Add Git hooks to check filenames listed in the commit message

See <https://lists.gnu.org/archive/html/emacs-devel/2023-04/msg00274.html>.

* build-aux/git-hooks/commit-msg-files.awk:
* build-aux/git-hooks/post-commit:
* build-aux/git-hooks/pre-push: New files...
* autogen.sh: ... add them.

autogen.sh

@@ -340,7 +340,8 @@ git_config diff.texinfo.xfuncname \
 tailored_hooks=
 sample_hooks=
 
-for hook in commit-msg pre-commit prepare-commit-msg; do
+for hook in commit-msg pre-commit prepare-commit-msg post-commit \
+            pre-push commit-msg-files.awk; do
     cmp -- build-aux/git-hooks/$hook "$hooks/$hook" >/dev/null 2>&1 ||
 	tailored_hooks="$tailored_hooks $hook"
 done

build-aux/git-hooks/commit-msg-files.awk

@@ -0,0 +1,113 @@
+# Check the file list of GNU Emacs change log entries for each commit SHA.
+
+# Copyright 2023 Free Software Foundation, Inc.
+
+# This file is part of GNU Emacs.
+
+# GNU Emacs is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+
+# GNU Emacs is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+
+# You should have received a copy of the GNU General Public License
+# along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>.
+
+### Commentary:
+
+# This script accepts a list of (unabbreviated) Git commit SHAs, and
+# will then iterate over them to check that any files mentioned in the
+# commit message are actually present in the commit's diff.  If not,
+# it will print out the incorrect file names and return 1.
+
+# You can also pass "-v reason=pre-push", which will add more-verbose
+# output, indicating the abbreviated commit SHA and first line of the
+# commit message for any improper commits.
+
+### Code:
+
+function get_commit_changes(commit_sha, changes,    cmd, i, j, len, \
+                            bits, filename) {
+  # Collect all the files touched in the specified commit.
+  cmd = ("git log -1 --name-status --format= " commit_sha)
+  while ((cmd | getline) > 0) {
+    for (i = 2; i <= NF; i++) {
+      len = split($i, bits, "/")
+      for (j = 1; j <= len; j++) {
+        if (j == 1)
+          filename = bits[j]
+        else
+          filename = filename "/" bits[j]
+        changes[filename] = 1
+      }
+    }
+  }
+  close(cmd)
+}
+
+function check_commit_msg_files(commit_sha, verbose,    changes, good, \
+                                cmd, msg, filenames_str, filenames, i) {
+  get_commit_changes(commit_sha, changes)
+  good = 1
+
+  cmd = ("git log -1 --format=%B " commit_sha)
+  while ((cmd | getline) > 0) {
+    if (verbose && ! msg)
+      msg = $0
+
+    # Find lines that reference files.  We look at any line starting
+    # with "*" (possibly prefixed by "; ") where the file part starts
+    # with an alphanumeric character.  The file part ends if we
+    # encounter any of the following characters: [ ( < { :
+    if (/^(; )?\*[ \t]+[[:alnum:]]/ && match($0, /[[:alnum:]][^[(<{:]*/)) {
+      # There might be multiple files listed on this line, separated
+      # by spaces (and possibly a comma).  Iterate over each of them.
+      split(substr($0, RSTART, RLENGTH), filenames, ",?([[:blank:]]+|$)")
+
+      for (i in filenames) {
+        # Remove trailing slashes from any directory entries.
+        sub(/\/$/, "", filenames[i])
+
+        if (length(filenames[i]) && ! (filenames[i] in changes)) {
+          if (good) {
+            # Print a header describing the error.
+            if (verbose)
+              printf("In commit %s \"%s\"...\n", substr(commit_sha, 1, 10), msg)
+            printf("Files listed in commit message, but not in diff:\n")
+          }
+          printf("  %s\n", filenames[i])
+          good = 0
+        }
+      }
+    }
+  }
+  close(cmd)
+
+  return good
+}
+
+BEGIN {
+  if (reason == "pre-push")
+    verbose = 1
+}
+
+/^[a-z0-9]{40}$/ {
+  if (! check_commit_msg_files($0, verbose)) {
+    status = 1
+  }
+}
+
+END {
+  if (status != 0) {
+    if (reason == "pre-push")
+      error_msg = "Push aborted"
+    else
+      error_msg = "Bad commit message"
+    printf("%s; please see the file 'CONTRIBUTE'\n", error_msg)
+  }
+  exit status
+}

build-aux/git-hooks/post-commit

@@ -0,0 +1,45 @@
+#!/bin/sh
+# Check the file list of GNU Emacs change log entries after committing.
+
+# Copyright 2023 Free Software Foundation, Inc.
+
+# This file is part of GNU Emacs.
+
+# GNU Emacs is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+
+# GNU Emacs is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+
+# You should have received a copy of the GNU General Public License
+# along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>.
+
+### Commentary:
+
+# This hook runs after a commit is finalized and checks that the files
+# mentioned in the commit message match the diff.  We perform this in
+# the post-commit phase so that we can be sure we properly detect all
+# the files in the diff (this is difficult during the commit-msg hook,
+# since there's no cross-platform way to detect when a commit is being
+# amended).
+
+# However, since this is a post-commit hook, it's too late to error
+# out and abort the commit: it's already done!  As a result, this hook
+# is purely advisory, and instead we error out when trying to push
+# (see "pre-push" in this directory).
+
+### Code:
+
+# Prefer gawk if available, as it handles NUL bytes properly.
+if type gawk >/dev/null 2>&1; then
+  awk="gawk"
+else
+  awk="awk"
+fi
+
+git rev-parse HEAD | $awk -v reason=post-commit \
+                          -f .git/hooks/commit-msg-files.awk

build-aux/git-hooks/pre-push

@@ -0,0 +1,83 @@
+#!/bin/sh
+# Check the file list of GNU Emacs change log entries before pushing.
+
+# Copyright 2023 Free Software Foundation, Inc.
+
+# This file is part of GNU Emacs.
+
+# GNU Emacs is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+
+# GNU Emacs is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+
+# You should have received a copy of the GNU General Public License
+# along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>.
+
+### Commentary:
+
+# This hook runs before pushing a series of commits and checks that
+# the files mentioned in each commit message match the diffs.  This
+# helps ensure that the resulting change logs are correct, which
+# should prevent errors when generating etc/AUTHORS.
+
+# These checks also happen in the "post-commit" hook (which see), but
+# that hook can't abort a commit; it just advises the committer to fix
+# the commit so that this hook runs without errors.
+
+### Code:
+
+# Prefer gawk if available, as it handles NUL bytes properly.
+if type gawk >/dev/null 2>&1; then
+  awk="gawk"
+else
+  awk="awk"
+fi
+
+# Standard input receives lines of the form:
+#   <local ref> SP <local name> SP <remote ref> SP <remote name> LF
+$awk -v origin_name="$1" '
+  # If the local SHA is all zeroes, ignore it.
+  $2 ~ /^0{40}$/ {
+    next
+  }
+
+  $2 ~ /^[a-z0-9]{40}$/ {
+    newref = $2
+    # If the remote SHA is all zeroes, this is a new object to be
+    # pushed (likely a branch).  Go backwards until we find a SHA on
+    # an origin branch.
+    if ($4 ~ /^0{40}$/) {
+      back = 0
+      cmd = ("git branch -r -l '\''" origin_name "/*'\'' --contains " \
+             newref "~" back)
+      while ((cmd | getline) == 0) {
+
+        # Only look back at most 1000 commits, just in case...
+        if (back++ > 1000)
+          break;
+      }
+      close(cmd)
+
+      cmd = ("git rev-parse " newref "~" back)
+      cmd | getline oldref
+      if (!(oldref ~ /^[a-z0-9]{40}$/)) {
+        # The SHA is misformatted!  Skip this line.
+        next
+      }
+      close(cmd)
+    } else if ($4 ~ /^[a-z0-9]{40}$/)  {
+      oldref = $4
+    } else {
+      # The SHA is misformatted!  Skip this line.
+      next
+    }
+
+    # Print every SHA after oldref, up to (and including) newref.
+    system("git rev-list --reverse " oldref ".." newref)
+  }
+' | $awk -v reason=pre-push -f .git/hooks/commit-msg-files.awk