use const keyword for final and effectively final variables

transpiler/src/main/java/org/jsweet/transpiler/ConstAnalyzer.java

@@ -0,0 +1,99 @@
+/* 
+ * JSweet transpiler - http://www.jsweet.org
+ * Copyright (C) 2015 CINCHEO SAS <renaud.pawlak@cincheo.fr>
+ * 
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 3 of the License, or
+ * (at your option) any later version.
+ *  
+ * This program 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 for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+package org.jsweet.transpiler;
+
+import java.util.HashSet;
+import java.util.List;
+import java.util.Set;
+
+import javax.lang.model.element.ElementKind;
+
+import org.jsweet.transpiler.util.AbstractTreeScanner;
+
+import com.sun.tools.javac.code.Symbol.VarSymbol;
+import com.sun.tools.javac.tree.JCTree;
+import com.sun.tools.javac.tree.JCTree.JCAssign;
+import com.sun.tools.javac.tree.JCTree.JCAssignOp;
+import com.sun.tools.javac.tree.JCTree.JCCompilationUnit;
+import com.sun.tools.javac.tree.JCTree.JCIdent;
+import com.sun.tools.javac.tree.JCTree.JCUnary;
+
+/**
+ * This AST scanner analyzes local variables to determine if they are locally
+ * assigned and can be assumed constant or not.
+ * 
+ * @see JSweetContext
+ * @author Renaud Pawlak
+ */
+public class ConstAnalyzer extends AbstractTreeScanner {
+
+    private Set<VarSymbol> modifiedVariables = new HashSet<>();
+
+    /**
+     * Gets all the local variables that are modified within the program. All other
+     * local variables can be assumed as constant.
+     */
+    public Set<VarSymbol> getModifiedVariables() {
+        return modifiedVariables;
+    }
+
+    /**
+     * Creates a new constant variable analyzer.
+     */
+    public ConstAnalyzer(TranspilationHandler logHandler, JSweetContext context) {
+        super(logHandler, context, null);
+    }
+
+    private void registerModification(JCTree tree) {
+        if (tree instanceof JCIdent && ((JCIdent) tree).sym.getKind() == ElementKind.LOCAL_VARIABLE) {
+            modifiedVariables.add((VarSymbol) ((JCIdent) tree).sym);
+        }
+    }
+
+    @Override
+    public void visitAssign(JCAssign assign) {
+        registerModification(assign.lhs);
+        super.visitAssign(assign);
+    }
+
+    @Override
+    public void visitAssignop(JCAssignOp assignOp) {
+        registerModification(assignOp.lhs);
+    }
+
+    @Override
+    public void visitUnary(JCUnary unary) {
+        switch (unary.getTag()) {
+        case PREINC:
+        case POSTINC:
+        case PREDEC:
+        case POSTDEC:
+            registerModification(unary.arg);
+        default:
+        }
+        super.visitUnary(unary);
+    }
+
+    public void process(List<JCCompilationUnit> compilationUnits) {
+        for (JCCompilationUnit compilationUnit : compilationUnits) {
+            scan(compilationUnit);
+        }
+    }
+
+}

transpiler/src/main/java/org/jsweet/transpiler/Java2TypeScriptTranslator.java

@@ -482,6 +482,8 @@ public class Java2TypeScriptTranslator extends AbstractTreePrinter {
 
 	private boolean isDefinitionScope = false;
 
+	private ConstAnalyzer constAnalyzer = null;
+	
 	protected final boolean isTopLevelScope() {
 		return getIndent() == 0;
 	}
@@ -736,7 +738,9 @@ public class Java2TypeScriptTranslator extends AbstractTreePrinter {
 		footer.delete(0, footer.length());
 
 		setCompilationUnit(topLevel);
-
+		constAnalyzer = new ConstAnalyzer(getLogHandler(), context);
+		constAnalyzer.scan(topLevel);
+		
 		String packge = topLevel.packge.toString();
 
 		boolean globalModule = JSweetConfig.GLOBALS_PACKAGE_NAME.equals(packge)
@@ -3404,7 +3408,12 @@ public class Java2TypeScriptTranslator extends AbstractTreePrinter {
 					if (isDefinitionScope) {
 						print("var ");
 					} else {
-						print(VAR_DECL_KEYWORD + " ");
+                        if (varDecl.sym.getModifiers().contains(Modifier.FINAL) || (constAnalyzer != null
+                                && !constAnalyzer.getModifiedVariables().contains(varDecl.sym))) {
+                            print("const ");
+                        } else {
+                            print(VAR_DECL_KEYWORD + " ");
+                        }
 					}
 				}
 			} else {

transpiler/src/main/java/org/jsweet/transpiler/util/AbstractTreeScanner.java

@@ -60,7 +60,7 @@ public abstract class AbstractTreeScanner extends TreeScanner {
 
 	private TranspilationHandler logHandler;
 
-	/**
+    /**
 	 * Report a JSweet problem on the given program element (tree).
 	 * 
 	 * @param tree
@@ -468,4 +468,11 @@ public abstract class AbstractTreeScanner extends TreeScanner {
 		return null;
 	}
 
+	/**
+	 * Gets the transpilation handler for this scanner.
+	 */
+    public TranspilationHandler getLogHandler() {
+        return logHandler;
+    }
+
 }

transpiler/src/test/java/source/syntax/FinalVariables.java

@@ -33,7 +33,11 @@ import def.js.Math;
 
 public class FinalVariables {
 
+    int finalField;
+    int modifiedField;
+    
 	void m1(HTMLElement e) {
+	    modifiedField++;
 		NodeList nodes = document.querySelectorAll("form .form-control");
 		for (int i = 0; i < nodes.length; i++) {
 			HTMLElement element = (HTMLElement) nodes.$get(i);
@@ -117,6 +121,12 @@ public class FinalVariables {
 		});
 	}
 
+    String notFinal() {
+        String s = "abc";
+        s = "bcd";
+        return s;
+    }
+	
 }
 
 // subset of promises API