gh-140006: Harden fish prompt against shadowed builtins#150936
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A user function that shadows the `.`/`source` builtin hijacks the activate.fish prompt. fish resolves functions ahead of builtins, so the `echo "exit $status" | .` line that restores the exit status pipes into the user function instead of sourcing. Dot-style directory navigators redefine `.`, which made the prompt list the directory on every command and dropped the exit status handed to the original prompt. Route every builtin the prompt path uses (`source`, `echo`, `printf`, `set_color`, `functions`) through `builtin` so no user function can intercept them. These have all been fish builtins with a stable interface since fish 2.0.0, the version the script already required through `functions --copy`, so the minimum supported fish version does not change.
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The
activate.fishprompt override restores the previous command's exit status withecho "exit $old_status" | .. fish resolves a function ahead of a builtin, so a userfunction .(orfunction source) shadows thesourcebuiltin even inside a pipe. The override then pipesexit $old_statusinto that function instead of sourcing. A dot-style directory navigator that lists the directory turns this into a directory listing on every prompt, and the exit status handed to the original prompt is lost.This routes every builtin the prompt path uses through
builtin:source,echo,printf,set_color, and thefunctionscalls indeactivateand activation.builtinforces builtin resolution, so no user function can intercept them.Compatibility
Every command goes through a builtin present with a stable interface since fish 2.0.0 (May 2013):
printfbecame a builtin in fish 2.0.0 (fish issue Only trigger AppVeyor on code or config changes #611, commitfa090f2).builtin,functions(-c/-e/-q),set_color(hex +normal),echo, andsource -(stdin) all exist in fish 2.0.0 with the interface used here.The script already required fish 2.0.0 through
functions --copy, so the minimum supported fish version does not change. No version check is added.Testing
test_venv.BasicTest.test_fish_activate_shadowed_builtinscreates a venv, shadows./source/echo/printf/set_colorwith functions, renders the prompt, and asserts the exit status is restored and no shadowed function ran. It fails against the current script and passes with this change. Verified on fish 4.1.2 (the reported version) and 4.7.1.