/*
* Copyright (c) 1999, 2009, Oracle and/or its affiliates. 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. Oracle designates this
* particular file as subject to the "Classpath" exception as provided
* by Oracle 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 Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
* or visit www.oracle.com if you need additional information or have any
* questions.
*/
package com.sun.tools.javac.comp;
import com.sun.tools.javac.util.*;
import com.sun.tools.javac.util.List;
import com.sun.tools.javac.code.*;
import com.sun.tools.javac.code.Type.*;
import com.sun.tools.javac.code.Type.ForAll.ConstraintKind;
import com.sun.tools.javac.code.Symbol.*;
import com.sun.tools.javac.util.JCDiagnostic;
import static com.sun.tools.javac.code.TypeTags.*;
/** Helper class for type parameter inference, used by the attribution phase.
*
* <p><b>This is NOT part of any supported API.
* 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 Infer {
protected static final Context.Key<Infer> inferKey =
new Context.Key<Infer>();
/** A value for prototypes that admit any type, including polymorphic ones. */
public static final Type anyPoly = new Type(NONE, null);
Symtab syms;
Types types;
Check chk;
Resolve rs;
JCDiagnostic.Factory diags;
public static Infer instance(Context context) {
Infer instance = context.get(inferKey);
if (instance == null)
instance = new Infer(context);
return instance;
}
protected Infer(Context context) {
context.put(inferKey, this);
syms = Symtab.instance(context);
types = Types.instance(context);
rs = Resolve.instance(context);
chk = Check.instance(context);
diags = JCDiagnostic.Factory.instance(context);
ambiguousNoInstanceException =
new NoInstanceException(true, diags);
unambiguousNoInstanceException =
new NoInstanceException(false, diags);
invalidInstanceException =
new InvalidInstanceException(diags);
}
public static class InferenceException extends RuntimeException {
private static final long serialVersionUID = 0;
JCDiagnostic diagnostic;
JCDiagnostic.Factory diags;
InferenceException(JCDiagnostic.Factory diags) {
this.diagnostic = null;
this.diags = diags;
}
InferenceException setMessage(String key, Object... args) {
this.diagnostic = diags.fragment(key, args);
return this;
}
public JCDiagnostic getDiagnostic() {
return diagnostic;
}
}
public static class NoInstanceException extends InferenceException {
private static final long serialVersionUID = 1;
boolean isAmbiguous; // exist several incomparable best instances?
NoInstanceException(boolean isAmbiguous, JCDiagnostic.Factory diags) {
super(diags);
this.isAmbiguous = isAmbiguous;
}
}
public static class InvalidInstanceException extends InferenceException {
private static final long serialVersionUID = 2;
InvalidInstanceException(JCDiagnostic.Factory diags) {
super(diags);
}
}
private final NoInstanceException ambiguousNoInstanceException;
private final NoInstanceException unambiguousNoInstanceException;
private final InvalidInstanceException invalidInstanceException;
/***************************************************************************
* Auxiliary type values and classes
***************************************************************************/
/** A mapping that turns type variables into undetermined type variables.
*/
Mapping fromTypeVarFun = new Mapping("fromTypeVarFun") {
public Type apply(Type t) {
if (t.tag == TYPEVAR) return new UndetVar(t);
else return t.map(this);
}
};
/** A mapping that returns its type argument with every UndetVar replaced
* by its `inst' field. Throws a NoInstanceException
* if this not possible because an `inst' field is null.
* Note: mutually referring undertvars will be left uninstantiated
* (that is, they will be replaced by the underlying type-variable).
*/
Mapping getInstFun = new Mapping("getInstFun") {
public Type apply(Type t) {
switch (t.tag) {
case UNKNOWN:
throw ambiguousNoInstanceException
.setMessage("undetermined.type");
case UNDETVAR:
UndetVar that = (UndetVar) t;
if (that.inst == null)
throw ambiguousNoInstanceException
.setMessage("type.variable.has.undetermined.type",
that.qtype);
return isConstraintCyclic(that) ?
that.qtype :
apply(that.inst);
default:
return t.map(this);
}
}
private boolean isConstraintCyclic(UndetVar uv) {
Types.UnaryVisitor<Boolean> constraintScanner =
new Types.UnaryVisitor<Boolean>() {
List<Type> seen = List.nil();
Boolean visit(List<Type> ts) {
for (Type t : ts) {
if (visit(t)) return true;
}
return false;
}
public Boolean visitType(Type t, Void ignored) {
return false;
}
@Override
public Boolean visitClassType(ClassType t, Void ignored) {
if (t.isCompound()) {
return visit(types.supertype(t)) ||
visit(types.interfaces(t));
} else {
return visit(t.getTypeArguments());
}
}
@Override
public Boolean visitWildcardType(WildcardType t, Void ignored) {
return visit(t.type);
}
@Override
public Boolean visitUndetVar(UndetVar t, Void ignored) {
if (seen.contains(t)) {
return true;
} else {
seen = seen.prepend(t);
return visit(t.inst);
}
}
};
return constraintScanner.visit(uv);
}
};
/***************************************************************************
* Mini/Maximization of UndetVars
***************************************************************************/
/** Instantiate undetermined type variable to its minimal upper bound.
* Throw a NoInstanceException if this not possible.
*/
void maximizeInst(UndetVar that, Warner warn) throws NoInstanceException {
if (that.inst == null) {
if (that.hibounds.isEmpty())
that.inst = syms.objectType;
else if (that.hibounds.tail.isEmpty())
that.inst = that.hibounds.head;
else
that.inst = types.glb(that.hibounds);
}
if (that.inst == null ||
that.inst.isErroneous())
throw ambiguousNoInstanceException
.setMessage("no.unique.maximal.instance.exists",
that.qtype, that.hibounds);
}
//where
private boolean isSubClass(Type t, final List<Type> ts) {
t = t.baseType();
if (t.tag == TYPEVAR) {
List<Type> bounds = types.getBounds((TypeVar)t);
for (Type s : ts) {
if (!types.isSameType(t, s.baseType())) {
for (Type bound : bounds) {
if (!isSubClass(bound, List.of(s.baseType())))
return false;
}
}
}
} else {
for (Type s : ts) {
if (!t.tsym.isSubClass(s.baseType().tsym, types))
return false;
}
}
return true;
}
/** Instantiate undetermined type variable to the lub of all its lower bounds.
* Throw a NoInstanceException if this not possible.
*/
void minimizeInst(UndetVar that, Warner warn) throws NoInstanceException {
if (that.inst == null) {
if (that.lobounds.isEmpty())
that.inst = syms.botType;
else if (that.lobounds.tail.isEmpty())
that.inst = that.lobounds.head.isPrimitive() ? syms.errType : that.lobounds.head;
else {
that.inst = types.lub(that.lobounds);
}
if (that.inst == null || that.inst.tag == ERROR)
throw ambiguousNoInstanceException
.setMessage("no.unique.minimal.instance.exists",
that.qtype, that.lobounds);
// VGJ: sort of inlined maximizeInst() below. Adding
// bounds can cause lobounds that are above hibounds.
if (that.hibounds.isEmpty())
return;
Type hb = null;
if (that.hibounds.tail.isEmpty())
hb = that.hibounds.head;
else for (List<Type> bs = that.hibounds;
bs.nonEmpty() && hb == null;
bs = bs.tail) {
if (isSubClass(bs.head, that.hibounds))
hb = types.fromUnknownFun.apply(bs.head);
}
if (hb == null ||
!types.isSubtypeUnchecked(hb, that.hibounds, warn) ||
!types.isSubtypeUnchecked(that.inst, hb, warn))
throw ambiguousNoInstanceException;
}
}
/***************************************************************************
* Exported Methods
***************************************************************************/
/** Try to instantiate expression type `that' to given type `to'.
* If a maximal instantiation exists which makes this type
* a subtype of type `to', return the instantiated type.
* If no instantiation exists, or if several incomparable
* best instantiations exist throw a NoInstanceException.
*/
public Type instantiateExpr(ForAll that,
Type to,
Warner warn) throws InferenceException {
List<Type> undetvars = Type.map(that.tvars, fromTypeVarFun);
for (List<Type> l = undetvars; l.nonEmpty(); l = l.tail) {
UndetVar uv = (UndetVar) l.head;
TypeVar tv = (TypeVar)uv.qtype;
ListBuffer<Type> hibounds = new ListBuffer<Type>();
for (Type t : that.getConstraints(tv, ConstraintKind.EXTENDS)) {
hibounds.append(types.subst(t, that.tvars, undetvars));
}
List<Type> inst = that.getConstraints(tv, ConstraintKind.EQUAL);
if (inst.nonEmpty() && inst.head.tag != BOT) {
uv.inst = inst.head;
}
uv.hibounds = hibounds.toList();
}
Type qtype1 = types.subst(that.qtype, that.tvars, undetvars);
if (!types.isSubtype(qtype1, to)) {
throw unambiguousNoInstanceException
.setMessage("no.conforming.instance.exists",
that.tvars, that.qtype, to);
}
for (List<Type> l = undetvars; l.nonEmpty(); l = l.tail)
maximizeInst((UndetVar) l.head, warn);
// System.out.println(" = " + qtype1.map(getInstFun));//DEBUG
// check bounds
List<Type> targs = Type.map(undetvars, getInstFun);
if (Type.containsAny(targs, that.tvars)) {
//replace uninferred type-vars
targs = types.subst(targs,
that.tvars,
instaniateAsUninferredVars(undetvars, that.tvars));
}
return chk.checkType(warn.pos(), that.inst(targs, types), to);
}
//where
private List<Type> instaniateAsUninferredVars(List<Type> undetvars, List<Type> tvars) {
ListBuffer<Type> new_targs = ListBuffer.lb();
//step 1 - create syntethic captured vars
for (Type t : undetvars) {
UndetVar uv = (UndetVar)t;
Type newArg = new CapturedType(t.tsym.name, t.tsym, uv.inst, syms.botType, null);
new_targs = new_targs.append(newArg);
}
//step 2 - replace synthetic vars in their bounds
for (Type t : new_targs.toList()) {
CapturedType ct = (CapturedType)t;
ct.bound = types.subst(ct.bound, tvars, new_targs.toList());
WildcardType wt = new WildcardType(ct.bound, BoundKind.EXTENDS, syms.boundClass);
ct.wildcard = wt;
}
return new_targs.toList();
}
/** Instantiate method type `mt' by finding instantiations of
* `tvars' so that method can be applied to `argtypes'.
*/
public Type instantiateMethod(final Env<AttrContext> env,
List<Type> tvars,
MethodType mt,
final Symbol msym,
final List<Type> argtypes,
final boolean allowBoxing,
final boolean useVarargs,
final Warner warn) throws InferenceException {
//-System.err.println("instantiateMethod(" + tvars + ", " + mt + ", " + argtypes + ")"); //DEBUG
List<Type> undetvars = Type.map(tvars, fromTypeVarFun);
List<Type> formals = mt.argtypes;
//need to capture exactly once - otherwise subsequent
//applicability checks might fail
final List<Type> capturedArgs = types.capture(argtypes);
List<Type> actuals = capturedArgs;
List<Type> actualsNoCapture = argtypes;
// instantiate all polymorphic argument types and
// set up lower bounds constraints for undetvars
Type varargsFormal = useVarargs ? formals.last() : null;
while (actuals.nonEmpty() && formals.head != varargsFormal) {
Type formal = formals.head;
Type actual = actuals.head.baseType();
Type actualNoCapture = actualsNoCapture.head.baseType();
if (actual.tag == FORALL)
actual = instantiateArg((ForAll)actual, formal, tvars, warn);
Type undetFormal = types.subst(formal, tvars, undetvars);
boolean works = allowBoxing
? types.isConvertible(actual, undetFormal, warn)
: types.isSubtypeUnchecked(actual, undetFormal, warn);
if (!works) {
throw unambiguousNoInstanceException
.setMessage("no.conforming.assignment.exists",
tvars, actualNoCapture, formal);
}
formals = formals.tail;
actuals = actuals.tail;
actualsNoCapture = actualsNoCapture.tail;
}
if (formals.head != varargsFormal || // not enough args
!useVarargs && actuals.nonEmpty()) { // too many args
// argument lists differ in length
throw unambiguousNoInstanceException
.setMessage("arg.length.mismatch");
}
// for varargs arguments as well
if (useVarargs) {
Type elemType = types.elemtype(varargsFormal);
Type elemUndet = types.subst(elemType, tvars, undetvars);
while (actuals.nonEmpty()) {
Type actual = actuals.head.baseType();
Type actualNoCapture = actualsNoCapture.head.baseType();
if (actual.tag == FORALL)
actual = instantiateArg((ForAll)actual, elemType, tvars, warn);
boolean works = types.isConvertible(actual, elemUndet, warn);
if (!works) {
throw unambiguousNoInstanceException
.setMessage("no.conforming.assignment.exists",
tvars, actualNoCapture, elemType);
}
actuals = actuals.tail;
actualsNoCapture = actualsNoCapture.tail;
}
}
// minimize as yet undetermined type variables
for (Type t : undetvars)
minimizeInst((UndetVar) t, warn);
/** Type variables instantiated to bottom */
ListBuffer<Type> restvars = new ListBuffer<Type>();
/** Undet vars instantiated to bottom */
final ListBuffer<Type> restundet = new ListBuffer<Type>();
/** Instantiated types or TypeVars if under-constrained */
ListBuffer<Type> insttypes = new ListBuffer<Type>();
/** Instantiated types or UndetVars if under-constrained */
ListBuffer<Type> undettypes = new ListBuffer<Type>();
for (Type t : undetvars) {
UndetVar uv = (UndetVar)t;
if (uv.inst.tag == BOT) {
restvars.append(uv.qtype);
restundet.append(uv);
insttypes.append(uv.qtype);
undettypes.append(uv);
uv.inst = null;
} else {
insttypes.append(uv.inst);
undettypes.append(uv.inst);
}
}
checkWithinBounds(tvars, undettypes.toList(), warn);
mt = (MethodType)types.subst(mt, tvars, insttypes.toList());
if (!restvars.isEmpty()) {
// if there are uninstantiated variables,
// quantify result type with them
final List<Type> inferredTypes = insttypes.toList();
final List<Type> all_tvars = tvars; //this is the wrong tvars
final MethodType mt2 = new MethodType(mt.argtypes, null, mt.thrown, syms.methodClass);
mt2.restype = new ForAll(restvars.toList(), mt.restype) {
@Override
public List<Type> getConstraints(TypeVar tv, ConstraintKind ck) {
for (Type t : restundet.toList()) {
UndetVar uv = (UndetVar)t;
if (uv.qtype == tv) {
switch (ck) {
case EXTENDS: return uv.hibounds.appendList(types.subst(types.getBounds(tv), all_tvars, inferredTypes));
case SUPER: return uv.lobounds;
case EQUAL: return uv.inst != null ? List.of(uv.inst) : List.<Type>nil();
}
}
}
return List.nil();
}
@Override
public Type inst(List<Type> inferred, Types types) throws NoInstanceException {
List<Type> formals = types.subst(mt2.argtypes, tvars, inferred);
if (!rs.argumentsAcceptable(capturedArgs, formals,
allowBoxing, useVarargs, warn)) {
// inferred method is not applicable
throw invalidInstanceException.setMessage("inferred.do.not.conform.to.params", formals, argtypes);
}
// check that inferred bounds conform to their bounds
checkWithinBounds(all_tvars,
types.subst(inferredTypes, tvars, inferred), warn);
if (useVarargs) {
chk.checkVararg(env.tree.pos(), formals, msym, env);
}
return super.inst(inferred, types);
}};
return mt2;
}
else if (!rs.argumentsAcceptable(capturedArgs, mt.getParameterTypes(), allowBoxing, useVarargs, warn)) {
// inferred method is not applicable
throw invalidInstanceException.setMessage("inferred.do.not.conform.to.params", mt.getParameterTypes(), argtypes);
}
else {
// return instantiated version of method type
return mt;
}
}
//where
/** Try to instantiate argument type `that' to given type `to'.
* If this fails, try to insantiate `that' to `to' where
* every occurrence of a type variable in `tvars' is replaced
* by an unknown type.
*/
private Type instantiateArg(ForAll that,
Type to,
List<Type> tvars,
Warner warn) throws InferenceException {
List<Type> targs;
try {
return instantiateExpr(that, to, warn);
} catch (NoInstanceException ex) {
Type to1 = to;
for (List<Type> l = tvars; l.nonEmpty(); l = l.tail)
to1 = types.subst(to1, List.of(l.head), List.of(syms.unknownType));
return instantiateExpr(that, to1, warn);
}
}
/** check that type parameters are within their bounds.
*/
void checkWithinBounds(List<Type> tvars,
List<Type> arguments,
Warner warn)
throws InvalidInstanceException {
for (List<Type> tvs = tvars, args = arguments;
tvs.nonEmpty();
tvs = tvs.tail, args = args.tail) {
if (args.head instanceof UndetVar) continue;
List<Type> bounds = types.subst(types.getBounds((TypeVar)tvs.head), tvars, arguments);
if (!types.isSubtypeUnchecked(args.head, bounds, warn))
throw invalidInstanceException
.setMessage("inferred.do.not.conform.to.bounds",
args.head, bounds);
}
}
}