daniellansun commented on code in PR #2773: URL: https://github.com/apache/groovy/pull/2773#discussion_r3740601359
########## src/main/java/org/codehaus/groovy/classgen/InstanceofFlowBindings.java: ########## @@ -0,0 +1,249 @@ +/* + * Licensed to the Apache Software Foundation (ASF) under one + * or more contributor license agreements. See the NOTICE file + * distributed with this work for additional information + * regarding copyright ownership. The ASF licenses this file + * to you 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.codehaus.groovy.classgen; + +import org.codehaus.groovy.ast.CodeVisitorSupport; +import org.codehaus.groovy.ast.expr.BinaryExpression; +import org.codehaus.groovy.ast.expr.BooleanExpression; +import org.codehaus.groovy.ast.expr.DeclarationExpression; +import org.codehaus.groovy.ast.expr.Expression; +import org.codehaus.groovy.ast.expr.NotExpression; +import org.codehaus.groovy.ast.expr.VariableExpression; +import org.codehaus.groovy.syntax.Types; + +import java.util.ArrayList; +import java.util.Collections; +import java.util.LinkedHashSet; +import java.util.List; +import java.util.Set; + +/** + * Flow-sensitive analysis of JEP 394 {@code instanceof} pattern bindings + * (GROOVY-12242). + * <p> + * This is pure <em>semantic</em> analysis: given a boolean expression, which + * pattern variables are <em>definitely bound</em> when the expression is + * {@code true} versus {@code false}? (Same idea as compiler “flow info” / + * JEP 394 flow scoping — not a bytecode construct.) + * <ul> + * <li>{@link #of(Expression)} — true/false binding sets for a condition</li> + * <li>{@link #containsPattern(Expression)} — nested type-pattern presence + * (e.g. whether an expression statement needs CompileStack isolation)</li> + * </ul> + * Covered shapes: {@code e instanceof T t}, negation / {@code !instanceof}, + * {@code &&} (union of true bindings), {@code ||} (union of false bindings). + * Other shapes contribute nothing (conservative). + * <p> + * Consumers: + * <ul> + * <li>{@link VariableScopeVisitor} — declare names on the live path</li> + * <li>{@link org.codehaus.groovy.classgen.asm.InstanceofFlowSlotPublisher} — + * publish/hide CompileStack slots from these bindings</li> + * </ul> + * + * @see org.codehaus.groovy.classgen.asm.InstanceofFlowSlotPublisher + * @since 6.0.0 + */ +public final class InstanceofFlowBindings { + + private static final InstanceofFlowBindings EMPTY = + new InstanceofFlowBindings(List.of(), List.of()); + + private final List<VariableExpression> whenTrue; + private final List<VariableExpression> whenFalse; + + private InstanceofFlowBindings(final List<VariableExpression> whenTrue, + final List<VariableExpression> whenFalse) { + this.whenTrue = whenTrue; + this.whenFalse = whenFalse; + } + + /** + * Pattern variables that are definitely assigned when the analysed expression + * evaluates to {@code true}. + */ + public List<VariableExpression> whenTrue() { + return whenTrue; + } + + /** + * Pattern variables that are definitely assigned when the analysed expression + * evaluates to {@code false}. + */ + public List<VariableExpression> whenFalse() { + return whenFalse; + } + + /** Whether any pattern variable is bound on either path. */ + public boolean isEmpty() { + return whenTrue.isEmpty() && whenFalse.isEmpty(); + } + + /** + * Names of pattern variables bound when the expression is {@code true}. + */ + public Set<String> whenTrueNames() { + return names(whenTrue); + } + + /** + * Names of pattern variables bound when the expression is {@code false}. + */ + public Set<String> whenFalseNames() { + return names(whenFalse); + } + + /** + * All pattern-variable names appearing in either path (stable encounter order). + */ + public Set<String> allNames() { + if (isEmpty()) return Collections.emptySet(); + Set<String> names = new LinkedHashSet<>(whenTrue.size() + whenFalse.size()); + for (VariableExpression ve : whenTrue) names.add(ve.getName()); + for (VariableExpression ve : whenFalse) names.add(ve.getName()); + return names; + } + + private static Set<String> names(final List<VariableExpression> vars) { + if (vars.isEmpty()) return Collections.emptySet(); + Set<String> result = new LinkedHashSet<>(vars.size()); + for (VariableExpression ve : vars) { + result.add(ve.getName()); + } + return result; + } + + /** + * Analyses {@code expression} for definite {@code instanceof} pattern bindings. + * + * @param expression a boolean condition (may be a {@link BooleanExpression} wrapper) + * @return the true/false binding sets; never {@code null} + */ + public static InstanceofFlowBindings of(final Expression expression) { + if (expression == null) { + return EMPTY; + } + return analyse(expression); + } + + /** + * Returns {@code true} if {@code expression} contains any JEP 394 type + * pattern ({@code e instanceof T t} or {@code e !instanceof T t}), including + * nested subexpressions. Used to decide whether expression-statement + * CompileStack isolation is required. + * + * @param expression any expression; {@code null} yields {@code false} + */ + public static boolean containsPattern(final Expression expression) { + if (expression == null) return false; + boolean[] found = {false}; + expression.visit(new CodeVisitorSupport() { + @Override + public void visitBinaryExpression(final BinaryExpression be) { + if (found[0]) return; + int op = be.getOperation().getType(); + if ((op == Types.KEYWORD_INSTANCEOF || op == Types.COMPARE_NOT_INSTANCEOF) + && isTypePattern(be.getRightExpression())) { + found[0] = true; + return; + } + super.visitBinaryExpression(be); + } + }); + return found[0]; + } + + private static boolean isTypePattern(final Expression right) { + return right instanceof DeclarationExpression decl + && !decl.isMultipleAssignmentDeclaration() + && decl.getVariableExpression() != null; + } + + private static InstanceofFlowBindings analyse(final Expression expression) { + Expression expr = expression; + + // Unwrap BooleanExpression wrappers; NotExpression is handled below so that + // nested negations compose correctly. + while (expr instanceof BooleanExpression && !(expr instanceof NotExpression)) { + expr = ((BooleanExpression) expr).getExpression(); + } + + if (expr instanceof NotExpression not) { + return analyse(not.getExpression()).negated(); + } + + if (expr instanceof BinaryExpression binary) { + int op = binary.getOperation().getType(); + if (op == Types.KEYWORD_INSTANCEOF) { + return ofInstanceof(binary); + } + if (op == Types.COMPARE_NOT_INSTANCEOF) { + // AST may still carry !instanceof before codegen rewrites it to !(… instanceof …). + return ofInstanceof(binary).negated(); + } + if (op == Types.LOGICAL_AND) { + InstanceofFlowBindings left = analyse(binary.getLeftExpression()); + InstanceofFlowBindings right = analyse(binary.getRightExpression()); + // True path evaluates both; false path is not definite for either side alone. + return new InstanceofFlowBindings( + union(left.whenTrue, right.whenTrue), + List.of()); + } + if (op == Types.LOGICAL_OR) { + InstanceofFlowBindings left = analyse(binary.getLeftExpression()); + InstanceofFlowBindings right = analyse(binary.getRightExpression()); + // False path evaluates both; true path is not definite for either side alone. + return new InstanceofFlowBindings( + List.of(), + union(left.whenFalse, right.whenFalse)); + } + } Review Comment: There are two methods with deliberately different traversal strategies: **`containsPattern(Expression)` — intentionally traverses the full subtree.** This method answers a conservative question: *"does any descendant node in this expression tree contain a type pattern?"* It is used for expression-statement isolation (deciding whether the statement's value needs CompileStack sandboxing). Even a pattern buried arbitrarily deep (e.g. inside a method-call argument: `print(o instanceof String s)`) may have caused `evaluateInstanceof` to define a CompileStack slot. That worst-case question requires a full subtree scan. Short-circuit optimisation (`found[0]` early-return) keeps the typical cost proportional to the depth of the first match, not the full tree size. **`analyse(Expression)` — does *not* traverse the full tree.** It is a recursive structural descent that follows only the operators that propagate *definite-assignment* (`instanceof`, `!instanceof`, `&&`, `||`, `!`) and returns `EMPTY` conservatively for any other shape. For a typical condition `o instanceof String s && s.length() > 0` the descent visits exactly three nodes. Both methods now have explicit **"Why a full subtree walk?"** / **"Why not a full subtree walk?"** Javadoc paragraphs to document this distinction for future contributors. -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: [email protected] For queries about this service, please contact Infrastructure at: [email protected]
