Generate readable names for method parameters

teavm-core/src/main/java/org/teavm/javascript/Renderer.java

@@ -65,6 +65,8 @@ public class Renderer implements ExprVisitor, StatementVisitor, RenderingContext
     private boolean wasGrouped;
     private Deque<OperatorPrecedence> precedenceStack = new ArrayDeque<>();
     private Map<String, String> blockIdMap = new HashMap<>();
+    private List<Set<String>> debugNames = new ArrayList<>();
+    private List<String> cachedVariableNames = new ArrayList<>();
 
     private static class OperatorPrecedence {
         Priority priority;
@@ -574,6 +576,9 @@ public class Renderer implements ExprVisitor, StatementVisitor, RenderingContext
     }
 
     public void renderBody(MethodNode method, boolean inner) throws IOException {
+        debugNames.clear();
+        cachedVariableNames.clear();
+        debugNames.addAll(method.getParameterDebugNames());
         blockIdMap.clear();
         MethodReference ref = method.getReference();
         debugEmitter.emitMethod(ref.getDescriptor());
@@ -627,6 +632,7 @@ public class Renderer implements ExprVisitor, StatementVisitor, RenderingContext
                     debugEmitter.emitVariable(method.getParameterDebugNames().get(i).toArray(new String[0]),
                             variableName(i));
                 }
+
                 int variableCount = 0;
                 for (int var : method.getVariables()) {
                     variableCount = Math.max(variableCount, var + 1);
@@ -1128,15 +1134,39 @@ public class Renderer implements ExprVisitor, StatementVisitor, RenderingContext
     }
 
     public String variableName(int index) {
+        while (index >= cachedVariableNames.size()) {
+            cachedVariableNames.add(null);
+        }
+        String name = cachedVariableNames.get(index);
+        if (name == null) {
+            name = generateVariableName(index);
+            cachedVariableNames.set(index, name);
+        }
+        return name;
+    }
+
+    private String generateVariableName(int index) {
         if (index == 0) {
             return minifying ? "$t" : "$this";
         }
-        --index;
-        if (index < variableNames.length()) {
-            return Character.toString(variableNames.charAt(index));
+
+        Set<String> names = index < debugNames.size() ? debugNames.get(index) : null;
+        if (minifying || names == null || names.isEmpty()) {
+            --index;
+            if (index < variableNames.length()) {
+                return Character.toString(variableNames.charAt(index));
+            } else {
+                return Character.toString(variableNames.charAt(index % variableNames.length())) +
+                        index / variableNames.length();
+            }
         } else {
-            return Character.toString(variableNames.charAt(index % variableNames.length())) +
-                    index / variableNames.length();
+            List<String> nameList = new ArrayList<>(names);
+            Collections.sort(nameList);
+            StringBuilder sb = new StringBuilder();
+            for (String name : nameList) {
+                sb.append('_').append(name);
+            }
+            return sb.toString();
         }
     }
 

teavm-core/src/main/java/org/teavm/javascript/ast/AsyncMethodNode.java

@@ -41,6 +41,7 @@ public class AsyncMethodNode extends MethodNode {
         return variables;
     }
 
+    @Override
     public List<Set<String>> getParameterDebugNames() {
         return parameterDebugNames;
     }

teavm-core/src/main/java/org/teavm/javascript/ast/MethodNode.java

@@ -16,6 +16,7 @@
 package org.teavm.javascript.ast;
 
 import java.util.EnumSet;
+import java.util.List;
 import java.util.Set;
 import org.teavm.model.MethodReference;
 
@@ -43,4 +44,6 @@ public abstract class MethodNode {
     public abstract void acceptVisitor(MethodNodeVisitor visitor);
 
     public abstract boolean isAsync();
+
+    public abstract List<Set<String>> getParameterDebugNames();
 }

teavm-core/src/main/java/org/teavm/javascript/ast/NativeMethodNode.java

@@ -15,6 +15,9 @@
  */
 package org.teavm.javascript.ast;
 
+import java.util.Collections;
+import java.util.List;
+import java.util.Set;
 import org.teavm.javascript.spi.Generator;
 import org.teavm.model.MethodReference;
 
@@ -51,4 +54,9 @@ public class NativeMethodNode extends MethodNode {
     public void acceptVisitor(MethodNodeVisitor visitor) {
         visitor.visit(this);
     }
+
+    @Override
+    public List<Set<String>> getParameterDebugNames() {
+        return Collections.emptyList();
+    }
 }

teavm-core/src/main/java/org/teavm/javascript/ast/RegularMethodNode.java

@@ -45,6 +45,7 @@ public class RegularMethodNode extends MethodNode {
         return variables;
     }
 
+    @Override
     public List<Set<String>> getParameterDebugNames() {
         return parameterDebugNames;
     }