Auto merge of #11472 - jdm:wip, r=mbrubeck

Report blank lines that follow an open brace

This automates something that I find myself frequently commenting on in PRs.

---
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- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] There are tests for these changes OR

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python/tidy/servo_tidy/tidy.py

@@ -299,6 +299,7 @@ def check_rust(file_name, lines):
     whitespace = False
 
     prev_use = None
+    prev_open_brace = False
     current_indent = 0
     prev_crate = {}
     prev_mod = {}
@@ -342,10 +343,10 @@ def check_rust(file_name, lines):
             line = re.sub(r"'(\\.|[^\\'])*?'", "''", line)
 
         # get rid of comments
-        line = re.sub('//.*?$|/\*.*?$|^\*.*?$', '', line)
+        line = re.sub('//.*?$|/\*.*?$|^\*.*?$', '//', line)
 
         # get rid of attributes that do not contain =
-        line = re.sub('^#[A-Za-z0-9\(\)\[\]_]*?$', '', line)
+        line = re.sub('^#[A-Za-z0-9\(\)\[\]_]*?$', '#[]', line)
 
         # flag this line if it matches one of the following regular expressions
         # tuple format: (pattern, format_message, filter_function(match, line))
@@ -401,6 +402,10 @@ def check_rust(file_name, lines):
 
                 yield (idx + 1, message.format(*match.groups(), **match.groupdict()))
 
+        if prev_open_brace and not line:
+            yield (idx + 1, "found an empty line following a {")
+        prev_open_brace = line.endswith("{")
+
         # check alphabetical order of extern crates
         if line.startswith("extern crate "):
             # strip "extern crate " from the begin and ";" from the end

python/tidy/servo_tidy_tests/test_tidy.py

@@ -58,6 +58,7 @@ class CheckTidiness(unittest.TestCase):
         self.assertTrue('mod declaration is not in alphabetical order' in errors.next()[2])
         self.assertEqual('mod declaration spans multiple lines', errors.next()[2])
         self.assertTrue('extern crate declaration is not in alphabetical order' in errors.next()[2])
+        self.assertEqual('found an empty line following a {', errors.next()[2])
         self.assertEqual('missing space before ->', errors.next()[2])
         self.assertEqual('missing space after ->', errors.next()[2])
         self.assertEqual('missing space after :', errors.next()[2])