SERVER-37607 SERVER-37608 Require C++17 and make it the default

4 files changed, 105 insertions, 262 deletions

diff --git a/SConstruct b/SConstruct
index 499697acc29..6697b787ee9 100644
--- a/SConstruct
+++ b/SConstruct
@@ -475,8 +475,8 @@ add_option('cache-dir',
 )
 
 add_option("cxx-std",
-    choices=["14", "17"],
-    default="14",
+    choices=["17"],
+    default="17",
     help="Select the C++ langauge standard to build with",
 )
 
@@ -1614,43 +1614,77 @@ elif env.TargetOSIs('windows'):
     env.Append( CPPDEFINES=[ "UNICODE" ] )
 
     # Temporary fixes to allow compilation with VS2017
-    env.Append( CPPDEFINES=[ "_SILENCE_FPOS_SEEKPOS_DEPRECATION_WARNING" ] )
+    env.Append(CPPDEFINES=[
+        "_SILENCE_ALL_CXX17_DEPRECATION_WARNINGS",
+        "_SILENCE_FPOS_SEEKPOS_DEPRECATION_WARNING",
+    ])
 
     # /EHsc exception handling style for visual studio
     # /W3 warning level
     env.Append(CCFLAGS=["/EHsc","/W3"])
 
-    # some warnings we don't like:
-    # c4355
-    # 'this' : used in base member initializer list
-    #    The this pointer is valid only within nonstatic member functions. It cannot be used in the initializer list for a base class.
-    # c4800
-    # 'type' : forcing value to bool 'true' or 'false' (performance warning)
-    #    This warning is generated when a value that is not bool is assigned or coerced into type bool.
-    # c4267
-    # 'var' : conversion from 'size_t' to 'type', possible loss of data
-    # When compiling with /Wp64, or when compiling on a 64-bit operating system, type is 32 bits but size_t is 64 bits when compiling for 64-bit targets. To fix this warning, use size_t instead of a type.
-    # c4244
-    # 'conversion' conversion from 'type1' to 'type2', possible loss of data
-    #  An integer type is converted to a smaller integer type.
-    # c4290
-    #  C++ exception specification ignored except to indicate a function is not __declspec(nothrow
-    #  A function is declared using exception specification, which Visual C++ accepts but does not
-    #  implement
-    # c4068
-    #  unknown pragma -- added so that we can specify unknown pragmas for other compilers
-    # c4351
-    #  on extremely old versions of MSVC (pre 2k5), default constructing an array member in a
-    #  constructor's initialization list would not zero the array members "in some cases".
-    #  since we don't target MSVC versions that old, this warning is safe to ignore.
-    # c4373
-    #  Older versions of MSVC would fail to make a function in a derived class override a virtual
-    #  function in the parent, when defined inline and at least one of the parameters is made const.
-    #  The behavior is incorrect under the standard.  MSVC is fixed now, and the warning exists
-    #  merely to alert users who may have relied upon the older, non-compliant behavior.  Our code
-    #  should not have any problems with the older behavior, so we can just disable this warning.
-    env.Append( CCFLAGS=["/wd4355", "/wd4800", "/wd4267", "/wd4244",
-                         "/wd4290", "/wd4068", "/wd4351", "/wd4373"] )
+    # Suppress some warnings we don't like, or find necessary to
+    # suppress. Please keep this list alphabetized and commented.
+    env.Append(CCFLAGS=[
+
+        # C4068: unknown pragma. added so that we can specify unknown
+        # pragmas for other compilers.
+        "/wd4068",
+
+        # C4244: 'conversion' conversion from 'type1' to 'type2',
+        # possible loss of data. An integer type is converted to a
+        # smaller integer type.
+        "/wd4244",
+
+        # C4267: 'var' : conversion from 'size_t' to 'type', possible
+        # loss of data. When compiling with /Wp64, or when compiling
+        # on a 64-bit operating system, type is 32 bits but size_t is
+        # 64 bits when compiling for 64-bit targets. To fix this
+        # warning, use size_t instead of a type.
+        "/wd4267",
+
+        # C4290: C++ exception specification ignored except to
+        # indicate a function is not __declspec(nothrow). A function
+        # is declared using exception specification, which Visual C++
+        # accepts but does not implement.
+        "/wd4290",
+
+        # C4351: On extremely old versions of MSVC (pre 2k5), default
+        # constructing an array member in a constructor's
+        # initialization list would not zero the array members "in
+        # some cases". Since we don't target MSVC versions that old,
+        # this warning is safe to ignore.
+        "/wd4351",
+
+        # C4355: 'this' : used in base member initializer list. The
+        # this pointer is valid only within nonstatic member
+        # functions. It cannot be used in the initializer list for a
+        # base class
+        "/wd4355",
+
+        # C4373: Older versions of MSVC would fail to make a function
+        # in a derived class override a virtual function in the
+        # parent, when defined inline and at least one of the
+        # parameters is made const. The behavior is incorrect under
+        # the standard. MSVC is fixed now, and the warning exists
+        # merely to alert users who may have relied upon the older,
+        # non-compliant behavior. Our code should not have any
+        # problems with the older behavior, so we can just disable
+        # this warning.
+        "/wd4373",
+
+        # C4800: 'type' : forcing value to bool 'true' or 'false'
+        # (performance warning). This warning is generated when a
+        # value that is not bool is assigned or coerced into type
+        # bool.
+        "/wd4800",
+
+        # C5041: out-of-line definition for constexpr static data
+        # member is not needed and is deprecated in C++17. We still
+        # have these, but we don't want to fix them up before we roll
+        # over to C++17.
+        "/wd5041",
+    ])
 
     # mozjs-60 requires the following
     #  'declaration' : no matching operator delete found; memory will not be freed if
@@ -2373,15 +2407,10 @@ def doConfigure(myenv):
 
     if myenv.ToolchainIs('msvc'):
         myenv.AppendUnique(CXXFLAGS=['/Zc:__cplusplus'])
-        if get_option('cxx-std') == "14":
-            myenv.AppendUnique(CCFLAGS=['/std:c++14'])
-        elif get_option('cxx-std') == "17":
+        if get_option('cxx-std') == "17":
             myenv.AppendUnique(CCFLAGS=['/std:c++17'])
     else:
-        if get_option('cxx-std') == "14":
-            if not AddToCXXFLAGSIfSupported(myenv, '-std=c++14'):
-                myenv.ConfError('Compiler does not honor -std=c++14')
-        elif get_option('cxx-std') == "17":
+        if get_option('cxx-std') == "17":
             if not AddToCXXFLAGSIfSupported(myenv, '-std=c++17'):
                 myenv.ConfError('Compiler does not honor -std=c++17')
 
@@ -2391,21 +2420,6 @@ def doConfigure(myenv):
     if using_system_version_of_cxx_libraries():
         print( 'WARNING: System versions of C++ libraries must be compiled with C++14/17 support' )
 
-    def CheckCxx14(context):
-        test_body = """
-        #if __cplusplus < 201402L
-        #error
-        #endif
-        auto DeducedReturnTypesAreACXX14Feature() {
-            return 0;
-        }
-        """
-
-        context.Message('Checking for C++14... ')
-        ret = context.TryCompile(textwrap.dedent(test_body), ".cpp")
-        context.Result(ret)
-        return ret
-
     def CheckCxx17(context):
         test_body = """
         #if __cplusplus < 201703L
@@ -2420,15 +2434,11 @@ def doConfigure(myenv):
         return ret
 
     conf = Configure(myenv, help=False, custom_tests = {
-        'CheckCxx14' : CheckCxx14,
         'CheckCxx17' : CheckCxx17,
     })
 
-    if not conf.CheckCxx14():
-        myenv.ConfError('C++14 support is required to build MongoDB')
-
     if get_option('cxx-std') == "17" and not conf.CheckCxx17():
-        myenv.ConfError('C++17 was requested, but the compiler appears not to offer it')
+        myenv.ConfError('C++17 support is required to build MongoDB')
 
     conf.Finish()
 
diff --git a/etc/evergreen.yml b/etc/evergreen.yml
index ade4c5ea1a6..7dbd64a7a60 100644
--- a/etc/evergreen.yml
+++ b/etc/evergreen.yml
@@ -8334,91 +8334,6 @@ buildvariants:
   - name: publish_packages
   - name: push
 
-- name: enterprise-ubuntu1804-64-gcc-cxx17
-  display_name: ~ Enterprise Ubuntu 18.04 (System GCC 7.x C++17 DEBUG)
-  modules:
-  - enterprise
-  run_on:
-  - ubuntu1804-test
-  batchtime: 1440 # 1 day
-  expansions:
-    compile_flags: >-
-      --dbg=on
-      --opt=on
-      --ssl
-      -j$(grep -c ^processor /proc/cpuinfo)
-      CC=gcc-7
-      CXX=g++-7
-      --cxx-std=17
-      --disable-warnings-as-errors
-    repo_edition: enterprise
-    scons_cache_scope: shared
-    tooltags: "ssl sasl"
-    build_mongoreplay: true
-  display_tasks:
-  - *dbtest
-  - *unittests
-  tasks:
-  - name: compile_all_run_unittests_TG
-    distros:
-    - ubuntu1804-build
-  - name: audit
-  - name: ese
-  - name: jsCore
-  - name: jsCore_auth
-  - name: jsCore_txns
-  - name: causally_consistent_jscore_txns_passthrough
-  - name: sasl
-  - name: snmp
-  - name: ssl
-  - name: sslSpecial
-
-- name: enterprise-ubuntu1804-64-clang-cxx17
-  display_name: ~ Enterprise Ubuntu 18.04 (System clang 6.0 C++17 libc++ DEBUG)
-  modules:
-  - enterprise
-  run_on:
-  - ubuntu1804-test
-  batchtime: 1440 # 1 day
-  expansions:
-    compile_flags: >-
-      --dbg=on
-      --opt=on
-      --ssl
-      -j$(grep -c ^processor /proc/cpuinfo)
-      CC=clang-6.0
-      CXX=clang++-6.0
-      --libc++
-      --cxx-std=17
-      --disable-warnings-as-errors
-      CXXFLAGS="-Wno-register"
-    repo_edition: enterprise
-    scons_cache_scope: shared
-    tooltags: "ssl sasl"
-    build_mongoreplay: true
-  display_tasks:
-  - *dbtest
-  - *unittests
-  tasks:
-  - name: compile_all_run_unittests_TG
-    distros:
-    - ubuntu1804-build
-  - name: audit
-  - name: ese
-  - name: jsCore
-  - name: jsCore_auth
-  - name: jsCore_txns
-  - name: causally_consistent_jscore_txns_passthrough
-  - name: replica_sets_auth
-  - name: sasl
-  - name: sharding_auth
-  - name: snmp
-  - name: ssl
-  - name: sslSpecial
-  - name: stitch_support_lib_build_and_test
-  - name: stitch_support_lib_build_and_archive
-  - name: watchdog_wiredtiger
-
 - name: ubuntu1604
   display_name: SSL Ubuntu 16.04
   run_on:
@@ -10361,55 +10276,6 @@ buildvariants:
     distros:
     - rhel70-small
 
-- name: enterprise-osx-1011-xcode-10-cxx17
-  display_name: ~ Enterprise macOS 10.11 (XCode 10.1 C++17)
-  modules:
-  - enterprise
-  run_on:
-  - macos-1014
-  batchtime: 1440 # 1 day
-  expansions:
-    test_flags: --excludeWithAnyTags=requires_ssl_mongo_tools
-    compile_env: DEVELOPER_DIR=/Applications/Xcode10.1.app
-    compile_flags: >-
-      --ssl
-      -j$(sysctl -n hw.logicalcpu)
-      --libc++
-      --variables-files=etc/scons/xcode_macosx.vars
-      --cxx-std=17
-      CXXFLAGS="-Wno-register"
-    resmoke_jobs_max: 1
-    tooltags: "ssl sasl"
-    build_mongoreplay: true
-  display_tasks:
-  - *dbtest
-  - *unittests
-  tasks:
-  - name: compile_all_run_unittests_TG
-  - name: audit
-  - name: auth_audit
-  - name: ese
-  - name: jsCore
-  - name: jsCore_auth
-  - name: jsCore_txns
-  - name: causally_consistent_jscore_txns_passthrough
-  - name: jstestfuzz_gen
-  - name: jstestfuzz_concurrent_gen
-  - name: jstestfuzz_concurrent_replication_gen
-  - name: jstestfuzz_concurrent_sharded_gen
-  - name: jstestfuzz_replication_gen
-  - name: jstestfuzz_sharded_gen
-  - name: logical_session_cache_replication_1sec_refresh_jscore_passthrough
-  - name: logical_session_cache_sharding_1sec_refresh_jscore_passthrough
-  - name: logical_session_cache_standalone_1sec_refresh_jscore_passthrough
-  - name: replica_sets_auth
-  - name: replica_sets_jscore_passthrough
-  - name: sasl
-  - name: ssl
-  - name: sslSpecial
-  - name: stitch_support_lib_build_and_test
-  - name: stitch_support_lib_build_and_archive
-
 - name: enterprise-osx-1010-openssl
   display_name: ~ Enterprise macOS 10.10 OpenSSL
   modules:
@@ -10739,7 +10605,6 @@ buildvariants:
       -j$(grep -c ^processor /proc/cpuinfo)
       --toolchain-root=$(dirname $(pwd))/android_toolchain-arm-21
       --variables-files=etc/scons/android_toolchain.vars
-      --cxx-std=17
       LIBS=clang_rt.builtins-arm-android
       LIBPATH="$(dirname $($(dirname $(pwd))/android_toolchain-arm-21/bin/clang -print-file-name=libclang_rt.builtins-arm-android.a)) \$BUILD_ROOT/mongo-embedded-sdk-\$MONGO_VERSION/lib"
       --lto
@@ -10782,7 +10647,6 @@ buildvariants:
       -j$(grep -c ^processor /proc/cpuinfo)
       --toolchain-root=$(dirname $(pwd))/android_toolchain-arm64-21
       --variables-files=etc/scons/android_toolchain.vars
-      --cxx-std=17
       LIBPATH="\$BUILD_ROOT/mongo-embedded-sdk-\$MONGO_VERSION/lib"
       --lto
       AR=$(dirname $(pwd))/android_toolchain-arm64-21/bin/llvm-ar
@@ -10824,7 +10688,6 @@ buildvariants:
       -j$(grep -c ^processor /proc/cpuinfo)
       --toolchain-root=$(dirname $(pwd))/android_toolchain-x86_64-21
       --variables-files=etc/scons/android_toolchain.vars
-      --cxx-std=17
       LIBPATH="\$BUILD_ROOT/mongo-embedded-sdk-\$MONGO_VERSION/lib"
       --lto
       AR=$(dirname $(pwd))/android_toolchain-x86_64-21/bin/llvm-ar
@@ -14419,43 +14282,3 @@ buildvariants:
   stepback: false
   tasks:
   - name: shared_scons_cache_pruning
-
-- name: windows-64-vs2017-cxx17
-  display_name: "Windows VS2017 Canary C++17 Builder"
-  run_on:
-  - windows-64-vs2017-test
-  modules:
-  - enterprise
-  expansions:
-    platform_decompress: unzip
-    exe: ".exe"
-    content_type: application/zip
-    compile_flags: CPPPATH="c:/sasl/include c:/snmp/include" LIBPATH="c:/sasl/lib c:/snmp/lib" MSVC_VERSION=14.1 CXXFLAGS="/wd4834 /wd5033 /wd5041" CPPDEFINES="_SILENCE_ALL_CXX17_DEPRECATION_WARNINGS" --cxx-std=17 --dynamic-windows --dbg=off --opt=on -j$(( $(grep -c ^processor /proc/cpuinfo) / 2 ))
-    # We invoke SCons using --jobs = (# of CPUs / 4) to avoid causing out of memory errors due to
-    # spawning a large number of linker processes.
-    num_scons_link_jobs_available: $(( $(grep -c ^processor /proc/cpuinfo) / 4 ))
-    python: python
-    python3: '/cygdrive/c/python/python36/python.exe'
-    ext: zip
-    use_scons_cache: true
-    multiversion_platform: windows
-    multiversion_edition: enterprise
-    tooltags: ""
-    build_mongoreplay: false
-  display_tasks:
-  - *dbtest
-  - *unittests
-  tasks:
-  - name: compile_all_run_unittests_TG
-    distros:
-    - windows-64-vs2017-compile
-  - name: audit
-  - name: ese
-  - name: jsCore
-  - name: jsCore_auth
-  - name: jsCore_txns
-  - name: causally_consistent_jscore_txns_passthrough
-  - name: sasl
-  - name: snmp
-  - name: ssl
-  - name: sslSpecial
diff --git a/src/mongo/db/index/sort_key_generator_test.cpp b/src/mongo/db/index/sort_key_generator_test.cpp
index 388eeb10f57..1618cb57495 100644
--- a/src/mongo/db/index/sort_key_generator_test.cpp
+++ b/src/mongo/db/index/sort_key_generator_test.cpp
@@ -136,35 +136,39 @@ TEST(SortKeyGeneratorTest, SortKeyGenerationForArraysRespectsCompoundOrdering) {
 DEATH_TEST(SortKeyGeneratorTest,
            SortPatternComponentWithStringIsFatal,
            "Invariant failure elt.type() == BSONType::Object") {
-    stdx::make_unique<SortKeyGenerator>(BSON("a"
-                                             << "foo"),
-                                        nullptr);
+    MONGO_COMPILER_VARIABLE_UNUSED auto ignored =
+        stdx::make_unique<SortKeyGenerator>(BSON("a"
+                                                 << "foo"),
+                                            nullptr);
 }
 
 DEATH_TEST(SortKeyGeneratorTest,
            SortPatternComponentWhoseObjectHasMultipleKeysIsFatal,
            "Invariant failure elt.embeddedObject().nFields() == 1") {
-    stdx::make_unique<SortKeyGenerator>(BSON("a" << BSON("$meta"
-                                                         << "textScore"
-                                                         << "extra"
-                                                         << 1)),
-                                        nullptr);
+    MONGO_COMPILER_VARIABLE_UNUSED auto ignored =
+        stdx::make_unique<SortKeyGenerator>(BSON("a" << BSON("$meta"
+                                                             << "textScore"
+                                                             << "extra"
+                                                             << 1)),
+                                            nullptr);
 }
 
 DEATH_TEST(SortKeyGeneratorTest,
            SortPatternComponentWithNonMetaObjectSortIsFatal,
            "Invariant failure metaElem.fieldNameStringData() == \"$meta\"_sd") {
-    stdx::make_unique<SortKeyGenerator>(BSON("a" << BSON("$unknown"
-                                                         << "textScore")),
-                                        nullptr);
+    MONGO_COMPILER_VARIABLE_UNUSED auto ignored =
+        stdx::make_unique<SortKeyGenerator>(BSON("a" << BSON("$unknown"
+                                                             << "textScore")),
+                                            nullptr);
 }
 
 DEATH_TEST(SortKeyGeneratorTest,
            SortPatternComponentWithUnknownMetaKeywordIsFatal,
            "Invariant failure metaElem.valueStringData() == \"randVal\"_sd") {
-    stdx::make_unique<SortKeyGenerator>(BSON("a" << BSON("$meta"
-                                                         << "unknown")),
-                                        nullptr);
+    MONGO_COMPILER_VARIABLE_UNUSED auto ignored =
+        stdx::make_unique<SortKeyGenerator>(BSON("a" << BSON("$meta"
+                                                             << "unknown")),
+                                            nullptr);
 }
 
 DEATH_TEST(SortKeyGeneratorTest,
diff --git a/src/mongo/db/update/push_node.cpp b/src/mongo/db/update/push_node.cpp
index c881c882e93..e214b25b458 100644
--- a/src/mongo/db/update/push_node.cpp
+++ b/src/mongo/db/update/push_node.cpp
@@ -227,16 +227,22 @@ ModifierNode::ModifyResult PushNode::insertElementsWithPosition(
         result = ModifyResult::kNormalUpdate;
     }
 
-    // We insert all the rest of the elements after the one we just inserted.
-    std::accumulate(std::next(valuesToPush.begin()),
-                    valuesToPush.end(),
-                    firstElementToInsert,
-                    [&document](auto& insertAfter, auto& valueToInsert) {
-                        auto nextElementToInsert =
-                            document.makeElementWithNewFieldName(StringData(), valueToInsert);
-                        invariant(insertAfter.addSiblingRight(nextElementToInsert));
-                        return nextElementToInsert;
-                    });
+    // We insert all the rest of the elements after the one we just
+    // inserted.
+    //
+    // TODO: The use of std::accumulate here is maybe questionable
+    // given that we are ignoring the return value. MSVC flagged this,
+    // and we worked around by tagging the result as unused.
+    MONGO_COMPILER_VARIABLE_UNUSED auto ignored =
+        std::accumulate(std::next(valuesToPush.begin()),
+                        valuesToPush.end(),
+                        firstElementToInsert,
+                        [&document](auto& insertAfter, auto& valueToInsert) {
+                            auto nextElementToInsert =
+                                document.makeElementWithNewFieldName(StringData(), valueToInsert);
+                            invariant(insertAfter.addSiblingRight(nextElementToInsert));
+                            return nextElementToInsert;
+                        });
 
     return result;
 }