guix, depends: Omit `GUIX_ENVIRONMENT` from `gen_id` calculations #35929

1. 
   hebasto commented at 1:22 PM on August 7, 2026: member

   This PR fixes a performance regression noticed during the review of #35537.

   Since commit 008a3e29c8844c0be4457279f5c27c1bc57401c7 ("guix: split builds into Linux(gui) and macOS/Windows"), each host is built in two containers: one instantiated from manifest_build.scm and the other from the union of manifest_build.scm and manifest_gui.scm. The resulting Guix profiles necessarily differ, and because $(realpath $(GUIX_ENVIRONMENT)) is hashed into every depends package id, the built-package cache is invalidated whenever the profile changes:

   1. All non-GUI packages are built twice per host, as the GUI container cannot reuse the packages just cached by the base container.
   2. All depends are rebuilt when switching to another branch with identical Guix scripts and the depends subdirectory.

   Drop GUIX_ENVIRONMENT from the gen_id inputs. The toolchain remains fully accounted for: the verbose compiler output hashed by gen_id embeds the store paths of the toolchain packages themselves, so any change to the toolchain still invalidates the cache. Given the pinned time-machine commit and the manifests, the only remaining user-provided inputs that can alter the build environment are the ADDITIONAL_GUIX_*_FLAGS, which are now conservatively folded into the ids by passing them to gen_id via the {BUILD,HOST}_ID_SALT variables.

   Related: #34228.

2. guix, depends: Omit `GUIX_ENVIRONMENT` from `gen_id` calculations

   Since commit 008a3e29c8844c0be4457279f5c27c1bc57401c7 ("guix: split
   builds into Linux(gui) and macOS/Windows"), each host is built in two
   containers: one instantiated from `manifest_build.scm` and the other
   from the union of `manifest_build.scm` and `manifest_gui.scm`. The
   resulting Guix profiles necessarily differ, and because
   `$(realpath $(GUIX_ENVIRONMENT))` is hashed into every depends package
   id, the built-package cache is invalidated whenever the profile
   changes:
   1. All non-GUI packages are built twice per host, as the GUI container
      cannot reuse the packages just cached by the base container.
   2. All depends are rebuilt when switching to another branch with
      identical Guix scripts and the depends subdirectory.
   
   Drop `GUIX_ENVIRONMENT` from the `gen_id` inputs. The toolchain remains
   fully accounted for: the verbose compiler output hashed by `gen_id`
   embeds the store paths of the toolchain packages themselves, so any
   change to the toolchain still invalidates the cache. Given the pinned
   time-machine commit and the manifests, the only remaining user-provided
   inputs that can alter the build environment are the
   `ADDITIONAL_GUIX_*_FLAGS`, which are now conservatively folded into the
   ids by passing them to `gen_id` via the `{BUILD,HOST}_ID_SALT`
   variables.

   488f4e1bd8
3. hebasto added the label Build system on Aug 7, 2026
4. 
   DrahtBot commented at 1:22 PM on August 7, 2026: contributor

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   For details see: https://corecheck.dev/bitcoin/bitcoin/pulls/35929.

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5. hebasto added this to the milestone 32.0 on Aug 7, 2026

Milestone
32.0