Frontend: Really allow any experimental feature when compiling a module interface.

The fix for https://github.com/apple/swift/pull/72632 was not sufficient
because when modules are built from textual interface that happens in a
sub-invocation which does not have typecheck-from-interface or
compile-from-interface requested action. Instead of checking a requested
action, set a language option to control whether non-production experimental
features are allowed.

Resolves rdar://125561443

include/swift/Basic/LangOptions.h

@@ -593,6 +593,14 @@ namespace swift {
     /// type-checking, SIL verification, and IR emission,
     bool BypassResilienceChecks = false;
 
+    /// Whether or not to allow experimental features that are only available
+    /// in "production".
+#ifdef NDEBUG
+    bool RestrictNonProductionExperimentalFeatures = true;
+#else
+    bool RestrictNonProductionExperimentalFeatures = false;
+#endif
+
     bool isConcurrencyModelTaskToThread() const {
       return ActiveConcurrencyModel == ConcurrencyModel::TaskToThread;
     }

lib/Frontend/CompilerInvocation.cpp

@@ -872,17 +872,14 @@ static bool ParseLangArgs(LangOptions &Opts, ArgList &Args,
     // If this is a known experimental feature, allow it in +Asserts
     // (non-release) builds for testing purposes.
     if (auto feature = getExperimentalFeature(value)) {
-#ifdef NDEBUG
-      if (!buildingFromInterface && !isFeatureAvailableInProduction(*feature)) {
+      if (Opts.RestrictNonProductionExperimentalFeatures &&
+          !isFeatureAvailableInProduction(*feature)) {
         Diags.diagnose(SourceLoc(), diag::experimental_not_supported_in_production,
                        A->getValue());
         HadError = true;
       } else {
         Opts.enableFeature(*feature);
       }
-#else
-      Opts.enableFeature(*feature);
-#endif
 
       if (*feature == Feature::NoncopyableGenerics2)
         Opts.enableFeature(Feature::NoncopyableGenerics);

lib/Frontend/ModuleInterfaceLoader.cpp

@@ -2066,6 +2066,12 @@ InterfaceSubContextDelegateImpl::runInSubCompilerInstance(StringRef moduleName,
   bool StrictImplicitModuleContext =
       subInvocation.getFrontendOptions().StrictImplicitModuleContext;
 
+  // It isn't appropriate to restrict use of experimental features in another
+  // module since it may have been built with a different compiler that allowed
+  // the use of the feature.
+  subInvocation.getLangOptions().RestrictNonProductionExperimentalFeatures =
+      false;
+
   // Save the target triple from the original context.
   llvm::Triple originalTargetTriple(subInvocation.getLangOptions().Target);
 

test/Frontend/experimental-features-asserts.swift

@@ -0,0 +1,12 @@
+// This test verifies that command line parsing allows use of any features with
+// an asserts compilers.
+
+// REQUIRES: asserts
+
+// 'AccessLevelOnImport' is allowed in production
+// RUN: %target-swift-frontend -typecheck %s -enable-experimental-feature AccessLevelOnImport -verify
+
+// 'ParserValidation' is NOT allowed in production, but we are building with an asserts compiler.
+// RUN: %target-swift-frontend -typecheck %s -enable-experimental-feature ParserValidation
+
+import Swift

test/Frontend/experimental-features-no-asserts.swift

@@ -0,0 +1,14 @@
+// This test verifies that command line parsing restricts use of features that
+// are not allowed non-production compilers.
+
+// REQUIRES: no_asserts
+
+// 'AccessLevelOnImport' is allowed in production
+// RUN: %target-swift-frontend -typecheck %s -enable-experimental-feature AccessLevelOnImport -verify
+
+// 'ParserValidation' is NOT allowed in production
+// RUN: not %target-swift-frontend -typecheck %s -enable-experimental-feature ParserValidation 2>&1 | %FileCheck %s
+
+// CHECK: <unknown>:0: error: experimental feature 'ParserValidation' cannot be enabled in production compiler
+
+import Swift

test/ModuleInterface/experimental-features.swift

@@ -1,14 +1,25 @@
-// swift-interface-format-version: 1.0
-// swift-module-flags: -module-name ExperimentalFeatures -enable-experimental-feature ParserRoundTrip
+// RUN: %empty-directory(%t)
+// RUN: split-file %s %t
 
 // Building a module from this interface should always succeed, even though
 // ParserRoundTrip is an experimental feature that is not enabled in production
 // compilers.
 
-// RUN: %target-swift-frontend -compile-module-from-interface -module-name ExperimentalFeatures -o /dev/null %s -verify
-// RUN: %target-swift-frontend -typecheck-module-from-interface -module-name ExperimentalFeatures %s -verify
+// RUN: %target-swift-frontend -typecheck %t/Client.swift -I %t
+// RUN: %target-swift-frontend -compile-module-from-interface -module-name ExperimentalFeatures -o /dev/null %t/ExperimentalFeatures.swiftinterface -verify
+// RUN: %target-swift-frontend -typecheck-module-from-interface -module-name ExperimentalFeatures %t/ExperimentalFeatures.swiftinterface -verify
+
+//--- ExperimentalFeatures.swiftinterface
+// swift-interface-format-version: 1.0
+// swift-module-flags: -module-name ExperimentalFeatures -enable-experimental-feature ParserRoundTrip
 
 import Swift
 extension Int {
   public static var fortytwo: Int = 42
 }
+
+//--- Client.swift
+
+import ExperimentalFeatures
+
+_ = Int.fortytwo