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`~/.vite-plus/env` costs 85-315 ms per shell start on long PATHs (super-linear `${var#*pattern}` in the dedupe loop)

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Since Oct 6, 2026.

  • #2905 by @jonatankruszewski — open

Assessment

Difficulty
2/5
Estimated time
1-3 hours
Newbie friendliness
82/100
Issue type
Bug
Clarity
Clearly specified
Activity status
Active
Tech stack
bash, rust, shell, zsh
Domain
cli, developer-experience, performance, tooling

Research direction

The POSIX env template is ENV_TEMPLATE_POSIX in crates/vp_global_cli/src/commands/env/setup.rs. Replace the ${__vp_tmp#*":${__vp_dir}:"} dedupe loop with the IFS-split rebuild given in the issue so PATH stays linear on zsh, bash, and dash. Slot the rewrite into the existing snapshot runner from #2494 (sh, bash, zsh) and confirm the emitted ~/.vite-plus/env still produces the same PATH.

Written by the indexing model from the issue text.

Description

contribution welcome

Summary

The PATH dedupe loop in the POSIX env script (ENV_TEMPLATE_POSIX in crates/vp_global_cli/src/commands/env/setup.rs, introduced by #2494, shipped as ~/.vite-plus/env) runs

__vp_after="${__vp_tmp#*":${__vp_dir}:"}"

once per occurrence of each vp dir in PATH. ${var#*X} (shortest-prefix removal with a leading *) is super-linear in the offset of X on every POSIX shell I tested. With a PATH of ~8 KB (147 entries, which is what mise activate produces for a user with ~110 globally installed tools) each expansion takes 50-260 ms depending on the shell, and the loop runs twice (bin and fallback-bin).

Because the installer puts . "$HOME/.vite-plus/env" into ~/.zshenv, this is paid by every zsh process on the machine, interactive or not: zsh -c true goes from 0 ms to 180 ms. Every #!/usr/bin/env zsh script, every zsh -c from a tool, every IDE env probe pays it.

Environment: vp v1.0.0, macOS 26 arm64, zsh 5.9 (/bin/zsh) and 5.9.2 (brew), bash 5.3.15 and 3.2, dash.

Repro (zsh, 3 lines)

PATH="$(printf '/Users/me/.local/share/mise/installs/tool-%03d/latest/bin:' {1..140})/x/bin"; tmp=":${PATH}:"; d=/x/bin
typeset -F3 SECONDS=0; a="${tmp#*":${d}:"}";  print "#*  : ${SECONDS}s"
SECONDS=0;              b="${tmp%%":${d}:"*}"; print "%%* : ${SECONDS}s"

#*  : 0.109s
%%* : 0.000s

Measurements

Single ${tmp#*":${dir}:"} on an 8.7 KB PATH, target dir last:

shell #* (shipped) %%
zsh 5.9 147 ms 5 ms
zsh 5.9.2 146 ms 5 ms
bash 5.3.15 63 ms 14 ms
bash 3.2 53 ms 13 ms
dash 264 ms 4 ms

Cost of sourcing the whole env file in zsh -f as PATH grows (vp dirs present, so the loop runs):

PATH entries chars time
20 1353 4 ms
40 2653 13 ms
80 5253 51 ms
147 9656 172 ms
300 19754 720 ms

Whole env file from the real 147-entry PATH, median of 5:

file zsh 5.9 zsh 5.9.2 bash 5.3 bash 3.2 dash
shipped ~/.vite-plus/env 177 178 85 83 315
literal-prefix one-liner (see below) 6 6 128 133 147
IFS-split loop (proposed) 6 6 9 13 5

Proposed fix

A literal-prefix strip (__vp_after="${__vp_tmp#"${__vp_before}:${__vp_dir}:"}") fixes zsh but makes bash and dash slower (table above). Splitting PATH on : once and rebuilding it is linear on every shell and produced an identical PATH to the current script in /bin/sh, dash, bash 3.2, bash 5.3 and zsh for a PATH containing both vp dirs, one of them twice:

__vp_bin="$HOME/.vite-plus/bin"
__vp_fallback="$HOME/.vite-plus/fallback-bin"
__vp_new=
__vp_ifs=$IFS
IFS=:
if [ -n "${ZSH_VERSION-}" ]; then setopt localoptions shwordsplit noglob; else set -f; fi
for __vp_p in $PATH; do
  case "$__vp_p" in "$__vp_bin"|"$__vp_fallback") ;; *) __vp_new="${__vp_new:+${__vp_new}:}${__vp_p}" ;; esac
done
IFS=$__vp_ifs
[ -n "${ZSH_VERSION-}" ] || set +f
PATH="${__vp_bin}${__vp_new:+:${__vp_new}}:${__vp_fallback}"
export PATH
unset __vp_bin __vp_fallback __vp_new __vp_ifs __vp_p

The snapshot runner from #2494 already exercises the file in sh, bash and zsh, so the rewrite can slot into the same tests.

Who hits this

Anyone whose PATH is long when a nested shell starts: mise/asdf/nix users with many tools, monorepo devs with per-package bin dirs, CI images. A fresh login shell with a 30-entry PATH pays ~4 ms, which is why it is easy to miss.

Dominant language
Rust
Stars
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Forks
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Avg merge
1d 15h
Merged PRs (30d)
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