Begin adding support for using swiftc as a linker driver (#236)

This is controlled via the LINKER_DRIVER setting

Author: owenv

Sources/SWBCore/Settings/BuiltinMacros.swift

@@ -822,6 +822,7 @@ public final class BuiltinMacros {
     public static let LIBTOOL_DEPENDENCY_INFO_FILE = BuiltinMacros.declarePathMacro("LIBTOOL_DEPENDENCY_INFO_FILE")
     public static let LIBTOOL_USE_RESPONSE_FILE = BuiltinMacros.declareBooleanMacro("LIBTOOL_USE_RESPONSE_FILE")
     public static let LINKER = BuiltinMacros.declareStringMacro("LINKER")
+    public static let LINKER_DRIVER = BuiltinMacros.declareEnumMacro("LINKER_DRIVER") as EnumMacroDeclaration<LinkerDriverChoice>
     public static let ALTERNATE_LINKER = BuiltinMacros.declareStringMacro("ALTERNATE_LINKER")
     public static let LINK_OBJC_RUNTIME = BuiltinMacros.declareBooleanMacro("LINK_OBJC_RUNTIME")
     public static let LINK_WITH_STANDARD_LIBRARIES = BuiltinMacros.declareBooleanMacro("LINK_WITH_STANDARD_LIBRARIES")
@@ -1371,6 +1372,7 @@ public final class BuiltinMacros {
         ALL_OTHER_LDFLAGS,
         ALL_SETTINGS,
         ALTERNATE_GROUP,
+        LINKER_DRIVER,
         ALTERNATE_LINKER,
         ALTERNATE_MODE,
         ALTERNATE_OWNER,
@@ -2662,6 +2664,13 @@ public enum ModuleVerifierKind: String, Equatable, Hashable, EnumerationMacroTyp
     case both
 }
 
+public enum LinkerDriverChoice: String, Equatable, Hashable, EnumerationMacroType {
+    public static let defaultValue: LinkerDriverChoice = .clang
+
+    case clang
+    case swiftc
+}
+
 /// Enumeration macro type for the value of the `INFOPLIST_KEY_LSApplicationCategoryType` build setting.
 public enum ApplicationCategory: String, Equatable, Hashable, EnumerationMacroType {
     public static let defaultValue = ApplicationCategory.none

Sources/SWBCore/SpecImplementations/ProductTypes.swift

@@ -270,12 +270,22 @@ public class ProductTypeSpec : Spec, SpecType, @unchecked Sendable {
         if producer.isApplePlatform {
             let compatibilityVersion = scope.evaluate(BuiltinMacros.DYLIB_COMPATIBILITY_VERSION)
             if !compatibilityVersion.isEmpty {
-                args += ["-compatibility_version", compatibilityVersion]
+                switch scope.evaluate(BuiltinMacros.LINKER_DRIVER) {
+                case .clang:
+                    args += ["-compatibility_version", compatibilityVersion]
+                case .swiftc:
+                    args += ["-Xlinker", "-compatibility_version", "-Xlinker", compatibilityVersion]
+                }
             }
 
             let currentVersion = scope.evaluate(BuiltinMacros.DYLIB_CURRENT_VERSION)
             if !currentVersion.isEmpty {
-                args += ["-current_version", currentVersion]
+                switch scope.evaluate(BuiltinMacros.LINKER_DRIVER) {
+                case .clang:
+                    args += ["-current_version", currentVersion]
+                case .swiftc:
+                    args += ["-Xlinker", "-current_version", "-Xlinker", currentVersion]
+                }
             }
         }
 

Sources/SWBCore/SpecImplementations/PropertyDomainSpec.swift

@@ -110,6 +110,8 @@ private final class EnumBuildOptionType : BuildOptionType {
             return try namespace.declareEnumMacro(name) as EnumMacroDeclaration<SwiftEnableExplicitModulesSetting>
         case "SWIFT_ENABLE_EXPLICIT_MODULES":
             return try namespace.declareEnumMacro(name) as EnumMacroDeclaration<SwiftEnableExplicitModulesSetting>
+        case "LINKER_DRIVER":
+            return try namespace.declareEnumMacro(name) as EnumMacroDeclaration<LinkerDriverChoice>
         default:
             return try namespace.declareStringMacro(name)
         }

Sources/SWBCore/SpecImplementations/Tools/LinkerTools.swift

@@ -234,7 +234,13 @@ public final class LdLinkerSpec : GenericLinkerSpec, SpecIdentifierType, @unchec
     public static let identifier = "com.apple.pbx.linkers.ld"
 
     public override func computeExecutablePath(_ cbc: CommandBuildContext) -> String {
-        return cbc.producer.hostOperatingSystem.imageFormat.executableName(basename: "clang")
+        // TODO: We should also provide an "auto" option which chooses based on the source files in the target
+        switch cbc.scope.evaluate(BuiltinMacros.LINKER_DRIVER) {
+        case .clang:
+            return cbc.producer.hostOperatingSystem.imageFormat.executableName(basename: "clang")
+        case .swiftc:
+            return cbc.producer.hostOperatingSystem.imageFormat.executableName(basename: "swiftc")
+        }
     }
 
     override public var toolBasenameAliases: [String] {

Sources/SWBGenericUnixPlatform/Specs/UnixLd.xcspec

@@ -26,7 +26,7 @@
         };
         Options = (
             {
-                Name = "MACH_O_TYPE";
+                Name = "CLANG_MACH_O_TYPE";
                 Type = Enumeration;
                 Values = (
                     {
@@ -46,13 +46,26 @@
                         CommandLineFlag = "-r";
                     },
                 );
+                Condition = "$(LINKER_DRIVER) == clang";
+                DefaultValue = "$(MACH_O_TYPE)";
             },
+            // We can inherit SWIFTC_MACHO_TYPE from the universal platform Ld.xcspec
             {
-                Name = SDKROOT;
+                Name = CLANG_SDKROOT_LINKER_INPUT;
                 Type = Path;
+                DefaultValue = "$(SDKROOT)";
+                Condition = "$(LINKER_DRIVER) == clang";
                 CommandLineFlag = "--sysroot";
                 IsInputDependency = Yes;
             },
+            {
+                Name = SWIFTC_SDKROOT_LINKER_INPUT;
+                Type = Path;
+                DefaultValue = "$(SDKROOT)";
+                Condition = "$(LINKER_DRIVER) == swiftc";
+                CommandLineFlag = "-sysroot";
+                IsInputDependency = Yes;
+            },
             {
                 Name = "LD_DYLIB_INSTALL_NAME";
                 Type = String;
@@ -65,6 +78,17 @@
                 );
                 Condition = "$(MACH_O_TYPE) == mh_dylib";
             },
+            // Override the differentiated settings to no-ops, both linker drivers use the same flags.
+            {
+                Name = "CLANG_LD_DYLIB_INSTALL_NAME";
+                Type = String;
+                Condition = "NO";
+            },
+            {
+                Name = "SWIFTC_LD_DYLIB_INSTALL_NAME";
+                Type = String;
+                Condition = "NO";
+            },
             {
                 Name = GOLD_BUILDID;
                 Type = Boolean;
@@ -130,6 +154,17 @@
                 );
                 IsInputDependency = Yes;
             },
+            // Override the differentiated settings to no-ops, both linker drivers use the same flags.
+            {
+                Name = "CLANG__INPUT_FILE_LIST_PATH__";
+                Type = Path;
+                Condition = "NO";
+            },
+            {
+                Name = "SWIFTC__INPUT_FILE_LIST_PATH__";
+                Type = Path;
+                Condition = "NO";
+            }
         );
     },
 )

Sources/SWBUniversalPlatform/Specs/Clang LLVM 1.0.xcspec

@@ -320,7 +320,7 @@
                 // that the ObjC runtime must be linked in (with possible
                 // backwards compatibility libraries linked in).
                 AdditionalLinkerArgs = {
-                    YES = ( "-fobjc-link-runtime" );
+                    YES = ( "$(LD_OBJC_RUNTIME_ARGS)" );
                     NO = ();
                 };
                 FileTypes = (