Re: commit -> public-inbox link helper

> Hi team,
>
> I found myself in dear need to quickly look up mails in the public-inbox
> mail archive corresponding to any given commit in git.git. Some time ago,
> I wrote a shell script to help me with that, and I found myself using it a
> couple of times, so I think it might be useful for others, too.
>
> This script (I call it lookup-commit.sh) needs to be dropped into a *bare*
> clone of http://public-inbox.org/git, and called with its absolute or
> relative path from a git.git worktree, e.g.
>
>         ~/public-inbox-git.git/lookup-commit.sh \
>                 fea16b47b603e7e4fa7fca198bd49229c0e5da3d
>
> This will take a while initially, or when the `master` branch of the
> public-inbox mirror was updated, as it will generate two files with
> plain-text mappings.
>
> In its default mode, it will print the Message-ID of the mail (if found).
>
> With --open, it opens the mail in a browser (macOS support is missing,
> mainly because I cannot test: just add an `open` alternative to
> `xdg-open`).
>
> With --reply, it puts the mail into the `from-public-inbox` folder of a
> maildir-formatted ~/Mail/, so it is pretty specific to my setup here.
>
> Note: the way mails are matched is by timestamp. In practice, this works
> amazingly often (although not always, I reported findings short after
> GitMerge 2017). My plan was to work on this when/as needed.
>
> Note also: the script is very much in a 'works-for-me' state, and I could
> imagine that others might want to modify it to their needs. I would be
> delighted if somebody would take custody of it (as in: start a repository
> on GitHub, adding a README.md, adding a config setting to point to the
> location of the public-inbox mirror without having to copy the script,
> adding an option to install an alias to run the script, etc).
>
> And now, without further ado, here it is, the script, in its current glory:
>
> -- snipsnap --
> #!/bin/sh
>
> # This is a very simple helper to assist with finding the mail (if any)
> # corresponding to a given commit in git.git.
>
> die () {
>         echo "$*" >&2
>         exit 1
> }
>
> mode=print
> while case "$1" in
> --open) mode=open;;
> --reply) mode=reply;;
> -*) die "Unknown option: $1";;
> *) break;;
> esac; do shift; done
>
> test $# = 1 ||
> die "Usage: $0 ( [--open] | [--reply] ) <commit>"
>
> test reply != $mode ||
> test -d "$HOME/Mail" ||
> die "Need $HOME/Mail to reply"
>
> commit="$1"
> tae="$(git show -s --format='%at %an <%ae>' "$1")" ||
> die "Could not get Timestamp/Author/Email triplet from $1"
>
> # We try to match the timestamp first; the author name and author email are
> # not as reliable: they might have been overridden via a "From:" line in the
> # mail's body
> timestamp=${tae%% *}
>
> cd "$(dirname "$0")" ||
> die "Could not cd to the public-inbox directory"
>
> git rev-parse --quiet --verify \
>         b60d038730d2c2bb8ab2b48c117db917ad529cf7 >/dev/null 2>&1 ||
> die "Not a public-inbox directory: $(pwd)"
>
> head="$(git rev-parse --verify master)" ||
> die "Could not determine tip of master"
>
> prevhead=
> test ! -f map.latest-rev ||
> prevhead="$(cat map.latest-rev)"
>
> if test $head != "$prevhead"
> then
>         range=${prevhead:+$prevhead..}$head
>         echo "Inserting records for $range" >&2
>         git log --format="%at %h %an <%ae>" $range >map.txt.add ||
>         die "Could not enumerate $range"
>
>         cat map.txt map.txt.add 2>/dev/null | sort -n >map.txt.new &&
>         mv -f map.txt.new map.txt ||
>         die "Could not insert new records"
>
>         echo $head >map.latest-rev
> fi
>
> lines="$(grep "^$timestamp " <map.txt)"
> if test 1 != $(echo "$lines" | wc -l)
> then
>         test -n "$lines" ||
>         die "No records found for timestamp $timestamp"
>
>         echo "Multiple records found:"
>
>         for h in $(echo "$lines" | cut -d ' ' -f 2)
>         do
>                 git show -s --format="%nOn %ad, %an <%ae> sent" $h
>                 git show $h |
>                 sed -n -e 's/^+Message-Id: <\(.*\)>/\1/ip' \
>                         -e 's/^+Subject: //ip'
>         done
>
>         exit 1
> fi
>
> # We found exactly one record: print the message ID
> h=${lines#$timestamp }
> h=${h%% *}
> messageid="$(git show $h | sed -n 's/^+Message-Id: <\(.*\)>/\1/ip')" ||
> die "Could not determine Message-Id from $h"
>
> case $mode in
> print) echo $messageid;;
> open)
>         url=https://public-inbox.org/git/$messageid
>         case "$(uname -s)" in
>         Linux) xdg-open "$url";;
>         MINGW*|MSYS*) start "$url";;

>         *) die "Need to learn how to open URLs on $(uname -s)";;
>         esac
>         ;;
> reply)
>         mkdir -p "$HOME/Mail/from-public-inbox/new" &&
>         mkdir -p "$HOME/Mail/from-public-inbox/cur" &&
>         mkdir -p "$HOME/Mail/from-public-inbox/tmp" ||
>         die "Could not set up mail folder 'from-public-inbox'"
>
>         path=$(git diff --name-only $h^!) &&
>         mail="$(printf "%s_%09d.%s:2," $(date +%s.%N) $$ $(hostname -f))"
> &&
>         git show $h:$path >"$HOME/Mail/from-public-inbox/new/$mail" ||
>         die "Could not write mail"
>         ;;
> *)
>         die "Unhandled mode: $mode"
>         ;;
> esac