Reland "Adding PRESUBMIT check to avoid mixing C, C++ and Objc-C/Obj-C++.""

This reverts commit 034a6b8a4cdf151ae7377c87c5b2b6156d658173.

Reason for revert: Trying to fix the issue of rtc_base:rtc_base which has 2 kind of source files but in exclusive if branches.

Original change's description:
> Revert "Adding PRESUBMIT check to avoid mixing C, C++ and Objc-C/Obj-C++."
> 
> This reverts commit 0c15c5332fea2bbf5fe29dd806f9f4e606eeb9b8.
> 
> Reason for revert: This causes problems in this moment. I have to fix a target in rtc_base before landing this presubmit check.
> 
> Original change's description:
> > Adding PRESUBMIT check to avoid mixing C, C++ and Objc-C/Obj-C++.
> > 
> > The error message will be something like:
> > 
> > GN targets cannot mix .c (or .cc) and .m (or .mm) source files.
> > Please create a separate target for each collection of sources.
> > Mixed sources:
> > {
> >   BUILD_GN_PATH: [
> >     [
> >       TARGET_NAME,
> >       [
> >         SOURCES
> >       ]
> >     ],
> >     ...
> >   ],
> >   ...
> > }
> > 
> > Bug: webrtc:7743
> > Change-Id: I45dd2c621b830e5aeb081fa8d17c9497a49c2554
> > Reviewed-on: https://webrtc-review.googlesource.com/1980
> > Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
> > Reviewed-by: Henrik Kjellander <kjellander@webrtc.org>
> > Cr-Commit-Position: refs/heads/master@{#19897}
> 
> TBR=kjellander@webrtc.org,mbonadei@webrtc.org
> 
> Change-Id: I73ff609b0140719473afd36ead1632e5cc3b41f6
> No-Presubmit: true
> No-Tree-Checks: true
> No-Try: true
> Bug: webrtc:7743
> Reviewed-on: https://webrtc-review.googlesource.com/2180
> Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
> Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
> Cr-Commit-Position: refs/heads/master@{#19898}

TBR=kjellander@webrtc.org,mbonadei@webrtc.org

Change-Id: I18dbb5a6a01ac2a184446542c29b25a3e33508ea
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: webrtc:7743
Reviewed-on: https://webrtc-review.googlesource.com/2181
Reviewed-by: Henrik Kjellander <kjellander@webrtc.org>
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#19900}
diff --git a/presubmit_test.py b/presubmit_test.py
index f17a20f..c9ee80b 100755
--- a/presubmit_test.py
+++ b/presubmit_test.py
@@ -60,7 +60,7 @@
     shutil.rmtree(self.tmp_dir, ignore_errors=True)
 
   def testErrorIfProtoFileDoesNotEndWithNewline(self):
-    self.__GenerateProtoWithoutNewlineAtTheEnd()
+    self._GenerateProtoWithoutNewlineAtTheEnd()
     self.input_api.files = [MockFile(self.proto_file_path)]
     errors = PRESUBMIT.CheckNewlineAtTheEndOfProtoFiles(self.input_api,
                                                         self.output_api)
@@ -70,13 +70,13 @@
         str(errors[0]))
 
   def testNoErrorIfProtoFileEndsWithNewline(self):
-    self.__GenerateProtoWithNewlineAtTheEnd()
+    self._GenerateProtoWithNewlineAtTheEnd()
     self.input_api.files = [MockFile(self.proto_file_path)]
     errors = PRESUBMIT.CheckNewlineAtTheEndOfProtoFiles(self.input_api,
                                                         self.output_api)
     self.assertEqual(0, len(errors))
 
-  def __GenerateProtoWithNewlineAtTheEnd(self):
+  def _GenerateProtoWithNewlineAtTheEnd(self):
     with open(self.proto_file_path, 'w') as f:
       f.write(textwrap.dedent("""
         syntax = "proto2";
@@ -84,7 +84,7 @@
         package webrtc.audioproc;
       """))
 
-  def __GenerateProtoWithoutNewlineAtTheEnd(self):
+  def _GenerateProtoWithoutNewlineAtTheEnd(self):
     with open(self.proto_file_path, 'w') as f:
       f.write(textwrap.dedent("""
         syntax = "proto2";
@@ -92,5 +92,157 @@
         package webrtc.audioproc;"""))
 
 
+class CheckNoMixingSourcesTest(unittest.TestCase):
+
+  def setUp(self):
+    self.tmp_dir = tempfile.mkdtemp()
+    self.file_path = os.path.join(self.tmp_dir, 'BUILD.gn')
+    self.input_api = MockInputApi()
+    self.output_api = MockOutputApi()
+
+  def tearDown(self):
+    shutil.rmtree(self.tmp_dir, ignore_errors=True)
+
+  def testErrorIfCAndCppAreMixed(self):
+    self._AssertNumberOfErrorsWithSources(1, ['foo.c', 'bar.cc', 'bar.h'])
+
+  def testErrorIfCAndObjCAreMixed(self):
+    self._AssertNumberOfErrorsWithSources(1, ['foo.c', 'bar.m', 'bar.h'])
+
+  def testErrorIfCAndObjCppAreMixed(self):
+    self._AssertNumberOfErrorsWithSources(1, ['foo.c', 'bar.mm', 'bar.h'])
+
+  def testErrorIfCppAndObjCAreMixed(self):
+    self._AssertNumberOfErrorsWithSources(1, ['foo.cc', 'bar.m', 'bar.h'])
+
+  def testErrorIfCppAndObjCppAreMixed(self):
+    self._AssertNumberOfErrorsWithSources(1, ['foo.cc', 'bar.mm', 'bar.h'])
+
+  def testNoErrorIfOnlyC(self):
+    self._AssertNumberOfErrorsWithSources(0, ['foo.c', 'bar.c', 'bar.h'])
+
+  def testNoErrorIfOnlyCpp(self):
+    self._AssertNumberOfErrorsWithSources(0, ['foo.cc', 'bar.cc', 'bar.h'])
+
+  def testNoErrorIfOnlyObjC(self):
+    self._AssertNumberOfErrorsWithSources(0, ['foo.m', 'bar.m', 'bar.h'])
+
+  def testNoErrorIfOnlyObjCpp(self):
+    self._AssertNumberOfErrorsWithSources(0, ['foo.mm', 'bar.mm', 'bar.h'])
+
+  def testNoErrorIfObjCAndObjCppAreMixed(self):
+    self._AssertNumberOfErrorsWithSources(0, ['foo.m', 'bar.mm', 'bar.h'])
+
+  def testNoErrorIfSourcesAreInExclusiveIfBranches(self):
+    self._GenerateBuildFile(textwrap.dedent("""
+      rtc_source_set("bar_foo") {
+        if (is_win) {
+          sources = [
+            "bar.cc",
+          ],
+        }
+        if (is_ios) {
+          sources = [
+            "bar.mm",
+          ],
+        }
+      }
+      rtc_source_set("foo_bar") {
+        if (is_win) {
+          sources = [
+            "foo.cc",
+          ],
+        }
+        if (is_ios) {
+          sources = [
+            "foo.mm",
+          ],
+        }
+      }
+    """))
+    self.input_api.files = [MockFile(self.file_path)]
+    errors = PRESUBMIT.CheckNoMixingSources(self.input_api,
+                                            [MockFile(self.file_path)],
+                                            self.output_api)
+    self.assertEqual(0, len(errors))
+
+  def testErrorIfSourcesAreNotInExclusiveIfBranches(self):
+    self._GenerateBuildFile(textwrap.dedent("""
+      rtc_source_set("bar_foo") {
+        if (is_win) {
+          sources = [
+            "bar.cc",
+          ],
+        }
+        if (foo_bar) {
+          sources += [
+            "bar.mm",
+          ],
+        }
+      }
+      rtc_source_set("foo_bar") {
+        if (is_win) {
+          sources = [
+            "foo.cc",
+          ],
+        }
+        if (foo_bar) {
+          sources += [
+            "foo.mm",
+          ],
+        }
+        if (is_ios) {
+          sources = [
+            "bar.m",
+            "bar.c",
+          ],
+        }
+      }
+    """))
+    self.input_api.files = [MockFile(self.file_path)]
+    errors = PRESUBMIT.CheckNoMixingSources(self.input_api,
+                                            [MockFile(self.file_path)],
+                                            self.output_api)
+    self.assertEqual(1, len(errors))
+    self.assertTrue('bar.cc' in str(errors[0]))
+    self.assertTrue('bar.mm' in str(errors[0]))
+    self.assertTrue('foo.cc' in str(errors[0]))
+    self.assertTrue('foo.mm' in str(errors[0]))
+    self.assertTrue('bar.m' in str(errors[0]))
+    self.assertTrue('bar.c' in str(errors[0]))
+
+  def _AssertNumberOfErrorsWithSources(self, number_of_errors, sources):
+    assert 3 == len(sources), 'This function accepts a list of 3 source files'
+    self._GenerateBuildFile(textwrap.dedent("""
+      rtc_static_library("bar_foo") {
+        sources = [
+          "%s",
+          "%s",
+          "%s",
+        ],
+      }
+      rtc_source_set("foo_bar") {
+        sources = [
+          "%s",
+          "%s",
+          "%s",
+        ],
+      }
+    """ % (tuple(sources) * 2)))
+    self.input_api.files = [MockFile(self.file_path)]
+    errors = PRESUBMIT.CheckNoMixingSources(self.input_api,
+                                            [MockFile(self.file_path)],
+                                            self.output_api)
+    self.assertEqual(number_of_errors, len(errors))
+    if number_of_errors == 1:
+      for source in sources:
+        if not source.endswith('.h'):
+          self.assertTrue(source in str(errors[0]))
+
+  def _GenerateBuildFile(self, content):
+    with open(self.file_path, 'w') as f:
+      f.write(content)
+
+
 if __name__ == '__main__':
   unittest.main()