rdar://144577495 Install name mapping not specifying the correct platform number (#147)

The `$ld$previous` syntax used to map a renamed debug dylib for previews does not properly set the platform field.

This plumbs them through as a new computed build macro and checks it in the previews settings test when `LD_CLIENT_NAME` is used.

Author: jonathanpenn

Sources/SWBCore/Settings/BuiltinMacros.swift

@@ -667,6 +667,7 @@ public final class BuiltinMacros {
     public static let EXECUTABLE_DEBUG_DYLIB_PATH = BuiltinMacros.declareStringMacro("EXECUTABLE_DEBUG_DYLIB_PATH")
     public static let EXECUTABLE_DEBUG_DYLIB_INSTALL_NAME = BuiltinMacros.declareStringMacro("EXECUTABLE_DEBUG_DYLIB_INSTALL_NAME")
     public static let EXECUTABLE_DEBUG_DYLIB_MAPPED_INSTALL_NAME = BuiltinMacros.declareStringMacro("EXECUTABLE_DEBUG_DYLIB_MAPPED_INSTALL_NAME")
+    public static let EXECUTABLE_DEBUG_DYLIB_MAPPED_PLATFORM = BuiltinMacros.declareStringMacro("EXECUTABLE_DEBUG_DYLIB_MAPPED_PLATFORM")
     public static let EXECUTABLE_BLANK_INJECTION_DYLIB_PATH = BuiltinMacros.declareStringMacro("EXECUTABLE_BLANK_INJECTION_DYLIB_PATH")
 
     public static let EXECUTABLE_SUFFIX = BuiltinMacros.declareStringMacro("EXECUTABLE_SUFFIX")
@@ -1685,6 +1686,7 @@ public final class BuiltinMacros {
         EXECUTABLE_DEBUG_DYLIB_PATH,
         EXECUTABLE_DEBUG_DYLIB_INSTALL_NAME,
         EXECUTABLE_DEBUG_DYLIB_MAPPED_INSTALL_NAME,
+        EXECUTABLE_DEBUG_DYLIB_MAPPED_PLATFORM,
         EXECUTABLE_BLANK_INJECTION_DYLIB_PATH,
         EXECUTABLE_SUFFIX,
         EXECUTABLE_VARIANT_SUFFIX,

Sources/SWBCore/Settings/Settings.swift

@@ -3326,6 +3326,18 @@ private class SettingsBuilder {
                             BuiltinMacros.EXECUTABLE_DEBUG_DYLIB_MAPPED_INSTALL_NAME,
                             table.namespace.parseString("@rpath/$(EXECUTABLE_NAME).debug.dylib")
                         )
+
+                        let sdkVariant = sdk?.variant(for: scope.evaluate(BuiltinMacros.SDK_VARIANT))
+                        let platform = sdk?.targetBuildVersionPlatform(sdkVariant: sdkVariant)
+
+                        // Platform version identifiers used in `$ld$previous` mappings.
+                        // Unknown values are specified with `0`.
+                        let appleLDPreviousPlatform = platform?.rawValue ?? 0
+
+                        table.push(
+                            BuiltinMacros.EXECUTABLE_DEBUG_DYLIB_MAPPED_PLATFORM,
+                            table.namespace.parseLiteralString("\(appleLDPreviousPlatform)")
+                        )
                     }
                     else {
                         table.push(

Sources/SWBCore/Specs/Tools/LinkerTools.swift

@@ -536,10 +536,11 @@ public final class LdLinkerSpec : GenericLinkerSpec, SpecIdentifierType, @unchec
                 // Aliasing a known symbol to this `$ld$previous` symbol is sufficient.
                 let ldFlagsForAllowableClientOverride: [String]
                 if let mappedInstallName = cbc.scope.evaluate(BuiltinMacros.EXECUTABLE_DEBUG_DYLIB_MAPPED_INSTALL_NAME).nilIfEmpty {
+                    let platform = cbc.scope.evaluate(BuiltinMacros.EXECUTABLE_DEBUG_DYLIB_MAPPED_PLATFORM)
                     ldFlagsForAllowableClientOverride = [
                         "-Xlinker", "-alias",
                         "-Xlinker", "___debug_main_executable_dylib_entry_point",
-                        "-Xlinker", "$ld$previous$\(mappedInstallName)$$1$1.0$9999.0$$",
+                        "-Xlinker", "$ld$previous$\(mappedInstallName)$$\(platform)$1.0$9999.0$$",
                     ]
                 } else {
                     ldFlagsForAllowableClientOverride = []

Tests/SWBCoreTests/SettingsTests.swift

@@ -2867,6 +2867,7 @@ import SWBMacro
         #expect(settings.globalScope.evaluate(BuiltinMacros.EXECUTABLE_DEBUG_DYLIB_INSTALL_NAME) == "@rpath/MyOtherClient.debug.dylib")
         // But should be mapped to the original install name
         #expect(settings.globalScope.evaluate(BuiltinMacros.EXECUTABLE_DEBUG_DYLIB_MAPPED_INSTALL_NAME) == "@rpath/Target1.debug.dylib")
+        #expect(settings.globalScope.evaluate(BuiltinMacros.EXECUTABLE_DEBUG_DYLIB_MAPPED_PLATFORM) == "2")
         #expect(settings.globalScope.evaluate(BuiltinMacros.EXECUTABLE_BLANK_INJECTION_DYLIB_PATH).suffix(15) == "__preview.dylib")
     }