check-files.py: clean up class structure

Line issue trackers are conceptually a subclass of file issue
trackers: they're file issue trackers where issues arise from checking
each line independently. So make it an actual subclass.

Pylint pointed out the design smell: there was an abstract method that
wasn't always overridden in concrete child classes.

tests/scripts/check-files.py

@@ -19,10 +19,12 @@ import codecs
 import sys
 
 
-class IssueTracker(object):
-    """Base class for issue tracking. Issues should inherit from this and
-    overwrite either issue_with_line if they check the file line by line, or
-    overwrite check_file_for_issue if they check the file as a whole."""
+class FileIssueTracker(object):
+    """Base class for file-wide issue tracking.
+
+    To implement a checker that processes a file as a whole, inherit from
+    this class and implement `check_file_for_issue`.
+    """
 
     def __init__(self):
         self.heading = ""
@@ -35,23 +37,14 @@ class IssueTracker(object):
                 return False
         return True
 
-    def issue_with_line(self, line):
-        raise NotImplementedError
-
     def check_file_for_issue(self, filepath):
-        with open(filepath, "rb") as f:
-            for i, line in enumerate(iter(f.readline, b"")):
-                self.check_file_line(filepath, line, i + 1)
+        raise NotImplementedError
 
     def record_issue(self, filepath, line_number):
         if filepath not in self.files_with_issues.keys():
             self.files_with_issues[filepath] = []
         self.files_with_issues[filepath].append(line_number)
 
-    def check_file_line(self, filepath, line, line_number):
-        if self.issue_with_line(line):
-            self.record_issue(filepath, line_number)
-
     def output_file_issues(self, logger):
         if self.files_with_issues.values():
             logger.info(self.heading)
@@ -64,8 +57,26 @@ class IssueTracker(object):
                     logger.info(filename)
             logger.info("")
 
+class LineIssueTracker(FileIssueTracker):
+    """Base class for line-by-line issue tracking.
 
-class PermissionIssueTracker(IssueTracker):
+    To implement a checker that processes files line by line, inherit from
+    this class and implement `line_with_issue`.
+    """
+
+    def issue_with_line(self, line, filepath):
+        raise NotImplementedError
+
+    def check_file_line(self, filepath, line, line_number):
+        if self.issue_with_line(line, filepath):
+            self.record_issue(filepath, line_number)
+
+    def check_file_for_issue(self, filepath):
+        with open(filepath, "rb") as f:
+            for i, line in enumerate(iter(f.readline, b"")):
+                self.check_file_line(filepath, line, i + 1)
+
+class PermissionIssueTracker(FileIssueTracker):
     """Track files with bad permissions.
 
     Files that are not executable scripts must not be executable."""
@@ -80,7 +91,7 @@ class PermissionIssueTracker(IssueTracker):
             self.files_with_issues[filepath] = None
 
 
-class EndOfFileNewlineIssueTracker(IssueTracker):
+class EndOfFileNewlineIssueTracker(FileIssueTracker):
     """Track files that end with an incomplete line
     (no newline character at the end of the last line)."""
 
@@ -94,7 +105,7 @@ class EndOfFileNewlineIssueTracker(IssueTracker):
                 self.files_with_issues[filepath] = None
 
 
-class Utf8BomIssueTracker(IssueTracker):
+class Utf8BomIssueTracker(FileIssueTracker):
     """Track files that start with a UTF-8 BOM.
     Files should be ASCII or UTF-8. Valid UTF-8 does not start with a BOM."""
 
@@ -108,18 +119,18 @@ class Utf8BomIssueTracker(IssueTracker):
                 self.files_with_issues[filepath] = None
 
 
-class LineEndingIssueTracker(IssueTracker):
+class LineEndingIssueTracker(LineIssueTracker):
     """Track files with non-Unix line endings (i.e. files with CR)."""
 
     def __init__(self):
         super().__init__()
         self.heading = "Non Unix line endings:"
 
-    def issue_with_line(self, line):
+    def issue_with_line(self, line, _filepath):
         return b"\r" in line
 
 
-class TrailingWhitespaceIssueTracker(IssueTracker):
+class TrailingWhitespaceIssueTracker(LineIssueTracker):
     """Track lines with trailing whitespace."""
 
     def __init__(self):
@@ -127,11 +138,11 @@ class TrailingWhitespaceIssueTracker(IssueTracker):
         self.heading = "Trailing whitespace:"
         self.files_exemptions = [".md"]
 
-    def issue_with_line(self, line):
+    def issue_with_line(self, line, _filepath):
         return line.rstrip(b"\r\n") != line.rstrip()
 
 
-class TabIssueTracker(IssueTracker):
+class TabIssueTracker(LineIssueTracker):
     """Track lines with tabs."""
 
     def __init__(self):
@@ -141,11 +152,11 @@ class TabIssueTracker(IssueTracker):
             "Makefile", "generate_visualc_files.pl"
         ]
 
-    def issue_with_line(self, line):
+    def issue_with_line(self, line, _filepath):
         return b"\t" in line
 
 
-class MergeArtifactIssueTracker(IssueTracker):
+class MergeArtifactIssueTracker(LineIssueTracker):
     """Track lines with merge artifacts.
     These are leftovers from a ``git merge`` that wasn't fully edited."""
 
@@ -153,22 +164,18 @@ class MergeArtifactIssueTracker(IssueTracker):
         super().__init__()
         self.heading = "Merge artifact:"
 
-    def issue_with_line(self, filepath, line):
+    def issue_with_line(self, line, _filepath):
         # Detect leftover git conflict markers.
         if line.startswith(b'<<<<<<< ') or line.startswith(b'>>>>>>> '):
             return True
         if line.startswith(b'||||||| '): # from merge.conflictStyle=diff3
             return True
         if line.rstrip(b'\r\n') == b'=======' and \
-           not filepath.endswith('.md'):
+           not _filepath.endswith('.md'):
             return True
         return False
 
-    def check_file_line(self, filepath, line, line_number):
-        if self.issue_with_line(filepath, line):
-            self.record_issue(filepath, line_number)
-
-class TodoIssueTracker(IssueTracker):
+class TodoIssueTracker(LineIssueTracker):
     """Track lines containing ``TODO``."""
 
     def __init__(self):
@@ -180,7 +187,7 @@ class TodoIssueTracker(IssueTracker):
             "pull_request_template.md",
         ]
 
-    def issue_with_line(self, line):
+    def issue_with_line(self, line, _filepath):
         return b"todo" in line.lower()