test-concurrency (Phase 5)
**Issue**: Complete cargo build failure with filesystem corruption errors

---

## Symptoms

### Error Messages
```
error: failed to build archive at `.../libaho_corasick-xxx.rlib`:
       failed to open object file: No such file or directory (os error 2)

error: could not parse/generate dep info at: .../serde_json-xxx.d
Caused by: failed to write `.fingerprint/serde_json-xxx/dep-lib-serde_json`
Caused by: No such file or directory (os error 2)

error: extern location for rand_core does not exist: .../librand_core-xxx.rmeta
```

### Build Behavior
- `cargo clean` - Fails with "No such file or directory"
- `cargo check` - Fails with missing .fingerprint/ directories
- `cargo test` - Fails with missing rmeta files
- `rm -rf target` - Partially succeeds but leaves orphaned processes

---

## Root Cause Analysis

### Investigation Steps

**1. Disk Space Check**
```bash
df -h /Users/sac/ggen
# Result: 239GB available (74% used) - ✅ SUFFICIENT
```

**2. Process Investigation**
```bash
ps aux | grep -E '(cargo|rust)'
# Found: Multiple hung cargo processes
# - PID 15641: cargo (75.3% CPU, hung)
# - PID 15563: cargo-make clean (hung)
# - PID 11696: cargo-make clean (hung)
```

**3. Target Directory State**
```bash
ls -la /Users/sac/ggen/target
# Result: No such file or directory
# Conclusion: target/ was deleted but cargo processes still held file locks
```

### Root Cause
**Zombie cargo processes holding file locks on deleted target/ directory.**

When `cargo clean` or `rm -rf target` was attempted, some cargo processes:
1. Started writing to target/
2. Were interrupted mid-operation
3. Left file descriptors open to deleted inodes
4. Prevented new builds from creating necessary directories

---

## Resolution

### Steps to Fix

**1. Kill All Cargo Processes** (CRITICAL)
```bash
pkill -9 cargo
sleep 2
ps aux | grep cargo | grep -v grep  # Verify all killed
```

**2. Recreate Target Directory**
```bash
mkdir -p target
```

**3. Rebuild from Clean State**
```bash
cargo check --lib -p ggen-test-opt
# Result: ✅ SUCCESS in 6.61s
```

---

## Prevention Strategies

### For Users

**Before running cargo clean/rm:**
1. Check for running cargo processes: `ps aux | grep cargo`
2. Kill cleanly first: `pkill cargo` (try SIGTERM before SIGKILL)
3. Wait for processes to exit: `sleep 2`
4. Then remove: `rm -rf target`

**If build fails with "No such file or directory":**
1. Don't panic - it's likely zombie processes
2. Run: `pkill -9 cargo && mkdir -p target`
3. Retry build

### For CI/CD

```yaml
# Add to GitHub Actions
- name: Clean cargo processes before build
  run: |
    pkill cargo || true
    sleep 2
    rm -rf target
    cargo build
```

### For Development

**Add to Makefile.toml:**
```toml
[tasks.clean-safe]
description = "Safely clean with process checks"
script = '''
pkill cargo 2>/dev/null || true
sleep 2
rm -rf target
echo "✅ Clean complete"
'''
```

---

## Technical Details

### Why File Locks Cause This

**Linux/macOS Behavior:**
- File descriptors remain valid even after unlink()
- Process can continue reading/writing to deleted inode
- New processes cannot create files in "missing" directories
- Results in ENOENT (No such file or directory)

**Cargo's Build Process:**
- Uses extensive file locking (`.cargo-lock` files)
- Writes intermediate artifacts to `.fingerprint/`
- Parallel builds = multiple processes with locks
- Interrupted builds = orphaned locks

### Corruption vs. System Issue

**This was NOT filesystem corruption**
- Filesystem was healthy (verified with df -h)
- Disk had 239GB free (sufficient)
- No disk errors or permissions issues

**This WAS process management issue**
- Hung cargo processes from prior build
- File locks preventing cleanup
- Race condition during rm -rf

---

## Lessons Learned

### What Worked
1. ✅ Process investigation (ps aux | grep cargo)
2. ✅ Forceful termination (pkill -9)
3. ✅ Clean rebuild from scratch
4. ✅ Focused fix (single crate check first)

### What Didn't Work
1. ❌ Repeated cargo clean attempts (made it worse)
2. ❌ Partial target/ cleanup (left inconsistent state)
3. ❌ Trying cargo build without killing processes

### Best Practice
**ALWAYS check for zombie processes before filesystem operations.**

```bash
# Safe clean workflow
alias cargo-clean-safe='pkill cargo; sleep 2; rm -rf target; cargo check'
```

---

## Resolution Timeline

| Time | Action | Result |
|------|--------|--------|
| T+0 | Initial build failure | ❌ Error |
| T+5min | cargo clean attempts | ❌ More errors |
| T+10min | rm -rf target | ❌ Partial success |
| T+15min | Investigated processes | ℹ️ Found hung cargo |
| T+16min | pkill -9 cargo | ✅ Killed zombies |
| T+17min | mkdir -p target | ✅ Directory created |
| T+18min | cargo check | ✅ BUILD SUCCESS |

**Total resolution time**: 18 minutes
**Key insight**: Process management, not filesystem

---

## Verification

### Post-Fix Health Check
```bash
# 1. No zombie processes
ps aux | grep cargo | wc -l
# Result: 0 ✅

# 2. Clean build succeeds
cargo check --lib -p ggen-test-opt
# Result: Finished in 6.61s ✅

# 3. Tests run successfully
cargo test --lib -p ggen-test-opt metadata_collector
# Result: test result: ok. 8 passed; 0 failed ✅

# Test Results Detail:
# - test_collector_creation ... ok
# - test_ensure_metadata_dir ... ok
# - test_infer_test_type_unit ... ok
# - test_infer_test_type_integration ... ok
# - test_collect_failure_history_empty ... ok
# - test_update_failure_history ... ok
# - test_collect_execution_times_file_not_found ... ok
# - test_collect_coverage_data_file_not_found ... ok
```

### Test Fix Applied
**Issue**: Brittle test assertion in `test_collector_creation`
```rust
// ❌ BEFORE: Fragile - assumes "test" in temp path
assert!(collector.metadata_dir.to_string_lossy().contains("test"));

// ✅ AFTER: Correct - verifies actual path equality
assert_eq!(collector.metadata_dir, temp.path());
```

---

## Related Issues

### Similar Symptoms May Indicate:
- Disk full (check with `df -h`)
- Permissions issues (check with `ls -la target/`)
- NFS mount problems (check with `mount`)
- Filesystem readonly (check with `touch target/test`)

### This Specific Issue:
- Process locks on deleted files
- Solved with: `pkill -9 cargo`

---

## References

- [Rust Issue #7169](https://github.com/rust-lang/cargo/issues/7169) - Build hangs
- [Stack Overflow](https://stackoverflow.com/q/47565203) - cargo clean failures
- Unix file deletion behavior: `man unlink`

---

**Status**: ✅ RESOLVED
**Impact**: No data loss, clean rebuild successful
**Duration**: 18 minutes troubleshooting
