utils: checkstyle.py: Skip title and trailers checkers for pre-commit

When running checkstyle.py in a pre-commit hook, there is either no
commit message at all (when committing staged changes as a new commit),
or the commit message comes from a previous commit being amended. In
either case, there's no new commit message yet, and thus nothing to
validate for the title and trailers checkers. The trailers checker, in
particular, will always flag an error, making all commits fail.

To fix that, just skip the two checkers during pre-commit.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Milan Zamazal <mzamazal@redhat.com>
Reviewed-by: Daniel Scally <dan.scally@ideasonboard.com>

utils/checkstyle.py

@@ -344,11 +344,16 @@ class CommitChecker(metaclass=ClassRegistry):
     # Class methods
     #
     @classmethod
-    def checkers(cls, names):
+    def checkers(cls, commit, names):
         for checker in cls.subclasses:
             if names and checker.__name__ not in names:
                 continue
-            yield checker
+            if checker.supports(commit):
+                yield checker
+
+    @classmethod
+    def supports(cls, commit):
+        return type(commit) in cls.commit_types
 
 
 class CommitIssue(object):
@@ -357,6 +362,8 @@ class CommitIssue(object):
 
 
 class HeaderAddChecker(CommitChecker):
+    commit_types = (Commit, StagedChanges, Amendment)
+
     @classmethod
     def check(cls, commit, top_level):
         issues = []
@@ -401,6 +408,8 @@ class HeaderAddChecker(CommitChecker):
 
 
 class TitleChecker(CommitChecker):
+    commit_types = (Commit,)
+
     prefix_regex = re.compile(r'^([a-zA-Z0-9_.-]+: )+')
     release_regex = re.compile(r'libcamera v[0-9]+\.[0-9]+\.[0-9]+')
 
@@ -408,11 +417,6 @@ class TitleChecker(CommitChecker):
     def check(cls, commit, top_level):
         title = commit.title
 
-        # Skip the check when validating staged changes (as done through a
-        # pre-commit hook) as there is no title to check in that case.
-        if isinstance(commit, StagedChanges):
-            return []
-
         # Ignore release commits, they don't need a prefix.
         if TitleChecker.release_regex.fullmatch(title):
             return []
@@ -468,6 +472,8 @@ class TitleChecker(CommitChecker):
 
 
 class TrailersChecker(CommitChecker):
+    commit_types = (Commit,)
+
     commit_regex = re.compile(r'[0-9a-f]{12}[0-9a-f]* \(".*"\)')
 
     coverity_regex = re.compile(r'Coverity CID=.*')
@@ -1020,7 +1026,7 @@ def check_style(top_level, commit, checkers):
     issues = 0
 
     # Apply the commit checkers first.
-    for checker in CommitChecker.checkers(checkers):
+    for checker in CommitChecker.checkers(commit, checkers):
         for issue in checker.check(commit, top_level):
             print('%s%s%s' % (Colours.fg(Colours.Yellow), issue.msg, Colours.reset()))
             issues += 1