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using System;
using System.Collections.Generic;
using System.Diagnostics.Contracts;
namespace Microsoft.Dafny
{
[ContractClass(typeof(IRewriterContracts))]
public interface IRewriter
{
void PreResolve(ModuleDefinition m);
void PostResolve(ModuleDefinition m);
}
[ContractClassFor(typeof(IRewriter))]
abstract class IRewriterContracts : IRewriter
{
public void PreResolve(ModuleDefinition m) {
Contract.Requires(m != null);
}
public void PostResolve(ModuleDefinition m) {
Contract.Requires(m != null);
}
}
public class AutoGeneratedToken : TokenWrapper
{
public AutoGeneratedToken(Boogie.IToken wrappedToken)
: base(wrappedToken)
{
Contract.Requires(wrappedToken != null);
}
}
/// <summary>
/// AutoContracts is an experimental feature that will fill much of the dynamic-frames boilerplate
/// into a class. From the user's perspective, what needs to be done is simply:
/// - mark the class with {:autocontracts}
/// - declare a function (or predicate) called Valid()
///
/// AutoContracts will then:
///
/// Declare:
/// ghost var Repr: set(object);
///
/// For function/predicate Valid(), insert:
/// reads this, Repr;
/// Into body of Valid(), insert (at the beginning of the body):
/// this in Repr && null !in Repr
/// and also insert, for every array-valued field A declared in the class:
/// (A != null ==> A in Repr) &&
/// and for every field F of a class type T where T has a field called Repr, also insert:
/// (F != null ==> F in Repr && F.Repr SUBSET Repr && this !in Repr)
/// Except, if A or F is declared with {:autocontracts false}, then the implication will not
/// be added.
///
/// For every constructor, add:
/// modifies this;
/// ensures Valid() && fresh(Repr - {this});
/// At the end of the body of the constructor, add:
/// Repr := {this};
/// if (A != null) { Repr := Repr + {A}; }
/// if (F != null) { Repr := Repr + {F} + F.Repr; }
///
/// For every method, add:
/// requires Valid();
/// modifies Repr;
/// ensures Valid() && fresh(Repr - old(Repr));
/// At the end of the body of the method, add:
/// if (A != null) { Repr := Repr + {A}; }
/// if (F != null) { Repr := Repr + {F} + F.Repr; }
/// </summary>
public class AutoContractsRewriter : IRewriter
{
public void PreResolve(ModuleDefinition m) {
foreach (var d in m.TopLevelDecls) {
bool sayYes = true;
if (d is ClassDecl && Attributes.ContainsBool(d.Attributes, "autocontracts", ref sayYes) && sayYes) {
ProcessClassPreResolve((ClassDecl)d);
}
}
}
void ProcessClassPreResolve(ClassDecl cl) {
// Add: ghost var Repr: set<object>;
// ...unless a field with that name is already present
if (!cl.Members.Exists(member => member is Field && member.Name == "Repr")) {
Type ty = new SetType(new ObjectType());
cl.Members.Add(new Field(new AutoGeneratedToken(cl.tok), "Repr", true, ty, null));
}
foreach (var member in cl.Members) {
bool sayYes = true;
if (Attributes.ContainsBool(member.Attributes, "autocontracts", ref sayYes) && !sayYes) {
continue;
}
Boogie.IToken tok = new AutoGeneratedToken(member.tok);
if (member is Function && member.Name == "Valid" && !member.IsStatic) {
var valid = (Function)member;
// reads this;
valid.Reads.Add(new FrameExpression(tok, new ThisExpr(tok), null));
// reads Repr;
valid.Reads.Add(new FrameExpression(tok, new FieldSelectExpr(tok, new ImplicitThisExpr(tok), "Repr"), null));
} else if (member is Constructor) {
var ctor = (Constructor)member;
// modifies this;
ctor.Mod.Expressions.Add(new FrameExpression(tok, new ImplicitThisExpr(tok), null));
// ensures Valid();
ctor.Ens.Insert(0, new MaybeFreeExpression(new FunctionCallExpr(tok, "Valid", new ImplicitThisExpr(tok), tok, new List<Expression>())));
// ensures fresh(Repr - {this});
var freshness = new FreshExpr(tok, new BinaryExpr(tok, BinaryExpr.Opcode.Sub,
new FieldSelectExpr(tok, new ImplicitThisExpr(tok), "Repr"),
new SetDisplayExpr(tok, new List<Expression>() { new ThisExpr(tok) })));
ctor.Ens.Insert(1, new MaybeFreeExpression(freshness));
} else if (member is Method && !member.IsStatic) {
var m = (Method)member;
// requires Valid();
m.Req.Insert(0, new MaybeFreeExpression(new FunctionCallExpr(tok, "Valid", new ImplicitThisExpr(tok), tok, new List<Expression>())));
// If this is a mutating method, we should also add a modifies clause and a postcondition, but we don't do that if it's
// a simple query method. However, we won't know if it's a simple query method until after resolution, so we'll add the
// rest of the spec then.
}
}
}
public void PostResolve(ModuleDefinition m) {
foreach (var d in m.TopLevelDecls) {
bool sayYes = true;
if (d is ClassDecl && Attributes.ContainsBool(d.Attributes, "autocontracts", ref sayYes) && sayYes) {
ProcessClassPostResolve((ClassDecl)d);
}
}
}
void ProcessClassPostResolve(ClassDecl cl) {
// Find all fields of a reference type, and make a note of whether or not the reference type has a Repr field.
// Also, find the Repr field and the function Valid in class "cl"
Field ReprField = null;
Function Valid = null;
var subobjects = new List<Tuple<Field, Field>>();
foreach (var member in cl.Members) {
var field = member as Field;
if (field != null) {
bool sayYes = true;
if (field.Name == "Repr") {
ReprField = field;
} else if (Attributes.ContainsBool(field.Attributes, "autocontracts", ref sayYes) && !sayYes) {
// ignore this field
} else if (field.Type is ObjectType) {
subobjects.Add(new Tuple<Field, Field>(field, null));
} else if (field.Type.IsRefType) {
var rcl = (ClassDecl)((UserDefinedType)field.Type).ResolvedClass;
Field rRepr = null;
foreach (var memb in rcl.Members) {
var f = memb as Field;
if (f != null && f.Name == "Repr") {
rRepr = f;
break;
}
}
subobjects.Add(new Tuple<Field, Field>(field, rRepr));
}
} else if (member is Function && member.Name == "Valid" && !member.IsStatic) {
var fn = (Function)member;
if (fn.Formals.Count == 0 && fn.ResultType is BoolType) {
Valid = fn;
}
}
}
Contract.Assert(ReprField != null); // we expect there to be a "Repr" field, since we added one in PreResolve
Boogie.IToken clTok = new AutoGeneratedToken(cl.tok);
Type ty = new UserDefinedType(clTok, cl.Name, cl, new List<Type>());
var self = new ThisExpr(clTok);
self.Type = ty;
var implicitSelf = new ImplicitThisExpr(clTok);
implicitSelf.Type = ty;
var Repr = new FieldSelectExpr(clTok, implicitSelf, "Repr");
Repr.Field = ReprField;
Repr.Type = ReprField.Type;
var cNull = new LiteralExpr(clTok);
cNull.Type = new ObjectType();
foreach (var member in cl.Members) {
bool sayYes = true;
if (Attributes.ContainsBool(member.Attributes, "autocontracts", ref sayYes) && !sayYes) {
continue;
}
Boogie.IToken tok = new AutoGeneratedToken(member.tok);
if (member is Function && member.Name == "Valid" && !member.IsStatic) {
var valid = (Function)member;
if (valid.IsGhost && valid.ResultType is BoolType) {
var c0 = BinBoolExpr(tok, BinaryExpr.ResolvedOpcode.InSet, self, Repr); // this in Repr
var c1 = BinBoolExpr(tok, BinaryExpr.ResolvedOpcode.NotInSet, cNull, Repr); // null !in Repr
var c = BinBoolExpr(tok, BinaryExpr.ResolvedOpcode.And, c0, c1);
foreach (var ff in subobjects) {
var F = new FieldSelectExpr(tok, implicitSelf, ff.Item1.Name);
F.Field = ff.Item1;
F.Type = ff.Item1.Type;
c0 = BinBoolExpr(tok, BinaryExpr.ResolvedOpcode.NeqCommon, F, cNull);
c1 = BinBoolExpr(tok, BinaryExpr.ResolvedOpcode.InSet, F, Repr);
if (ff.Item2 == null) {
// F != null ==> F in Repr (so, nothing else to do)
} else {
// F != null ==> F in Repr && F.Repr <= Repr && this !in F.Repr
var FRepr = new FieldSelectExpr(tok, F, ff.Item2.Name);
FRepr.Field = ff.Item2;
FRepr.Type = ff.Item2.Type;
var c2 = BinBoolExpr(tok, BinaryExpr.ResolvedOpcode.Subset, FRepr, Repr);
var c3 = BinBoolExpr(tok, BinaryExpr.ResolvedOpcode.NotInSet, self, FRepr);
c1 = BinBoolExpr(tok, BinaryExpr.ResolvedOpcode.And, c1, BinBoolExpr(tok, BinaryExpr.ResolvedOpcode.And, c2, c3));
}
c = BinBoolExpr(tok, BinaryExpr.ResolvedOpcode.And, c, BinBoolExpr(tok, BinaryExpr.ResolvedOpcode.Imp, c0, c1));
}
if (valid.Body == null) {
valid.Body = c;
} else {
valid.Body = BinBoolExpr(tok, BinaryExpr.ResolvedOpcode.And, c, valid.Body);
}
}
} else if (member is Constructor) {
var ctor = (Constructor)member;
if (ctor.Body == null) {
ctor.Body = new BlockStmt(tok, new List<Statement>());
}
// TODO: these assignments should be included on every return path
var bodyStatements = ((BlockStmt)ctor.Body).Body;
// Repr := {this};
var e = new SetDisplayExpr(tok, new List<Expression>() { self });
e.Type = new SetType(new ObjectType());
Statement s = new AssignStmt(tok, Repr, new ExprRhs(e));
s.IsGhost = true;
bodyStatements.Add(s);
AddSubobjectReprs(tok, subobjects, bodyStatements, self, implicitSelf, cNull, Repr);
} else if (member is Method && !member.IsStatic) {
var m = (Method)member;
if (Valid != null && !IsSimpleQueryMethod(m)) {
// modifies Repr;
m.Mod.Expressions.Add(new FrameExpression(Repr.tok, Repr, null));
// ensures Valid();
var valid = new FunctionCallExpr(tok, "Valid", implicitSelf, tok, new List<Expression>());
valid.Function = Valid;
valid.Type = Type.Bool;
m.Ens.Insert(0, new MaybeFreeExpression(valid));
// ensures fresh(Repr - old(Repr));
var e0 = new OldExpr(tok, Repr);
e0.Type = Repr.Type;
var e1 = new BinaryExpr(tok, BinaryExpr.Opcode.Sub, Repr, e0);
e1.ResolvedOp = BinaryExpr.ResolvedOpcode.SetDifference;
e1.Type = Repr.Type;
var freshness = new FreshExpr(tok, e1);
freshness.Type = Type.Bool;
m.Ens.Insert(1, new MaybeFreeExpression(freshness));
if (m.Body == null) {
m.Body = new BlockStmt(tok, new List<Statement>());
}
// TODO: these assignments should be included on every return path
var bodyStatements = ((BlockStmt)m.Body).Body;
AddSubobjectReprs(tok, subobjects, bodyStatements, self, implicitSelf, cNull, Repr);
}
}
}
}
void AddSubobjectReprs(Boogie.IToken tok, List<Tuple<Field, Field>> subobjects, List<Statement> bodyStatements,
Expression self, Expression implicitSelf, Expression cNull, Expression Repr) {
foreach (var ff in subobjects) {
var F = new FieldSelectExpr(tok, implicitSelf, ff.Item1.Name);
F.Field = ff.Item1;
F.Type = ff.Item1.Type;
Expression e = new SetDisplayExpr(tok, new List<Expression>() { F });
e.Type = new SetType(new ObjectType());
var rhs = new BinaryExpr(tok, BinaryExpr.Opcode.Add, Repr, e);
rhs.ResolvedOp = BinaryExpr.ResolvedOpcode.Union;
rhs.Type = Repr.Type;
if (ff.Item2 == null) {
// Repr := Repr + {F} (so, nothing else to do)
} else {
// Repr := Repr + {F} + F.Repr
var FRepr = new FieldSelectExpr(tok, F, ff.Item2.Name);
FRepr.Field = ff.Item2;
FRepr.Type = ff.Item2.Type;
rhs = new BinaryExpr(tok, BinaryExpr.Opcode.Add, rhs, FRepr);
rhs.ResolvedOp = BinaryExpr.ResolvedOpcode.Union;
rhs.Type = Repr.Type;
}
// Repr := Repr + ...;
Statement s = new AssignStmt(tok, Repr, new ExprRhs(rhs));
s.IsGhost = true;
// wrap if statement around s
e = BinBoolExpr(tok, BinaryExpr.ResolvedOpcode.NeqCommon, F, cNull);
var thn = new BlockStmt(tok, new List<Statement>() { s });
thn.IsGhost = true;
s = new IfStmt(tok, e, thn, null);
s.IsGhost = true;
// finally, add s to the body
bodyStatements.Add(s);
}
}
bool IsSimpleQueryMethod(Method m) {
// A simple query method has out parameters, its body has no effect other than to assign to them,
// and the postcondition does not explicitly mention the pre-state.
return m.Outs.Count != 0 && m.Body != null && LocalAssignsOnly(m.Body) &&
m.Ens.TrueForAll(mfe => !Translator.MentionsOldState(mfe.E));
}
bool LocalAssignsOnly(Statement s) {
Contract.Requires(s != null);
if (s is AssignStmt) {
var ss = (AssignStmt)s;
return ss.Lhs.Resolved is IdentifierExpr;
} else if (s is ConcreteUpdateStatement) {
var ss = (ConcreteUpdateStatement)s;
return ss.Lhss.TrueForAll(e => e.Resolved is IdentifierExpr);
} else if (s is CallStmt) {
return false;
} else {
foreach (var ss in s.SubStatements) {
if (!LocalAssignsOnly(ss)) {
return false;
}
}
}
return true;
}
public static BinaryExpr BinBoolExpr(Boogie.IToken tok, BinaryExpr.ResolvedOpcode rop, Expression e0, Expression e1) {
var p = new BinaryExpr(tok, BinaryExpr.ResolvedOp2SyntacticOp(rop), e0, e1);
p.ResolvedOp = rop;
p.Type = Type.Bool;
return p;
}
}
}
|