js: make names of variables in minified mode never interfering with JS keywords

core/src/main/java/org/teavm/backend/javascript/rendering/StatementRenderer.java

@@ -21,11 +21,9 @@ import java.io.IOException;
 import java.util.ArrayList;
 import java.util.Collections;
 import java.util.HashMap;
-import java.util.HashSet;
 import java.util.List;
 import java.util.Map;
 import java.util.Properties;
-import java.util.Set;
 import org.teavm.ast.ArrayFromDataExpr;
 import org.teavm.ast.AssignmentStatement;
 import org.teavm.ast.BinaryExpr;
@@ -66,7 +64,6 @@ import org.teavm.ast.TryCatchStatement;
 import org.teavm.ast.UnaryExpr;
 import org.teavm.ast.UnwrapArrayExpr;
 import org.teavm.ast.VariableExpr;
-import org.teavm.ast.VariableNode;
 import org.teavm.ast.WhileStatement;
 import org.teavm.backend.javascript.codegen.NamingStrategy;
 import org.teavm.backend.javascript.codegen.SourceWriter;
@@ -98,14 +95,12 @@ public class StatementRenderer implements ExprVisitor, StatementVisitor {
     private DeferredCallSite prevCallSite;
     private boolean end;
     private final Map<String, String> blockIdMap = new HashMap<>();
-    private final List<String> cachedVariableNames = new ArrayList<>();
-    private final Set<String> usedVariableNames = new HashSet<>();
-    private MethodNode currentMethod;
     private int currentPart;
     private List<String> blockIds = new ArrayList<>();
     private IntIndexedContainer blockIndexMap = new IntArrayList();
     private boolean longLibraryUsed;
     private static final MethodDescriptor CLINIT_METHOD = new MethodDescriptor("<clinit>", ValueType.VOID);
+    private VariableNameGenerator variableNameGenerator;
 
     public StatementRenderer(RenderingContext context, SourceWriter writer) {
         this.context = context;
@@ -114,11 +109,7 @@ public class StatementRenderer implements ExprVisitor, StatementVisitor {
         this.minifying = context.isMinifying();
         this.naming = context.getNaming();
         this.debugEmitter = context.getDebugEmitter();
-        if (!minifying) {
+        variableNameGenerator = new VariableNameGenerator(minifying);
-            usedVariableNames.add("$tmp");
-            usedVariableNames.add("$ptr");
-            usedVariableNames.add("$thread");
-        }
     }
 
     public boolean isLongLibraryUsed() {
@@ -134,7 +125,7 @@ public class StatementRenderer implements ExprVisitor, StatementVisitor {
     }
 
     public void setCurrentMethod(MethodNode currentMethod) {
-        this.currentMethod = currentMethod;
+        variableNameGenerator.setCurrentMethod(currentMethod);
     }
 
     public void setCurrentPart(int currentPart) {
@@ -492,38 +483,7 @@ public class StatementRenderer implements ExprVisitor, StatementVisitor {
     }
 
     public String variableName(int index) {
-        while (index >= cachedVariableNames.size()) {
+        return variableNameGenerator.variableName(index);
-            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 (!minifying) {
-            VariableNode variable = currentMethod != null && index < currentMethod.getVariables().size()
-                    ? currentMethod.getVariables().get(index)
-                    : null;
-            if (variable != null && variable.getName() != null) {
-                String result = "$" + RenderingUtil.escapeName(variable.getName());
-                if (RenderingUtil.KEYWORDS.contains(result) || !usedVariableNames.add(result)) {
-                    String base = result;
-                    int suffix = 0;
-                    do {
-                        result = base + "_" + suffix++;
-                    } while (!usedVariableNames.add(result));
-                }
-                return result;
-            } else {
-                return "var$" + index;
-            }
-        } else {
-            return RenderingUtil.indexToId(index);
-        }
     }
 
     private void visitBinary(BinaryExpr expr, String op, boolean guarded) {

core/src/main/java/org/teavm/backend/javascript/rendering/VariableNameGenerator.java

@@ -0,0 +1,85 @@
+/*
+ *  Copyright 2023 Alexey Andreev.
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *       http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+package org.teavm.backend.javascript.rendering;
+
+import java.util.ArrayList;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Set;
+import org.teavm.ast.MethodNode;
+
+public class VariableNameGenerator {
+    private boolean minifying;
+    private final List<String> cachedVariableNames = new ArrayList<>();
+    private int cachedVariableNameLastIndex;
+    private MethodNode currentMethod;
+    private Set<String> usedVariableNames = new HashSet<>();
+
+    public VariableNameGenerator(boolean minifying) {
+        this.minifying = minifying;
+        if (!minifying) {
+            usedVariableNames.add("$tmp");
+            usedVariableNames.add("$ptr");
+            usedVariableNames.add("$thread");
+        }
+    }
+
+    public void setCurrentMethod(MethodNode currentMethod) {
+        this.currentMethod = currentMethod;
+    }
+
+    public String variableName(int index) {
+        if (!minifying) {
+            while (index >= cachedVariableNames.size()) {
+                cachedVariableNames.add(null);
+            }
+            String name = cachedVariableNames.get(index);
+            if (name == null) {
+                name = generateVariableName(index);
+                cachedVariableNames.set(index, name);
+            }
+            return name;
+        } else {
+            while (index >= cachedVariableNames.size()) {
+                String name;
+                do {
+                    name = RenderingUtil.indexToId(cachedVariableNameLastIndex++);
+                } while (RenderingUtil.KEYWORDS.contains(name));
+                cachedVariableNames.add(name);
+            }
+            return cachedVariableNames.get(index);
+        }
+    }
+
+    private String generateVariableName(int index) {
+        var variable = currentMethod != null && index < currentMethod.getVariables().size()
+                ? currentMethod.getVariables().get(index)
+                : null;
+        if (variable != null && variable.getName() != null) {
+            String result = "$" + RenderingUtil.escapeName(variable.getName());
+            if (RenderingUtil.KEYWORDS.contains(result) || !usedVariableNames.add(result)) {
+                String base = result;
+                int suffix = 0;
+                do {
+                    result = base + "_" + suffix++;
+                } while (!usedVariableNames.add(result));
+            }
+            return result;
+        } else {
+            return "var$" + index;
+        }
+    }
+}

core/src/test/java/org/teavm/backend/javascript/rendering/VariableRenderingTest.java

@@ -0,0 +1,34 @@
+/*
+ *  Copyright 2023 Alexey Andreev.
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *       http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+package org.teavm.backend.javascript.rendering;
+
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+import java.util.HashSet;
+import org.junit.Test;
+
+public class VariableRenderingTest {
+    @Test
+    public void shortenedNames() {
+        var generator = new VariableNameGenerator(true);
+        var usedNames = new HashSet<String>();
+        for (var i = 0; i < 10000; ++i) {
+            var name = generator.variableName(i);
+            assertTrue(usedNames.add(name));
+            assertFalse(RenderingUtil.KEYWORDS.contains(name));
+        }
+    }
+}