Merge branch 'v1.3-blog'

devenv/init/.envrc

@@ -1,3 +1,3 @@
-source_url "https://raw.githubusercontent.com/cachix/devenv/95f329d49a8a5289d31e0982652f7058a189bfca/direnvrc" "sha256-d+8cBpDfDBj41inrADaJt+bDWhOktwslgoP5YiGJ1v0="
+source_url "https://raw.githubusercontent.com/cachix/devenv/82c0147677e510b247d8b9165c54f73d32dfd899/direnvrc" "sha256-7u4iDd1nZpxL4tCzmPG0dQgC5V+/44Ba+tHkPob1v2k="
 
-use devenv
+use devenv

docs/blog/posts/devenv-v1.3-instant-developer-environments-with-nix-caching.md

@@ -0,0 +1,97 @@
+---
+draft: false
+date: 2024-10-03
+authors:
+  - sandydoo
+  - domenkozar
+---
+
+# devenv 1.3: Instant developer environments with Nix caching
+
+Hot on the heels of the [previous release of tasks](/blog/2024/09/24/devenv-12-tasks-for-convergent-configuration-with-nix/),
+ we're releasing devenv 1.3! 🎉
+
+This release brings precise caching to Nix evaluation, significantly speeding up developer environments.
+
+Once cached, the results of a Nix eval or build can be recalled in single-digit milliseconds.
+
+If any of the automatically-detected inputs change, the cache is invalidated and the build is performed.
+
+![Caching comparison](/assets/images/caching.gif)
+
+!!!note
+
+     If you run into any issues, run devenv with `--refresh-eval-cache` and report
+     [an issue](https://github.com/cachix/devenv/issues/new?assignees=&labels=bug&projects=&template=bug_report.md&title=).
+
+## How does it work?
+
+Behind the scenes, devenv now parses Nix's internal logs to determine which files and directories were accessed during evaluation.
+
+This approach is very much inspired by [lorri](https://github.com/nix-community/lorri), but doesn't require a daemon running in the background.
+
+The caching process works as follows:
+
+1. During Nix evaluation, devenv parses the Nix logs for any files and directories that are accessed.
+2. For each accessed path, we store:
+   - the full path
+   - a hash of the file contents
+   - the last modification timestamp
+
+This metadata is then saved to a SQLite database for quick retrieval.
+
+When you run a devenv command, we:
+
+1. Check the database for all previously accessed paths
+2. Compare the current file hashes and timestamps to the stored values
+3. If any differences are detected, we invalidate the cache and perform a full re-evaluation
+4. If no differences are found, we use the cached results, significantly speeding up the process
+
+This approach allows us to efficiently detect changes in your project, including:
+
+- Direct modifications to Nix files
+- Changes to imported files or directories
+- Updates to files read using Nix built-ins, like `readFile` or `readDir`
+
+## Comparison with Nix's built-in flake evaluation cache
+
+Nix's built-in flake evaluation caches outputs based on the lock of the inputs,
+ignoring changes to Nix evaluation that often happen during development workflow.
+
+## Comparison with existing tools
+
+Let's take a closer look at how devenv's new caching system compares to other popular tools in the Nix ecosystem.
+Running our own cache gives us more control and visibility over the caching process, and allows us to improve our integration with other tools, like direnv.
+
+### lorri
+
+While lorri pioneered the approach of parsing Nix's internal logs for caching,
+devenv builds on this concept, integrating caching as a built-in feature that works automatically without additional setup.
+
+### direnv and nix-direnv
+
+These tools excel at caching evaluated Nix environments, but have limitations in change detection:
+
+- Manual file watching: Users often need to manually specify which files to watch for changes.
+- Limited scope: They typically can't detect changes in deeply nested imports or files read by Nix built-ins.
+
+To leverage devenv's caching capabilities with direnv, we've updated the `.envrc` file to utilize devenv's new caching logic.
+
+If you currently enjoy the convenience of our direnv integration to reload your development environment, make sure to update your `.envrc` to:
+
+```
+source_url "https://raw.githubusercontent.com/cachix/devenv/82c0147677e510b247d8b9165c54f73d32dfd899/direnvrc" "sha256-7u4iDd1nZpxL4tCzmPG0dQgC5V+/44Ba+tHkPob1v2k="
+
+use devenv
+```
+
+to benefit from the new caching system.
+
+## What's next?
+
+`nix develop` currently remains the last bit that's rather slow and uncacheable, particularly on macOS.
+We're working on bringing its functionality in-house to further bring down the overhead of launching a cached shell to under 100ms.
+
+Join us on [Discord](https://discord.gg/naMgvexb6q) if you have any questions,
+
+Domen & Sander