Speed up custom checkers in ./tools/lint.

The main thing here is to make looping over lines be the inner
loop, instead of looping over rules.  This keeps regexes in
cache, and it also avoids some O(N) checks.

This is a significant speedup for me, reducing time from 16s
to 11s.

tools/linter_lib/custom_check.py

@@ -15,12 +15,12 @@ def build_custom_checkers(by_lang):
     def custom_check_file(fn, rules, skip_rules=None, max_length=None):
         # type: (str, RuleList, Optional[Any], Optional[int]) -> bool
         failed = False
-        lineFlag = False
+
+        line_tups = []
         for i, line in enumerate(open(fn)):
             line_newline_stripped = line.strip('\n')
             line_fully_stripped = line_newline_stripped.strip()
             skip = False
-            lineFlag = True
             for rule in skip_rules or []:
                 if re.match(rule, line):
                     skip = True
@@ -28,12 +28,14 @@ def build_custom_checkers(by_lang):
                 continue
             if skip:
                 continue
+            tup = (i, line, line_newline_stripped, line_fully_stripped)
+            line_tups.append(tup)
+
+        rules_to_apply = []
+        fn_dirname = os.path.dirname(fn)
         for rule in rules:
             exclude_list = rule.get('exclude', set())
-                if fn in exclude_list or os.path.dirname(fn) in exclude_list:
+            if fn in exclude_list or fn_dirname in exclude_list:
-                    continue
-                exclude_list = rule.get('exclude_line', set())
-                if (fn, line_fully_stripped) in exclude_list:
                 continue
             if rule.get("include_only"):
                 found = False
@@ -42,6 +44,16 @@ def build_custom_checkers(by_lang):
                         found = True
                 if not found:
                     continue
+            rules_to_apply.append(rule)
+
+        for rule in rules_to_apply:
+            exclude_list = rule.get('exclude_line', set())
+
+            pattern = rule['pattern']
+            for (i, line, line_newline_stripped, line_fully_stripped) in line_tups:
+                if (fn, line_fully_stripped) in exclude_list:
+                    continue
+
                 try:
                     line_to_check = line_fully_stripped
                     if rule.get('strip') is not None:
@@ -49,13 +61,16 @@ def build_custom_checkers(by_lang):
                             line_to_check = line_newline_stripped
                         else:
                             raise Exception("Invalid strip rule")
-                    if re.search(rule['pattern'], line_to_check):
+                    if re.search(pattern, line_to_check):
                         sys.stdout.write(rule['description'] + ' at %s line %s:\n' % (fn, i+1))
                         print(line)
                         failed = True
                 except Exception:
                     print("Exception with %s at %s line %s" % (rule['pattern'], fn, i+1))
                     traceback.print_exc()
+
+        lastLine = None
+        for (i, line, line_newline_stripped, line_fully_stripped) in line_tups:
             if isinstance(line, bytes):
                 line_length = len(line.decode("utf-8"))
             else:
@@ -68,9 +83,11 @@ def build_custom_checkers(by_lang):
                 print("Line too long (%s) at %s line %s: %s" % (len(line), fn, i+1, line_newline_stripped))
                 failed = True
             lastLine = line
-        if lineFlag and '\n' not in lastLine:
+
+        if lastLine and ('\n' not in lastLine):
             print("No newline at the end of file.  Fix with `sed -i '$a\\' %s`" % (fn,))
             failed = True
+
         return failed
 
     whitespace_rules = [