---
title: "Debugging in Ruby—Busting a Year-old Bug in Sprockets"
description: "Sprockets, the Ruby asset packaging system used in Rails’ asset-processing pipeline, had a bug that made assets:precompile fail after a project directory was renamed between runs. The debugging walkthrough reproduces the failure with CodeTriage by clearing caches, compiling assets, moving the project, and compiling again, yielding an error for an outdated absolute path. It then uses bundle open, source inspection, recursive grep, and IRB to examine Sprockets’ dependency cache; the IRB cache lookup does not work because the cache key differs from the cache ID, but the on-disk record exposes an absolute asset path where a relative path is expected. The proposed fix updates loader.rb’s to_load and to_link handling with compress_from_root, and the pull request adds a regression test."
---

# Debugging in Ruby—Busting a Year-old Bug in Sprockets

[Heroku](https://yomu.fyi/company/heroku) · Richard Schneeman · Feb 27, 2019

**Type:** Tutorial

## Summary

Sprockets, the Ruby asset packaging system used in Rails’ asset-processing pipeline, had a bug that made assets:precompile fail after a project directory was renamed between runs. The debugging walkthrough reproduces the failure with CodeTriage by clearing caches, compiling assets, moving the project, and compiling again, yielding an error for an outdated absolute path. It then uses bundle open, source inspection, recursive grep, and IRB to examine Sprockets’ dependency cache; the IRB cache lookup does not work because the cache key differs from the cache ID, but the on-disk record exposes an absolute asset path where a relative path is expected. The proposed fix updates loader.rb’s to\_load and to\_link handling with compress\_from\_root, and the pull request adds a regression test.

## Context

Sprockets’ assets:precompile task failed when the project folder name changed between successive executions. The failure occurred because the cache contained an absolute path to an asset from the previous project directory, a situation that can occur when Heroku builds use unique directory names.

## Approach / What changed

The debugging process reproduces the issue in CodeTriage, opens the Sprockets gem with bundle open, inspects cached records with grep, and examines Ruby behavior with IRB. The fix changes loader.rb’s to\_load and to\_link handling to use compress\_from\_root, forcing relative paths in cached data, and adds a test in the pull request.

## Takeaways

- Changing a project directory between asset precompilation runs exposed an absolute asset path persisted in Sprockets’ cache.
- bundle open provides direct access to a gem’s source, while grep -R can locate a Sprockets cache record by its cache key.
- The fix applies compress\_from\_root to to\_load and to\_link values and includes a test intended to prevent the bug from returning.

**Tags:** [Caching](https://yomu.fyi/topic/caching), [Ruby](https://yomu.fyi/topic/ruby), [Sprockets](https://yomu.fyi/topic/sprockets)

- Source: [Heroku](https://www.heroku.com/blog/debugging-year-old-sprockets-bug)
- Source URL: https://www.heroku.com/blog/debugging-year-old-sprockets-bug
- Ingested by Yomu: 2026-09-09T14:27:05.281Z

[Read original post](https://www.heroku.com/blog/debugging-year-old-sprockets-bug)