Toolchains: Detect unspecified language version

We checked the command line from the project manager for "-std=X" and
friends to figure out the language version to use. However, if such a
flag was not provided, we assumed the latest version we support. This
could conflict with the actual version of the compiler and its
predefined macros.

Figure out the version by inspecting __cplusplus/__STDC_VERSION__ in the
predefined macros of the toolchain. The MSVC compiler is an exception to
this, as it does not seem to properly set the value - check for
_MSVC_LANG if possible, otherwise simply assume some versions as before.

While at it, add also support for C17/C18 and the upcoming C++2a.

Task-number: QTCREATORBUG-20884
Task-number: QTCREATORBUG-21188
Change-Id: I464ffcd52d2120c0208275a050e82efda44fae1c
Reviewed-by: Ivan Donchevskii <ivan.donchevskii@qt.io>

10 files changed, 217 insertions, 119 deletions

diff --git a/src/plugins/projectexplorer/abstractmsvctoolchain.cpp b/src/plugins/projectexplorer/abstractmsvctoolchain.cpp
index 4bd77d1462..151c4400ef 100644
--- a/src/plugins/projectexplorer/abstractmsvctoolchain.cpp
+++ b/src/plugins/projectexplorer/abstractmsvctoolchain.cpp
@@ -99,23 +99,88 @@ QString AbstractMsvcToolChain::originalTargetTriple() const
             : QLatin1String("i686-pc-windows-msvc");
 }
 
-ToolChain::PredefinedMacrosRunner AbstractMsvcToolChain::createPredefinedMacrosRunner() const
+//
+// We want to detect the language version based on the predefined macros.
+// Unfortunately MSVC does not conform to standard when it comes to the predefined
+// __cplusplus macro - it reports "199711L", even for newer language versions.
+//
+// However:
+//   * For >= Visual Studio 2015 Update 3 predefines _MSVC_LANG which has the proper value
+//     of __cplusplus.
+//     See https://docs.microsoft.com/en-us/cpp/preprocessor/predefined-macros?view=vs-2017
+//   * For >= Visual Studio 2017 Version 15.7 __cplusplus is correct once /Zc:__cplusplus
+//     is provided on the command line. Then __cplusplus == _MSVC_LANG.
+//     See https://blogs.msdn.microsoft.com/vcblog/2018/04/09/msvc-now-correctly-reports-__cplusplus
+//
+// We rely on _MSVC_LANG if possible, otherwise on some hard coded language versions
+// depending on _MSC_VER.
+//
+// For _MSV_VER values, see https://docs.microsoft.com/en-us/cpp/preprocessor/predefined-macros?view=vs-2017.
+//
+ToolChain::LanguageVersion static languageVersionForMsvc(const Core::Id &language,
+                                                         const Macros &macros)
+{
+    using LanguageVersion = ToolChain::LanguageVersion;
+
+    int mscVer = -1;
+    QByteArray msvcLang;
+    for (const ProjectExplorer::Macro &macro : macros) {
+        if (macro.key == "_MSVC_LANG")
+            msvcLang = macro.value;
+        if (macro.key == "_MSC_VER")
+            mscVer = macro.value.toInt(nullptr);
+    }
+    QTC_CHECK(mscVer > 0);
+
+    if (language == Constants::CXX_LANGUAGE_ID) {
+        if (!msvcLang.isEmpty()) // >= Visual Studio 2015 Update 3
+            return ToolChain::cxxLanguageVersion(msvcLang);
+        if (mscVer >= 1800) // >= Visual Studio 2013 (12.0)
+            return LanguageVersion::CXX14;
+        if (mscVer >= 1600) // >= Visual Studio 2010 (10.0)
+            return LanguageVersion::CXX11;
+        return LanguageVersion::CXX98;
+    } else if (language == Constants::C_LANGUAGE_ID) {
+        if (mscVer >= 1910) // >= Visual Studio 2017 RTW (15.0)
+            return LanguageVersion::C11;
+        return LanguageVersion::C99;
+    } else {
+        QTC_CHECK(false && "Unexpected toolchain language, assuming latest C++ we support.");
+        return LanguageVersion::LatestCxxVersion;
+    }
+}
+
+Q_GLOBAL_STATIC_WITH_ARGS(const QVector<QByteArray>, unwantedMacrosMsvc,
+                          ({"_MSVC_LANG",
+                            "_MSC_BUILD",
+                            "_MSC_FULL_VER",
+                            "_MSC_VER"}))
+
+ToolChain::MacroInspectionRunner AbstractMsvcToolChain::createMacroInspectionRunner() const
 {
     Utils::Environment env(m_lastEnvironment);
     addToEnvironment(env);
+    const Core::Id lang = language();
 
     // This runner must be thread-safe!
-    return [this, env](const QStringList &cxxflags) {
+    return [this, env, lang](const QStringList &cxxflags) {
         QMutexLocker locker(m_predefinedMacrosMutex);
-        if (m_predefinedMacros.isEmpty())
+        if (m_predefinedMacros.isEmpty() || m_cxxFlags != cxxflags) {
             m_predefinedMacros = msvcPredefinedMacros(cxxflags, env);
-        return m_predefinedMacros;
+            m_cxxFlags = cxxflags;
+        }
+
+        const QVector<Macro> filteredMacros = Utils::filtered(m_predefinedMacros, [](const Macro &m) {
+            return !ToolChain::isUnwantedMacro(m) && !unwantedMacrosMsvc->contains(m.key);
+        });
+        return MacroInspectionReport{filteredMacros,
+                                     languageVersionForMsvc(lang, m_predefinedMacros)};
     };
 }
 
 ProjectExplorer::Macros AbstractMsvcToolChain::predefinedMacros(const QStringList &cxxflags) const
 {
-    return createPredefinedMacrosRunner()(cxxflags);
+    return createMacroInspectionRunner()(cxxflags).macros;
 }
 
 ToolChain::CompilerFlags AbstractMsvcToolChain::compilerFlags(const QStringList &cxxflags) const
@@ -128,35 +193,6 @@ ToolChain::CompilerFlags AbstractMsvcToolChain::compilerFlags(const QStringList
     if (cxxflags.contains(QLatin1String("/Za")))
         flags &= ~MicrosoftExtensions;
 
-    bool cLanguage = (language() == ProjectExplorer::Constants::C_LANGUAGE_ID);
-
-    switch (m_abi.osFlavor()) {
-    case Abi::WindowsMsvc2010Flavor:
-    case Abi::WindowsMsvc2012Flavor:
-        if (cLanguage)
-            flags |= StandardC99;
-        else
-            flags |= StandardCxx11;
-        break;
-    case Abi::WindowsMsvc2013Flavor:
-    case Abi::WindowsMsvc2015Flavor:
-        if (cLanguage)
-            flags |= StandardC99;
-        else
-            flags |= StandardCxx14;
-        break;
-    case Abi::WindowsMsvc2017Flavor:
-        if (cLanguage)
-            flags |= StandardC11;
-        else if (cxxflags.contains("/std:c++17") || cxxflags.contains("/std:c++latest"))
-            flags |= StandardCxx17;
-        else
-            flags |= StandardCxx14;
-        break;
-    default:
-        break;
-    }
-
     return flags;
 }
 
diff --git a/src/plugins/projectexplorer/abstractmsvctoolchain.h b/src/plugins/projectexplorer/abstractmsvctoolchain.h
index 2979e728cc..d949073f46 100644
--- a/src/plugins/projectexplorer/abstractmsvctoolchain.h
+++ b/src/plugins/projectexplorer/abstractmsvctoolchain.h
@@ -53,7 +53,7 @@ public:
 
     QString originalTargetTriple() const override;
 
-    PredefinedMacrosRunner createPredefinedMacrosRunner() const override;
+    MacroInspectionRunner createMacroInspectionRunner() const override;
     Macros predefinedMacros(const QStringList &cxxflags) const override;
     CompilerFlags compilerFlags(const QStringList &cxxflags) const override;
     WarningFlags warningFlags(const QStringList &cflags) const override;
@@ -99,8 +99,11 @@ protected:
 
 
     Utils::FileName m_debuggerCommand;
+
     mutable QMutex *m_predefinedMacrosMutex = nullptr;
     mutable Macros m_predefinedMacros;
+    mutable QStringList m_cxxFlags;
+
     mutable Utils::Environment m_lastEnvironment;   // Last checked 'incoming' environment.
     mutable Utils::Environment m_resultEnvironment; // Resulting environment for VC
     mutable QMutex *m_headerPathsMutex = nullptr;
diff --git a/src/plugins/projectexplorer/customtoolchain.cpp b/src/plugins/projectexplorer/customtoolchain.cpp
index f9cb0a81a7..7b952e0fe2 100644
--- a/src/plugins/projectexplorer/customtoolchain.cpp
+++ b/src/plugins/projectexplorer/customtoolchain.cpp
@@ -116,12 +116,13 @@ bool CustomToolChain::isValid() const
     return true;
 }
 
-ToolChain::PredefinedMacrosRunner CustomToolChain::createPredefinedMacrosRunner() const
+ToolChain::MacroInspectionRunner CustomToolChain::createMacroInspectionRunner() const
 {
     const Macros theMacros = m_predefinedMacros;
+    const Core::Id lang = language();
 
     // This runner must be thread-safe!
-    return [theMacros](const QStringList &cxxflags){
+    return [theMacros, lang](const QStringList &cxxflags){
         Macros macros = theMacros;
         for (const QString &cxxFlag : cxxflags) {
             if (cxxFlag.startsWith(QLatin1String("-D")))
@@ -130,20 +131,17 @@ ToolChain::PredefinedMacrosRunner CustomToolChain::createPredefinedMacrosRunner(
                 macros.append({cxxFlag.mid(2).trimmed().toUtf8(), MacroType::Undefine});
 
         }
-        return macros;
+        return MacroInspectionReport{macros, ToolChain::languageVersion(lang, macros)};
     };
 }
 
 Macros CustomToolChain::predefinedMacros(const QStringList &cxxflags) const
 {
-    return createPredefinedMacrosRunner()(cxxflags);
+    return createMacroInspectionRunner()(cxxflags).macros;
 }
 
-ToolChain::CompilerFlags CustomToolChain::compilerFlags(const QStringList &cxxflags) const
+ToolChain::CompilerFlags CustomToolChain::compilerFlags(const QStringList &) const
 {
-    for (const QString &cxx11Flag : m_cxx11Flags)
-        if (cxxflags.contains(cxx11Flag))
-            return StandardCxx11;
     return NoFlags;
 }
 
diff --git a/src/plugins/projectexplorer/customtoolchain.h b/src/plugins/projectexplorer/customtoolchain.h
index 23abb2e730..28fd7a1828 100644
--- a/src/plugins/projectexplorer/customtoolchain.h
+++ b/src/plugins/projectexplorer/customtoolchain.h
@@ -71,7 +71,7 @@ public:
 
     bool isValid() const override;
 
-    PredefinedMacrosRunner createPredefinedMacrosRunner() const override;
+    MacroInspectionRunner createMacroInspectionRunner() const override;
     Macros predefinedMacros(const QStringList &cxxflags) const override;
     CompilerFlags compilerFlags(const QStringList &cxxflags) const override;
     WarningFlags warningFlags(const QStringList &cxxflags) const override;
diff --git a/src/plugins/projectexplorer/gcctoolchain.cpp b/src/plugins/projectexplorer/gcctoolchain.cpp
index 622b477ca2..2fa6de6737 100644
--- a/src/plugins/projectexplorer/gcctoolchain.cpp
+++ b/src/plugins/projectexplorer/gcctoolchain.cpp
@@ -254,7 +254,7 @@ GccToolChain::GccToolChain(Detection d) :
 
 GccToolChain::GccToolChain(Core::Id typeId, Detection d) :
     ToolChain(typeId, d),
-    m_predefinedMacrosCache(std::make_shared<Cache<QVector<Macro>, 64>>()),
+    m_predefinedMacrosCache(std::make_shared<Cache<MacroInspectionReport, 64>>()),
     m_headerPathsCache(std::make_shared<Cache<HeaderPaths>>())
 { }
 
@@ -385,9 +385,7 @@ static Utils::FileName findLocalCompiler(const Utils::FileName &compilerPath,
     return path.isEmpty() ? compilerPath : path;
 }
 
-Q_GLOBAL_STATIC_WITH_ARGS(const QVector<QByteArray>, unwantedMacros, ({"__cplusplus"}))
-
-ToolChain::PredefinedMacrosRunner GccToolChain::createPredefinedMacrosRunner() const
+ToolChain::MacroInspectionRunner GccToolChain::createMacroInspectionRunner() const
 {
     // Using a clean environment breaks ccache/distcc/etc.
     Environment env = Environment::systemEnvironment();
@@ -396,7 +394,7 @@ ToolChain::PredefinedMacrosRunner GccToolChain::createPredefinedMacrosRunner() c
     const QStringList platformCodeGenFlags = m_platformCodeGenFlags;
     OptionsReinterpreter reinterpretOptions = m_optionsReinterpreter;
     QTC_CHECK(reinterpretOptions);
-    std::shared_ptr<Cache<QVector<Macro>, 64>> macroCache = m_predefinedMacrosCache;
+    std::shared_ptr<Cache<MacroInspectionReport, 64>> macroCache = m_predefinedMacrosCache;
     Core::Id lang = language();
 
     // This runner must be thread-safe!
@@ -436,20 +434,22 @@ ToolChain::PredefinedMacrosRunner GccToolChain::createPredefinedMacrosRunner() c
         }
 
         arguments = reinterpretOptions(arguments);
-        const Utils::optional<QVector<Macro>> cachedMacros = macroCache->check(arguments);
+        const Utils::optional<MacroInspectionReport> cachedMacros = macroCache->check(arguments);
         if (cachedMacros)
             return cachedMacros.value();
 
-        const QVector<Macro> macros
-                = gccPredefinedMacros(findLocalCompiler(compilerCommand, env),
-                                      arguments,
-                                      env.toStringList());
+        const Macros macros = gccPredefinedMacros(findLocalCompiler(compilerCommand, env),
+                                                  arguments,
+                                                  env.toStringList());
         const QVector<Macro> filteredMacros = Utils::filtered(macros, [](const Macro &m) {
-            return !unwantedMacros->contains(m.key);
+            return !isUnwantedMacro(m);
         });
-        macroCache->insert(arguments, filteredMacros);
 
-        qCDebug(gccLog) << "Reporting macros to code model:";
+        const auto report = MacroInspectionReport{filteredMacros, languageVersion(lang, macros)};
+        macroCache->insert(arguments, report);
+
+        qCDebug(gccLog) << "MacroInspectionReport for code model:";
+        qCDebug(gccLog) << "Language version:" << report.languageVersion;
         for (const Macro &m : filteredMacros) {
             qCDebug(gccLog) << compilerCommand.toUserOutput()
                             << (lang == Constants::CXX_LANGUAGE_ID ? ": C++ [" : ": C [")
@@ -457,7 +457,7 @@ ToolChain::PredefinedMacrosRunner GccToolChain::createPredefinedMacrosRunner() c
                             << QString::fromUtf8(m.toByteArray());
         }
 
-        return filteredMacros;
+        return report;
     };
 }
 
@@ -472,7 +472,7 @@ ToolChain::PredefinedMacrosRunner GccToolChain::createPredefinedMacrosRunner() c
  */
 ProjectExplorer::Macros GccToolChain::predefinedMacros(const QStringList &cxxflags) const
 {
-    return createPredefinedMacrosRunner()(cxxflags);
+    return createMacroInspectionRunner()(cxxflags).macros;
 }
 
 /**
@@ -487,55 +487,14 @@ ToolChain::CompilerFlags GccToolChain::compilerFlags(const QStringList &cxxflags
     foreach (const QString &flag, allCxxflags) {
         if (flag.startsWith("-std=")) {
             const QByteArray std = flag.mid(5).toLatin1();
-            if (std == "c++98" || std == "c++03") {
-                flags &= ~CompilerFlags(StandardCxx11 | StandardCxx14 | StandardCxx17 | GnuExtensions);
-                flags |= StandardCxx98;
-            } else if (std == "gnu++98" || std == "gnu++03") {
-                flags &= ~CompilerFlags(StandardCxx11 | StandardCxx14 | StandardCxx17);
-                flags |= GnuExtensions;
-            } else if (std == "c++0x" || std == "c++11") {
-                flags |= StandardCxx11;
-                flags &= ~CompilerFlags(StandardCxx14 | StandardCxx17 | GnuExtensions);
-            } else if (std == "c++14" || std == "c++1y") {
-                flags |= StandardCxx14;
-                flags &= ~CompilerFlags(StandardCxx11 | StandardCxx17 | GnuExtensions);
-            } else if (std == "c++17" || std == "c++1z") {
-                flags |= StandardCxx17;
-                flags &= ~CompilerFlags(StandardCxx11 | StandardCxx14 | GnuExtensions);
-            } else if (std == "gnu++0x" || std == "gnu++11") {
-                flags |= CompilerFlags(StandardCxx11 | GnuExtensions);
-                flags &= ~CompilerFlags(StandardCxx14 | StandardCxx17);
-            } else if (std== "gnu++14" || std == "gnu++1y") {
-                flags |= CompilerFlags(StandardCxx14 | GnuExtensions);
-                flags &= ~CompilerFlags(StandardCxx11 | StandardCxx17);
-            } else if (std== "gnu++17" || std == "gnu++1z") {
-                flags |= CompilerFlags(StandardCxx17 | GnuExtensions);
-                flags &= ~CompilerFlags(StandardCxx11 | StandardCxx14);
-            } else if (std == "c89" || std == "c90"
-                       || std == "iso9899:1990" || std == "iso9899:199409") {
-                flags &= ~CompilerFlags(StandardC99 | StandardC11);
-            } else if (std == "gnu89" || std == "gnu90") {
-                flags &= ~CompilerFlags(StandardC99 | StandardC11);
-                flags |= GnuExtensions;
-            } else if (std == "c99" || std == "c9x"
-                       || std == "iso9899:1999" || std == "iso9899:199x") {
-                flags |= StandardC99;
-                flags &= ~StandardC11;
-            } else if (std == "gnu99" || std == "gnu9x") {
-                flags |= CompilerFlags(StandardC99 | GnuExtensions);
-                flags &= ~StandardC11;
-            } else if (std == "c11" || std == "c1x" || std == "iso9899:2011") {
-                flags |= CompilerFlags(StandardC99 | StandardC11);
-            } else if (std == "gnu11" || std == "gnu1x") {
-                flags |= CompilerFlags(StandardC99 | StandardC11 | GnuExtensions);
-            }
+            if (std.startsWith("gnu"))
+                flags |= CompilerFlags(GnuExtensions);
+            else
+                flags &= ~CompilerFlags(GnuExtensions);
         } else if (flag == "-fopenmp") {
             flags |= OpenMP;
         } else if (flag == "-fms-extensions") {
             flags |= MicrosoftExtensions;
-        } else if (flag == "-ansi") {
-            flags &= ~CompilerFlags(StandardCxx11 | GnuExtensions
-                                    | StandardC99 | StandardC11);
         }
     }
 
@@ -1069,7 +1028,10 @@ QList<ToolChain *> GccToolChainFactory::autoDetectToolChain(const FileName &comp
             return result;
 
         tc->setLanguage(language);
-        tc->m_predefinedMacrosCache->insert(QStringList(), macros);
+        tc->m_predefinedMacrosCache
+            ->insert(QStringList(),
+                     ToolChain::MacroInspectionReport{macros,
+                                                      ToolChain::languageVersion(language, macros)});
         tc->setCompilerCommand(compilerPath);
         tc->setSupportedAbis(detectedAbis.supportedAbis);
         tc->setTargetAbi(abi);
@@ -1134,7 +1096,11 @@ void GccToolChainConfigWidget::applyImpl()
     tc->setDisplayName(displayName); // reset display name
     tc->setPlatformCodeGenFlags(splitString(m_platformCodeGenFlagsLineEdit->text()));
     tc->setPlatformLinkerFlags(splitString(m_platformLinkerFlagsLineEdit->text()));
-    tc->m_predefinedMacrosCache->insert(tc->platformCodeGenFlags(), m_macros);
+    tc->m_predefinedMacrosCache
+        ->insert(tc->platformCodeGenFlags(),
+                 ToolChain::MacroInspectionReport{m_macros,
+                                                  ToolChain::languageVersion(tc->language(),
+                                                                             m_macros)});
 }
 
 void GccToolChainConfigWidget::setFromToolchain()
@@ -1319,7 +1285,7 @@ void ClangToolChain::addToEnvironment(Environment &env) const
 
 ToolChain::CompilerFlags ClangToolChain::defaultCompilerFlags() const
 {
-    return CompilerFlags(GnuExtensions | StandardCxx11);
+    return CompilerFlags(GnuExtensions);
 }
 
 IOutputParser *ClangToolChain::outputParser() const
diff --git a/src/plugins/projectexplorer/gcctoolchain.h b/src/plugins/projectexplorer/gcctoolchain.h
index 3458f63414..64e2acbe51 100644
--- a/src/plugins/projectexplorer/gcctoolchain.h
+++ b/src/plugins/projectexplorer/gcctoolchain.h
@@ -143,7 +143,7 @@ public:
     CompilerFlags compilerFlags(const QStringList &cxxflags) const override;
     WarningFlags warningFlags(const QStringList &cflags) const override;
 
-    PredefinedMacrosRunner createPredefinedMacrosRunner() const override;
+    MacroInspectionRunner createMacroInspectionRunner() const override;
     Macros predefinedMacros(const QStringList &cxxflags) const override;
 
     BuiltInHeaderPathsRunner createBuiltInHeaderPathsRunner() const override;
@@ -253,7 +253,7 @@ private:
     mutable HeaderPaths m_headerPaths;
     mutable QString m_version;
 
-    mutable std::shared_ptr<Cache<QVector<Macro>, 64>> m_predefinedMacrosCache;
+    mutable std::shared_ptr<Cache<MacroInspectionReport, 64>> m_predefinedMacrosCache;
     mutable std::shared_ptr<Cache<HeaderPaths>> m_headerPathsCache;
     mutable ExtraHeaderPathsFunction m_extraHeaderPathsFunction = [](HeaderPaths &) {};
 
diff --git a/src/plugins/projectexplorer/msvctoolchain.cpp b/src/plugins/projectexplorer/msvctoolchain.cpp
index 765dc86d38..7fb74661ec 100644
--- a/src/plugins/projectexplorer/msvctoolchain.cpp
+++ b/src/plugins/projectexplorer/msvctoolchain.cpp
@@ -334,6 +334,7 @@ static QByteArray msvcCompilationFile()
         "__CLR_VER",
         "_CMMN_INTRIN_FUNC",
         "_CONTROL_FLOW_GUARD",
+        "__cplusplus",
         "__cplusplus_cli",
         "__cplusplus_winrt",
         "_CPPLIB_VER",
diff --git a/src/plugins/projectexplorer/toolchain.cpp b/src/plugins/projectexplorer/toolchain.cpp
index e0c1b113a8..e11481d06f 100644
--- a/src/plugins/projectexplorer/toolchain.cpp
+++ b/src/plugins/projectexplorer/toolchain.cpp
@@ -286,6 +286,79 @@ bool ToolChain::fromMap(const QVariantMap &data)
     return true;
 }
 
+static long toLanguageVersionAsLong(QByteArray dateAsByteArray)
+{
+    dateAsByteArray.chop(1); // Strip 'L'.
+    return dateAsByteArray.toLong(nullptr);
+}
+
+ToolChain::LanguageVersion ToolChain::cxxLanguageVersion(const QByteArray &cplusplusMacroValue)
+{
+    const long version = toLanguageVersionAsLong(cplusplusMacroValue);
+
+    if (version > 201703L)
+        return LanguageVersion::LatestCxxVersion;
+
+    switch (version) {
+    case 201703L: return LanguageVersion::CXX17;
+    case 201403L: Q_FALLTHROUGH();
+    case 201402L: return LanguageVersion::CXX14;
+    case 201103L: return LanguageVersion::CXX11;
+    case 199711L: return LanguageVersion::CXX03;
+    default:
+        QTC_CHECK(false && "Unexpected __cplusplus value, assuming latest C++ we support.");
+        return LanguageVersion::LatestCxxVersion;
+    }
+}
+
+ToolChain::LanguageVersion ToolChain::languageVersion(const Core::Id &language, const Macros &macros)
+{
+    if (language == Constants::CXX_LANGUAGE_ID) {
+        for (const ProjectExplorer::Macro &macro : macros) {
+            if (macro.key == "__cplusplus") // Check for the C++ identifying macro
+                return cxxLanguageVersion(macro.value);
+        }
+
+        QTC_CHECK(false && "__cplusplus is not predefined, assuming latest C++ we support.");
+        return LanguageVersion::LatestCxxVersion;
+    } else if (language == Constants::C_LANGUAGE_ID) {
+        for (const ProjectExplorer::Macro &macro : macros) {
+            if (macro.key == "__STDC_VERSION__") {
+                const long version = toLanguageVersionAsLong(macro.value);
+
+                if (version > 201710L)
+                    return LanguageVersion::LatestCVersion;
+
+                switch (version) {
+                case 201710L: return LanguageVersion::C18;
+                case 201112L: return LanguageVersion::C11;
+                case 199901L: return LanguageVersion::C99;
+                case 199409L: return LanguageVersion::C89; // C89 as amended in 1994
+                default:
+                    QTC_CHECK(false && "Unexpected __STDC_VERSION__ value, "
+                                       "assuming latest C version we support.");
+                    return LanguageVersion::LatestCVersion;
+                }
+            }
+        }
+
+        // The __STDC_VERSION__ macro was introduced after C89.
+        // We haven't seen it, so it must be C89.
+        return LanguageVersion::C89;
+    } else {
+        QTC_CHECK(false && "Unexpected toolchain language, assuming latest C++ we support.");
+        return LanguageVersion::LatestCxxVersion;
+    }
+}
+
+Q_GLOBAL_STATIC_WITH_ARGS(const QVector<QByteArray>, unwantedMacros,
+                          ({"__cplusplus", "__STDC_VERSION__"}))
+
+bool ToolChain::isUnwantedMacro(const Macro &macro)
+{
+    return unwantedMacros->contains(macro.key);
+}
+
 /*!
     Used by the tool chain kit information to validate the kit.
 */
diff --git a/src/plugins/projectexplorer/toolchain.h b/src/plugins/projectexplorer/toolchain.h
index fcc7e93d06..89bbab09b4 100644
--- a/src/plugins/projectexplorer/toolchain.h
+++ b/src/plugins/projectexplorer/toolchain.h
@@ -109,26 +109,44 @@ public:
 
     enum CompilerFlag {
         NoFlags = 0,
-        StandardCxx11 = 0x1,
-        StandardC99 = 0x2,
-        StandardC11 = 0x4,
         GnuExtensions = 0x8,
         MicrosoftExtensions = 0x10,
         BorlandExtensions = 0x20,
         OpenMP = 0x40,
         ObjectiveC = 0x80,
-        StandardCxx14 = 0x100,
-        StandardCxx17 = 0x200,
-        StandardCxx98 = 0x400,
     };
+
+    // Keep in sync with ProjectPart::LanguageVersion!
+    enum LanguageVersion {
+        C89,
+        C99,
+        C11,
+        C18,
+        LatestCVersion = C18,
+        CXX98,
+        CXX03,
+        CXX11,
+        CXX14,
+        CXX17,
+        CXX2a,
+        LatestCxxVersion = CXX2a,
+    };
+
     Q_DECLARE_FLAGS(CompilerFlags, CompilerFlag)
 
     virtual CompilerFlags compilerFlags(const QStringList &cxxflags) const = 0;
     virtual WarningFlags warningFlags(const QStringList &cflags) const = 0;
 
-    // A PredefinedMacrosRunner is created in the ui thread and runs in another thread.
-    using PredefinedMacrosRunner = std::function<Macros(const QStringList &cxxflags)>;
-    virtual PredefinedMacrosRunner createPredefinedMacrosRunner() const = 0;
+    class MacroInspectionReport
+    {
+    public:
+        Macros macros;
+        LanguageVersion languageVersion;
+    };
+
+    // A MacroInspectionRunner is created in the ui thread and runs in another thread.
+    using MacroInspectionRunner = std::function<MacroInspectionReport(const QStringList &cxxflags)>;
+    virtual MacroInspectionRunner createMacroInspectionRunner() const = 0;
     virtual Macros predefinedMacros(const QStringList &cxxflags) const = 0;
 
     // A BuiltInHeaderPathsRunner is created in the ui thread and runs in another thread.
@@ -157,6 +175,9 @@ public:
     virtual QList<Task> validateKit(const Kit *k) const;
 
     void setLanguage(Core::Id language);
+    static LanguageVersion cxxLanguageVersion(const QByteArray &cplusplusMacroValue);
+    static LanguageVersion languageVersion(const Core::Id &language, const Macros &macros);
+    static bool isUnwantedMacro(const Macro &macro);
 
 protected:
     explicit ToolChain(Core::Id typeId, Detection d);
diff --git a/src/plugins/projectexplorer/toolchainsettingsaccessor.cpp b/src/plugins/projectexplorer/toolchainsettingsaccessor.cpp
index 409812440f..e0055bfe81 100644
--- a/src/plugins/projectexplorer/toolchainsettingsaccessor.cpp
+++ b/src/plugins/projectexplorer/toolchainsettingsaccessor.cpp
@@ -308,7 +308,7 @@ public:
     QString typeDisplayName() const override { return QString("Test Tool Chain"); }
     Abi targetAbi() const override { return Abi::hostAbi(); }
     bool isValid() const override { return m_valid; }
-    PredefinedMacrosRunner createPredefinedMacrosRunner() const override { return PredefinedMacrosRunner(); }
+    MacroInspectionRunner createMacroInspectionRunner() const override { return MacroInspectionRunner(); }
     Macros predefinedMacros(const QStringList &cxxflags) const override { Q_UNUSED(cxxflags); return Macros(); }
     CompilerFlags compilerFlags(const QStringList &cxxflags) const override { Q_UNUSED(cxxflags); return NoFlags; }
     WarningFlags warningFlags(const QStringList &cflags) const override { Q_UNUSED(cflags); return WarningFlags::NoWarnings; }