transtypes.java

是一款用JAVA 编写的编译器 具有很强的编译功能

/*
 * Copyright 1999-2006 Sun Microsystems, Inc.  All Rights Reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Sun designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Sun in the LICENSE file that accompanied this code.
 *
 * This code 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
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
 * CA 95054 USA or visit www.sun.com if you need additional information or
 * have any questions.
 */

package com.sun.tools.javac.comp;

import java.util.*;

import com.sun.tools.javac.code.*;
import com.sun.tools.javac.code.Symbol.*;
import com.sun.tools.javac.tree.*;
import com.sun.tools.javac.tree.JCTree.*;
import com.sun.tools.javac.util.*;
import com.sun.tools.javac.util.JCDiagnostic.DiagnosticPosition;
import com.sun.tools.javac.util.List;

import static com.sun.tools.javac.code.Flags.*;
import static com.sun.tools.javac.code.Kinds.*;
import static com.sun.tools.javac.code.TypeTags.*;

/** This pass translates Generic Java to conventional Java.
 *
 *  <p><b>This is NOT part of any API supported by Sun Microsystems.  If
 *  you write code that depends on this, you do so at your own risk.
 *  This code and its internal interfaces are subject to change or
 *  deletion without notice.</b>
 */
public class TransTypes extends TreeTranslator {
    /** The context key for the TransTypes phase. */
    protected static final Context.Key<TransTypes> transTypesKey =
        new Context.Key<TransTypes>();

    /** Get the instance for this context. */
    public static TransTypes instance(Context context) {
        TransTypes instance = context.get(transTypesKey);
        if (instance == null)
            instance = new TransTypes(context);
        return instance;
    }

    private Name.Table names;
    private Log log;
    private Symtab syms;
    private TreeMaker make;
    private Enter enter;
    private boolean allowEnums;
    private Types types;
    private final Resolve resolve;

    /**
     * Flag to indicate whether or not to generate bridge methods.
     * For pre-Tiger source there is no need for bridge methods, so it
     * can be skipped to get better performance for -source 1.4 etc.
     */
    private final boolean addBridges;

    protected TransTypes(Context context) {
        context.put(transTypesKey, this);
        names = Name.Table.instance(context);
        log = Log.instance(context);
        syms = Symtab.instance(context);
        enter = Enter.instance(context);
        overridden = new HashMap<MethodSymbol,MethodSymbol>();
        Source source = Source.instance(context);
        allowEnums = source.allowEnums();
        addBridges = source.addBridges();
        types = Types.instance(context);
        make = TreeMaker.instance(context);
        resolve = Resolve.instance(context);
    }

    /** A hashtable mapping bridge methods to the methods they override after
     *  type erasure.
     */
    Map<MethodSymbol,MethodSymbol> overridden;

    /** Construct an attributed tree for a cast of expression to target type,
     *  unless it already has precisely that type.
     *  @param tree    The expression tree.
     *  @param target  The target type.
     */
    JCExpression cast(JCExpression tree, Type target) {
        int oldpos = make.pos;
        make.at(tree.pos);
        if (!types.isSameType(tree.type, target)) {
            if (!resolve.isAccessible(env, target.tsym))
                resolve.logAccessError(env, tree, target);
            tree = make.TypeCast(make.Type(target), tree).setType(target);
        }
        make.pos = oldpos;
        return tree;
    }

    /** Construct an attributed tree to coerce an expression to some erased
     *  target type, unless the expression is already assignable to that type.
     *  If target type is a constant type, use its base type instead.
     *  @param tree    The expression tree.
     *  @param target  The target type.
     */
    JCExpression coerce(JCExpression tree, Type target) {
        Type btarget = target.baseType();
        if (tree.type.isPrimitive() == target.isPrimitive()) {
            return types.isAssignable(tree.type, btarget, Warner.noWarnings)
                ? tree
                : cast(tree, btarget);
        }
        return tree;
    }

    /** Given an erased reference type, assume this type as the tree's type.
     *  Then, coerce to some given target type unless target type is null.
     *  This operation is used in situations like the following:
     *
     *  class Cell<A> { A value; }
     *  ...
     *  Cell<Integer> cell;
     *  Integer x = cell.value;
     *
     *  Since the erasure of Cell.value is Object, but the type
     *  of cell.value in the assignment is Integer, we need to
     *  adjust the original type of cell.value to Object, and insert
     *  a cast to Integer. That is, the last assignment becomes:
     *
     *  Integer x = (Integer)cell.value;
     *
     *  @param tree       The expression tree whose type might need adjustment.
     *  @param erasedType The expression's type after erasure.
     *  @param target     The target type, which is usually the erasure of the
     *                    expression's original type.
     */
    JCExpression retype(JCExpression tree, Type erasedType, Type target) {
//      System.err.println("retype " + tree + " to " + erasedType);//DEBUG
        if (erasedType.tag > lastBaseTag) {
            if (target != null && target.isPrimitive())
                target = erasure(tree.type);
            tree.type = erasedType;
            if (target != null) return coerce(tree, target);
        }
        return tree;
    }

    /** Translate method argument list, casting each argument
     *  to its corresponding type in a list of target types.
     *  @param _args            The method argument list.
     *  @param parameters       The list of target types.
     *  @param varargsElement   The erasure of the varargs element type,
     *  or null if translating a non-varargs invocation
     */
    <T extends JCTree> List<T> translateArgs(List<T> _args,
                                           List<Type> parameters,
                                           Type varargsElement) {
        if (parameters.isEmpty()) return _args;
        List<T> args = _args;
        while (parameters.tail.nonEmpty()) {
            args.head = translate(args.head, parameters.head);
            args = args.tail;
            parameters = parameters.tail;
        }
        Type parameter = parameters.head;
        assert varargsElement != null || args.length() == 1;
        if (varargsElement != null) {
            while (args.nonEmpty()) {
                args.head = translate(args.head, varargsElement);
                args = args.tail;
            }
        } else {
            args.head = translate(args.head, parameter);
        }
        return _args;
    }

    /** Add a bridge definition and enter corresponding method symbol in
     *  local scope of origin.
     *
     *  @param pos     The source code position to be used for the definition.
     *  @param meth    The method for which a bridge needs to be added
     *  @param impl    That method's implementation (possibly the method itself)
     *  @param origin  The class to which the bridge will be added
     *  @param hypothetical
     *                 True if the bridge method is not strictly necessary in the
     *                 binary, but is represented in the symbol table to detect
     *                 erasure clashes.
     *  @param bridges The list buffer to which the bridge will be added
     */
    void addBridge(DiagnosticPosition pos,
                   MethodSymbol meth,
                   MethodSymbol impl,
                   ClassSymbol origin,
                   boolean hypothetical,
                   ListBuffer<JCTree> bridges) {
        make.at(pos);
        Type origType = types.memberType(origin.type, meth);
        Type origErasure = erasure(origType);

        // Create a bridge method symbol and a bridge definition without a body.
        Type bridgeType = meth.erasure(types);
        long flags = impl.flags() & AccessFlags | SYNTHETIC | BRIDGE;
        if (hypothetical) flags |= HYPOTHETICAL;
        MethodSymbol bridge = new MethodSymbol(flags,
                                               meth.name,
                                               bridgeType,
                                               origin);
        if (!hypothetical) {
            JCMethodDecl md = make.MethodDef(bridge, null);

            // The bridge calls this.impl(..), if we have an implementation
            // in the current class, super.impl(...) otherwise.
            JCExpression receiver = (impl.owner == origin)
                ? make.This(origin.erasure(types))
                : make.Super(types.supertype(origin.type).tsym.erasure(types), origin);

            // The type returned from the original method.
            Type calltype = erasure(impl.type.getReturnType());

            // Construct a call of  this.impl(params), or super.impl(params),
            // casting params and possibly results as needed.
            JCExpression call =
                make.Apply(
                           null,
                           make.Select(receiver, impl).setType(calltype),
                           translateArgs(make.Idents(md.params), origErasure.getParameterTypes(), null))
                .setType(calltype);
            JCStatement stat = (origErasure.getReturnType().tag == VOID)
                ? make.Exec(call)
                : make.Return(coerce(call, bridgeType.getReturnType()));
            md.body = make.Block(0, List.of(stat));

            // Add bridge to `bridges' buffer
            bridges.append(md);
        }

        // Add bridge to scope of enclosing class and `overridden' table.
        origin.members().enter(bridge);
        overridden.put(bridge, meth);
    }

    /** Add bridge if given symbol is a non-private, non-static member
     *  of the given class, which is either defined in the class or non-final
     *  inherited, and one of the two following conditions holds:
     *  1. The method's type changes in the given class, as compared to the
     *     class where the symbol was defined, (in this case
     *     we have extended a parameterized class with non-trivial parameters).
     *  2. The method has an implementation with a different erased return type.
     *     (in this case we have used co-variant returns).