Revert js launcher default languages to js only, but include wasm if --webassembly flag is set.

Fixes running `js` with --engine.SpawnIsolates=true.

(cherry picked from commit 3b2c114)

Author: woess

graal-js/src/com.oracle.truffle.js.shell/src/com/oracle/truffle/js/shell/JSLauncher.java

@@ -46,6 +46,7 @@
 
 import java.io.File;
 import java.io.IOException;
+import java.io.OutputStream;
 import java.io.PrintStream;
 import java.nio.charset.StandardCharsets;
 import java.nio.file.Files;
@@ -69,6 +70,7 @@
 
 public class JSLauncher extends AbstractLanguageLauncher {
     static final String MODULE_MIME_TYPE = "application/javascript+module";
+    private static final String WASM_LANGUAGE_ID = "wasm";
     private static final String PROMPT = "> ";
 
     public static void main(String[] args) {
@@ -79,6 +81,7 @@ public static void main(String[] args) {
     private boolean fuzzilliREPRL = false;
     private boolean allowExperimentalOptions = false;
     private boolean useSharedEngine = false;
+    private boolean wasmEnabled = false;
     private String[] programArgs;
     private final List<UnparsedSource> unparsedSources = new LinkedList<>();
     private VersionAction versionAction = VersionAction.None;
@@ -104,7 +107,11 @@ protected String getLanguageId() {
 
     @Override
     protected String[] getDefaultLanguages() {
-        return new String[0];
+        if (wasmEnabled && isLanguageAvailable(WASM_LANGUAGE_ID)) {
+            return new String[]{getLanguageId(), WASM_LANGUAGE_ID};
+        } else {
+            return super.getDefaultLanguages();
+        }
     }
 
     protected void preEval(@SuppressWarnings("unused") Context context) {
@@ -146,7 +153,8 @@ protected List<String> preprocessArguments(List<String> arguments, Map<String, S
 
                 String value;
                 int equalsIndex = flag.indexOf('=');
-                if (equalsIndex > 0) {
+                boolean hasEquals = equalsIndex > 0;
+                if (hasEquals) {
                     value = flag.substring(equalsIndex + 1);
                     flag = flag.substring(0, equalsIndex);
                 } else if (iterator.hasNext()) {
@@ -162,8 +170,12 @@ protected List<String> preprocessArguments(List<String> arguments, Map<String, S
                         throw abort("Missing argument for " + arg);
                 }
 
+                if (flag.equals("js.webassembly") || flag.equals("webassembly")) {
+                    wasmEnabled = !hasEquals || "true".equals(value);
+                }
+
                 unrecognizedOptions.add(arg);
-                if (equalsIndex < 0 && value != null) {
+                if (!hasEquals && value != null) {
                     iterator.previous();
                 }
             } else {
@@ -536,6 +548,16 @@ private static void printStackTraceSkipTrailingHost(PolyglotException e, StringB
         }
     }
 
+    private static boolean isLanguageAvailable(String languageId) {
+        try (Engine tempEngine = Engine.newBuilder().useSystemProperties(false).//
+                        out(OutputStream.nullOutputStream()).//
+                        err(OutputStream.nullOutputStream()).//
+                        option("engine.WarnInterpreterOnly", "false").//
+                        build()) {
+            return tempEngine.getLanguages().containsKey(languageId);
+        }
+    }
+
     private enum SourceType {
         FILE,
         EVAL,