Update go version on cd (OSX, bash@3, zsh, gimme)

.zshrc

gimme_after_cd() {
    debug_log() {
        test "$DEBUG" = "1" && echo "[debug] $1"
    }

    find_go_mod() {
        dir=$PWD
        while [ "$dir" != "/" ]; do
            if [ -f "$dir/go.mod" ]; then
                echo "$dir/go.mod"
                return
            else
                dir=$(dirname "$dir") 
            fi
        done

        echo
    }

    resolve_version() {
        version="$1"
        if [[ "$version" =~ ^[0-9]+(\.[0-9]+)?$ ]]; then
            major=$(echo "$version" | cut -d '.' -f 1)
            minor=$(echo "$version" | cut -d '.' -f 2);minor=${minor:=x}
            patch=$(echo "$version" | cut -d '.' -f 3);patch=${patch:=x}
            version="$major.$minor.$patch"
        fi
        gimme --resolve "$version" | head -1
    }

    debug_log "checking for gimme"
    if command -v gimme >/dev/null; then
        debug_log "gimme found!"
    else
        echo "[error] Please install gimme to install go versions (see https://github.com/travis-ci/gimme#installation--usage)"
        return
    fi

    debug_log "searching for go.mod"
    GO_MOD_FILE=$(find_go_mod)
    if [ -n "$GO_MOD_FILE" ]; then
        debug_log "go.mod found: $GO_MOD_FILE"
        FOUND=$(sed -En 's/^go[[:space:]]+([[:digit:].]+)$/\1/p' $GO_MOD_FILE)
        WANT=$(resolve_version "$FOUND")
        debug_log "extracted go version: $FOUND ($WANT)"
    else
        debug_log "go.mod not found"
        WANT=$(resolve_version stable)
        debug_log "defaulting to stable ($WANT)"
    fi
    
    debug_log "checking current go version"
    if command -v go >/dev/null; then
        GOT=$(resolve_version $(go version | cut -d " " -f 3 | cut -c 3-))
        debug_log "go version is $GOT"
    else
        debug_log "go not found"
        GOT="none"
    fi

    if [ "$WANT" = "$GOT" ]; then
        debug_log "versions match; nothing to do"
    else
        debug_log "updating to go $WANT from $GOT"
        echo -n "Using " && eval "$(gimme $WANT)"
    fi
}

gimme_after_cd
add-zsh-hook chpwd gimme_after_cd