Introduce SWIFT_ENABLE_LANGUAGE_FEATURE_ENABLEMENT_DIAGNOSTICS setting.

This setting must be enabled in order for Swift language feature enablement
diagnostics specified by `swift-language-feature-enablement.json` to be
emitted.

Resolves rdar://151977874.

Author: tshortli

Sources/SWBCore/Settings/BuiltinMacros.swift

@@ -1009,6 +1009,7 @@ public final class BuiltinMacros {
     public static let SWIFT_ENABLE_BARE_SLASH_REGEX = BuiltinMacros.declareBooleanMacro("SWIFT_ENABLE_BARE_SLASH_REGEX")
     public static let SWIFT_ENABLE_EMIT_CONST_VALUES = BuiltinMacros.declareBooleanMacro("SWIFT_ENABLE_EMIT_CONST_VALUES")
     public static let SWIFT_ENABLE_OPAQUE_TYPE_ERASURE = BuiltinMacros.declareBooleanMacro("SWIFT_ENABLE_OPAQUE_TYPE_ERASURE")
+    public static let SWIFT_ENABLE_LANGUAGE_FEATURE_ENABLEMENT_DIAGNOSTICS = BuiltinMacros.declareBooleanMacro("SWIFT_ENABLE_LANGUAGE_FEATURE_ENABLEMENT_DIAGNOSTICS")
     public static let SWIFT_EMIT_CONST_VALUE_PROTOCOLS = BuiltinMacros.declareStringListMacro("SWIFT_EMIT_CONST_VALUE_PROTOCOLS")
     public static let SWIFT_GENERATE_ADDITIONAL_LINKER_ARGS = BuiltinMacros.declareBooleanMacro("SWIFT_GENERATE_ADDITIONAL_LINKER_ARGS")
     public static let SWIFT_USE_INTEGRATED_DRIVER = BuiltinMacros.declareBooleanMacro("SWIFT_USE_INTEGRATED_DRIVER")
@@ -2178,6 +2179,7 @@ public final class BuiltinMacros {
         SWIFT_ENABLE_BARE_SLASH_REGEX,
         SWIFT_ENABLE_EMIT_CONST_VALUES,
         SWIFT_ENABLE_OPAQUE_TYPE_ERASURE,
+        SWIFT_ENABLE_LANGUAGE_FEATURE_ENABLEMENT_DIAGNOSTICS,
         SWIFT_EMIT_CONST_VALUE_PROTOCOLS,
         SWIFT_GENERATE_ADDITIONAL_LINKER_ARGS,
         SWIFT_ENABLE_TESTABILITY,

Sources/SWBCore/SpecImplementations/Tools/SwiftCompiler.swift

@@ -1446,6 +1446,9 @@ public final class SwiftCompilerSpec : CompilerSpec, SpecIdentifierType, SwiftDi
     }
 
     private func diagnoseFeatureEnablement(_ cbc: CommandBuildContext, _ languageFeatureEnablementInfo: SwiftBlocklists.LanguageFeatureEnablementInfo, _ delegate: any TaskGenerationDelegate) {
+        guard cbc.scope.evaluate(BuiltinMacros.SWIFT_ENABLE_LANGUAGE_FEATURE_ENABLEMENT_DIAGNOSTICS) else {
+            return
+        }
         let moduleName = cbc.scope.evaluate(BuiltinMacros.SWIFT_MODULE_NAME)
         let otherFlags = cbc.scope.evaluate(BuiltinMacros.OTHER_SWIFT_FLAGS)
         var otherFlagsFeatures: [String] = []

Tests/SWBBuildSystemTests/SwiftDriverTests.swift

@@ -4821,6 +4821,7 @@ fileprivate struct SwiftDriverTests: CoreBasedTests {
                             TestBuildConfiguration(
                                 "Debug",
                                 buildSettings: [
+                                    "SWIFT_ENABLE_LANGUAGE_FEATURE_ENABLEMENT_DIAGNOSTICS": "YES",
                                     "PRODUCT_NAME": "$(TARGET_NAME)",
                                     "SWIFT_VERSION": "5",
                                     "BUILD_VARIANTS": "normal",