Re-pushing PR after github mess.

* fixing tests after refactoring
* Fixing up after dependent PR changes
* feedback and remove unused code
* new tests for ImageLocation
* Restoring lost changes and updating some comments.
* add system property guard to preview mode
* Remove TODOs now jimage version is bumped
* jimage writer changes to support preview mode.

Author: david-beaumont

src/java.base/share/classes/jdk/internal/jimage/ImageLocation.java

@@ -26,6 +26,7 @@
 package jdk.internal.jimage;
 
 import java.nio.ByteBuffer;
+import java.util.List;
 import java.util.Objects;
 import java.util.function.Predicate;
 
@@ -159,6 +160,29 @@ public static int getFlags(String name, Predicate<String> hasEntry) {
         }
     }
 
+    /**
+     * Helper function to calculate package flags for {@code "/packages/xxx"}
+     * directory entries.
+     *
+     * <p>Based on the module references, the flags are:
+     * <ul>
+     *     <li>{@code FLAGS_HAS_PREVIEW_VERSION} if <em>any</em> referenced
+     *     package has a preview version.
+     *     <li>{@code FLAGS_IS_PREVIEW_ONLY} if <em>all</em> referenced packages
+     *     are preview only.
+     * </ul>
+     *
+     * @return package flags for {@code "/packages/xxx"} directory entries.
+     */
+    public static int getPackageFlags(List<ModuleReference> moduleReferences) {
+        boolean hasPreviewVersion =
+                moduleReferences.stream().anyMatch(ModuleReference::hasPreviewVersion);
+        boolean isPreviewOnly =
+                moduleReferences.stream().allMatch(ModuleReference::isPreviewOnly);
+        return (hasPreviewVersion ? ImageLocation.FLAGS_HAS_PREVIEW_VERSION : 0)
+                | (isPreviewOnly ? ImageLocation.FLAGS_IS_PREVIEW_ONLY : 0);
+    }
+
     /**
      * Tests a non-preview image location's flags to see if it has preview
      * content associated with it.

src/java.base/share/classes/jdk/internal/jimage/ModuleReference.java

@@ -53,8 +53,7 @@ public final class ModuleReference implements Comparable<ModuleReference> {
     /** If set, this package exists in non-preview mode. */
     private static final int FLAGS_PKG_HAS_NORMAL_VERSION = 0x2;
     /** If set, the associated module has resources (in normal or preview mode). */
-    // TODO: Make this private again when image writer code is updated.
-    public static final int FLAGS_PKG_HAS_RESOURCES = 0x4;
+    private static final int FLAGS_PKG_HAS_RESOURCES = 0x4;
 
     /**
      * References are ordered with preview versions first which permits early
@@ -118,7 +117,7 @@ public String name() {
      * under many modules, it only has resources in one.
      */
     public boolean hasResources() {
-        return ((flags & FLAGS_PKG_HAS_RESOURCES) != 0);
+        return (flags & FLAGS_PKG_HAS_RESOURCES) != 0;
     }
 
     /**
@@ -176,9 +175,9 @@ public static Iterator<Integer> readNameOffsets(
         if (bufferSize == 0 || (bufferSize & 0x1) != 0) {
             throw new IllegalArgumentException("Invalid buffer size");
         }
-        int testFlags = (includeNormal ? FLAGS_PKG_HAS_NORMAL_VERSION : 0)
+        int includeMask = (includeNormal ? FLAGS_PKG_HAS_NORMAL_VERSION : 0)
                 + (includePreview ? FLAGS_PKG_HAS_PREVIEW_VERSION : 0);
-        if (testFlags == 0) {
+        if (includeMask == 0) {
             throw new IllegalArgumentException("Invalid flags");
         }
 
@@ -188,14 +187,7 @@ public static Iterator<Integer> readNameOffsets(
             int nextIdx(int idx) {
                 for (; idx < bufferSize; idx += 2) {
                     // If any of the test flags are set, include this entry.
-
-                    // Temporarily allow for *neither* flag to be set. This is what would
-                    // be written by a 1.0 version of the jimage flag, and indicates a
-                    // normal resource without a preview version.
-                    // TODO: Remove the zero-check below once image writer code is updated.
-                    int previewFlags =
-                            buffer.get(idx) & (FLAGS_PKG_HAS_NORMAL_VERSION | FLAGS_PKG_HAS_PREVIEW_VERSION);
-                    if (previewFlags == 0 || (previewFlags & testFlags) != 0) {
+                    if ((buffer.get(idx) & includeMask) != 0) {
                         return idx;
                     } else if (!includeNormal) {
                         // Preview entries are first in the offset buffer, so we

src/java.base/share/classes/jdk/internal/jimage/PreviewMode.java

@@ -56,6 +56,9 @@ public enum PreviewMode {
      * Resolves whether preview mode should be enabled for an {@link ImageReader}.
      */
     public boolean isPreviewModeEnabled() {
+        if (!ENABLE_PREVIEW_MODE) {
+            return false;
+        }
         // A switch, instead of an abstract method, saves 3 subclasses.
         switch (this) {
             case DISABLED:
@@ -83,4 +86,14 @@ public boolean isPreviewModeEnabled() {
                 throw new IllegalStateException("Invalid mode: " + this);
         }
     }
+    ;
+
+    // Temporary system property to disable preview patching and enable the new preview mode
+    // feature for testing/development. Once the preview mode feature is finished, the value
+    // will be always 'true' and this code, and all related dead-code can be removed.
+    private static final boolean DISABLE_PREVIEW_PATCHING_DEFAULT = false;
+    private static final boolean ENABLE_PREVIEW_MODE = Boolean.parseBoolean(
+            System.getProperty(
+                    "DISABLE_PREVIEW_PATCHING",
+                    Boolean.toString(DISABLE_PREVIEW_PATCHING_DEFAULT)));
 }

src/java.base/share/native/libjimage/imageFile.cpp

@@ -319,12 +319,7 @@ bool ImageFileReader::open() {
         !read_at((u1*)&_header, header_size, 0) ||
         _header.magic(_endian) != IMAGE_MAGIC ||
         _header.major_version(_endian) != MAJOR_VERSION ||
-        // Temporarily, we allow either version (1.1 or 1.0) of the file to
-        // be read so this code can be committed before image writing changes
-        // for preview mode. Preview mode changes do not modify any structure,
-        // so a 1.0 file will look like a jimage without any preview resources.
-        // TODO: Restore equality check for MINOR_VERSION.
-        _header.minor_version(_endian) > MINOR_VERSION) {
+        _header.minor_version(_endian) != MINOR_VERSION) {
         close();
         return false;
     }

src/jdk.jlink/share/classes/jdk/tools/jlink/internal/BasicImageWriter.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2014, 2020, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2014, 2025, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -36,21 +36,17 @@
 public final class BasicImageWriter {
     public static final String MODULES_IMAGE_NAME = "modules";
 
-    private ByteOrder byteOrder;
-    private ImageStringsWriter strings;
+    private final ByteOrder byteOrder;
+    private final ImageStringsWriter strings;
     private int length;
     private int[] redirect;
     private ImageLocationWriter[] locations;
-    private List<ImageLocationWriter> input;
-    private ImageStream headerStream;
-    private ImageStream redirectStream;
-    private ImageStream locationOffsetStream;
-    private ImageStream locationStream;
-    private ImageStream allIndexStream;
-
-    public BasicImageWriter() {
-        this(ByteOrder.nativeOrder());
-    }
+    private final List<ImageLocationWriter> input;
+    private final ImageStream headerStream;
+    private final ImageStream redirectStream;
+    private final ImageStream locationOffsetStream;
+    private final ImageStream locationStream;
+    private final ImageStream allIndexStream;
 
     public BasicImageWriter(ByteOrder byteOrder) {
         this.byteOrder = Objects.requireNonNull(byteOrder);
@@ -75,11 +71,15 @@ public String getString(int offset) {
         return strings.get(offset);
     }
 
-    public void addLocation(String fullname, long contentOffset,
-            long compressedSize, long uncompressedSize) {
+    public void addLocation(
+            String fullname,
+            long contentOffset,
+            long compressedSize,
+            long uncompressedSize,
+            int previewFlags) {
         ImageLocationWriter location =
                 ImageLocationWriter.newLocation(fullname, strings,
-                        contentOffset, compressedSize, uncompressedSize);
+                        contentOffset, compressedSize, uncompressedSize, previewFlags);
         input.add(location);
         length++;
     }
@@ -88,10 +88,6 @@ ImageLocationWriter[] getLocations() {
         return locations;
     }
 
-    int getLocationsCount() {
-        return input.size();
-    }
-
     private void generatePerfectHash() {
         PerfectHashBuilder<ImageLocationWriter> builder =
             new PerfectHashBuilder<>(
@@ -174,16 +170,4 @@ public byte[] getBytes() {
 
         return allIndexStream.toArray();
     }
-
-    ImageLocationWriter find(String key) {
-        int index = redirect[ImageStringsReader.hashCode(key) % length];
-
-        if (index < 0) {
-            index = -index - 1;
-        } else {
-            index = ImageStringsReader.hashCode(key, index) % length;
-        }
-
-        return locations[index];
-    }
 }

src/jdk.jlink/share/classes/jdk/tools/jlink/internal/ImageFileCreator.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2014, 2024, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2014, 2025, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -49,6 +49,7 @@
 import java.util.stream.Collectors;
 import java.util.stream.Stream;
 
+import jdk.internal.jimage.ImageLocation;
 import jdk.tools.jlink.internal.Archive.Entry;
 import jdk.tools.jlink.internal.Archive.Entry.EntryType;
 import jdk.tools.jlink.internal.JRTArchive.ResourceFileEntry;
@@ -227,31 +228,8 @@ private static ResourcePool generateJImage(ResourcePoolManager allContent,
             DataOutputStream out,
             boolean generateRuntimeImage
     ) throws IOException {
-        ResourcePool resultResources;
-        try {
-            resultResources = pluginSupport.visitResources(allContent);
-            if (generateRuntimeImage) {
-                // Keep track of non-modules resources for linking from a run-time image
-                resultResources = addNonClassResourcesTrackFiles(resultResources,
-                                                                 writer);
-                // Generate the diff between the input resources from packaged
-                // modules in 'allContent' to the plugin- or otherwise
-                // generated-content in 'resultResources'
-                resultResources = addResourceDiffFiles(allContent.resourcePool(),
-                                                       resultResources,
-                                                       writer);
-            }
-        } catch (PluginException pe) {
-            if (JlinkTask.DEBUG) {
-                pe.printStackTrace();
-            }
-            throw pe;
-        } catch (Exception ex) {
-            if (JlinkTask.DEBUG) {
-                ex.printStackTrace();
-            }
-            throw new IOException(ex);
-        }
+        ResourcePool resultResources =
+                getResourcePool(allContent, writer, pluginSupport, generateRuntimeImage);
         Set<String> duplicates = new HashSet<>();
         long[] offset = new long[1];
 
@@ -282,8 +260,10 @@ private static ResourcePool generateJImage(ResourcePoolManager allContent,
                     offset[0] += onFileSize;
                     return;
                 }
+                int locFlags = ImageLocation.getFlags(
+                        res.path(), p -> resultResources.findEntry(p).isPresent());
                 duplicates.add(path);
-                writer.addLocation(path, offset[0], compressedSize, uncompressedSize);
+                writer.addLocation(path, offset[0], compressedSize, uncompressedSize, locFlags);
                 paths.add(path);
                 offset[0] += onFileSize;
             }
@@ -307,6 +287,40 @@ private static ResourcePool generateJImage(ResourcePoolManager allContent,
         return resultResources;
     }
 
+    private static ResourcePool getResourcePool(
+            ResourcePoolManager allContent,
+            BasicImageWriter writer,
+            ImagePluginStack pluginSupport,
+            boolean generateRuntimeImage)
+            throws IOException {
+        ResourcePool resultResources;
+        try {
+            resultResources = pluginSupport.visitResources(allContent);
+            if (generateRuntimeImage) {
+                // Keep track of non-modules resources for linking from a run-time image
+                resultResources = addNonClassResourcesTrackFiles(resultResources,
+                        writer);
+                // Generate the diff between the input resources from packaged
+                // modules in 'allContent' to the plugin- or otherwise
+                // generated-content in 'resultResources'
+                resultResources = addResourceDiffFiles(allContent.resourcePool(),
+                        resultResources,
+                        writer);
+            }
+        } catch (PluginException pe) {
+            if (JlinkTask.DEBUG) {
+                pe.printStackTrace();
+            }
+            throw pe;
+        } catch (Exception ex) {
+            if (JlinkTask.DEBUG) {
+                ex.printStackTrace();
+            }
+            throw new IOException(ex);
+        }
+        return resultResources;
+    }
+
     /**
      * Support for creating a runtime suitable for linking from the run-time
      * image.

src/jdk.jlink/share/classes/jdk/tools/jlink/internal/ImageLocationWriter.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2014, 2017, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2014, 2025, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -53,9 +53,13 @@ private ImageLocationWriter addAttribute(int kind, String value) {
         return addAttribute(kind, strings.add(value));
     }
 
-    static ImageLocationWriter newLocation(String fullName,
+    static ImageLocationWriter newLocation(
+            String fullName,
             ImageStringsWriter strings,
-            long contentOffset, long compressedSize, long uncompressedSize) {
+            long contentOffset,
+            long compressedSize,
+            long uncompressedSize,
+            int previewFlags) {
         String moduleName = "";
         String parentName = "";
         String baseName;
@@ -90,13 +94,14 @@ static ImageLocationWriter newLocation(String fullName,
         }
 
         return new ImageLocationWriter(strings)
-               .addAttribute(ATTRIBUTE_MODULE, moduleName)
-               .addAttribute(ATTRIBUTE_PARENT, parentName)
-               .addAttribute(ATTRIBUTE_BASE, baseName)
-               .addAttribute(ATTRIBUTE_EXTENSION, extensionName)
-               .addAttribute(ATTRIBUTE_OFFSET, contentOffset)
-               .addAttribute(ATTRIBUTE_COMPRESSED, compressedSize)
-               .addAttribute(ATTRIBUTE_UNCOMPRESSED, uncompressedSize);
+                .addAttribute(ATTRIBUTE_MODULE, moduleName)
+                .addAttribute(ATTRIBUTE_PARENT, parentName)
+                .addAttribute(ATTRIBUTE_BASE, baseName)
+                .addAttribute(ATTRIBUTE_EXTENSION, extensionName)
+                .addAttribute(ATTRIBUTE_OFFSET, contentOffset)
+                .addAttribute(ATTRIBUTE_COMPRESSED, compressedSize)
+                .addAttribute(ATTRIBUTE_UNCOMPRESSED, uncompressedSize)
+                .addAttribute(ATTRIBUTE_PREVIEW_FLAGS, previewFlags);
     }
 
     @Override