Detect C standard and try using the most recent

Fixes the default C version used with gcc < 5

Change-Id: I948dece961caed8e6b181e1c6e6b9dc43c46583f
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@qt.io>

7 files changed, 37 insertions, 2 deletions

diff --git a/mkspecs/common/android-base-tail.conf b/mkspecs/common/android-base-tail.conf
index 160caf011f..464b60b1c4 100644
--- a/mkspecs/common/android-base-tail.conf
+++ b/mkspecs/common/android-base-tail.conf
@@ -38,6 +38,8 @@ QMAKE_CFLAGS_THREAD     = -D_REENTRANT
 QMAKE_CFLAGS_HIDESYMS   = -fvisibility=hidden
 QMAKE_CFLAGS_NEON       = -mfpu=neon
 
+QMAKE_CFLAGS_GNUC99     = -std=gnu99
+QMAKE_CFLAGS_GNUC11     = -std=gnu11
 QMAKE_CXXFLAGS_CXX11    = -std=c++11
 QMAKE_CXXFLAGS_CXX14    = -std=c++14
 QMAKE_CXXFLAGS_CXX1Z    = -std=c++1z
diff --git a/mkspecs/common/clang.conf b/mkspecs/common/clang.conf
index e003b947aa..6122a37213 100644
--- a/mkspecs/common/clang.conf
+++ b/mkspecs/common/clang.conf
@@ -21,6 +21,8 @@ QMAKE_CFLAGS_PRECOMPILE          = -x c-header -c ${QMAKE_PCH_INPUT} -o ${QMAKE_
 QMAKE_CFLAGS_USE_PRECOMPILE      = -Xclang -include-pch -Xclang ${QMAKE_PCH_OUTPUT}
 QMAKE_CFLAGS_LTCG                = -flto
 QMAKE_CFLAGS_DISABLE_LTCG        = -fno-lto
+QMAKE_CFLAGS_GNUC99              = -std=gnu99
+QMAKE_CFLAGS_GNUC11              = -std=gnu11
 
 QMAKE_CXXFLAGS_PRECOMPILE        = -x c++-header -c ${QMAKE_PCH_INPUT} -o ${QMAKE_PCH_OUTPUT}
 QMAKE_CXXFLAGS_USE_PRECOMPILE    = $$QMAKE_CFLAGS_USE_PRECOMPILE
diff --git a/mkspecs/common/g++-base.conf b/mkspecs/common/g++-base.conf
index c42c46b0ec..fa0f0c391d 100644
--- a/mkspecs/common/g++-base.conf
+++ b/mkspecs/common/g++-base.conf
@@ -27,6 +27,8 @@ QMAKE_CFLAGS_USE_PRECOMPILE   = -include ${QMAKE_PCH_OUTPUT_BASE}
 QMAKE_CXXFLAGS_PRECOMPILE     = -x c++-header -c ${QMAKE_PCH_INPUT} -o ${QMAKE_PCH_OUTPUT}
 QMAKE_CXXFLAGS_USE_PRECOMPILE = $$QMAKE_CFLAGS_USE_PRECOMPILE
 
+QMAKE_CFLAGS_GNUC99     = -std=gnu99
+QMAKE_CFLAGS_GNUC11     = -std=gnu11
 QMAKE_CXXFLAGS_CXX11    = -std=c++11
 QMAKE_CXXFLAGS_CXX14    = -std=c++1y
 QMAKE_CXXFLAGS_CXX1Z    = -std=c++1z
diff --git a/mkspecs/common/gcc-base.conf b/mkspecs/common/gcc-base.conf
index 234f71d495..0407ba9724 100644
--- a/mkspecs/common/gcc-base.conf
+++ b/mkspecs/common/gcc-base.conf
@@ -81,6 +81,9 @@ QMAKE_LFLAGS_RELEASE_WITH_DEBUGINFO +=
 QMAKE_LFLAGS_EXCEPTIONS_OFF +=
 QMAKE_LFLAGS_LTCG       = $$QMAKE_CFLAGS_LTCG -fuse-linker-plugin
 
+QMAKE_CFLAGS_C99       = -std=c99
+QMAKE_CFLAGS_C11       = -std=c11
+
 QMAKE_CFLAGS_SSE2      += -msse2
 QMAKE_CFLAGS_SSE3      += -msse3
 QMAKE_CFLAGS_SSSE3     += -mssse3
diff --git a/mkspecs/features/default_post.prf b/mkspecs/features/default_post.prf
index 9eba5bcf00..bf5acdefc4 100644
--- a/mkspecs/features/default_post.prf
+++ b/mkspecs/features/default_post.prf
@@ -143,6 +143,21 @@ c++11|c++14|c++1z {
     unset(cxxstd)
 }
 
+c99|c11 {
+    c11:       cstd = C11
+    else:      cstd = C99
+
+    # Check if we should disable compiler extensions or not
+    !isEmpty(QMAKE_CFLAGS_GNU$$cstd) {
+        # Let strict C++ imply strict C
+        !strict_c++: cstd = GNU$$cstd
+    }
+
+    QMAKE_CFLAGS += $$eval(QMAKE_CFLAGS_$$cstd)
+
+    unset(cstd)
+}
+
 utf8_source {
     QMAKE_CFLAGS += $$QMAKE_CFLAGS_UTF8_SOURCE
     QMAKE_CXXFLAGS += $$QMAKE_CFLAGS_UTF8_SOURCE
diff --git a/mkspecs/features/qt_common.prf b/mkspecs/features/qt_common.prf
index f4ae5bde80..40f03d2186 100644
--- a/mkspecs/features/qt_common.prf
+++ b/mkspecs/features/qt_common.prf
@@ -17,6 +17,8 @@ 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(c99): CONFIG += c99
+qtConfig(c11): CONFIG += c11
 qtConfig(stack-protector-strong): CONFIG += stack_protector_strong
 contains(TEMPLATE, .*lib) {
     # module and plugins
diff --git a/mkspecs/features/qt_configure.prf b/mkspecs/features/qt_configure.prf
index 98fff59ea1..a7da26c745 100644
--- a/mkspecs/features/qt_configure.prf
+++ b/mkspecs/features/qt_configure.prf
@@ -866,6 +866,15 @@ defineTest(qtConfTestPrepare_compile) {
 defineTest(qtConfPrepareCompileTestSource) {
     test_dir = $$2
 
+    test_lang = $$eval($${1}.lang)
+    isEmpty(test_lang): test_lang = "c++"
+
+    equals(test_lang, "c++"): suffix = "cpp"
+    else: equals(test_lang, "c"): suffix = "c"
+    else: equals(test_lang, "objc"): suffix = "m"
+    else: equals(test_lang, "objc++"): suffix = "mm"
+    else: error("Unknown language '$$test_lang' in compile test $$1")
+
     # Create source code
     contents = "/* Generated by configure */"
     # Custom code before includes
@@ -889,10 +898,10 @@ defineTest(qtConfPrepareCompileTestSource) {
         "    /* END TEST */" \
         "    return 0;" \
         "}"
-    write_file($$test_dir/main.cpp, contents)|error()
+    write_file($$test_dir/main.$$suffix, contents)|error()
 
     # Create stub .pro file
-    contents = "SOURCES = main.cpp"
+    contents = "SOURCES = main.$$suffix"
     # Custom project code
     for (ent, $$qtConfScalarOrList($${1}.qmake)): \
         contents += $$ent