filter-repo: ignore comment lines in --paths-from-file

Allow lines starting with '#' to be treated as a comment and be ignored.
Update the documentation to note that both blank lines and comment lines
are ignored, and mention how filenames starting with '#' can be matched
(namely, the same way that filenames startwith with 'regex:', 'glob:',
or 'literal:' can be -- by prefixing the filename with 'literal:').

Signed-off-by: Elijah Newren <newren@gmail.com>

Documentation/git-filter-repo.txt

@@ -129,7 +129,11 @@ Path shortcuts
 	Specify several path filtering and renaming directives, one
 	per line. Lines with `==>` in them specify path renames, and
 	lines can begin with `literal:` (the default), `glob:`, or
-	`regex:` to specify different matching styles
+	`regex:` to specify different matching styles.  Blank lines
+	and lines starting with a `#` are ignored (if you have a
+	filename that you want to filter on that starts with
+	`literal:`, `#`, `glob:`, or `regex:`, then prefix the line
+	with 'literal:').
 
 --subdirectory-filter <directory>::
 	Only look at history that touches the given subdirectory and
@@ -676,12 +680,22 @@ expressions to filter on, you can stick them in a file and use
 contents of
 
 --------------------------------------------------
+# Blank lines and comment lines are ignored.
+# Examples similar to --path:
 README.md
 guides/
 tools/releases
+
+# An example that is like --path-glob:
 glob:*.py
+
+# An example that is like --path-regex:
 regex:^.*/.*/[0-9]{4}-[0-9]{2}-[0-9]{2}.txt$
+
+# An example of renaming a path
 tools/==>scripts/
+
+# An example of using a regex to rename a path
 regex:(.*)/([^/]*)/([^/]*)\.text$==>\2/\1/\3.txt
 --------------------------------------------------
 

git-filter-repo

@@ -1807,7 +1807,8 @@ EXAMPLES
         help=_("Specify several path filtering and renaming directives, one "
                "per line.  Lines with '==>' in them specify path renames, "
                "and lines can begin with 'literal:' (the default), 'glob:', "
-               "or 'regex:' to specify different matching styles"))
+               "or 'regex:' to specify different matching styles.  Blank "
+               "lines and lines starting with a '#' are ignored."))
     helpers.add_argument('--subdirectory-filter', metavar='DIRECTORY',
         action=FilteringOptions.HelperFilter, type=os.fsencode,
         help=_("Only look at history that touches the given subdirectory "
@@ -2123,6 +2124,9 @@ EXAMPLES
         # Skip blank lines
         if not line:
           continue
+        # Skip comment lines
+        if line.startswith(b'#'):
+          continue
 
         # Determine the replacement
         match_type, repl = 'literal', None

t/t9390-filter-repo.sh

@@ -165,6 +165,7 @@ test_expect_success '--paths-from-file' '
 		values/huge==>values/gargantuan
 		glob:*rge
 
+		# Comments and blank lines are ignored
 		regex:.*med.*
 		regex:^([^/]*)/(.*)ge$==>\2/\1/ge
 		EOF