brew/share/doc/homebrew/Homebrew-0.9.3.md

Homebrew 0.9.3

What is Superenv?

Superenv is an attempt to improve build-reliability and end-build-quality. It is:

• The user’s PATH is ignored. Thus, only tools we authorize can be used during builds¹.
• PATH is reconstructed. For example: /usr/local/Library/$ENV/4.3:/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin.
• /usr/local/Library/$ENV/4.3 (superbin²) contains wrapper-scripts for cc, etc.)
• We unset all build-related ENV variables.
• Build systems now pick their preferred compilers from superbin.
• superbin scripts are smart. They forcibly insert all include-paths and library-paths that Homebrew formulae need to compile, as well as remove flags that break builds.

Rationale & Benefits

Because we are working with a practically virgin environment, we are essentially giving build-systems the kind of environments that the developers are using to build with. This makes them more reliable. By stepping into the toolchain between the build-system and the compiler, we have complete control over the toolchain. We can prevent a good deal of breakage, and it ensures that Homebrew uses the same executables that the compiler sees (and not those bundled with the system).

So:

• We no longer worry about MacPorts/Fink being installed⁰
• We no longer worry about system duplicates⁰
• We override common tools and fix them—we no longer have to do so with workarounds in affected formula, waiting for a fix from Apple.
• Builds are forcibly optimized how we want, and debug info forcibly removed.

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Footnotes

• ⁰: Nearly as much, anyway.
• ¹: Formula can opt-into re-adding the user’s PATH again. Some formulae need this.
• ²: Indeed; this is selected based on Xcode version.