pw_polyfill: Remove code related to C++11 support

C++14 is now required for all Pigweed modules. - Add a section to the style guide about the C++ standard. - Remove the tokenizer and polyfill C++11 tests. - Remove the cpp11 GN config. - Remove unnecessary features and workarounds for C++11. - Update C++14 tests to use EXPECT_EQ, EXPECT_NE, etc. since these are supported by C++14, but not C++11. Change-Id: I6082ff01b4410db8a322cf8cefee60d3787443ff Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/65240 Pigweed-Auto-Submit: Wyatt Hepler <[email protected]> Reviewed-by: Keir Mierle <[email protected]> Reviewed-by: Ted Pudlik <[email protected]> Commit-Queue: Wyatt Hepler <[email protected]>
google · Oct 12, 2021 · 0132da5 · 0132da5
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diff --git a/docs/index.rst b/docs/index.rst
@@ -149,7 +149,7 @@ Here is a selection of interesting modules:
 
  - :ref:`module-pw_polyfill` - Similar to JavaScript “polyfill” libraries, this
    module provides selected C++17 standard library components that are
-   compatible with C++11 and C++14.
+   compatible with C++14.
 
  - :ref:`module-pw_tokenizer` - Replace string literals from log statements
    with 32-bit tokens, to reduce flash use, reduce logging bandwidth, and save

diff --git a/docs/style_guide.rst b/docs/style_guide.rst
@@ -13,7 +13,6 @@ Style Guide and Conventions
 ---------
 C++ style
 ---------
-
 The Pigweed C++ style guide is closely based on Google's external C++ Style
 Guide, which is found on the web at
 https://google.github.io/styleguide/cppguide.html. The Google C++ Style Guide
@@ -28,6 +27,20 @@ Recommendations in the :doc:`embedded_cpp_guide` are considered part of the
 Pigweed style guide, but are separated out since it covers more general
 embedded development beyond just C++ style.
 
+C++ standard
+============
+Pigweed primarily uses the C++17 standard. A few modules maintain support for
+C++14, however (e.g. :ref:`module-pw_kvs` and its dependencies).
+
+All Pigweed C++ code must compile with ``-std=C++17`` in Clang and GCC. C++20
+features may be used as long as the code still compiles unmodified with C++17.
+See ``pw_polyfill/language_feature_macros.h`` for macros that provide C++20
+features when supported.
+
+Compiler extensions should not be used unless wrapped in a macro or properly
+guarded in the preprocessor. See ``pw_processor/compiler.h`` for macros that
+wrap compiler-specific features.
+
 Automatic formatting
 ====================
 Pigweed uses `clang-format <https://clang.llvm.org/docs/ClangFormat.html>`_ to

diff --git a/docs/targets.rst b/docs/targets.rst
@@ -51,7 +51,7 @@ build argument defined in Pigweed. Some notable arguments include:
 * ``default_public_deps``: List of GN targets which are added as a dependency
   to all ``pw_*`` GN targets. This is used to add global module dependencies;
   for example, in upstream, ``pw_polyfill`` is added here to provide C++17
-  features in C++11/C++14 code.
+  features in C++14 code.
 * Facade backends: Pigweed defines facades to provide a common interface for
   core system features such as logging without assuming an implementation.
   When building a Pigweed target, the implementations for each of these must be

diff --git a/pw_build/BUILD.gn b/pw_build/BUILD.gn
@@ -105,10 +105,6 @@ config("extra_strict_warnings") {
   cflags_c = [ "-Wstrict-prototypes" ]
 }
 
-config("cpp11") {
-  cflags_cc = [ "-std=c++11" ]
-}
-
 config("cpp14") {
   cflags_cc = [ "-std=c++14" ]
 }

diff --git a/pw_polyfill/BUILD.gn b/pw_polyfill/BUILD.gn
@@ -88,7 +88,6 @@ pw_source_set("standard_library") {
 pw_test_group("tests") {
   tests = [
     ":default_cpp_test",
-    ":cpp11_test",
     ":cpp14_test",
   ]
   group_deps = [ "$dir_pw_span:tests" ]
@@ -99,13 +98,6 @@ pw_test("default_cpp_test") {
   sources = [ "test.cc" ]
 }
 
-pw_test("cpp11_test") {
-  remove_configs = [ "$dir_pw_build:cpp17" ]
-  configs = [ "$dir_pw_build:cpp11" ]
-  sources = [ "test.cc" ]
-  deps = [ ":pw_polyfill" ]
-}
-
 pw_test("cpp14_test") {
   remove_configs = [ "$dir_pw_build:cpp17" ]
   configs = [ "$dir_pw_build:cpp14" ]

diff --git a/pw_polyfill/README.md b/pw_polyfill/README.md
@@ -1 +1 @@
-# pw\_polyfill: Backports C++17 features to C++11 and C++14
+# pw\_polyfill: Backports C++17 features to C++14
diff --git a/pw_polyfill/docs.rst b/pw_polyfill/docs.rst
@@ -3,9 +3,7 @@
 ===========
 pw_polyfill
 ===========
-The ``pw_polyfill`` module backports new C++ features to older C++ standards.
-When possible, features are adapted to work with in standards as old as C++11.
-Pigweed does not support C++ standards older than C++11.
+The ``pw_polyfill`` module backports new C++ features to C++14.
 
 ------------------------------------------------
 Backport new C++ features to older C++ standards
@@ -22,7 +20,7 @@ C headers. The wrapper headers include the original header using
 `#include_next <https://gcc.gnu.org/onlinedocs/cpp/Wrapper-Headers.html>`_, then
 add missing features. The backported features are only defined if they aren't
 provided by the standard header, so ``pw_polyfill`` is safe to use when
-compiling with any standard C++11 or newer.
+compiling with any standard C++14 or newer.
 
 Language features are backported or stubbed via the
 ``pw_polyfill/language_features.h`` header. This header is included in files
@@ -39,17 +37,17 @@ for the ``language_features.h`` header.
 
 Backported features
 ===================
-==================  ================================  ============================================  ========================================
-Header              Feature                           Level of support                              Feature test macro
-==================  ================================  ============================================  ========================================
-<bit>               std::endian                       full                                          __cpp_lib_endian
-<cstdlib>           std::byte                         full; some operators not constexpr in C++11   __cpp_lib_byte
-<iterator>          std::data, std::size              full                                          __cpp_lib_nonmember_container_access
-<type_traits>       \*_t trait aliases                partial (can expand as needed)                __cpp_lib_transformation_trait_aliases
-<type_traits>       std::is_null_pointer              full                                          __cpp_lib_is_null_pointer
-<utilty>            std::integer_sequence & helpers   full                                          __cpp_lib_integer_sequence
-(language feature)  static_assert with no message     full                                          __cpp_static_assert
-==================  ================================  ============================================  ========================================
+==================  ================================  ===============================  ========================================
+Header              Feature                           Level of support                 Feature test macro
+==================  ================================  ===============================  ========================================
+<bit>               std::endian                       full                             __cpp_lib_endian
+<cstdlib>           std::byte                         full                             __cpp_lib_byte
+<iterator>          std::data, std::size              full                             __cpp_lib_nonmember_container_access
+<type_traits>       \*_t trait aliases                partial (can expand as needed)   __cpp_lib_transformation_trait_aliases
+<type_traits>       std::is_null_pointer              full                             __cpp_lib_is_null_pointer
+<utilty>            std::integer_sequence & helpers   full                             __cpp_lib_integer_sequence
+(language feature)  static_assert with no message     full                             __cpp_static_assert
+==================  ================================  ===============================  ========================================
 
 ----------------------------------------------------
 Adapt code to compile with different versions of C++
@@ -67,7 +65,6 @@ Language feature macros
 Macro                   Feature                           Description                               Feature test macro
 ======================  ================================  ========================================  ==========================
 PW_INLINE_VARIABLE      inline variables                  inline if supported by the compiler       __cpp_inline_variables
-PW_CONSTEXPR_FUNCTION   relaxed constexpr function rules  constexpr if relaxed rules are supported  __cpp_constexpr >= 201304L
 PW_CONSTEXPR_CPP20      constexpr in C++20                constexpr if compiling for C++20          __cplusplus >= 202002L
 PW_CONSTEVAL            consteval                         consteval if supported by the compiler    __cpp_consteval
 PW_CONSTINIT            constinit                         constinit in clang and GCC 10+            __cpp_constinit
@@ -81,4 +78,4 @@ systems, add ``pw_polyfill/standard_library_public`` and
 -------------
 Compatibility
 -------------
-C++11
+C++14
diff --git a/pw_polyfill/public/pw_polyfill/language_feature_macros.h b/pw_polyfill/public/pw_polyfill/language_feature_macros.h
@@ -23,13 +23,6 @@
 #define PW_INLINE_VARIABLE
 #endif  // __cpp_inline_variables
 
-// Mark functions as constexpr if the relaxed constexpr rules are supported.
-#if __cpp_constexpr >= 201304L
-#define PW_CONSTEXPR_FUNCTION constexpr
-#else
-#define PW_CONSTEXPR_FUNCTION
-#endif  // __cpp_constexpr >= 201304L
-
 // Mark functions as constexpr if C++20 or newer
 #if __cplusplus >= 202002L
 #define PW_CONSTEXPR_CPP20 constexpr

diff --git a/pw_polyfill/standard_library_public/pw_polyfill/standard_library/cstddef.h b/pw_polyfill/standard_library_public/pw_polyfill/standard_library/cstddef.h
@@ -56,20 +56,10 @@ constexpr byte operator>>(byte b, I shift) noexcept {
   return byte(static_cast<unsigned int>(b) >> shift);
 }
 
-#if __cpp_constexpr >= 201304L
-
 constexpr byte& operator|=(byte& l, byte r) noexcept { return l = l | r; }
 constexpr byte& operator&=(byte& l, byte r) noexcept { return l = l & r; }
 constexpr byte& operator^=(byte& l, byte r) noexcept { return l = l ^ r; }
 
-#else  // For C++11 compatiblity, these operators cannot be constexpr.
-
-inline byte& operator|=(byte& l, byte r) noexcept { return l = l | r; }
-inline byte& operator&=(byte& l, byte r) noexcept { return l = l & r; }
-inline byte& operator^=(byte& l, byte r) noexcept { return l = l ^ r; }
-
-#endif  // __cpp_constexpr >= 201304L
-
 template <typename I>
 inline byte& operator<<=(byte& b, I shift) noexcept {
   return b = b << shift;

diff --git a/pw_polyfill/test.cc b/pw_polyfill/test.cc
@@ -33,12 +33,7 @@ static_assert(foo == 42, "Error!");
 
 static_assert(PW_CXX_STANDARD_IS_SUPPORTED(98), "C++98 must be supported");
 static_assert(PW_CXX_STANDARD_IS_SUPPORTED(11), "C++11 must be supported");
-
-#if __cplusplus >= 201402L
-static_assert(PW_CXX_STANDARD_IS_SUPPORTED(14), "C++14 must be not supported");
-#else
-static_assert(!PW_CXX_STANDARD_IS_SUPPORTED(14), "C++14 must be supported");
-#endif  // __cplusplus >= 201402L
+static_assert(PW_CXX_STANDARD_IS_SUPPORTED(14), "C++14 must be supported");
 
 #if __cplusplus >= 201703L
 static_assert(PW_CXX_STANDARD_IS_SUPPORTED(17), "C++17 must be not supported");
@@ -48,31 +43,31 @@ static_assert(!PW_CXX_STANDARD_IS_SUPPORTED(17), "C++17 must be supported");
 
 TEST(Bit, Endian) {
   if (__BYTE_ORDER__ == __ORDER_BIG_ENDIAN__) {
-    EXPECT_TRUE(std::endian::native == std::endian::big);
+    EXPECT_EQ(std::endian::native, std::endian::big);
   } else if (__BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__) {
-    EXPECT_TRUE(std::endian::native == std::endian::little);
+    EXPECT_EQ(std::endian::native, std::endian::little);
   } else {
     FAIL();
   }
 }
 
 TEST(Cstddef, Byte_Operators) {
   std::byte value = std::byte(0);
-  EXPECT_TRUE((value | std::byte(0x12)) == std::byte(0x12));
-  EXPECT_TRUE((value & std::byte(0x12)) == std::byte(0));
-  EXPECT_TRUE((value ^ std::byte(0x12)) == std::byte(0x12));
-  EXPECT_TRUE(~std::byte(0) == std::byte(-1));
-  EXPECT_TRUE((std::byte(1) << 3) == std::byte(0x8));
-  EXPECT_TRUE((std::byte(0x8) >> 3) == std::byte(1));
+  EXPECT_EQ((value | std::byte(0x12)), std::byte(0x12));
+  EXPECT_EQ((value & std::byte(0x12)), std::byte(0));
+  EXPECT_EQ((value ^ std::byte(0x12)), std::byte(0x12));
+  EXPECT_EQ(~std::byte(0), std::byte(-1));
+  EXPECT_EQ((std::byte(1) << 3), std::byte(0x8));
+  EXPECT_EQ((std::byte(0x8) >> 3), std::byte(1));
 }
 
 TEST(Cstddef, Byte_AssignmentOperators) {
   std::byte value = std::byte(0);
-  EXPECT_TRUE((value |= std::byte(0x12)) == std::byte(0x12));
-  EXPECT_TRUE((value &= std::byte(0x0F)) == std::byte(0x02));
-  EXPECT_TRUE((value ^= std::byte(0xFF)) == std::byte(0xFD));
-  EXPECT_TRUE((value <<= 4) == std::byte(0xD0));
-  EXPECT_TRUE((value >>= 5) == std::byte(0x6));
+  EXPECT_EQ((value |= std::byte(0x12)), std::byte(0x12));
+  EXPECT_EQ((value &= std::byte(0x0F)), std::byte(0x02));
+  EXPECT_EQ((value ^= std::byte(0xFF)), std::byte(0xFD));
+  EXPECT_EQ((value <<= 4), std::byte(0xD0));
+  EXPECT_EQ((value >>= 5), std::byte(0x6));
 }
 
 // Check that consteval is at least equivalent to constexpr.
@@ -83,13 +78,13 @@ int c_array[5423] = {};
 std::array<int, 32> array;
 
 TEST(Iterator, Size) {
-  EXPECT_TRUE(std::size(c_array) == sizeof(c_array) / sizeof(*c_array));
-  EXPECT_TRUE(std::size(array) == array.size());
+  EXPECT_EQ(std::size(c_array), sizeof(c_array) / sizeof(*c_array));
+  EXPECT_EQ(std::size(array), array.size());
 }
 
 TEST(Iterator, Data) {
-  EXPECT_TRUE(std::data(c_array) == c_array);
-  EXPECT_TRUE(std::data(array) == array.data());
+  EXPECT_EQ(std::data(c_array), c_array);
+  EXPECT_EQ(std::data(array), array.data());
 }
 
 PW_CONSTINIT bool mutable_value = true;

diff --git a/pw_result/docs.rst b/pw_result/docs.rst
@@ -78,7 +78,7 @@ similar type.
 
 Compatibility
 =============
-Works with C++11, but some features require C++17.
+Works with C++14, but some features require C++17.
 
 Size report
 ===========

diff --git a/pw_ring_buffer/docs.rst b/pw_ring_buffer/docs.rst
@@ -10,7 +10,7 @@ This documentation is incomplete :)
 
 Compatibility
 =============
-* C++11
+* C++14
 
 Iterator
 ========

diff --git a/pw_span/docs.rst b/pw_span/docs.rst
@@ -68,4 +68,4 @@ Pointer and size arguments can be replaced with a ``std::span``:
 
 Compatibility
 =============
-Works with C++11, but some features require C++17.
+Works with C++14, but some features require C++17.
diff --git a/pw_span/public/pw_span/internal/span.h b/pw_span/public/pw_span/internal/span.h
@@ -320,7 +320,7 @@ class span : public pw_span_internal::ExtentStorage<Extent> {
   constexpr span(const span<U, OtherExtent>& other)
       : span(other.data(), other.size()) {}
 
-  PW_CONSTEXPR_FUNCTION span& operator=(const span& other) noexcept = default;
+  constexpr span& operator=(const span& other) noexcept = default;
   ~span() noexcept = default;
 
   // [span.sub], span subviews

diff --git a/pw_status/docs.rst b/pw_status/docs.rst
@@ -292,4 +292,4 @@ the size from the StatusWithSize on ok.
 
 Compatibility
 =============
-C++11
+C++14
diff --git a/pw_tokenizer/BUILD.gn b/pw_tokenizer/BUILD.gn
@@ -194,7 +194,6 @@ pw_test_group("tests") {
     ":detokenize_test",
     ":global_handlers_test",
     ":hash_test",
-    ":simple_tokenize_test_cpp11",
     ":simple_tokenize_test_cpp14",
     ":simple_tokenize_test_cpp17",
     ":token_database_fuzzer",
@@ -270,8 +269,7 @@ pw_test("hash_test") {
   deps = [ ":pw_tokenizer" ]
 }
 
-# Fully test C++11 and C++14 compatibility by compiling all sources as C++11 or
-# C++14.
+# Fully test C++14 compatibility by compiling all sources as C++14.
 _simple_tokenize_test_sources = [
   "$dir_pw_containers/public/pw_containers/to_array.h",
   "$dir_pw_varint/public/pw_varint/varint.h",
@@ -301,13 +299,6 @@ _simple_tokenize_test_configs = [
   "$dir_pw_containers:public_include_path",
 ]
 
-pw_test("simple_tokenize_test_cpp11") {
-  remove_configs = [ "$dir_pw_build:cpp17" ]
-  configs = [ "$dir_pw_build:cpp11" ] + _simple_tokenize_test_configs
-  sources = _simple_tokenize_test_sources
-  deps = [ dir_pw_preprocessor ]
-}
-
 pw_test("simple_tokenize_test_cpp14") {
   remove_configs = [ "$dir_pw_build:cpp17" ]
   configs = [ "$dir_pw_build:cpp14" ] + _simple_tokenize_test_configs

diff --git a/pw_tokenizer/docs.rst b/pw_tokenizer/docs.rst
@@ -1144,7 +1144,7 @@ The Python tooling continues to support the legacy tokenized string ELF format.
 Compatibility
 =============
   * C11
-  * C++11
+  * C++14
   * Python 3
 
 Dependencies

diff --git a/pw_tokenizer/public/pw_tokenizer/internal/argument_types.h b/pw_tokenizer/public/pw_tokenizer/internal/argument_types.h
@@ -105,7 +105,7 @@ constexpr pw_tokenizer_ArgTypes VarargsType() {
   }
 }
 
-#else  // C++11 or C++14 version
+#else  // C++14 version
 
 template <typename T,
           bool kIsDouble = std::is_floating_point<T>(),
Original file line number	Diff line number	Diff line change
		@@ -1 +1 @@
		# pw\_polyfill: Backports C++17 features to C++11 and C++14
		# pw\_polyfill: Backports C++17 features to C++14
-Original file line number
+Diff line change
@@ Expand Up / @@ -292,4 +292,4 @@ the size from the StatusWithSize on ok. @@
     Compatibility
     =============
-    C++11
+    C++14