Introduce new defines to enable #bundle in Swift Packages

Author: matthewseaman

Sources/SwiftBuildSupport/PackagePIFProjectBuilder+Modules.swift

@@ -602,6 +602,18 @@ extension PackagePIFProjectBuilder {
             settings[.COREML_COMPILER_CONTAINER] = "swift-package"
         }
 
+        // Leave an explicit indicator regarding whether we are generating a Bundle.module accessor.
+        // This will be read by the #bundle macro defined in Foundation.
+        if !shouldGenerateBundleAccessor {
+            // No resources, so explicitly indicate that.
+            // #bundle will then produce an error about there being no resources.
+            settings[.SWIFT_ACTIVE_COMPILATION_CONDITIONS].lazilyInitializeAndMutate(initialValue: ["$(inherited)"]) { $0.append("SWIFT_MODULE_RESOURCE_BUNDLE_UNAVAILABLE") }
+        } else if !(resourceBundleName?.isEmpty ?? true) {
+            // We have an explicit resource bundle via Bundle.module.
+            // #bundle should call into that.
+            settings[.SWIFT_ACTIVE_COMPILATION_CONDITIONS].lazilyInitializeAndMutate(initialValue: ["$(inherited)"]) { $0.append("SWIFT_MODULE_RESOURCE_BUNDLE_AVAILABLE") }
+        } // else we won't set either of those and just let #bundle point to the same bundle as the source code.
+
         if desiredModuleType == .macro {
             settings[.SWIFT_IMPLEMENTS_MACROS_FOR_MODULE_NAMES] = [sourceModule.c99name]
         }

Sources/SwiftBuildSupport/PackagePIFProjectBuilder+Products.swift

@@ -245,6 +245,9 @@ extension PackagePIFProjectBuilder {
 
             if result.shouldGenerateBundleAccessor {
                 settings[.GENERATE_RESOURCE_ACCESSORS] = "YES"
+
+                // Do not set `SWIFT_MODULE_RESOURCE_BUNDLE_AVAILABLE` here since it is just going to point to the same bundle as code.
+                // #bundle can use its default implementation for that.
             }
             if result.shouldGenerateEmbedInCodeAccessor {
                 settings[.GENERATE_EMBED_IN_CODE_ACCESSORS] = "YES"
@@ -264,6 +267,9 @@ extension PackagePIFProjectBuilder {
 
                 if result.shouldGenerateBundleAccessor {
                     settings[.GENERATE_RESOURCE_ACCESSORS] = "YES"
+                    settings[.SWIFT_ACTIVE_COMPILATION_CONDITIONS].lazilyInitializeAndMutate(initialValue: ["$(inherited)"]) { $0.append("SWIFT_MODULE_RESOURCE_BUNDLE_AVAILABLE") }
+                } else {
+                    settings[.SWIFT_ACTIVE_COMPILATION_CONDITIONS].lazilyInitializeAndMutate(initialValue: ["$(inherited)"]) { $0.append("SWIFT_MODULE_RESOURCE_BUNDLE_UNAVAILABLE") }
                 }
                 if result.shouldGenerateEmbedInCodeAccessor {
                     settings[.GENERATE_EMBED_IN_CODE_ACCESSORS] = "YES"
@@ -305,6 +311,9 @@ extension PackagePIFProjectBuilder {
                 settings[.GENERATE_RESOURCE_ACCESSORS] = "YES"
                 settings[.GENERATE_EMBED_IN_CODE_ACCESSORS] = "NO"
 
+                // Do not set `SWIFT_MODULE_RESOURCE_BUNDLE_AVAILABLE` here since it is just going to point to the same bundle as code.
+                // #bundle can use its default implementation for that.
+
                 // If we did not create a resource bundle target,
                 // we still need to add build tool commands for any generated files.
                 addBuildToolCommands(

Sources/XCBuildSupport/PIFBuilder.swift

@@ -501,6 +501,9 @@ final class PackagePIFProjectBuilder: PIFProjectBuilder {
         if let resourceBundle = addResourceBundle(for: mainTarget, in: pifTarget) {
             settings[.PACKAGE_RESOURCE_BUNDLE_NAME] = resourceBundle
             settings[.GENERATE_RESOURCE_ACCESSORS] = "YES"
+            settings[.SWIFT_ACTIVE_COMPILATION_CONDITIONS, default: ["$(inherited)"]].append("SWIFT_MODULE_RESOURCE_BUNDLE_AVAILABLE")
+        } else {
+            settings[.SWIFT_ACTIVE_COMPILATION_CONDITIONS, default: ["$(inherited)"]].append("SWIFT_MODULE_RESOURCE_BUNDLE_UNAVAILABLE")
         }
 
         // For targets, we use the common build settings for both the "Debug" and the "Release" configurations (all
@@ -729,7 +732,10 @@ final class PackagePIFProjectBuilder: PIFProjectBuilder {
         if let resourceBundle = addResourceBundle(for: target, in: pifTarget) {
             settings[.PACKAGE_RESOURCE_BUNDLE_NAME] = resourceBundle
             settings[.GENERATE_RESOURCE_ACCESSORS] = "YES"
+            settings[.SWIFT_ACTIVE_COMPILATION_CONDITIONS, default: ["$(inherited)"]].append("SWIFT_MODULE_RESOURCE_BUNDLE_AVAILABLE")
             impartedSettings[.EMBED_PACKAGE_RESOURCE_BUNDLE_NAMES, default: ["$(inherited)"]].append(resourceBundle)
+        } else {
+            settings[.SWIFT_ACTIVE_COMPILATION_CONDITIONS, default: ["$(inherited)"]].append("SWIFT_MODULE_RESOURCE_BUNDLE_UNAVAILABLE")
         }
 
         // For targets, we use the common build settings for both the "Debug" and the "Release" configurations (all