Add heuristics for C++ macros

lib/linguist/heuristics.yml

@@ -835,6 +835,7 @@ named_patterns:
   - '^[ \t]*catch\s*\('
   - '^[ \t]*(class|(using[ \t]+)?namespace)\s+\w+'
   - '^[ \t]*(private|public|protected):$'
+  - '__has_cpp_attribute|__cplusplus >'
   - 'std::\w+'
   euphoria:
   - '^\s*namespace\s'

samples/C++/NoDiscard.h

@@ -0,0 +1,24 @@
+//===--- NoDiscard.h ------------------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2022 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef SWIFT_BASIC_NODISCARD_H
+#define SWIFT_BASIC_NODISCARD_H
+
+#if __cplusplus > 201402l && __has_cpp_attribute(nodiscard)
+#define SWIFT_NODISCARD [[nodiscard]]
+#elif __has_cpp_attribute(clang::warn_unused_result)
+#define SWIFT_NODISCARD [[clang::warn_unused_result]]
+#else
+#define SWIFT_NODISCARD
+#endif
+
+#endif

test/test_blob.rb

@@ -260,7 +260,7 @@ def test_vendored
 
   def test_language
     allowed_failures = {
-      "#{samples_path}/C++/rpc.h" => ["C", "C++"],
+      "#{samples_path}/C/rpc.h" => ["C", "C++"],
     }
     Samples.each do |sample|
       blob = sample_blob_memory(sample[:path])

test/test_classifier.rb

@@ -46,7 +46,7 @@ def test_instance_classify_nil
   def test_classify_ambiguous_languages
     # Failures are reasonable in some cases, such as when a file is fully valid in more than one language.
     allowed_failures = {
-      "#{samples_path}/C++/rpc.h" => ["C", "C++"],
+      "#{samples_path}/C/rpc.h" => ["C", "C++"],
     }
 
     # Skip extensions with catch-all rule

test/test_file_blob.rb

@@ -670,7 +670,7 @@ def test_documentation
   def test_language
     # Failures are reasonable in some cases, such as when a file is fully valid in more than one language.
     allowed_failures = {
-      "#{samples_path}/C++/rpc.h" => ["C", "C++"],
+      "#{samples_path}/C/rpc.h" => ["C", "C++"],
     }
     Samples.each do |sample|
       blob = sample_blob(sample[:path])