1 files changed, 161 insertions, 0 deletions
diff --git a/clang-tools-extra/test/clang-tidy/performance-implicit-conversion-in-loop.cpp b/clang-tools-extra/test/clang-tidy/performance-implicit-conversion-in-loop.cpp
new file mode 100644
index 00000000000..7b1ad3967f0
--- /dev/null
+++ b/clang-tools-extra/test/clang-tidy/performance-implicit-conversion-in-loop.cpp
@@ -0,0 +1,161 @@
+// RUN: %check_clang_tidy %s performance-implicit-conversion-in-loop %t
+
+// ---------- Classes used in the tests ----------
+
+// Iterator returning by value.
+template <typename T>
+struct Iterator {
+  void operator++();
+  T operator*();
+  bool operator!=(const Iterator& other);
+};
+
+// Iterator returning by reference.
+template <typename T>
+struct RefIterator {
+  void operator++();
+  T& operator*();
+  bool operator!=(const RefIterator& other);
+};
+
+// The template argument is an iterator type, and a view is an object you can
+// run a for loop on.
+template <typename T>
+struct View {
+  T begin();
+  T end();
+};
+
+// With this class, the implicit conversion is a call to the (implicit)
+// constructor of the class.
+template <typename T>
+class ImplicitWrapper {
+ public:
+  // Implicit!
+  ImplicitWrapper(const T& t);
+};
+
+// With this class, the implicit conversion is a call to the conversion
+// operators of SimpleClass and ComplexClass.
+template <typename T>
+class OperatorWrapper {
+ public:
+  explicit OperatorWrapper(const T& t);
+};
+
+struct SimpleClass {
+  int foo;
+  operator OperatorWrapper<SimpleClass>();
+};
+
+// The materialize expression is not the same when the class has a destructor,
+// so we make sure we cover that case too.
+class ComplexClass {
+ public:
+  ComplexClass();
+  ~ComplexClass();
+  operator OperatorWrapper<ComplexClass>();
+};
+
+typedef View<Iterator<SimpleClass>> SimpleView;
+typedef View<RefIterator<SimpleClass>> SimpleRefView;
+typedef View<Iterator<ComplexClass>> ComplexView;
+typedef View<RefIterator<ComplexClass>> ComplexRefView;
+
+// ---------- The test themselves ----------
+// For each test we do, in the same order, const ref, non const ref, const
+// value, non const value.
+
+void SimpleClassIterator() {
+  for (const SimpleClass& foo : SimpleView()) {}
+  // This line does not compile because a temporary cannot be assigned to a non
+  // const reference.
+  // for (SimpleClass& foo : SimpleView()) {}
+  for (const SimpleClass foo : SimpleView()) {}
+  for (SimpleClass foo : SimpleView()) {}
+}
+
+void SimpleClassRefIterator() {
+  for (const SimpleClass& foo : SimpleRefView()) {}
+  for (SimpleClass& foo : SimpleRefView()) {}
+  for (const SimpleClass foo : SimpleRefView()) {}
+  for (SimpleClass foo : SimpleRefView()) {}
+}
+
+void ComplexClassIterator() {
+  for (const ComplexClass& foo : ComplexView()) {}
+  // for (ComplexClass& foo : ComplexView()) {}
+  for (const ComplexClass foo : ComplexView()) {}
+  for (ComplexClass foo : ComplexView()) {}
+}
+
+void ComplexClassRefIterator() {
+  for (const ComplexClass& foo : ComplexRefView()) {}
+  for (ComplexClass& foo : ComplexRefView()) {}
+  for (const ComplexClass foo : ComplexRefView()) {}
+  for (ComplexClass foo : ComplexRefView()) {}
+}
+
+void ImplicitSimpleClassIterator() {
+  for (const ImplicitWrapper<SimpleClass>& foo : SimpleView()) {}
+  // CHECK-MESSAGES: [[@LINE-1]]:{{[0-9]*}}: warning: the type of the loop variable 'foo' is different from the one returned by the iterator and generates an implicit conversion; you can either change the type to the matching one ('const SimpleClass &' but 'const auto&' is always a valid option) or remove the reference to make it explicit that you are creating a new value [performance-implicit-conversion-in-loop]
+  // for (ImplicitWrapper<SimpleClass>& foo : SimpleView()) {}
+  for (const ImplicitWrapper<SimpleClass> foo : SimpleView()) {}
+  for (ImplicitWrapper<SimpleClass>foo : SimpleView()) {}
+}
+
+void ImplicitSimpleClassRefIterator() {
+  for (const ImplicitWrapper<SimpleClass>& foo : SimpleRefView()) {}
+  // CHECK-MESSAGES: [[@LINE-1]]:{{[0-9]*}}: warning: the type of the{{.*'const SimpleClass &'.*}}
+  // for (ImplicitWrapper<SimpleClass>& foo : SimpleRefView()) {}
+  for (const ImplicitWrapper<SimpleClass> foo : SimpleRefView()) {}
+  for (ImplicitWrapper<SimpleClass>foo : SimpleRefView()) {}
+}
+
+void ImplicitComplexClassIterator() {
+  for (const ImplicitWrapper<ComplexClass>& foo : ComplexView()) {}
+  // CHECK-MESSAGES: [[@LINE-1]]:{{[0-9]*}}: warning: the type of the{{.*'const ComplexClass &'.*}}
+  // for (ImplicitWrapper<ComplexClass>& foo : ComplexView()) {}
+  for (const ImplicitWrapper<ComplexClass> foo : ComplexView()) {}
+  for (ImplicitWrapper<ComplexClass>foo : ComplexView()) {}
+}
+
+void ImplicitComplexClassRefIterator() {
+  for (const ImplicitWrapper<ComplexClass>& foo : ComplexRefView()) {}
+  // CHECK-MESSAGES: [[@LINE-1]]:{{[0-9]*}}: warning: the type of the{{.*'const ComplexClass &'.*}}
+  // for (ImplicitWrapper<ComplexClass>& foo : ComplexRefView()) {}
+  for (const ImplicitWrapper<ComplexClass> foo : ComplexRefView()) {}
+  for (ImplicitWrapper<ComplexClass>foo : ComplexRefView()) {}
+}
+
+void OperatorSimpleClassIterator() {
+  for (const OperatorWrapper<SimpleClass>& foo : SimpleView()) {}
+  // CHECK-MESSAGES: [[@LINE-1]]:{{[0-9]*}}: warning: the type of the{{.*'const SimpleClass &'.*}}
+  // for (OperatorWrapper<SimpleClass>& foo : SimpleView()) {}
+  for (const OperatorWrapper<SimpleClass> foo : SimpleView()) {}
+  for (OperatorWrapper<SimpleClass>foo : SimpleView()) {}
+}
+
+void OperatorSimpleClassRefIterator() {
+  for (const OperatorWrapper<SimpleClass>& foo : SimpleRefView()) {}
+  // CHECK-MESSAGES: [[@LINE-1]]:{{[0-9]*}}: warning: the type of the{{.*'const SimpleClass &'.*}}
+  // for (OperatorWrapper<SimpleClass>& foo : SimpleRefView()) {}
+  for (const OperatorWrapper<SimpleClass> foo : SimpleRefView()) {}
+  for (OperatorWrapper<SimpleClass>foo : SimpleRefView()) {}
+}
+
+void OperatorComplexClassIterator() {
+  for (const OperatorWrapper<ComplexClass>& foo : ComplexView()) {}
+  // CHECK-MESSAGES: [[@LINE-1]]:{{[0-9]*}}: warning: the type of the{{.*'const ComplexClass &'.*}}
+  // for (OperatorWrapper<ComplexClass>& foo : ComplexView()) {}
+  for (const OperatorWrapper<ComplexClass> foo : ComplexView()) {}
+  for (OperatorWrapper<ComplexClass>foo : ComplexView()) {}
+}
+
+void OperatorComplexClassRefIterator() {
+  for (const OperatorWrapper<ComplexClass>& foo : ComplexRefView()) {}
+  // CHECK-MESSAGES: [[@LINE-1]]:{{[0-9]*}}: warning: the type of the{{.*'const ComplexClass &'.*}}
+  // for (OperatorWrapper<ComplexClass>& foo : ComplexRefView()) {}
+  for (const OperatorWrapper<ComplexClass> foo : ComplexRefView()) {}
+  for (OperatorWrapper<ComplexClass>foo : ComplexRefView()) {}
+}