[GR-61288] Make -H:Backend= a real option

web-image/mx.web-image/mx_web_image.py

@@ -647,7 +647,7 @@ def get_or_compute_lines(self) -> List[str]:
             lines: List[str] = [
                 "# This file is auto-generated",
                 "ExcludeFromAll = true",
-                "ProvidedHostedOptions = " + " ".join(self.subject.provided_hosted_options + ["Backend="]),
+                "ProvidedHostedOptions = " + " ".join(self.subject.provided_hosted_options),
             ]
 
             if builder_jars:

web-image/src/com.oracle.svm.hosted.webimage/src/META-INF/services/com.oracle.svm.hosted.NativeImageClassLoaderPostProcessing

@@ -0,0 +1 @@
+com.oracle.svm.hosted.webimage.WebImagePlatformInjector

web-image/src/com.oracle.svm.hosted.webimage/src/com/oracle/svm/hosted/webimage/NativeImageWasmGeneratorRunner.java

@@ -26,15 +26,11 @@
 
 import java.lang.reflect.Method;
 import java.util.ArrayList;
-import java.util.Arrays;
 import java.util.Comparator;
-import java.util.Iterator;
 import java.util.List;
-import java.util.Locale;
 
 import org.graalvm.collections.EconomicMap;
 import org.graalvm.collections.Pair;
-import org.graalvm.nativeimage.Platform;
 import org.graalvm.nativeimage.c.type.CIntPointer;
 import org.graalvm.nativeimage.c.type.CShortPointer;
 
@@ -74,60 +70,11 @@
  */
 public class NativeImageWasmGeneratorRunner extends NativeImageGeneratorRunner {
 
-    public static final String BACKEND_ARG = "-H:Backend(@[^=]*)?=.*";
-
     /**
      * @param args Hosted and runtime options
      */
     public static void main(String[] args) {
-        List<String> arguments = Arrays.asList(args);
-        arguments = extractDriverArguments(arguments);
-
-        CompilerBackend backend;
-        if (WebImageOptions.isNativeImageBackend()) {
-            // Under native-image, selection of the Web Image backend is not allowed
-            backend = CompilerBackend.WASMGC;
-        } else {
-            backend = extractBackend(arguments);
-        }
-
-        // installNativeImageClassLoader uses this property to create the platform instance.
-        System.setProperty(Platform.PLATFORM_PROPERTY_NAME, backend.platform.getName());
-        new NativeImageWasmGeneratorRunner().start(arguments.toArray(String[]::new));
-    }
-
-    /**
-     * Extracts the {@link NativeImageWasmGeneratorRunner#BACKEND_ARG} argument as a
-     * {@link CompilerBackend} from the list of arguments.
-     *
-     * @param arguments The list of arguments. The backend argument will be removed from the list if
-     *            specified.
-     * @return The appropriate compiler backend for the given arguments or
-     *         {@link CompilerBackend#JS} if none was specified
-     */
-    public static CompilerBackend extractBackend(List<String> arguments) {
-        Iterator<String> it = arguments.iterator();
-
-        while (it.hasNext()) {
-            String param = it.next();
-
-            if (param.matches(BACKEND_ARG)) {
-                it.remove();
-                String[] parts = param.split("=", 2);
-                if (parts.length != 2) {
-                    throw new IllegalArgumentException(BACKEND_ARG + " needs an argument");
-                }
-                String backendName = parts[1].toUpperCase(Locale.ROOT);
-                try {
-                    return CompilerBackend.valueOf(backendName);
-                } catch (IllegalArgumentException e) {
-                    throw new IllegalArgumentException("No backend with name " + backendName + " exists", e);
-                }
-            }
-        }
-
-        // Use JS backend by default
-        return CompilerBackend.JS;
+        new NativeImageWasmGeneratorRunner().start(args);
     }
 
     /**
@@ -142,7 +89,16 @@ private static void dumpProvidedHostedOptions(HostedOptionParser optionParser) {
         List<String> names = new ArrayList<>();
 
         for (OptionDescriptor value : allHostedOptions.getValues()) {
-            if (!value.getDeclaringClass().getPackageName().contains("webimage") || WebImageOptions.DebugOptions.DumpProvidedHostedOptionsAndExit == value.getOptionKey()) {
+            if (!value.getDeclaringClass().getPackageName().contains("webimage")) {
+                continue;
+            }
+
+            if (WebImageOptions.DebugOptions.DumpProvidedHostedOptionsAndExit == value.getOptionKey()) {
+                continue;
+            }
+
+            // Do not print the Backend option, it's not available in the svm-wasm macro
+            if (WebImageOptions.Backend == value.getOptionKey()) {
                 continue;
             }
 

web-image/src/com.oracle.svm.hosted.webimage/src/com/oracle/svm/hosted/webimage/WebImagePlatformInjector.java

@@ -0,0 +1,61 @@
+/*
+ * Copyright (c) 2025, 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
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.  Oracle designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+package com.oracle.svm.hosted.webimage;
+
+import static com.oracle.svm.hosted.webimage.options.WebImageOptions.CompilerBackend;
+import static com.oracle.svm.hosted.webimage.options.WebImageOptions.isNativeImageBackend;
+
+import org.graalvm.nativeimage.Platform;
+
+import com.oracle.svm.hosted.NativeImageClassLoaderPostProcessing;
+import com.oracle.svm.hosted.NativeImageClassLoaderSupport;
+import com.oracle.svm.hosted.webimage.options.WebImageOptions;
+
+/**
+ * Sets the {@link Platform#PLATFORM_PROPERTY_NAME} property based on which code-generation backend
+ * is selected.
+ * <p>
+ * In the {@code native-image} launcher this is always the WasmGC backend. Under {@code web-image},
+ * it is determined by the {@link WebImageOptions#Backend} option.
+ */
+public class WebImagePlatformInjector implements NativeImageClassLoaderPostProcessing {
+    @Override
+    public void apply(NativeImageClassLoaderSupport support) {
+        CompilerBackend backend;
+        if (isNativeImageBackend()) {
+            // Under native-image, selection of the Web Image backend is not allowed
+            backend = CompilerBackend.WASMGC;
+        } else {
+            backend = WebImageOptions.Backend.getValue(support.getParsedHostedOptions());
+        }
+
+        /*
+         * installNativeImageClassLoader uses this property at the end to create the platform
+         * instance. This method is called before that.
+         */
+        System.setProperty(Platform.PLATFORM_PROPERTY_NAME, backend.platform.getName());
+    }
+}

web-image/src/com.oracle.svm.hosted.webimage/src/com/oracle/svm/hosted/webimage/options/WebImageOptions.java

@@ -135,6 +135,15 @@ public static final class DebugOptions {
         public static final HostedOptionKey<Boolean> DumpProvidedHostedOptionsAndExit = new HostedOptionKey<>(false);
     }
 
+    /**
+     * Web Image only.
+     * <p>
+     * Do not read this value directly. Instead, look it up based on the selected {@link Platform}
+     * using {@link #getBackend}.
+     */
+    @Option(help = "The Web Image Backend to use.") //
+    public static final EnumOptionKey<CompilerBackend> Backend = new EnumOptionKey<>(CompilerBackend.JS);
+
     @Option(help = "Report the code sizes of different parts of the generated JavaScript image. If the closure compiler is applied, this instruments the generated javascript code by injecting labels.")//
     public static final HostedOptionKey<Boolean> ReportImageSizeBreakdown = new HostedOptionKey<>(false);