NCGenerics: add flag to opt-out SE-427 strictness

This is mainly for tests to avoid the reverse condfail.

Author: kavon

include/swift/Basic/Features.def

@@ -397,6 +397,8 @@ EXPERIMENTAL_FEATURE(DebugDescriptionMacro, true)
 
 EXPERIMENTAL_FEATURE(ReinitializeConsumeInMultiBlockDefer, false)
 
+EXPERIMENTAL_FEATURE(SE427NoInferenceOnExtension, false)
+
 #undef EXPERIMENTAL_FEATURE_EXCLUDED_FROM_MODULE_INTERFACE
 #undef EXPERIMENTAL_FEATURE
 #undef UPCOMING_FEATURE

lib/AST/FeatureSet.cpp

@@ -772,6 +772,7 @@ static bool usesFeatureSensitive(Decl *decl) {
 
 UNINTERESTING_FEATURE(DebugDescriptionMacro)
 UNINTERESTING_FEATURE(ReinitializeConsumeInMultiBlockDefer)
+UNINTERESTING_FEATURE(SE427NoInferenceOnExtension)
 
 // ----------------------------------------------------------------------------
 // MARK: - FeatureSet

lib/Sema/TypeCheckGeneric.cpp

@@ -792,7 +792,8 @@ GenericSignatureRequest::evaluate(Evaluator &evaluator,
     //  the extension is in a swiftinterface file. This is temporary and should
     //  be removed soon. (rdar://130424971)
     if (auto *sf = ext->getOutermostParentSourceFile()) {
-      if (sf->Kind == SourceFileKind::Interface)
+      if (sf->Kind == SourceFileKind::Interface
+          && !ctx.LangOpts.hasFeature(Feature::SE427NoInferenceOnExtension))
         inferInvertibleReqs = true;
     }
 

test/ModuleInterface/noncopyable_generics.swift

@@ -1,15 +1,20 @@
 // RUN: %empty-directory(%t)
 
+// Due to SE427NoInferenceOnExtension not being in production
+// REQUIRES: asserts
+
 // RUN: %target-swift-frontend -swift-version 5 -enable-library-evolution -emit-module \
 // RUN:     -enable-experimental-feature SuppressedAssociatedTypes \
 // RUN:     -enable-experimental-feature NonescapableTypes \
+// RUN:     -enable-experimental-feature SE427NoInferenceOnExtension \
 // RUN:     -o %t/NoncopyableGenerics_Misc.swiftmodule \
 // RUN:     -emit-module-interface-path %t/NoncopyableGenerics_Misc.swiftinterface \
 // RUN:     %S/Inputs/NoncopyableGenerics_Misc.swift
 
 // RUN: %target-swift-frontend -swift-version 5 -enable-library-evolution -emit-module \
 // RUN:     -enable-experimental-feature SuppressedAssociatedTypes \
 // RUN:     -enable-experimental-feature NonescapableTypes \
+// RUN:     -enable-experimental-feature SE427NoInferenceOnExtension \
 // RUN:     -o %t/Swiftskell.swiftmodule \
 // RUN:     -emit-module-interface-path %t/Swiftskell.swiftinterface \
 // RUN:     %S/../Inputs/Swiftskell.swift
@@ -24,16 +29,19 @@
 // RUN: %target-swift-frontend -compile-module-from-interface \
 // RUN:     -enable-experimental-feature SuppressedAssociatedTypes \
 // RUN:     -enable-experimental-feature NonescapableTypes \
+// RUN:     -enable-experimental-feature SE427NoInferenceOnExtension \
 // RUN:    %t/NoncopyableGenerics_Misc.swiftinterface -o %t/NoncopyableGenerics_Misc.swiftmodule
 
 // RUN: %target-swift-frontend -compile-module-from-interface \
 // RUN:     -enable-experimental-feature SuppressedAssociatedTypes \
 // RUN:     -enable-experimental-feature NonescapableTypes \
+// RUN:     -enable-experimental-feature SE427NoInferenceOnExtension \
 // RUN:    %t/Swiftskell.swiftinterface -o %t/Swiftskell.swiftmodule
 
 // RUN: %target-swift-frontend -emit-silgen -I %t %s \
 // RUN:     -enable-experimental-feature SuppressedAssociatedTypes \
 // RUN:    -enable-experimental-feature NonescapableTypes \
+// RUN:     -enable-experimental-feature SE427NoInferenceOnExtension \
 // RUN:    -o %t/final.silgen
 
 // RUN: %FileCheck %s --check-prefix=CHECK-SILGEN < %t/final.silgen