Add qmake support for c++2a

Makes it possible to build user projects and Qt with C++2a. It is not
automatically upgraded to yet though.

Change-Id: I949ce94871ddc53f21b7265a52b9c0e1370456c8
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

config_help.txt

@@ -139,7 +139,7 @@ Build options:
   -coverage {trace-pc-guard}
                          Add code coverage instrumentation (Clang only)
 
-  -c++std <edition> .... Select C++ standard <edition> [c++17/c++14/c++11]
+  -c++std <edition> .... Select C++ standard <edition> [c++2a/c++17/c++14/c++11]
                          (Not supported with MSVC 2015)
 
   -sse2 ................ Use SSE2 instructions [auto]

configure.json

@@ -339,6 +339,20 @@
                 "qmake": "CONFIG += c++11 c++14 c++1z"
             }
         },
+        "c++2a": {
+            "label": "C++2a support",
+            "type": "compile",
+            "test": {
+                "head": [
+                    "#if __cplusplus > 201703L",
+                    "// Compiler claims to support experimental C++2a, trust it",
+                    "#else",
+                    "#  error __cplusplus must be > 201703L (the value for C++17)",
+                    "#endif"
+                ],
+                "qmake": "CONFIG += c++11 c++14 c++1z c++2a"
+            }
+        },
         "precompile_header": {
             "label": "precompiled header support",
             "type": "compile",
@@ -911,6 +925,12 @@
             "condition": "features.c++14 && tests.c++1z",
             "output": [ "publicFeature", "publicQtConfig" ]
         },
+        "c++2a": {
+            "label": "C++2a",
+            "autoDetect": false,
+            "condition": "features.c++1z && tests.c++2a",
+            "output": [ "publicFeature", "publicQtConfig" ]
+        },
         "c89": {
             "label": "C89"
         },
@@ -1413,7 +1433,7 @@ Configure with '-qreal float' to create a build that is binary-compatible with 5
                 {
                     "message": "Using C++ standard",
                     "type": "firstAvailableFeature",
-                    "args": "c++1z c++14 c++11"
+                    "args": "c++2a c++1z c++14 c++11"
                 },
                 {
                     "type": "feature",

configure.pri

@@ -20,12 +20,20 @@ defineTest(qtConfCommandline_cxxstd) {
     !contains(val, "^-.*"):!isEmpty(val) {
         contains(val, "(c\+\+)?11") {
             qtConfCommandlineSetInput("c++14", "no")
+            qtConfCommandlineSetInput("c++1z", "no")
+            qtConfCommandlineSetInput("c++2a", "no")
         } else: contains(val, "(c\+\+)?(14|1y)") {
             qtConfCommandlineSetInput("c++14", "yes")
             qtConfCommandlineSetInput("c++1z", "no")
+            qtConfCommandlineSetInput("c++2a", "no")
         } else: contains(val, "(c\+\+)?(17|1z)") {
             qtConfCommandlineSetInput("c++14", "yes")
             qtConfCommandlineSetInput("c++1z", "yes")
+            qtConfCommandlineSetInput("c++2a", "no")
+        } else: contains(val, "(c\+\+)?(2a)") {
+            qtConfCommandlineSetInput("c++14", "yes")
+            qtConfCommandlineSetInput("c++1z", "yes")
+            qtConfCommandlineSetInput("c++2a", "yes")
         } else {
             qtConfAddError("Invalid argument $$val to command line parameter $$arg")
         }

mkspecs/common/clang.conf

@@ -31,9 +31,11 @@ QMAKE_CXXFLAGS_DISABLE_LTCG      = $$QMAKE_CFLAGS_DISABLE_LTCG
 QMAKE_CXXFLAGS_CXX11             = -std=c++11
 QMAKE_CXXFLAGS_CXX14             = -std=c++1y
 QMAKE_CXXFLAGS_CXX1Z             = -std=c++1z
+QMAKE_CXXFLAGS_CXX2A             = -std=c++2a
 QMAKE_CXXFLAGS_GNUCXX11          = -std=gnu++11
 QMAKE_CXXFLAGS_GNUCXX14          = -std=gnu++1y
 QMAKE_CXXFLAGS_GNUCXX1Z          = -std=gnu++1z
+QMAKE_CXXFLAGS_GNUCXX2A          = -std=gnu++2a
 
 QMAKE_LFLAGS_CXX11      =
 QMAKE_LFLAGS_CXX14      =

mkspecs/common/g++-base.conf

@@ -32,9 +32,11 @@ QMAKE_CFLAGS_GNUC11     = -std=gnu11
 QMAKE_CXXFLAGS_CXX11    = -std=c++11
 QMAKE_CXXFLAGS_CXX14    = -std=c++1y
 QMAKE_CXXFLAGS_CXX1Z    = -std=c++1z
+QMAKE_CXXFLAGS_CXX2A    = -std=c++2a
 QMAKE_CXXFLAGS_GNUCXX11 = -std=gnu++11
 QMAKE_CXXFLAGS_GNUCXX14 = -std=gnu++1y
 QMAKE_CXXFLAGS_GNUCXX1Z = -std=gnu++1z
+QMAKE_CXXFLAGS_GNUCXX2A = -std=gnu++2a
 QMAKE_LFLAGS_CXX11      =
 QMAKE_LFLAGS_CXX14      =
 QMAKE_LFLAGS_CXX1Z      =

mkspecs/common/msvc-version.conf

@@ -116,6 +116,8 @@ greaterThan(QMAKE_MSC_VER, 1910) {
 greaterThan(QMAKE_MSC_VER, 1919) {
     # Visual Studio 2019 (16.0) / Visual C++ 19.20 and up
     MSVC_VER            = 16.0
+    QMAKE_CXXFLAGS_CXX2A = -std:c++latest
+
 }
 
 !isEmpty(COMPAT_MKSPEC):!$$COMPAT_MKSPEC: CONFIG += $$COMPAT_MKSPEC

mkspecs/features/default_post.prf

@@ -121,15 +121,16 @@ breakpad {
 
 c++17: CONFIG += c++1z
 
-!c++11:!c++14:!c++1z {
+!c++11:!c++14:!c++1z:!c++2a {
     # Qt requires C++11 since 5.7, check if we need to force a compiler option
     QT_COMPILER_STDCXX_no_L = $$replace(QT_COMPILER_STDCXX, "L$", "")
     !greaterThan(QT_COMPILER_STDCXX_no_L, 199711): CONFIG += c++11
 }
-c++11|c++14|c++1z {
+c++11|c++14|c++1z|c++2a {
     # Disable special compiler flags for host builds
     !host_build|!cross_compile {
-        c++1z:       cxxstd = CXX1Z
+        c++2a:       cxxstd = CXX2A
+        else: c++1z: cxxstd = CXX1Z
         else: c++14: cxxstd = CXX14
         else:        cxxstd = CXX11
     } else {

mkspecs/features/qt_common.prf

@@ -17,6 +17,7 @@ DEFINES *= QT_NO_NARROWING_CONVERSIONS_IN_CONNECT
 qtConfig(c++11): CONFIG += c++11 strict_c++
 qtConfig(c++14): CONFIG += c++14
 qtConfig(c++1z): CONFIG += c++1z
+qtConfig(c++2a): CONFIG += c++2a
 qtConfig(c99): CONFIG += c99
 qtConfig(c11): CONFIG += c11
 qtConfig(stack-protector-strong): CONFIG += stack_protector_strong