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Wrapper recursion: why filter Bear's lookup PATH, not the alternatives

docs/rationale/wrapper-recursion-ccache-alternatives.md

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Wrapper recursion: why filter Bear's lookup PATH, not the alternatives

Context

In wrapper mode, a compiler env var or PATH discovery can resolve to a masquerade wrapper (ccache, distcc, icecc, ...) rather than the real compiler. If Bear records that path, the build loops the wrapper into itself. Several fixes were considered before settling on "resolve past the masquerade dir and record the real compiler".

Decision

Filter Bear's own lookup PATH so resolution lands on the real compiler past any masquerade directory, and record that path. Do not touch the child's PATH or set ccache-specific variables.

Consequences

The rejected alternatives were each narrower or more fragile:

  • Set CCACHE_COMPILER in the wrapper's child environment (the original proposal). The path the wrapper knows IS the ccache symlink (that is what which gcc returned at setup), and CCACHE_COMPILER pointing at a symlink-to-ccache makes ccache recurse into itself. Empirically verified on Fedora: CCACHE_COMPILER=/usr/lib64/ccache/gcc ccache gcc -c foo.c hangs and must be killed; CCACHE_COMPILER=/usr/bin/gcc works. Fixing it would require resolving past ccache to get the real path anyway - which is what this requirement does, making CCACHE_COMPILER redundant. It is also ccache-specific and would not help icecc or distcc.
  • CCACHE_PATH set to PATH minus .bear/. ccache-specific (no equivalent for other wrappers), still requires enumerating a safe PATH, and does not address Bear's config pointing at the wrong executable.
  • Removing masquerade directories from the child's PATH. Heavy- handed: a masquerade dir might also hold binaries that do not loop (some installs put distcc itself there); stripping it globally would break those. Filtering Bear's own lookup PATH is the narrower intervention.

References