Fix false-positive in unique_ptr presubmit check with mismatched <>

Presubmit was preventing upload of crrev.com/c/5534806 due to changed
line:
` std::unique_ptr<WebAppInstallInfo>>(`
being interpreted as a call to the unique_ptr constructor. IIUC this was
because the check only looks at the changed lines and missed the extra
">" indicating this was really part of a larger template expression.

Added a condition that suppresses the check when selected brackets are
mismatching (ie. number of < and > are not equal). Added tests for these
cases.

Change-Id: I260b7826eb1f55764a8a93b3402888afa5032eed
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5538411
Reviewed-by: Dirk Pranke <[email protected]>
Auto-Submit: Glen Robertson <[email protected]>
Commit-Queue: Glen Robertson <[email protected]>
Cr-Commit-Position: refs/heads/main@{#1301700}

PRESUBMIT.py

@@ -3548,8 +3548,9 @@ def CheckForAnonymousVariables(input_api, output_api):
 
 def CheckUniquePtrOnUpload(input_api, output_api):
     # Returns whether |template_str| is of the form <T, U...> for some types T
-    # and U. Assumes that |template_str| is already in the form <...>.
-    def HasMoreThanOneArg(template_str):
+    # and U, or is invalid due to mismatched angle bracket pairs. Assumes that
+    # |template_str| is already in the form <...>.
+    def HasMoreThanOneArgOrInvalid(template_str):
         # Level of <...> nesting.
         nesting = 0
         for c in template_str:
@@ -3559,6 +3560,9 @@ def HasMoreThanOneArg(template_str):
                 nesting -= 1
             elif c == ',' and nesting == 1:
                 return True
+        if nesting != 0:
+          # Invalid.
+          return True
         return False
 
     file_inclusion_pattern = [r'.+%s' % _IMPLEMENTATION_EXTENSIONS]
@@ -3615,7 +3619,7 @@ def HasMoreThanOneArg(template_str):
             # bar = std::unique_ptr<T, U>(foo);
             local_path = f.LocalPath()
             return_construct_result = return_construct_pattern.search(line)
-            if return_construct_result and not HasMoreThanOneArg(
+            if return_construct_result and not HasMoreThanOneArgOrInvalid(
                     return_construct_result.group('template_arg')):
                 problems_constructor.append(
                     '%s:%d\n    %s' % (local_path, line_number, line.strip()))

PRESUBMIT_test.py

@@ -3164,6 +3164,9 @@ def testFalsePositives(self):
       ]),
       MockFile('dir/nested.cc', ['set<std::unique_ptr<T>>();']),
       MockFile('dir/nested2.cc', ['map<U, std::unique_ptr<T>>();']),
+      # Changed line is inside a multiline template block.
+      MockFile('dir/template.cc', [' std::unique_ptr<T>>(']),
+      MockFile('dir/template2.cc', [' std::unique_ptr<T>>()']),
 
       # Two-argument invocation of std::unique_ptr is exempt because there is
       # no equivalent using std::make_unique.
@@ -3172,7 +3175,7 @@ def testFalsePositives(self):
     ]
 
     results = PRESUBMIT.CheckUniquePtrOnUpload(mock_input_api, MockOutputApi())
-    self.assertEqual(0, len(results))
+    self.assertEqual([], results)
 
 class CheckNoDirectIncludesHeadersWhichRedefineStrCat(unittest.TestCase):
   def testBlocksDirectIncludes(self):