SERVER-23520 Add a C++14 canary builder

Author: acmorrow

SConstruct

@@ -445,6 +445,12 @@ add_option("experimental-decimal-support",
     nargs='?',
 )
 
+add_option("cxx-std",
+    choices=["11", "14"],
+    default="11",
+    help="Select the C++ langauge standard to build with",
+)
+
 def find_mongo_custom_variables():
     files = []
     for path in sys.path:
@@ -1854,13 +1860,17 @@ def doConfigure(myenv):
         conf.Finish()
 
     if not myenv.ToolchainIs('msvc'):
-        if not AddToCXXFLAGSIfSupported(myenv, '-std=c++11'):
-            myenv.ConfError('Compiler does not honor -std=c++11')
+        if get_option('cxx-std') == "11":
+            if not AddToCXXFLAGSIfSupported(myenv, '-std=c++11'):
+                myenv.ConfError('Compiler does not honor -std=c++11')
+        elif get_option('cxx-std') == "14":
+            if not AddToCXXFLAGSIfSupported(myenv, '-std=c++14'):
+                myenv.ConfError('Compiler does not honor -std=c++14')
         if not AddToCFLAGSIfSupported(myenv, '-std=c99'):
             myenv.ConfError("C++11 mode selected for C++ files, but can't enable C99 for C files")
 
     if using_system_version_of_cxx_libraries():
-        print( 'WARNING: System versions of C++ libraries must be compiled with C++11 support' )
+        print( 'WARNING: System versions of C++ libraries must be compiled with C++11/14 support' )
 
     # We appear to have C++11, or at least a flag to enable it. Check that the declared C++
     # language level is not less than C++11, and that we can at least compile an 'auto'
@@ -1883,13 +1893,35 @@ def doConfigure(myenv):
         context.Result(ret)
         return ret
 
+    def CheckCxx14(context):
+        test_body = """
+        #ifndef _MSC_VER
+        #if __cplusplus < 201402L
+        #error
+        #endif
+        #endif
+        auto DeducedReturnTypesAreACXX14Feature() {
+            return 0;
+        }
+        """
+
+        context.Message('Checking for C++14... ')
+        ret = context.TryCompile(textwrap.dedent(test_body), ".cpp")
+        context.Result(ret)
+        return ret
+
     conf = Configure(myenv, help=False, custom_tests = {
         'CheckCxx11' : CheckCxx11,
+        'CheckCxx14' : CheckCxx14,
     })
 
     if not conf.CheckCxx11():
         myenv.ConfError('C++11 support is required to build MongoDB')
 
+    if get_option('cxx-std') == "14":
+        if not conf.CheckCxx14():
+            myenv.ConfError('C++14 does not appear to work with the current toolchain')
+
     conf.Finish()
 
     def CheckMemset_s(context):

etc/evergreen.yml

@@ -6030,8 +6030,8 @@ buildvariants:
     distros:
     - ubuntu1404-build
 
-- name: enterprise-rhel-62-gcc-530
-  display_name: ~ Enterprise RHEL 6.2 GCC 5.3.0
+- name: enterprise-debug-rhel-62-cxx14
+  display_name: ~ Enterprise RHEL 6.2 C++14 DEBUG
   modules:
   - enterprise
   run_on:
@@ -6041,7 +6041,7 @@ buildvariants:
     gorootvars: GOROOT=/opt/go PATH="/opt/go/bin:$PATH"
     tooltags: "-tags 'ssl sasl'"
     rlp_environment: MONGOD_UNITTEST_RLP_LANGUAGE_TEST_BTROOT=/opt/basis
-    compile_flags: --ssl MONGO_DISTMOD=rhel62 -j$(grep -c ^processor /proc/cpuinfo) --release CC=/opt/mongodbtoolchain/v2/bin/gcc CXX=/opt/mongodbtoolchain/v2/bin/g++ CPPPATH="/opt/basis/rlp/rlp/include /opt/basis/rlp/utilities/include" --use-basis-tech-rosette-linguistics-platform=on
+    compile_flags: --allocator=system --ssl -j$(grep -c ^processor /proc/cpuinfo) CC=/opt/mongodbtoolchain/v2/bin/gcc CXX=/opt/mongodbtoolchain/v2/bin/g++ CPPPATH="/opt/basis/rlp/rlp/include /opt/basis/rlp/utilities/include" --use-basis-tech-rosette-linguistics-platform=on --cxx-std=14
     num_jobs_available: $(grep -c ^processor /proc/cpuinfo)
   tasks:
   - name: compile

src/mongo/client/fetcher_test.cpp

@@ -504,7 +504,7 @@ TEST_F(FetcherTest, SetNextActionToContinueWhenNextBatchIsNotAvailable) {
                       Fetcher::NextAction* nextAction,
                       BSONObjBuilder* getMoreBob) {
         ASSERT_OK(fetchResult.getStatus());
-        Fetcher::QueryResponse batchData{fetchResult.getValue()};
+        Fetcher::QueryResponse batchData = fetchResult.getValue();
 
         ASSERT(nextAction);
         *nextAction = Fetcher::NextAction::kGetMore;
@@ -856,7 +856,7 @@ void shutdownDuringSecondBatch(const StatusWith<Fetcher::QueryResponse>& fetchRe
 
     // First time during second batch
     ASSERT_OK(fetchResult.getStatus());
-    Fetcher::QueryResponse batchData{fetchResult.getValue()};
+    Fetcher::QueryResponse batchData = fetchResult.getValue();
     ASSERT_EQUALS(1U, batchData.documents.size());
     ASSERT_EQUALS(doc2, batchData.documents.front());
     ASSERT_TRUE(Fetcher::NextAction::kGetMore == *nextAction);