Make tidy check that opening and closing braces that begin a line do so with proper alignment.

python/tidy/servo_tidy/tidy.py

@@ -450,6 +450,8 @@ def check_rust(file_name, lines):
     prev_crate = {}
     prev_mod = {}
     prev_feature_name = ""
+    indent = 0
+    prev_indent = 0
 
     decl_message = "{} is not in alphabetical order"
     decl_expected = "\n\t\033[93mexpected: {}\033[0m"
@@ -458,6 +460,9 @@ def check_rust(file_name, lines):
     for idx, original_line in enumerate(lines):
         # simplify the analysis
         line = original_line.strip()
+        prev_indent = indent
+        indent = len(original_line) - len(line)
+
         is_attribute = re.search(r"#\[.*\]", line)
         is_comment = re.search(r"^//|^/\*|^\*", line)
 
@@ -577,11 +582,17 @@ def check_rust(file_name, lines):
             yield (idx + 1, "found an empty line following a {")
         prev_open_brace = line.endswith("{")
 
+        # ensure a line starting with { or } has a number of leading spaces that is a multiple of 4
+        if line.startswith(("{", "}")):
+            match = re.match(r"(?: {4})* {1,3}([{}])", original_line)
+            if match:
+                if indent != prev_indent - 4:
+                    yield (idx + 1, "space before {} is not a multiple of 4".format(match.group(1)))
+
         # check alphabetical order of extern crates
         if line.startswith("extern crate "):
             # strip "extern crate " from the begin and ";" from the end
             crate_name = line[13:-1]
-            indent = len(original_line) - len(line)
             if indent not in prev_crate:
                 prev_crate[indent] = ""
             if prev_crate[indent] > crate_name:
@@ -616,7 +627,6 @@ def check_rust(file_name, lines):
         # into a single import block
         if line.startswith("use "):
             import_block = True
-            indent = len(original_line) - len(line)
             if not line.endswith(";") and '{' in line:
                 yield (idx + 1, "use statement spans multiple lines")
             if '{ ' in line:
@@ -645,7 +655,6 @@ def check_rust(file_name, lines):
 
         # modules must be in the same line and alphabetically sorted
         if line.startswith("mod ") or line.startswith("pub mod "):
-            indent = len(original_line) - len(line)
             # strip /(pub )?mod/ from the left and ";" from the right
             mod = line[4:-1] if line.startswith("mod ") else line[8:-1]
 

python/tidy/servo_tidy_tests/rust_tidy.rs

@@ -63,4 +63,13 @@ impl test {
 
     let var
         = "val";
+
+    fn test_fun4()
+       {
+     }
+    let var = if true {
+          "true"
+      } else { // Should not trigger
+          "false"
+      } // Should not trigger
 }

python/tidy/servo_tidy_tests/test_tidy.py

@@ -131,6 +131,8 @@ class CheckTidiness(unittest.TestCase):
         self.assertEqual('extra space after (', errors.next()[2])
         self.assertEqual('extra space after test_fun', errors.next()[2])
         self.assertEqual('no = in the beginning of line', errors.next()[2])
+        self.assertEqual('space before { is not a multiple of 4', errors.next()[2])
+        self.assertEqual('space before } is not a multiple of 4', errors.next()[2])
         self.assertNoMoreErrors(errors)
 
         feature_errors = tidy.collect_errors_for_files(iterFile('lib.rs'), [], [tidy.check_rust], print_text=False)