home/git: add author-lines script

home/programs/git/default.nix

@@ -352,6 +352,11 @@ lib.mkIf cfg.enable {
         "SC2001" # (style): See if you can use ${variable//search/replace} instead. (sed invocation)
       ];
     })
+    (pkgs.writeShellApplication {
+      name = "git-author-lines";
+      runtimeInputs = with pkgs; [ cfg.package gnused gnugrep gawk uutils-coreutils-noprefix ];
+      text = lib.fileContents ./scripts/git-author-lines.sh;
+    })
     ((pkgs.writers.writePython3Bin "git-post-pr" {
       libraries = with pkgs.python3Packages; [
         tkinter

home/programs/git/scripts/git-author-lines.sh

@@ -0,0 +1,19 @@
+set -euo pipefail
+
+if [ -n "${1:-}" ]; then
+  REF="${1}"
+else
+  REF="HEAD"
+fi
+
+# TODO: optionally keep track of which files the authors were present in,
+#       and print a list of up to N files where the authors contributed the most.
+
+git ls-tree -r "${REF}" \
+| while read -r _filemode _objtype _githash filepath; do
+  git blame --line-porcelain "${filepath}"
+done \
+| grep --binary-files=without-match '^author ' \
+| sed -e 's/author //' \
+| awk '{ a[$0]+=1 } END{ for (i in a) { print a[i],i } }' \
+| sort --numeric-sort --key 1 --reverse