javaparser-core/src/main/java/com/github/javaparser/ast/validator/chunks/VarValidator.java

package com.github.javaparser.ast.validator.chunks;

import com.github.javaparser.ast.Node;
import com.github.javaparser.ast.body.Parameter;
import com.github.javaparser.ast.body.VariableDeclarator;
import com.github.javaparser.ast.expr.ArrayCreationExpr;
import com.github.javaparser.ast.expr.LambdaExpr;
import com.github.javaparser.ast.expr.NullLiteralExpr;
import com.github.javaparser.ast.expr.VariableDeclarationExpr;
import com.github.javaparser.ast.stmt.ExpressionStmt;
import com.github.javaparser.ast.stmt.ForStmt;
import com.github.javaparser.ast.stmt.ForeachStmt;
import com.github.javaparser.ast.type.VarType;
import com.github.javaparser.ast.validator.ProblemReporter;
import com.github.javaparser.ast.validator.TypedValidator;

import java.util.Optional;

public class VarValidator implements TypedValidator<VarType> {
    private boolean varAllowedInLambdaParameters;

    public VarValidator(boolean varAllowedInLambdaParameters) {
        this.varAllowedInLambdaParameters = varAllowedInLambdaParameters;
    }

    @Override
    public void accept(VarType node, ProblemReporter reporter) {
        // All allowed locations are within a VariableDeclaration inside a VariableDeclarationExpr inside something else.
        Optional<VariableDeclarator> variableDeclarator = node.findParent(VariableDeclarator.class);
        if (!variableDeclarator.isPresent()) {
            // Java 11's var in lambda's
            if (varAllowedInLambdaParameters) {
                boolean valid = node
                        .findParent(Parameter.class)
                        .flatMap(Node::getParentNode)
                        .map((Node p) -> p instanceof LambdaExpr).orElse(false);
                if (valid) {
                    return;
                }
            }
            reportIllegalPosition(node, reporter);
            return;
        }
        variableDeclarator.ifPresent(vd -> {
            Optional<Node> variableDeclarationExpr = vd.getParentNode();
            if (!variableDeclarationExpr.isPresent()) {
                reportIllegalPosition(node, reporter);
                return;
            }
            variableDeclarationExpr.ifPresent(vdeNode -> {
                if (!(vdeNode instanceof VariableDeclarationExpr)) {
                    reportIllegalPosition(node, reporter);
                    return;
                }
                VariableDeclarationExpr vde = (VariableDeclarationExpr) vdeNode;
                if (vde.getVariables().size() > 1) {
                    reporter.report(vde, "\"var\" only takes a single variable.");
                }
                Optional<Node> container = vdeNode.getParentNode();
                if (!container.isPresent()) {
                    reportIllegalPosition(node, reporter);
                    return;
                }
                container.ifPresent(c -> {
                    boolean positionIsFine = c instanceof ForStmt || c instanceof ForeachStmt || c instanceof ExpressionStmt;
                    if (!positionIsFine) {
                        reportIllegalPosition(node, reporter);
                    }
                    // A local variable declaration ends up inside an ExpressionStmt.
                    if (c instanceof ExpressionStmt) {
                        if (!vd.getInitializer().isPresent()) {
                            reporter.report(node, "\"var\" needs an initializer.");
                        }
                        vd.getInitializer().ifPresent(initializer -> {
                            if (initializer instanceof NullLiteralExpr) {
                                reporter.report(node, "\"var\" cannot infer type from just null.");
                            }
                            if (initializer instanceof ArrayCreationExpr) {
                                reporter.report(node, "\"var\" cannot infer array types.");
                            }
                        });

                    }
                });
            });
        });

    }

    private void reportIllegalPosition(VarType n, ProblemReporter reporter) {
        reporter.report(n, "\"var\" is not allowed here.");
    }
}