update-hash: New executable.

Useful only for software-release development, not usage, so not adding it
to packaging, only to repository.

update-hash

+#!/usr/bin/env python
+"""
+Suggested installation:
+$ cp update-hash .git/hooks/
+
+$ $EDITOR .git/hooks/pre-commit
+#!/bin/bash
+set -e
+touch "$(git rev-parse --git-dir)/hooks/.need-post-commit"
+
+$ $EDITOR .git/hooks/post-commit
+#!/bin/bash
+set -e
+MARKER="$(git rev-parse --git-dir)/hooks/.need-post-commit"
+UPDATE_HASH="$(git rev-parse --git-dir)/hooks/update-hash"
+if [ -e "$MARKER" -a -x "$UPDATE_HASH" ]; then
+  rm "$MARKER"
+  if git diff-index --quiet HEAD -- ; then
+    # nothing
+    true
+  else
+    git stash save --keep-index --quiet "update-hash pre-commit hook"
+    trap "git stash pop" EXIT
+  fi
+  find "$(git rev-parse --show-toplevel)" -name "buildout.hash.cfg" | while IFS= read -r HASHFILE; do
+    "$UPDATE_HASH" "$HASHFILE"
+    git add "$HASHFILE"
+  done
+  git commit --amend --no-verify -C HEAD
+fi
+
+BEWARE: rebasing does not trigger this hook, so you have to commit each
+change explicitely. Improvements welcome.
+"""
+import hashlib
+import os
+import shutil
+import sys
+import tempfile
+
+# Note: this is an intentionally very restrictive and primitive
+# ConfigParser-ish parser.
+# buildout.hash.cfg files are ConfigParser-compatible, but they are *not*
+# ConfigParser syntax in order to be strictly validated, to prevent misuse
+# and allow easy extension (ex: to other hashes).
+
+FILENAME_KEY = 'filename'
+HASH_MAP = {
+    'md5sum': hashlib.md5,
+}
+
+def main():
+    for infile_path in sys.argv[1:] or ['buildout.hash.cfg']:
+        eol = None
+        hash_file_path = None
+        hash_name = None
+        current_section = None
+        infile_dirname = os.path.dirname(infile_path)
+        outfile_path = infile_path + '.tmp'
+        infile = open(infile_path, 'r')
+        outfile_fd = os.open(outfile_path, os.O_EXCL | os.O_CREAT | os.O_WRONLY)
+        try:
+            outfile = os.fdopen(outfile_fd, 'w')
+            write = outfile.write
+            nextLine = iter(infile).next
+            while True:
+                try:
+                    line = nextLine()
+                except StopIteration:
+                    line = None
+                if line is None or not line.startswith('#'):
+                    if line is None or line.startswith('['):
+                        if hash_file_path is not None:
+                            current_section.insert(
+                                2,
+                                '%s = %s%s' % (
+                                    hash_name,
+                                    HASH_MAP[hash_name](
+                                        open(
+                                            os.path.join(
+                                                infile_dirname,
+                                                hash_file_path,
+                                            )
+                                        ).read()
+                                    ).hexdigest(),
+                                    eol,
+                                ),
+                            )
+                            outfile.writelines(current_section)
+                            hash_file_path = hash_name = None
+                        if line is None:
+                            break
+                        current_section = []
+                    elif '=' in line:
+                        assert current_section is not None, line
+                        name, value = line.split('=', 1)
+                        name = name.strip()
+                        value = value.strip()
+                        if name == FILENAME_KEY:
+                            hash_file_path = value
+                            current_section.append(line)
+                        else:
+                            for hash_name in HASH_MAP:
+                                if name == hash_name:
+                                    break
+                            else:
+                                raise ValueError('Unknown key: %r' % (name, ))
+                            # NOT appending this line, it will be re-generated from
+                            # scratch
+                            eol = ''.join(x for x in line if x in ('\r', '\n'))
+                        continue
+                if current_section is None:
+                    write(line)
+                else:
+                    current_section.append(line)
+            outfile.close()
+            shutil.copymode(infile_path, outfile_path)
+            shutil.move(outfile_path, infile_path)
+        except Exception:
+            os.unlink(outfile_path)
+            raise
+
+if __name__ == '__main__':
+    main()