introduce tests for metadata size etc

Previously this was just in a hello world app.

Author: ktoso

Samples/SwiftKitSampleApp/src/main/java/com/example/swift/HelloJava2Swift.java

@@ -34,7 +34,7 @@ public static void main(String[] args) {
 
         final var dylibNames = List.of(
                 "swiftCore",
-                "JavaKitExample"
+                "ExampleSwiftLibrary"
         );
 
 
@@ -61,12 +61,5 @@ static void examples() {
 
         obj.voidMethod();
         obj.takeIntMethod(42);
-
-        MemorySegment swiftType = SwiftKit.getTypeByMangledNameInEnvironment("SiSg");
-        System.out.println("Memory layout for Swift.Int?:");
-        System.out.println("  size = " + SwiftKit.sizeOfSwiftType(swiftType));
-        System.out.println("  stride = " + SwiftKit.strideOfSwiftType(swiftType));
-        System.out.println("  alignment = " + SwiftKit.alignmentOfSwiftType(swiftType));
-        System.out.println("  Java layout = " + SwiftKit.layoutOfSwiftType(swiftType));
     }
 }

SwiftKit/src/main/java/org/swift/swiftkit/SwiftKit.java

@@ -48,6 +48,7 @@ private static SymbolLookup getSymbolLookup() {
                     .or(Linker.nativeLinker().defaultLookup());
         }
     }
+
     public SwiftKit() {
     }
 
@@ -313,6 +314,9 @@ public static MemorySegment valueWitnessTable(MemorySegment typeMetadata) {
 
     /**
      * Determine the size of a Swift type given its type metadata.
+     *
+     * @param typeMetadata the memory segment must point to a Swift metadata,
+     *                     e.g. the result of a {@link SwiftKit.swift_getTypeByMangledNameInEnvironment} call
      */
     public static long sizeOfSwiftType(MemorySegment typeMetadata) {
         return getSwiftInt(valueWitnessTable(typeMetadata), SwiftValueWitnessTable.$size$offset);
@@ -321,14 +325,22 @@ public static long sizeOfSwiftType(MemorySegment typeMetadata) {
     /**
      * Determine the stride of a Swift type given its type metadata, which is
      * how many bytes are between successive elements of this type within an
-     * array. It is >= the size.
+     * array.
+     *
+     * It is >= the size.
+     *
+     * @param typeMetadata the memory segment must point to a Swift metadata,
+     *                     e.g. the result of a {@link SwiftKit.swift_getTypeByMangledNameInEnvironment} call
      */
     public static long strideOfSwiftType(MemorySegment typeMetadata) {
         return getSwiftInt(valueWitnessTable(typeMetadata), SwiftValueWitnessTable.$stride$offset);
     }
 
     /**
      * Determine the alignment of the given Swift type.
+     *
+     * @param typeMetadata the memory segment must point to a Swift metadata,
+     *                     e.g. the result of a {@link SwiftKit.swift_getTypeByMangledNameInEnvironment} call
      */
     public static long alignmentOfSwiftType(MemorySegment typeMetadata) {
         long flags = getSwiftInt(valueWitnessTable(typeMetadata), SwiftValueWitnessTable.$flags$offset);
@@ -365,6 +377,9 @@ private static class swift_getTypeName {
      * <p>
      * If 'qualified' is true, leave all the qualification in place to
      * disambiguate the type, producing a more complete (but longer) type name.
+     *
+     * @param typeMetadata the memory segment must point to a Swift metadata,
+     *                     e.g. the result of a {@link SwiftKit.swift_getTypeByMangledNameInEnvironment} call
      */
     public static String nameOfSwiftType(MemorySegment typeMetadata, boolean qualified) {
         try {
@@ -388,14 +403,29 @@ public static String nameOfSwiftType(MemorySegment typeMetadata, boolean qualifi
      * <p>
      * In the future, this layout could be extended to provide more detail,
      * such as the fields of a Swift struct.
+     *
+     * @param typeMetadata the memory segment must point to a Swift metadata,
+     *                     e.g. the result of a {@link SwiftKit.swift_getTypeByMangledNameInEnvironment} call
      */
     public static MemoryLayout layoutOfSwiftType(MemorySegment typeMetadata) {
         long size = sizeOfSwiftType(typeMetadata);
         long stride = strideOfSwiftType(typeMetadata);
+        long padding = stride - size;
+
+        // constructing a zero-length paddingLayout is illegal, so we avoid doing so
+        MemoryLayout[] layouts = padding == 0 ?
+                new MemoryLayout[]{
+                        MemoryLayout.sequenceLayout(size, JAVA_BYTE)
+                                .withByteAlignment(alignmentOfSwiftType(typeMetadata))
+                } :
+                new MemoryLayout[]{
+                        MemoryLayout.sequenceLayout(size, JAVA_BYTE)
+                                .withByteAlignment(alignmentOfSwiftType(typeMetadata)),
+                        MemoryLayout.paddingLayout(stride - size)
+                };
+
         return MemoryLayout.structLayout(
-                MemoryLayout.sequenceLayout(size, JAVA_BYTE)
-                        .withByteAlignment(alignmentOfSwiftType(typeMetadata)),
-                MemoryLayout.paddingLayout(stride - size)
+                layouts
         ).withName(nameOfSwiftType(typeMetadata, true));
     }
 }

SwiftKit/src/test/java/org/swift/swiftkit/SwiftRuntimeMetadataTest.java

@@ -0,0 +1,62 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2024 Apple Inc. and the Swift.org project authors
+// Licensed under Apache License v2.0
+//
+// See LICENSE.txt for license information
+// See CONTRIBUTORS.txt for the list of Swift.org project authors
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+//===----------------------------------------------------------------------===//
+
+package org.swift.swiftkit;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+import java.lang.foreign.MemorySegment;
+
+public class SwiftRuntimeMetadataTest {
+
+    @Test
+    public void integer_layout_metadata() {
+        MemorySegment swiftType = SwiftKit.getTypeByMangledNameInEnvironment("Si");
+
+        if (SwiftValueLayout.addressByteSize() == 4) {
+            // 32-bit platform
+            Assertions.assertEquals(8, SwiftKit.sizeOfSwiftType(swiftType));
+            Assertions.assertEquals(8, SwiftKit.strideOfSwiftType(swiftType));
+            Assertions.assertEquals(8, SwiftKit.alignmentOfSwiftType(swiftType));
+            Assertions.assertEquals("[8%[9:b1]x7](Swift.Int)", SwiftKit.layoutOfSwiftType(swiftType).toString());
+        } else {
+            // 64-bit platform
+            Assertions.assertEquals(8, SwiftKit.sizeOfSwiftType(swiftType));
+            Assertions.assertEquals(8, SwiftKit.strideOfSwiftType(swiftType));
+            Assertions.assertEquals(8, SwiftKit.alignmentOfSwiftType(swiftType));
+            Assertions.assertEquals("[8%[8:b1]](Swift.Int)", SwiftKit.layoutOfSwiftType(swiftType).toString());
+        }
+    }
+
+    @Test
+    public void optional_integer_layout_metadata() {
+        MemorySegment swiftType = SwiftKit.getTypeByMangledNameInEnvironment("SiSg");
+
+        if (SwiftValueLayout.addressByteSize() == 4) {
+            // 64-bit platform
+            Assertions.assertEquals(9, SwiftKit.sizeOfSwiftType(swiftType));
+            Assertions.assertEquals(16, SwiftKit.strideOfSwiftType(swiftType));
+            Assertions.assertEquals(8, SwiftKit.alignmentOfSwiftType(swiftType));
+            Assertions.assertEquals("[8%[9:b1]x7](Swift.Optional<Swift.Int>)", SwiftKit.layoutOfSwiftType(swiftType).toString());
+        } else {
+            // 64-bit platform
+            Assertions.assertEquals(9, SwiftKit.sizeOfSwiftType(swiftType));
+            Assertions.assertEquals(16, SwiftKit.strideOfSwiftType(swiftType));
+            Assertions.assertEquals(8, SwiftKit.alignmentOfSwiftType(swiftType));
+            Assertions.assertEquals("[8%[9:b1]x7](Swift.Optional<Swift.Int>)", SwiftKit.layoutOfSwiftType(swiftType).toString());
+        }
+    }
+
+}