checkpatch: warn on possible bare return

void functions do not need to have a return statement, because
such statements are redundant. Warn the user of such instances.

An interim line check is added to allow gathering additional
context for each line that is being processed.

Signed-off-by: Bala Sankaran <bsankara@redhat.com>
Signed-off-by: Ben Pfaff <blp@ovn.org>

utilities/checkpatch.py

@@ -74,8 +74,12 @@ try:
 except:
     no_spellcheck = True
 
+RETURN_CHECK_INITIAL_STATE = 0
+RETURN_CHECK_STATE_WITH_RETURN = 1
+RETURN_CHECK_AWAITING_BRACE = 2
 __errors = 0
 __warnings = 0
+empty_return_check_state = 0
 print_file_name = None
 checking_file = False
 total_line = 0
@@ -158,6 +162,7 @@ __regex_conditional_else_bracing2 = re.compile(r'^\s*}\selse\s*$')
 __regex_has_xxx_mark = re.compile(r'.*xxx.*', re.IGNORECASE)
 __regex_added_doc_rst = re.compile(
                     r'\ndiff .*Documentation/.*rst\nnew file mode')
+__regex_empty_return = re.compile(r'\s*return;')
 
 skip_leading_whitespace_check = False
 skip_trailing_whitespace_check = False
@@ -454,6 +459,33 @@ def check_new_docs_index(text):
     return __check_new_docs(text, 'rst')
 
 
+def empty_return_with_brace(line):
+    """Returns TRUE if a function contains a return; followed
+       by one or more line feeds and terminates with a '}'
+       at start of line"""
+
+    def empty_return(line):
+        """Returns TRUE if a function has a 'return;'"""
+        return __regex_empty_return.match(line) is not None
+
+    global empty_return_check_state
+    if empty_return_check_state == RETURN_CHECK_INITIAL_STATE \
+       and empty_return(line):
+        empty_return_check_state = RETURN_CHECK_STATE_WITH_RETURN
+    elif empty_return_check_state == RETURN_CHECK_STATE_WITH_RETURN \
+         and (re.match(r'^}$', line) or len(line) == 0):
+        if re.match('^}$', line):
+            empty_return_check_state = RETURN_CHECK_AWAITING_BRACE
+    else:
+        empty_return_check_state = RETURN_CHECK_INITIAL_STATE
+
+    if empty_return_check_state == RETURN_CHECK_AWAITING_BRACE:
+        empty_return_check_state = RETURN_CHECK_INITIAL_STATE
+        return True
+
+    return False
+
+
 file_checks = [
         {'regex': __regex_added_doc_rst,
          'check': check_new_docs_index},
@@ -505,6 +537,13 @@ checks = [
     {'regex': '(\.c|\.h)(\.in)?$', 'match_name': None,
      'prereq': lambda x: has_comment(x),
      'check': lambda x: check_comment_spelling(x)},
+
+    {'regex': '(\.c|\.h)(\.in)?$', 'match_name': None,
+     'check': lambda x: empty_return_with_brace(x),
+     'interim_line': True,
+     'print':
+     lambda: print_warning("Empty return followed by brace, consider omitting")
+     },
 ]
 
 
@@ -599,6 +638,29 @@ def run_checks(current_file, line, lineno):
         print("%s\n" % line)
 
 
+def interim_line_check(current_file, line, lineno):
+    """Runs the various checks for the particular interim line.  This will
+       take filename into account, and will check for the 'interim_line'
+       key before running the check."""
+    global checking_file, total_line
+    print_line = False
+    for check in get_file_type_checks(current_file):
+        if 'prereq' in check and not check['prereq'](line):
+            continue
+        if 'interim_line' in check and check['interim_line']:
+            if check['check'](line):
+                if 'print' in check:
+                    check['print']()
+                    print_line = True
+
+    if print_line:
+        if checking_file:
+            print("%s:%d:" % (current_file, lineno))
+        else:
+            print("#%d FILE: %s:%d:" % (total_line, current_file, lineno))
+        print("%s\n" % line)
+
+
 def run_file_checks(text):
     """Runs the various checks for the text."""
     for check in file_checks:
@@ -607,7 +669,8 @@ def run_file_checks(text):
 
 
 def ovs_checkpatch_parse(text, filename):
-    global print_file_name, total_line, checking_file
+    global print_file_name, total_line, checking_file, \
+        empty_return_check_state
 
     PARSE_STATE_HEADING = 0
     PARSE_STATE_DIFF_HEADER = 1
@@ -680,17 +743,22 @@ def ovs_checkpatch_parse(text, filename):
                 continue
             reset_line_number = hunk_differences.match(line)
             if reset_line_number:
+                empty_return_check_state = RETURN_CHECK_INITIAL_STATE
                 lineno = int(reset_line_number.group(3))
                 if lineno < 0:
                     lineno = -1 * lineno
                 lineno -= 1
+
             if is_subtracted_line(line):
                 lineno -= 1
-            if not is_added_line(line):
                 continue
 
             cmp_line = added_line(line)
 
+            if not is_added_line(line):
+                interim_line_check(current_file, cmp_line, lineno)
+                continue
+
             # Skip files which have /datapath in them, since they are
             # linux or windows coding standards
             if current_file.startswith('datapath'):