Compare a commit in the current (input-wacom) repository with its upstream source.

compare-commit-upstream.sh

#!/bin/bash

# compare-commit-upstream.sh
#
# Given a commit ID in the current repository, find the corresponding
# upstream commit and print out the difference, if any. If no upstream
# commit can be found, print a message and exit with code 0.
#
# Usage: ./compare-commit-upstream.sh <local-git-commit-id>

function extract_unifed_without_context() {
    # Read a patch file in unified diff format and print out only the
    # added and removed lines. Removes all context (unchanged lines)
    # and other non-patch data (e.g. commit messages from git patches).
    awk '/^@@/,/^diff/' "$1" | grep -E "^[+-]"
}

function patch_diff() {
    # Compare two unified diff patches to see if they are "identical".
    #
    # Given two files in unified diff format, this function checks to
    # see if they add and remove the same text. This function is very
    # stupid and doesn't care what the surrounding lines look like,
    # what the file names are, etc.
    LEFT=$(extract_unifed_without_context "$1")
    RIGHT=$(extract_unifed_without_context "$2")
    diff -u <(echo "$LEFT") <(echo "$RIGHT")
}

function find_upstream_commit_id() {
    # Extract the commit ID of the upstream parent, if possible.
    #
    # Given the ID of a commit in the local repository, we search for the
    # line of information in the sign-off block that contains information
    # on the upstream commit and return its ID.
    KEYWORD="Imported into input-wacom"
    git log -1 "$1" | grep "$KEYWORD" | grep -Eo '\([0-9a-fA-F]+\)' | tr -d '()'
}

function print_upstream_commit() {
    # Print out a commit which has been accepted upstream.
    #
    # Given the ID of a commit accepted upstream, find and print out the
    # commt in patch form. This function should find any commit merged
    # into the HID tree, even if Linus has not picked it up yet.
    URLBASE="https://git.kernel.org/pub/scm/linux/kernel/git/hid/hid.git/patch/"
    curl "${URLBASE}?id=${1}" | head -n -3
}

function compare_commit_to_upstream() {
    # Compare a commit in the current repository with its upstream source.
    #
    # Given a commit ID in the current repository, find the corresponding
    # upstream commit and print out the difference, if any. If no upstream
    # commit can be found, print a message and exit with code 0.
    DOWNSTREAM="$1"
    UPSTREAM=$(find_upstream_commit_id "$DOWNSTREAM")
    if [[ -z "$UPSTREAM" ]]; then
        echo "No upstream commit found for $DOWNSTREAM. Exiting."
        exit 0
    fi
    echo "Comparing $DOWNSTREAM locally to $UPSTREAM upstream"

    LEFT=$(git log -1 -p "$DOWNSTREAM")
    RIGHT=$(print_upstream_commit "$UPSTREAM")
    patch_diff <(echo "$LEFT") <(echo "$RIGHT")
}

compare_commit_to_upstream "$1"