CodeHealth: Enabling clang-tidy google-explicit-constructor (#3250)

* Adding google-explicit-constructor to .clang-tidy

* clang-tidy explicit attr.h (all automatic)

* clang-tidy explicit cast.h (all automatic)

* clang-tidy detail/init.h (1 NOLINT)

* clang-tidy detail/type_caster_base.h (2 NOLINT)

* clang-tidy pybind11.h (7 NOLINT)

* clang-tidy detail/common.h (3 NOLINT)

* clang-tidy detail/descr.h (2 NOLINT)

* clang-tidy pytypes.h (23 NOLINT, only 1 explicit)

* clang-tidy eigen.h (7 NOLINT, 0 explicit)

* Adding 2 explicit in functional.h

* Adding 4 explicit in iostream.h

* clang-tidy numpy.h (1 NOLINT, 1 explicit)

* clang-tidy embed.h (0 NOLINT, 1 explicit)

* clang-tidy tests/local_bindings.h (0 NOLINT, 4 explicit)

* clang-tidy tests/pybind11_cross_module_tests.cpp (0 NOLINT, 1 explicit)

* clang-tidy tests/pybind11_tests.h (0 NOLINT, 2 explicit)

* clang-tidy tests/test_buffers.cpp (0 NOLINT, 2 explicit)

* clang-tidy tests/test_builtin_casters.cpp (0 NOLINT, 4 explicit)

* clang-tidy tests/test_class.cpp (0 NOLINT, 6 explicit)

* clang-tidy tests/test_copy_move.cpp (0 NOLINT, 7 explicit)

* clang-tidy tests/test_embed/external_module.cpp (0 NOLINT, 1 explicit)

* clang-tidy tests/test_embed/test_interpreter.cpp (0 NOLINT, 1 explicit)

* clang-tidy tests/object.h (0 NOLINT, 2 explicit)

* clang-tidy batch of fully automatic fixes.

* Workaround for MSVC 19.16.27045.0 C++17 Python 2 C++ syntax error.

tests/test_sequences_and_iterators.cpp

@@ -20,7 +20,7 @@ template<typename T>
 class NonZeroIterator {
     const T* ptr_;
 public:
-    NonZeroIterator(const T* ptr) : ptr_(ptr) {}
+    explicit NonZeroIterator(const T *ptr) : ptr_(ptr) {}
     const T& operator*() const { return *ptr_; }
     NonZeroIterator& operator++() { ++ptr_; return *this; }
 };
@@ -77,9 +77,9 @@ TEST_SUBMODULE(sequences_and_iterators, m) {
     // test_sliceable
     class Sliceable{
     public:
-      Sliceable(int n): size(n) {}
-      int start,stop,step;
-      int size;
+        explicit Sliceable(int n) : size(n) {}
+        int start, stop, step;
+        int size;
     };
     py::class_<Sliceable>(m, "Sliceable")
         .def(py::init<int>())
@@ -96,12 +96,12 @@ TEST_SUBMODULE(sequences_and_iterators, m) {
     // test_sequence
     class Sequence {
     public:
-        Sequence(size_t size) : m_size(size) {
+        explicit Sequence(size_t size) : m_size(size) {
             print_created(this, "of size", m_size);
             m_data = new float[size];
             memset(m_data, 0, sizeof(float) * size);
         }
-        Sequence(const std::vector<float> &value) : m_size(value.size()) {
+        explicit Sequence(const std::vector<float> &value) : m_size(value.size()) {
             print_created(this, "of size", m_size, "from std::vector");
             m_data = new float[m_size];
             memcpy(m_data, &value[0], sizeof(float) * m_size);
@@ -239,7 +239,7 @@ TEST_SUBMODULE(sequences_and_iterators, m) {
     class StringMap {
     public:
         StringMap() = default;
-        StringMap(std::unordered_map<std::string, std::string> init)
+        explicit StringMap(std::unordered_map<std::string, std::string> init)
             : map(std::move(init)) {}
 
         void set(const std::string &key, std::string val) { map[key] = std::move(val); }
@@ -276,7 +276,7 @@ TEST_SUBMODULE(sequences_and_iterators, m) {
     // test_generalized_iterators
     class IntPairs {
     public:
-        IntPairs(std::vector<std::pair<int, int>> data) : data_(std::move(data)) {}
+        explicit IntPairs(std::vector<std::pair<int, int>> data) : data_(std::move(data)) {}
         const std::pair<int, int>* begin() const { return data_.data(); }
     private:
         std::vector<std::pair<int, int>> data_;