Auto-detect std::string_view support by default

Instead of opting in std::string_view support via PUGIXML_STRING_VIEW
define, always enable it when C++17 is supported; this still requires
enabling C++17 support in the compiler, which this change doesn't
attempt to do yet.

.github/workflows/build.yml

@@ -12,7 +12,7 @@ jobs:
       matrix:
         os: [ubuntu, macos]
         compiler: [g++, clang++]
-        defines: [standard, PUGIXML_WCHAR_MODE, PUGIXML_COMPACT, PUGIXML_NO_EXCEPTIONS, PUGIXML_STRING_VIEW]
+        defines: [standard, PUGIXML_WCHAR_MODE, PUGIXML_COMPACT, PUGIXML_NO_EXCEPTIONS]
         exclude:
           - os: macos
             compiler: g++
@@ -39,7 +39,7 @@ jobs:
     strategy:
       matrix:
         arch: [Win32, x64]
-        defines: [standard, PUGIXML_WCHAR_MODE, PUGIXML_COMPACT, PUGIXML_NO_EXCEPTIONS, PUGIXML_STRING_VIEW]
+        defines: [standard, PUGIXML_WCHAR_MODE, PUGIXML_COMPACT, PUGIXML_NO_EXCEPTIONS]
     steps:
     - uses: actions/checkout@v1
     - name: cmake configure

CMakeLists.txt

@@ -32,7 +32,7 @@ set(PUGIXML_BUILD_DEFINES CACHE STRING "Build defines for custom options")
 separate_arguments(PUGIXML_BUILD_DEFINES)
 
 # Technically not needed for this file. This is builtin CMAKE global variable.
-option(BUILD_SHARED_LIBS "Build shared instead of static library" OFF) 
+option(BUILD_SHARED_LIBS "Build shared instead of static library" OFF)
 
 # Expose option to build PUGIXML as static as well when the global BUILD_SHARED_LIBS variable is set
 cmake_dependent_option(PUGIXML_BUILD_SHARED_AND_STATIC_LIBS
@@ -48,16 +48,14 @@ option(PUGIXML_INSTALL "Enable installation rules" ON)
 option(PUGIXML_NO_XPATH "Disable XPath" OFF)
 option(PUGIXML_NO_STL "Disable STL" OFF)
 option(PUGIXML_NO_EXCEPTIONS "Disable Exceptions" OFF)
-option(PUGIXML_STRING_VIEW "Enable std::string_view overloads" OFF) # requires C++17 and for PUGIXML_NO_STL to be OFF
-mark_as_advanced(PUGIXML_NO_XPATH PUGIXML_NO_STL PUGIXML_NO_EXCEPTIONS PUGIXML_STRING_VIEW)
+mark_as_advanced(PUGIXML_NO_XPATH PUGIXML_NO_STL PUGIXML_NO_EXCEPTIONS)
 
 set(PUGIXML_PUBLIC_DEFINITIONS
   $<$<BOOL:${PUGIXML_WCHAR_MODE}>:PUGIXML_WCHAR_MODE>
   $<$<BOOL:${PUGIXML_COMPACT}>:PUGIXML_COMPACT>
   $<$<BOOL:${PUGIXML_NO_XPATH}>:PUGIXML_NO_XPATH>
   $<$<BOOL:${PUGIXML_NO_STL}>:PUGIXML_NO_STL>
   $<$<BOOL:${PUGIXML_NO_EXCEPTIONS}>:PUGIXML_NO_EXCEPTIONS>
-  $<$<BOOL:${PUGIXML_STRING_VIEW}>:PUGIXML_STRING_VIEW>
 )
 
 # This is used to backport a CMake 3.15 feature, but is also forwards compatible
@@ -66,10 +64,6 @@ if (NOT DEFINED CMAKE_MSVC_RUNTIME_LIBRARY)
     MultiThreaded$<$<CONFIG:Debug>:Debug>$<$<NOT:$<BOOL:${PUGIXML_STATIC_CRT}>>:DLL>)
 endif()
 
-if (PUGIXML_STRING_VIEW AND (NOT DEFINED CMAKE_CXX_STANDARD OR CMAKE_CXX_STANDARD LESS 17))
-  message(WARNING "PUGIXML_STRING_VIEW requires CMAKE_CXX_STANDARD to be set to 17 or later")
-endif()
-
 if (NOT DEFINED CMAKE_CXX_STANDARD_REQUIRED)
   set(CMAKE_CXX_STANDARD_REQUIRED ON)
 endif()

src/pugiconfig.hpp

@@ -46,13 +46,11 @@
 // Uncomment this to switch to header-only version
 // #define PUGIXML_HEADER_ONLY
 
-// Uncomment this to enable long long support
+// Uncomment this to enable long long support (usually enabled automatically)
 // #define PUGIXML_HAS_LONG_LONG
 
-// Uncomment this to enable support for std::string_view (requires c++17 and for PUGIXML_NO_STL to not be set)
-// Note: In a future version of pugixml this macro will become obsolete.
-//       Support will then be enabled automatically if the used C++ standard supports it.
-// #define PUGIXML_STRING_VIEW
+// Uncomment this to enable support for std::string_view (usually enabled automatically)
+// #define PUGIXML_HAS_STRING_VIEW
 
 #endif
 

src/pugixml.hpp

@@ -38,8 +38,8 @@
 #	include <string>
 #endif
 
-// Check if std::string_view is both requested and available
-#if defined(PUGIXML_STRING_VIEW) && !defined(PUGIXML_NO_STL)
+// Check if std::string_view is available
+#if !defined(PUGIXML_HAS_STRING_VIEW) && !defined(PUGIXML_NO_STL)
 #	if __cplusplus >= 201703L
 #		define PUGIXML_HAS_STRING_VIEW
 #	elif defined(_MSVC_LANG) && _MSVC_LANG >= 201703L
@@ -231,7 +231,7 @@ namespace pugi
 	// the document; this flag is only recommended for parsing documents with many PCDATA nodes in memory-constrained environments.
 	// This flag is off by default.
 	const unsigned int parse_embed_pcdata = 0x2000;
-	
+
 	// This flag determines whether determines whether the the two pcdata should be merged or not, if no intermediatory data are parsed in the document.
 	// This flag is off by default.
 	const unsigned int parse_merge_pcdata = 0x4000;