[cxx-interop] Use C++17 standard by default

Clang is using C++17 standard version by default since Clang 16.

Swift’s ClangImporter should do the same, to make sure that clients who run clang and then swiftc without explicit std version see consistent behavior.

rdar://125777068

Author: egorzhdan

lib/ClangImporter/ClangImporter.cpp

@@ -541,7 +541,7 @@ void importer::getNormalInvocationArguments(
         *clang::LangStandard::getLangStandardForName(CLANG_DEFAULT_STD_CXX);
 #else
         clang::LangStandard::getLangStandardForKind(
-            clang::LangStandard::lang_gnucxx14);
+            clang::LangStandard::lang_gnucxx17);
 #endif
 
     const clang::LangStandard &stdc =

test/Interop/Cxx/class/method/msvc-abi-return-indirect-trivial-record.swift

@@ -1,6 +1,6 @@
 // RUN: rm -rf %t
 // RUN: split-file %s %t
-// RUN: %target-swift-emit-irgen -I %t/Inputs -enable-experimental-cxx-interop  -Xcc -std=c++17 %t/test.swift -module-name Test | %FileCheck %s -check-prefix=CHECK -check-prefix=CHECK-%target-cpu
+// RUN: %target-swift-emit-irgen -I %t/Inputs -enable-experimental-cxx-interop %t/test.swift -module-name Test | %FileCheck %s -check-prefix=CHECK -check-prefix=CHECK-%target-cpu
 
 // REQUIRES: OS=windows-msvc
 

test/Interop/Cxx/class/structured-bindings-get-method.swift

@@ -1,4 +1,4 @@
-// RUN: %target-swiftxx-frontend -I %S/Inputs %s -emit-ir -Xcc -std=c++17 | %FileCheck %s
+// RUN: %target-swiftxx-frontend -I %S/Inputs %s -emit-ir | %FileCheck %s
 
 import StructuredBindingsGetMethod
 

test/Interop/Cxx/reference/reference-silgen-cxx-objc-ctors+init.swift

@@ -1,5 +1,5 @@
 // REQUIRES: objc_interop
-// RUN: %target-swift-emit-sil -I %S/Inputs -enable-experimental-cxx-interop -Xcc -std=c++17 -Ounchecked %s | %FileCheck %s
+// RUN: %target-swift-emit-sil -I %S/Inputs -enable-experimental-cxx-interop -Ounchecked %s | %FileCheck %s
 
 import ConstRefCxxObjCCtorInitParameter
 

test/Interop/Cxx/static/constexpr-static-member-var-errors.swift

@@ -1,7 +1,8 @@
-// RUN: %target-swift-ide-test -print-module -module-to-print=ConstexprStaticMemberVarErrors -I %S/Inputs -source-filename=x -enable-experimental-cxx-interop 2>&1 | %FileCheck %s
+// RUN: %target-swift-ide-test -print-module -module-to-print=ConstexprStaticMemberVarErrors -I %S/Inputs -source-filename=x -enable-experimental-cxx-interop -Xcc -std=c++14 2>&1 | %FileCheck %s
 
 // Check that we properly report the error and don't crash when importing an
 // invalid decl.
+// When using C++17, this C++ header doesn't trigger any Clang error. This is expected.
 
 // Windows doesn't fail at all here which seems ok (and probably should be the case for other platforms too).
 // XFAIL: OS=windows-msvc

test/Interop/Cxx/stdlib/avoid-import-cxx-math.swift

@@ -1,6 +1,6 @@
-// RUN: %target-swift-frontend %s -typecheck -verify -enable-experimental-cxx-interop -Xcc -std=c++17
-// RUN: %target-swift-frontend %s -typecheck -verify -cxx-interoperability-mode=swift-6 -Xcc -std=c++17
-// RUN: %target-swift-frontend %s -typecheck -verify -cxx-interoperability-mode=upcoming-swift -Xcc -std=c++17
+// RUN: %target-swift-frontend %s -typecheck -verify -enable-experimental-cxx-interop
+// RUN: %target-swift-frontend %s -typecheck -verify -cxx-interoperability-mode=swift-6
+// RUN: %target-swift-frontend %s -typecheck -verify -cxx-interoperability-mode=upcoming-swift
 
 // REQUIRES: OS=macosx || OS=linux-gnu
 

test/Interop/Cxx/stdlib/import-cxx-math-ambiguities.swift

@@ -1,6 +1,6 @@
-// RUN: %target-swift-frontend %s -typecheck -enable-experimental-cxx-interop -Xcc -std=c++17
-// RUN: %target-swift-frontend %s -typecheck -cxx-interoperability-mode=swift-6 -Xcc -std=c++17
-// RUN: %target-swift-frontend %s -typecheck -cxx-interoperability-mode=upcoming-swift -Xcc -std=c++17
+// RUN: %target-swift-frontend %s -typecheck -enable-experimental-cxx-interop
+// RUN: %target-swift-frontend %s -typecheck -cxx-interoperability-mode=swift-6
+// RUN: %target-swift-frontend %s -typecheck -cxx-interoperability-mode=upcoming-swift
 
 #if canImport(Foundation)
 // Foundation depends on C++ standard library

test/Interop/Cxx/stdlib/import-string-view-from-std.swift

@@ -1,6 +1,6 @@
 // RUN: %empty-directory(%t)
 // RUN: split-file %s %t
-// RUN: %target-swift-frontend %t/test.swift -c -enable-experimental-cxx-interop -Xcc -std=c++17 -Xcc -fmodules-cache-path=%t/cache -I %t/Inputs
+// RUN: %target-swift-frontend %t/test.swift -c -enable-experimental-cxx-interop -Xcc -fmodules-cache-path=%t/cache -I %t/Inputs
 // RUN: find %t/cache | %FileCheck %s
 
 // REQUIRES: OS=macosx || OS=linux-gnu

test/Interop/Cxx/stdlib/msvc-abi-use-vector-iterator.swift

@@ -1,4 +1,4 @@
-// RUN: %target-run-simple-swift(-I %S/Inputs -Xfrontend -enable-experimental-cxx-interop -Xcc -std=c++17)
+// RUN: %target-run-simple-swift(-I %S/Inputs -Xfrontend -enable-experimental-cxx-interop)
 
 // REQUIRES: OS=windows-msvc
 // REQUIRES: executable_test

test/Interop/Cxx/stdlib/use-std-chrono.swift

@@ -1,5 +1,6 @@
 // RUN: %target-run-simple-swift(-I %S/Inputs -cxx-interoperability-mode=swift-6)
 // RUN: %target-run-simple-swift(-I %S/Inputs -cxx-interoperability-mode=upcoming-swift)
+// RUN: %target-run-simple-swift(-I %S/Inputs -cxx-interoperability-mode=upcoming-swift -Xcc -std=c++14)
 // RUN: %target-run-simple-swift(-I %S/Inputs -cxx-interoperability-mode=upcoming-swift -Xcc -std=c++17)
 // RUN: %target-run-simple-swift(-I %S/Inputs -cxx-interoperability-mode=upcoming-swift -Xcc -std=c++20)