Why does git difftool return "cannot run git-difftool--helper" error?

Question

git difftool stopped working and I have no idea why.

# git difftool --tool=vimdiff
error: cannot run git-difftool--helper: No such file or directory
fatal: external diff died, stopping at  ...

vimdiff is installed on /bin/vimdiff and working correctly.

# vimdiff --version
VIM - Vi IMproved 7.4 (2013 Aug 10, compiled Aug  9 2019 03:17:15)

• The same problem happens when replacing the --tool to something other than vimdiff.
• It happens on any repo on that machine, so it's not a repo specific problem.
• Tried to reinstall git by yum reinstall git222-core.x86_64. The reininstall succeeded but the problem persists.
• git difftool used to work in the past on the same machine, so my guess is that something changed in the machine's configuration and causes this.
• Other git commands (status, diff, commit, push, etc) work correctly. The problem seems to be limited to git difftool.

git version is 2.22.3, running on CentOS Linux release 7.7.1908 (Core)

Any idea what could be wrong and how to further debug this?

Answer 1

Thanks to @phd comment, I found out that the file /usr/lib/git-core/git-difftool--helper was missing.
Possibly missing in the git package itself, since reinstalling git did not solve this.

So I downloaded it from git repo (the same tag as my git version):

wget https://raw.githubusercontent.com/git/git/v2.22.4/git-difftool--helper.sh

Moved (and renamed it) to /usr/lib/git-core/git-difftool--helper, chmod a+x, and now it's working.

---

Update 1

Opened an issue on ius git222

---

Update 2

According to @carlwgeorge who maintains git222 on ius, git-difftool--helper is part of git222 and not git222-core.

This can be verified like this:

# repoquery -q --whatprovides /usr/libexec/git-core/git-difftool--helper
git-0:1.8.3.1-23.el7_8.x86_64
git-0:1.8.3.1-21.el7_7.x86_64
git-0:1.8.3.1-22.el7_8.x86_64
git222-0:2.22.2-1.el7.ius.x86_64
git224-0:2.24.3-1.el7.ius.x86_64
git222-0:2.22.3-1.el7.ius.x86_64
git224-0:2.24.2-1.el7.ius.x86_64
git222-0:2.22.4-1.el7.ius.x86_64

And after running yum install git222, git-difftool--helper is restored:

# rpm -q --whatprovides /usr/libexec/git-core/git-difftool--helper
git222-2.22.4-1.el7.ius.x86_64

Answer 2

The IUS git222 package was forked from the Fedora git package. It follows the same layout, with a minimal set of functionality in the git222-core package, and the rest of the functionality (and all their dependencies) in the main git222 package. This hasn't changed in the lifecycle of git222, so the most likely situation is that someone thought they only needed git222-core and thus uninstalled git222. To get that functionality back, install git222 again.

yum install git222

Answer 3

I Fixed This Problem

Go to the location where Visual Studio has created installed Git:

C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\Common7\IDE\CommonExtensions\Microsoft\TeamFoundation\Team Explorer\Git\mingw32\libexec\git-core

That folder requires update with 2 files:

• git-difftool--helper
• git-mergetool--lib

So we will update them.

1. Create a new file and name it git-difftool--helper, with the following content:

#!/bin/sh
# git-difftool--helper is a GIT_EXTERNAL_DIFF-compatible diff tool launcher.
# This script is typically launched by using the 'git difftool'
# convenience command.
#
# Copyright (c) 2009, 2010 David Aguilar

TOOL_MODE=diff
. git-mergetool--lib

# difftool.prompt controls the default prompt/no-prompt behavior
# and is overridden with $GIT_DIFFTOOL*_PROMPT.
should_prompt () {
    prompt_merge=$(git config --bool mergetool.prompt || echo true)
    prompt=$(git config --bool difftool.prompt || echo $prompt_merge)
    if test "$prompt" = true
    then
        test -z "$GIT_DIFFTOOL_NO_PROMPT"
    else
        test -n "$GIT_DIFFTOOL_PROMPT"
    fi
}

# Indicates that --extcmd=... was specified
use_ext_cmd () {
    test -n "$GIT_DIFFTOOL_EXTCMD"
}

launch_merge_tool () {
    # Merged is the filename as it appears in the work tree
    # Local is the contents of a/filename
    # Remote is the contents of b/filename
    # Custom merge tool commands might use $BASE so we provide it
    MERGED="$1"
    LOCAL="$2"
    REMOTE="$3"
    BASE="$1"

    # $LOCAL and $REMOTE are temporary files so prompt
    # the user with the real $MERGED name before launching $merge_tool.
    if should_prompt
    then
        printf "\nViewing (%s/%s): '%s'\n" "$GIT_DIFF_PATH_COUNTER" \
            "$GIT_DIFF_PATH_TOTAL" "$MERGED"
        if use_ext_cmd
        then
            printf "Launch '%s' [Y/n]? " \
                "$GIT_DIFFTOOL_EXTCMD"
        else
            printf "Launch '%s' [Y/n]? " "$merge_tool"
        fi
        read ans || return
        if test "$ans" = n
        then
            return
        fi
    fi

    if use_ext_cmd
    then
        export BASE
        eval $GIT_DIFFTOOL_EXTCMD '"$LOCAL"' '"$REMOTE"'
    else
        run_merge_tool "$merge_tool"
    fi
}

if ! use_ext_cmd
then
    if test -n "$GIT_DIFF_TOOL"
    then
        merge_tool="$GIT_DIFF_TOOL"
    else
        merge_tool="$(get_merge_tool)"
    fi
fi

if test -n "$GIT_DIFFTOOL_DIRDIFF"
then
    LOCAL="$1"
    REMOTE="$2"
    run_merge_tool "$merge_tool" false
else
    # Launch the merge tool on each path provided by 'git diff'
    while test $# -gt 6
    do
        launch_merge_tool "$1" "$2" "$5"
        status=$?
        if test $status -ge 126
        then
            # Command not found (127), not executable (126) or
            # exited via a signal (>= 128).
            exit $status
        fi

        if test "$status" != 0 &&
            test "$GIT_DIFFTOOL_TRUST_EXIT_CODE" = true
        then
            exit $status
        fi
        shift 7
    done
fi

exit 0

2. Edit the existing file that its name is git-mergetool--lib, to have the following content:

# git-mergetool--lib is a shell library for common merge tool functions

: ${MERGE_TOOLS_DIR=$(git --exec-path)/mergetools}

IFS='
'

mode_ok () {
    if diff_mode
    then
        can_diff
    elif merge_mode
    then
        can_merge
    else
        false
    fi
}

is_available () {
    merge_tool_path=$(translate_merge_tool_path "$1") &&
    type "$merge_tool_path" >/dev/null 2>&1
}

list_config_tools () {
    section=$1
    line_prefix=${2:-}

    git config --get-regexp $section'\..*\.cmd' |
    while read -r key value
    do
        toolname=${key#$section.}
        toolname=${toolname%.cmd}

        printf "%s%s\n" "$line_prefix" "$toolname"
    done
}

show_tool_names () {
    condition=${1:-true} per_line_prefix=${2:-} preamble=${3:-}
    not_found_msg=${4:-}
    extra_content=${5:-}

    shown_any=
    ( cd "$MERGE_TOOLS_DIR" && ls ) | {
        while read scriptname
        do
            setup_tool "$scriptname" 2>/dev/null
            variants="$variants$(list_tool_variants)\n"
        done
        variants="$(echo "$variants" | sort | uniq)"

        for toolname in $variants
        do
            if setup_tool "$toolname" 2>/dev/null &&
                (eval "$condition" "$toolname")
            then
                if test -n "$preamble"
                then
                    printf "%s\n" "$preamble"
                    preamble=
                fi
                shown_any=yes
                printf "%s%s\n" "$per_line_prefix" "$toolname"
            fi
        done

        if test -n "$extra_content"
        then
            if test -n "$preamble"
            then
                # Note: no '\n' here since we don't want a
                # blank line if there is no initial content.
                printf "%s" "$preamble"
                preamble=
            fi
            shown_any=yes
            printf "\n%s\n" "$extra_content"
        fi

        if test -n "$preamble" && test -n "$not_found_msg"
        then
            printf "%s\n" "$not_found_msg"
        fi

        test -n "$shown_any"
    }
}

diff_mode () {
    test "$TOOL_MODE" = diff
}

merge_mode () {
    test "$TOOL_MODE" = merge
}

gui_mode () {
    test "$GIT_MERGETOOL_GUI" = true
}

translate_merge_tool_path () {
    echo "$1"
}

check_unchanged () {
    if test "$MERGED" -nt "$BACKUP"
    then
        return 0
    else
        while true
        do
            echo "$MERGED seems unchanged."
            printf "Was the merge successful [y/n]? "
            read answer || return 1
            case "$answer" in
            y*|Y*) return 0 ;;
            n*|N*) return 1 ;;
            esac
        done
    fi
}

valid_tool () {
    setup_tool "$1" && return 0
    cmd=$(get_merge_tool_cmd "$1")
    test -n "$cmd"
}

setup_user_tool () {
    merge_tool_cmd=$(get_merge_tool_cmd "$tool")
    test -n "$merge_tool_cmd" || return 1

    diff_cmd () {
        ( eval $merge_tool_cmd )
    }

    merge_cmd () {
        ( eval $merge_tool_cmd )
    }

    list_tool_variants () {
        echo "$tool"
    }
}

setup_tool () {
    tool="$1"

    # Fallback definitions, to be overridden by tools.
    can_merge () {
        return 0
    }

    can_diff () {
        return 0
    }

    diff_cmd () {
        return 1
    }

    merge_cmd () {
        return 1
    }

    translate_merge_tool_path () {
        echo "$1"
    }

    list_tool_variants () {
        echo "$tool"
    }

    # Most tools' exit codes cannot be trusted, so By default we ignore
    # their exit code and check the merged file's modification time in
    # check_unchanged() to determine whether or not the merge was
    # successful.  The return value from run_merge_cmd, by default, is
    # determined by check_unchanged().
    #
    # When a tool's exit code can be trusted then the return value from
    # run_merge_cmd is simply the tool's exit code, and check_unchanged()
    # is not called.
    #
    # The return value of exit_code_trustable() tells us whether or not we
    # can trust the tool's exit code.
    #
    # User-defined and built-in tools default to false.
    # Built-in tools advertise that their exit code is trustable by
    # redefining exit_code_trustable() to true.

    exit_code_trustable () {
        false
    }

    if test -f "$MERGE_TOOLS_DIR/$tool"
    then
        . "$MERGE_TOOLS_DIR/$tool"
    elif test -f "$MERGE_TOOLS_DIR/${tool%[0-9]}"
    then
        . "$MERGE_TOOLS_DIR/${tool%[0-9]}"
    else
        setup_user_tool
        return $?
    fi

    # Now let the user override the default command for the tool.  If
    # they have not done so then this will return 1 which we ignore.
    setup_user_tool

    if ! list_tool_variants | grep -q "^$tool$"
    then
        return 1
    fi

    if merge_mode && ! can_merge
    then
        echo "error: '$tool' can not be used to resolve merges" >&2
        return 1
    elif diff_mode && ! can_diff
    then
        echo "error: '$tool' can only be used to resolve merges" >&2
        return 1
    fi
    return 0
}

get_merge_tool_cmd () {
    merge_tool="$1"
    if diff_mode
    then
        git config "difftool.$merge_tool.cmd" ||
        git config "mergetool.$merge_tool.cmd"
    else
        git config "mergetool.$merge_tool.cmd"
    fi
}

trust_exit_code () {
    if git config --bool "mergetool.$1.trustExitCode"
    then
        :; # OK
    elif exit_code_trustable
    then
        echo true
    else
        echo false
    fi
}


# Entry point for running tools
run_merge_tool () {
    # If GIT_PREFIX is empty then we cannot use it in tools
    # that expect to be able to chdir() to its value.
    GIT_PREFIX=${GIT_PREFIX:-.}
    export GIT_PREFIX

    merge_tool_path=$(get_merge_tool_path "$1") || exit
    base_present="$2"

    # Bring tool-specific functions into scope
    setup_tool "$1" || return 1

    if merge_mode
    then
        run_merge_cmd "$1"
    else
        run_diff_cmd "$1"
    fi
}

# Run a either a configured or built-in diff tool
run_diff_cmd () {
    diff_cmd "$1"
}

# Run a either a configured or built-in merge tool
run_merge_cmd () {
    mergetool_trust_exit_code=$(trust_exit_code "$1")
    if test "$mergetool_trust_exit_code" = "true"
    then
        merge_cmd "$1"
    else
        touch "$BACKUP"
        merge_cmd "$1"
        check_unchanged
    fi
}

list_merge_tool_candidates () {
    if merge_mode
    then
        tools="tortoisemerge"
    else
        tools="kompare"
    fi
    if test -n "$DISPLAY"
    then
        if test -n "$GNOME_DESKTOP_SESSION_ID"
        then
            tools="meld opendiff kdiff3 tkdiff xxdiff $tools"
        else
            tools="opendiff kdiff3 tkdiff xxdiff meld $tools"
        fi
        tools="$tools gvimdiff diffuse diffmerge ecmerge"
        tools="$tools p4merge araxis bc codecompare"
        tools="$tools smerge"
    fi
    case "${VISUAL:-$EDITOR}" in
    *nvim*)
        tools="$tools nvimdiff vimdiff emerge"
        ;;
    *vim*)
        tools="$tools vimdiff nvimdiff emerge"
        ;;
    *)
        tools="$tools emerge vimdiff nvimdiff"
        ;;
    esac
}

show_tool_help () {
    tool_opt="'git ${TOOL_MODE}tool --tool=<tool>'"

    tab='   '
    LF='
'
    any_shown=no

    cmd_name=${TOOL_MODE}tool
    config_tools=$({
        diff_mode && list_config_tools difftool "$tab$tab"
        list_config_tools mergetool "$tab$tab"
    } | sort)
    extra_content=
    if test -n "$config_tools"
    then
        extra_content="${tab}user-defined:${LF}$config_tools"
    fi

    show_tool_names 'mode_ok && is_available' "$tab$tab" \
        "$tool_opt may be set to one of the following:" \
        "No suitable tool for 'git $cmd_name --tool=<tool>' found." \
        "$extra_content" &&
        any_shown=yes

    show_tool_names 'mode_ok && ! is_available' "$tab$tab" \
        "${LF}The following tools are valid, but not currently available:" &&
        any_shown=yes

    if test "$any_shown" = yes
    then
        echo
        echo "Some of the tools listed above only work in a windowed"
        echo "environment. If run in a terminal-only session, they will fail."
    fi
    exit 0
}

guess_merge_tool () {
    list_merge_tool_candidates
    cat >&2 <<-EOF

    This message is displayed because '$TOOL_MODE.tool' is not configured.
    See 'git ${TOOL_MODE}tool --tool-help' or 'git help config' for more details.
    'git ${TOOL_MODE}tool' will now attempt to use one of the following tools:
    $tools
    EOF

    # Loop over each candidate and stop when a valid merge tool is found.
    IFS=' '
    for tool in $tools
    do
        is_available "$tool" && echo "$tool" && return 0
    done

    echo >&2 "No known ${TOOL_MODE} tool is available."
    return 1
}

get_configured_merge_tool () {
    keys=
    if diff_mode
    then
        if gui_mode
        then
            keys="diff.guitool merge.guitool diff.tool merge.tool"
        else
            keys="diff.tool merge.tool"
        fi
    else
        if gui_mode
        then
            keys="merge.guitool merge.tool"
        else
            keys="merge.tool"
        fi
    fi

    merge_tool=$(
        IFS=' '
        for key in $keys
        do
            selected=$(git config $key)
            if test -n "$selected"
            then
                echo "$selected"
                return
            fi
        done)

    if test -n "$merge_tool" && ! valid_tool "$merge_tool"
    then
        echo >&2 "git config option $TOOL_MODE.${gui_prefix}tool set to unknown tool: $merge_tool"
        echo >&2 "Resetting to default..."
        return 1
    fi
    echo "$merge_tool"
}

get_merge_tool_path () {
    # A merge tool has been set, so verify that it's valid.
    merge_tool="$1"
    if ! valid_tool "$merge_tool"
    then
        echo >&2 "Unknown merge tool $merge_tool"
        exit 1
    fi
    if diff_mode
    then
        merge_tool_path=$(git config difftool."$merge_tool".path ||
                  git config mergetool."$merge_tool".path)
    else
        merge_tool_path=$(git config mergetool."$merge_tool".path)
    fi
    if test -z "$merge_tool_path"
    then
        merge_tool_path=$(translate_merge_tool_path "$merge_tool")
    fi
    if test -z "$(get_merge_tool_cmd "$merge_tool")" &&
        ! type "$merge_tool_path" >/dev/null 2>&1
    then
        echo >&2 "The $TOOL_MODE tool $merge_tool is not available as"\
             "'$merge_tool_path'"
        exit 1
    fi
    echo "$merge_tool_path"
}

get_merge_tool () {
    is_guessed=false
    # Check if a merge tool has been configured
    merge_tool=$(get_configured_merge_tool)
    # Try to guess an appropriate merge tool if no tool has been set.
    if test -z "$merge_tool"
    then
        merge_tool=$(guess_merge_tool) || exit
        is_guessed=true
    fi
    echo "$merge_tool"
    test "$is_guessed" = false
}

mergetool_find_win32_cmd () {
    executable=$1
    sub_directory=$2

    # Use $executable if it exists in $PATH
    if type -p "$executable" >/dev/null 2>&1
    then
        printf '%s' "$executable"
        return
    fi

    # Look for executable in the typical locations
    for directory in $(env | grep -Ei '^PROGRAM(FILES(\(X86\))?|W6432)=' |
        cut -d '=' -f 2- | sort -u)
    do
        if test -n "$directory" && test -x "$directory/$sub_directory/$executable"
        then
            printf '%s' "$directory/$sub_directory/$executable"
            return
        fi
    done

    printf '%s' "$executable"
}