Module brew_emulate 

Brew-emulate fallback: build a homebrew-core formula with real Homebrew installed at the keg prefix, for the macOS long tail the generic crate::source_build recipe runner cannot reproduce.

When this runs

crate::source_build::ensure_from_source handles the homebrew-core C-tool population with a generic autotools/CMake/Makefile runner. Some formulae have custom .rb install do logic (compile a single file by hand, run a bespoke install.sh, cargo install / go build, apply patches, …) that a generic build-system detector cannot reproduce — for those the generic runner either fails detection (no configure/CMakeLists.txt/Makefile) or errors mid-build. This module is the fallback: it runs the formula’s actual Homebrew install recipe, so whatever custom logic the formula carries is executed faithfully.

Why install Homebrew AT the keg prefix

The keg must be self-contained and relocation-free — no @@HOMEBREW@@ placeholders in any binary’s load commands (those abort under a darwin Seatbelt container, see crate::source_build module docs). Two properties get us there:

1. A non-default prefix forces build-from-source. We additionally pass --build-from-source, so Homebrew compiles the named formula instead of pouring a relocatable bottle (a poured bottle is exactly where the @@HOMEBREW@@ install-name placeholders come from). A compiled binary bakes the absolute prefix path into its LC_LOAD_DYLIB / rpath load commands.
2. The prefix lives inside the keg, permanently. We clone Homebrew into <keg>/brew and point HOMEBREW_PREFIX/HOMEBREW_CELLAR/ HOMEBREW_REPOSITORY there, so those baked-in absolute paths (<keg>/brew/opt/<dep>/lib/...) remain valid for the life of the keg — no post-install relocation, ever.

The resulting keg has the standard layout the resolver expects (a bin of the installed formula’s executables, reached via the Homebrew prefix’s opt/<formula>/bin + bin symlink dirs) plus a KegManifest.

Functions

ensure_via_brew

Build formula into a self-contained keg by running its real Homebrew install recipe at a keg-rooted prefix, returning the keg path.