maintainers/scripts: add get-maintainer-pings-between.sh

[`maintainer-list.nix`]: ../maintainer-list.nix

### `get-maintainer-pings-between.sh`

Gets which maintainers would be pinged between two Nixpkgs revisions.

Outputs a JSON object on stdout mapping GitHub usernames to the attributes

that they would be getting pinged for.

Example:

```sh

maintainers/scripts/get-maintainer-pings-between.sh HEAD^ HEAD

```

## Conventions

#!/usr/bin/env nix-shell

#!nix-shell -i bash -p git jq

# Outputs a list of maintainers that would be pinged across two nixpkgs revisions.

# Authors:

#  Morgan Jones (@numinit)

#  Tristan Ross (@RossComputerGuy)

set -euo pipefail

if [ $# -lt 2 ]; then

    echo "Usage: $0 <rev-from> <rev-to>" >&2

    exit 1

fi

repo="$(git rev-parse --show-toplevel)"

system="$(nix-instantiate --eval --expr builtins.currentSystem)"

rev1="$(git -C "$repo" rev-parse "$1")"

rev2="$(git -C "$repo" rev-parse "$2")"

echo "Touched files:" >&2

git -C "$repo" diff --name-only "$rev1" "$rev2" \

    | jq --raw-input --slurp 'split("\n")[:-1]' | tee "$TMPDIR/touched-files.json" >&2

# Runs an eval in the given worktree, outputting the path to $TMPDIR/$1.path.

# $1: The revision SHA.

eval_in_worktree() (

    mkdir -p .worktree

    local rev="$1"

    local tree=".worktree/$rev"

    if [ ! -d "$tree" ]; then

        git -C "$repo" worktree add -f -d "$tree" "$rev" >&2

    fi

    cd "$tree"

    local workdir="$TMPDIR/$rev"

    rm -rf "$workdir"

    mkdir -p "$workdir"

    nix-build ci -A eval.attrpathsSuperset -o "$workdir/paths" >&2

    mkdir -p "$workdir/intermediates"

    nix-build ci -A eval.singleSystem \

        --arg evalSystem "$system" \

        --arg attrpathFile "$workdir/paths/paths.json" \

        --arg chunkSize ${CHUNK_SIZE:-10000} \

        -o "$workdir/intermediates/.intermediate-1" >&2

    # eval.combine nix-build needs a directory, not a symlink

    cp -RL "$workdir/intermediates/.intermediate-1" "$workdir/intermediates/intermediate-1"

    chmod -R +w "$workdir/intermediates/intermediate-1"

    rm -rf "$workdir/intermediates/.intermediate-1"

    nix-build ci -A eval.combine \

        --arg resultsDir "$workdir/intermediates" \

        -o "$workdir/result" >&2

)

eval_in_worktree "$rev1" &

pid1=$!

eval_in_worktree "$rev2" &

pid2=$!

wait $pid1

wait $pid2

path1="$TMPDIR/$rev1"

path2="$TMPDIR/$rev2"

# Use the repo this script was executed in to get accurate maintainer info

nix-build "$repo/ci" -A eval.compare \

    --arg beforeResultDir "$path1/result" \

    --arg afterResultDir "$path2/result" \

    --arg touchedFilesJson "$TMPDIR/touched-files.json" \

    --arg byName true \

    -o comparison

echo "Pinged maintainers (check $repo/comparison for more details)" >&2

jq < comparison/maintainers.json