Pure bash implementation seems to be fast enough too?

[roxma]

#!/bin/bash
PROMPT_COMMAND=envrc_prompt_command

function envrc_find() {
    local d="$PWD"

    while :
    do
        if [ -f "$d/.envrc" ]
        then
            echo "$d/.envrc"
        fi

        if [ "$d" == "/" -o "$d" == "." ]
        then
            return
        fi

        d="$(exec dirname "$d")"
    done
}

function envrc_prompt_command() {
    local rc_found="$(envrc_find)"

    if [ "$rc_found" == "$ENVRC_LOAD" ]
    then
        if [ -n "$ENVRC_LOAD" -a -z "$ENVRC_LOADED" -a "$ENVRC_PPID" == "$PPID" ]
        then
            ENVRC_LOADED=1
            . "$ENVRC_LOAD"
        elif [ -n "$ENVRC_LOAD" -a "$ENVRC_PPID" != "$PPID" ]
        then
            unset ENVRC_LOAD
            unset ENVRC_LOADED
            unset ENVRC_PPID
            unset ENVRC_TMP
            envrc_prompt_command
        fi
        return
    fi

    if [ "$ENVRC_LOAD" == "" ]
    then
        local tmp="$(mktemp --suffix=_envrc)"
        if [ -z "$tmp" ]
        then
            return
        fi
        echo "exit 0" > "$tmp"

        echo "envrc: spawn for [$rc_found]"
        ENVRC_TMP="$tmp" ENVRC_LOAD="$rc_found" ENVRC_PPID=$$ $BASH
        eval "$(cat "$tmp"; rm "$tmp")"
        envrc_prompt_command
    else
        echo "cd '$PWD'
        export OLDPWD='$OLDPWD'" > $ENVRC_TMP
        echo "envrc: exit [$ENVRC_LOAD]"
        exit 0
    fi
}

$ time envrc_prompt_command 

real    0m0.010s
user    0m0.000s
sys     0m0.000s

Most of the time is spent on bash's forking child processes and sub shells. The directory gets deeper, it takes longer. When the directory gets deep enough, the time lag starts to get annoying.

The rust implementation always takes about 0.002 seconds (overhead of system exec-fork).

[pjeby]

Just an FYI, but you could make the execution time constant by replacing the use of dirname with a bash one-liner cribbed from realpaths:

dirname() { REPLY=.; ! [[ $1 =~ /+[^/]+/*$ ]] || REPLY="${1%${BASH_REMATCH[0]}}"; REPLY=${REPLY:-/}; }

It functions identically to single-argument dirname but returns the result in the REPLY variable and does no fork-and-exec. (For that matter, inlining envrc_find would drop another such fork-and-exec.)