/exp/types/staging: expression and statement type checking

Still lots of pieces missing, but basic framework working.
Lots of tests.

R=rsc
CC=golang-dev
https://golang.org/cl/6594054

src/pkg/exp/types/staging/conversions.go

@@ -0,0 +1,39 @@
+// Copyright 2012 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// This file implements typechecking of conversions.
+
+package types
+
+import (
+	"go/ast"
+)
+
+// conversion typechecks the type conversion conv to type typ. iota is the current
+// value of iota or -1 if iota doesn't have a value in the current context. The result
+// of the conversion is returned via x. If the conversion has type errors, the returned
+// x is marked as invalid (x.mode == invalid).
+//
+func (check *checker) conversion(x *operand, conv *ast.CallExpr, typ Type, iota int) {
+	// all conversions have one argument
+	if len(conv.Args) != 1 {
+		check.invalidOp(conv.Pos(), "%s conversion requires exactly one argument", conv)
+		goto Error
+	}
+
+	// evaluate argument
+	check.expr(x, conv.Args[0], nil, iota)
+	if x.mode == invalid {
+		goto Error
+	}
+
+	// TODO(gri) fix this - implement all checks and constant evaluation
+	x.mode = value
+	x.expr = conv
+	x.typ = typ
+	return
+
+Error:
+	x.mode = invalid
+}

src/pkg/exp/types/staging/expr.go

@@ -0,0 +1,793 @@
+// Copyright 2012 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// This file implements typechecking of expressions.
+
+package types
+
+import (
+	"go/ast"
+	"go/token"
+	"strconv"
+)
+
+// TODO(gri)
+// - don't print error messages referring to invalid types (they are likely spurious errors)
+// - simplify invalid handling: maybe just use Typ[Invalid] as marker, get rid of invalid Mode for values?
+
+func (check *checker) tag(field *ast.Field) string {
+	if t := field.Tag; t != nil {
+		assert(t.Kind == token.STRING)
+		if tag, err := strconv.Unquote(t.Value); err == nil {
+			return tag
+		}
+		check.invalidAST(t.Pos(), "incorrect tag syntax: %q", t.Value)
+	}
+	return ""
+}
+
+// collectFields collects interface methods (tok = token.INTERFACE), and function arguments/results (tok = token.FUNC).
+func (check *checker) collectFields(tok token.Token, list *ast.FieldList, cycleOk bool) (fields ObjList, tags []string, isVariadic bool) {
+	if list != nil {
+		for _, field := range list.List {
+			ftype := field.Type
+			if t, ok := ftype.(*ast.Ellipsis); ok {
+				ftype = t.Elt
+				isVariadic = true
+			}
+			typ := check.typ(ftype, cycleOk)
+			tag := check.tag(field)
+			if len(field.Names) > 0 {
+				// named fields
+				for _, name := range field.Names {
+					obj := name.Obj
+					obj.Type = typ
+					fields = append(fields, obj)
+					if tok == token.STRUCT {
+						tags = append(tags, tag)
+					}
+				}
+			} else {
+				// anonymous field
+				switch tok {
+				case token.FUNC:
+					obj := ast.NewObj(ast.Var, "")
+					obj.Type = typ
+					fields = append(fields, obj)
+				case token.INTERFACE:
+					utyp := underlying(typ)
+					if typ, ok := utyp.(*Interface); ok {
+						// TODO(gri) This is not good enough. Check for double declarations!
+						fields = append(fields, typ.Methods...)
+					} else if utyp != Typ[Invalid] {
+						// if utyp is invalid, don't complain (the root cause was reported before)
+						check.errorf(ftype.Pos(), "interface contains embedded non-interface type")
+					}
+				default:
+					panic("unreachable")
+				}
+			}
+		}
+	}
+	return
+}
+
+func (check *checker) collectStructFields(list *ast.FieldList, cycleOk bool) (fields []*StructField) {
+	if list == nil {
+		return
+	}
+	for _, f := range list.List {
+		typ := check.typ(f.Type, cycleOk)
+		tag := check.tag(f)
+		if len(f.Names) > 0 {
+			// named fields
+			for _, name := range f.Names {
+				fields = append(fields, &StructField{name.Name, typ, tag, false})
+			}
+		} else {
+			// anonymous field
+			switch t := deref(typ).(type) {
+			case *Basic:
+				fields = append(fields, &StructField{t.Name, t, tag, true})
+			case *NamedType:
+				fields = append(fields, &StructField{t.Obj.Name, t, tag, true})
+			default:
+				if typ != Typ[Invalid] {
+					check.errorf(f.Type.Pos(), "invalid anonymous field type %s", typ)
+				}
+			}
+		}
+	}
+	return
+}
+
+type opPredicates map[token.Token]func(Type) bool
+
+var unaryOpPredicates = opPredicates{
+	token.ADD:   isNumeric,
+	token.SUB:   isNumeric,
+	token.XOR:   isInteger,
+	token.NOT:   isBoolean,
+	token.ARROW: func(typ Type) bool { t, ok := underlying(typ).(*Chan); return ok && t.Dir&ast.RECV != 0 },
+}
+
+func (check *checker) op(m opPredicates, x *operand, op token.Token) bool {
+	if pred := m[op]; pred != nil {
+		if !pred(x.typ) {
+			// TODO(gri) better error message for <-x where x is a send-only channel
+			//           (<- is defined but not permitted). Special-case here or
+			//           handle higher up.
+			check.invalidOp(x.pos(), "operator %s not defined for %s", op, x)
+			return false
+		}
+	} else {
+		check.invalidAST(x.pos(), "unknown operator %s", op)
+		return false
+	}
+	return true
+}
+
+func (check *checker) unary(x *operand, op token.Token) {
+	if op == token.AND {
+		// TODO(gri) need to check for composite literals, somehow (they are not variables, in general)
+		if x.mode != variable {
+			check.invalidOp(x.pos(), "cannot take address of %s", x)
+			x.mode = invalid
+			return
+		}
+		x.typ = &Pointer{Base: x.typ}
+		return
+	}
+
+	if !check.op(unaryOpPredicates, x, op) {
+		x.mode = invalid
+		return
+	}
+
+	if x.mode == constant {
+		switch op {
+		case token.ADD:
+			// nothing to do
+		case token.SUB:
+			x.val = binaryOpConst(zeroConst, x.val, token.SUB, false)
+		case token.XOR:
+			x.val = binaryOpConst(minusOneConst, x.val, token.XOR, false)
+		case token.NOT:
+			x.val = !x.val.(bool)
+		default:
+			unreachable()
+		}
+		// Typed constants must be representable in
+		// their type after each constant operation.
+		check.isRepresentable(x, x.typ.(*Basic))
+		return
+	}
+
+	x.mode = value
+}
+
+func isShift(op token.Token) bool {
+	return op == token.SHL || op == token.SHR
+}
+
+func isComparison(op token.Token) bool {
+	// Note: tokens are not ordered well to make this much easier
+	switch op {
+	case token.EQL, token.NEQ, token.LSS, token.LEQ, token.GTR, token.GEQ:
+		return true
+	}
+	return false
+}
+
+// isRepresentable checks that a constant operand is representable in the given type.
+func (check *checker) isRepresentable(x *operand, typ *Basic) {
+	if x.mode != constant || isUntyped(typ) {
+		return
+	}
+
+	if !isRepresentableConst(x.val, typ.Kind) {
+		var msg string
+		if isNumeric(x.typ) && isNumeric(typ) {
+			msg = "%s overflows %s"
+		} else {
+			msg = "cannot convert %s to %s"
+		}
+		check.errorf(x.pos(), msg, x, typ)
+		x.mode = invalid
+	}
+}
+
+// convertUntyped attempts to set the type of an untyped value to the target type.
+func (check *checker) convertUntyped(x *operand, target Type) {
+	if x.mode == invalid || !isUntyped(x.typ) {
+		return
+	}
+
+	// TODO(gri) Sloppy code - clean up. This function is central
+	//           to assignment and expression checking.
+
+	if isUntyped(target) {
+		// both x and target are untyped
+		xkind := x.typ.(*Basic).Kind
+		tkind := target.(*Basic).Kind
+		if isNumeric(x.typ) && isNumeric(target) {
+			if xkind < tkind {
+				x.typ = target
+			}
+		} else if xkind != tkind {
+			check.errorf(x.pos(), "cannot convert %s to %s", x, target)
+			x.mode = invalid // avoid spurious errors
+		}
+		return
+	}
+
+	// typed target
+	switch t := underlying(target).(type) {
+	case *Basic:
+		check.isRepresentable(x, t)
+
+	case *Pointer, *Signature, *Interface, *Slice, *Map, *Chan:
+		if x.typ != Typ[UntypedNil] {
+			check.errorf(x.pos(), "cannot convert %s to %s", x, target)
+			x.mode = invalid
+		}
+	}
+
+	x.typ = target
+}
+
+func (check *checker) comparison(x, y *operand, op token.Token) {
+	// TODO(gri) deal with interface vs non-interface comparison
+
+	valid := false
+	if x.isAssignable(y.typ) || y.isAssignable(x.typ) {
+		switch op {
+		case token.EQL, token.NEQ:
+			valid = isComparable(x.typ)
+		case token.LSS, token.LEQ, token.GTR, token.GEQ:
+			valid = isOrdered(y.typ)
+		default:
+			unreachable()
+		}
+	}
+
+	if !valid {
+		check.invalidOp(x.pos(), "cannot compare %s and %s", x, y)
+		x.mode = invalid
+		return
+	}
+
+	if x.mode == constant && y.mode == constant {
+		x.val = compareConst(x.val, y.val, op)
+	} else {
+		x.mode = value
+	}
+
+	x.typ = Typ[UntypedBool]
+}
+
+// untyped lhs shift operands convert to the hint type
+// TODO(gri) shift hinting is not correct
+func (check *checker) shift(x, y *operand, op token.Token, hint Type) {
+	// The right operand in a shift expression must have unsigned integer type
+	// or be an untyped constant that can be converted to unsigned integer type.
+	if y.mode == constant && isUntyped(y.typ) {
+		if isRepresentableConst(y.val, UntypedInt) {
+			y.typ = Typ[UntypedInt]
+		}
+	}
+	if !isInteger(y.typ) || !isUnsigned(y.typ) && !isUntyped(y.typ) {
+		check.invalidOp(y.pos(), "shift count %s must be unsigned integer", y)
+		x.mode = invalid
+		return
+	}
+
+	// If the left operand of a non-constant shift expression is an untyped
+	// constant, the type of the constant is what it would be if the shift
+	// expression were replaced by its left operand alone; the type is int
+	// if it cannot be determined from the context (for instance, if the
+	// shift expression is an operand in a comparison against an untyped
+	// constant)
+	if x.mode == constant && isUntyped(x.typ) {
+		if y.mode == constant {
+			// constant shift - accept values of any (untyped) type
+			// as long as the value is representable as an integer
+			if isRepresentableConst(x.val, UntypedInt) {
+				x.typ = Typ[UntypedInt]
+			}
+		} else {
+			// non-constant shift
+			if hint != nil {
+				check.convertUntyped(x, hint)
+				if x.mode == invalid {
+					return
+				}
+			}
+		}
+	}
+
+	if !isInteger(x.typ) {
+		check.invalidOp(x.pos(), "shifted operand %s must be integer", x)
+		x.mode = invalid
+		return
+	}
+
+	if y.mode == constant {
+		const stupidShift = 1024
+		s, ok := y.val.(int64)
+		if !ok || s < 0 || s >= stupidShift {
+			check.invalidOp(y.pos(), "%s: stupid shift", y)
+			x.mode = invalid
+			return
+		}
+		if x.mode == constant {
+			x.val = shiftConst(x.val, uint(s), op)
+			return
+		}
+		x.mode = value
+	}
+
+	// x.mode, x.Typ are unchanged
+}
+
+var binaryOpPredicates = opPredicates{
+	token.ADD: func(typ Type) bool { return isNumeric(typ) || isString(typ) },
+	token.SUB: isNumeric,
+	token.MUL: isNumeric,
+	token.QUO: isNumeric,
+	token.REM: isInteger,
+
+	token.AND:     isInteger,
+	token.OR:      isInteger,
+	token.XOR:     isInteger,
+	token.AND_NOT: isInteger,
+
+	token.LAND: isBoolean,
+	token.LOR:  isBoolean,
+}
+
+func (check *checker) binary(x, y *operand, op token.Token, hint Type) {
+	if isShift(op) {
+		check.shift(x, y, op, hint)
+		return
+	}
+
+	check.convertUntyped(x, y.typ)
+	if x.mode == invalid {
+		return
+	}
+	check.convertUntyped(y, x.typ)
+	if y.mode == invalid {
+		x.mode = invalid
+		return
+	}
+
+	if isComparison(op) {
+		check.comparison(x, y, op)
+		return
+	}
+
+	if !isIdentical(x.typ, y.typ) {
+		check.invalidOp(x.pos(), "mismatched types %s and %s", x.typ, y.typ)
+		x.mode = invalid
+		return
+	}
+
+	if !check.op(binaryOpPredicates, x, op) {
+		x.mode = invalid
+		return
+	}
+
+	if (op == token.QUO || op == token.REM) && y.mode == constant && isZeroConst(y.val) {
+		check.invalidOp(y.pos(), "division by zero")
+		x.mode = invalid
+		return
+	}
+
+	if x.mode == constant && y.mode == constant {
+		x.val = binaryOpConst(x.val, y.val, op, isInteger(x.typ))
+		// Typed constants must be representable in
+		// their type after each constant operation.
+		check.isRepresentable(x, x.typ.(*Basic))
+		return
+	}
+
+	x.mode = value
+	// x.typ is unchanged
+}
+
+func (check *checker) index(x *operand, e ast.Expr, iota int) {
+	check.expr(x, e, nil, iota)
+	if !isInteger(x.typ) {
+		check.errorf(x.pos(), "array index %s must be integer", x)
+	}
+}
+
+func (check *checker) callRecord(x *operand) {
+	if x.mode != invalid {
+		check.mapf(x.expr, x.typ)
+	}
+}
+
+// expr typechecks expression e and initializes x with the expression
+// value or type. If an error occured, x.mode is set to invalid.
+// A hint != nil is used as operand type for untyped shifted operands;
+// iota >= 0 indicates that the expression is part of a constant declaration.
+// cycleOk indicates whether it is ok for a type expression to refer to itself.
+//
+func (check *checker) exprOrType(x *operand, e ast.Expr, hint Type, iota int, cycleOk bool) {
+	if check.mapf != nil {
+		defer check.callRecord(x)
+	}
+
+	switch e := e.(type) {
+	case *ast.BadExpr:
+		x.mode = invalid
+
+	case *ast.Ident:
+		if e.Name == "_" {
+			check.invalidOp(e.Pos(), "cannot use _ as value or type")
+			goto Error
+		}
+		obj := e.Obj
+		if obj == nil {
+			// unresolved identifier (error has been reported before)
+			goto Error
+		}
+		check.ident(e, cycleOk)
+		switch obj.Kind {
+		case ast.Bad:
+			goto Error
+		case ast.Pkg:
+			check.errorf(e.Pos(), "use of package %s not in selector", obj.Name)
+			goto Error
+		case ast.Con:
+			if obj.Data == nil {
+				goto Error // cycle detected
+			}
+			x.mode = constant
+			if obj == universeIota {
+				if iota < 0 {
+					check.invalidAST(e.Pos(), "cannot use iota outside constant declaration")
+					goto Error
+				}
+				x.val = int64(iota)
+			} else {
+				x.val = obj.Data
+			}
+		case ast.Typ:
+			x.mode = typexpr
+			if !cycleOk && underlying(obj.Type.(Type)) == nil {
+				check.errorf(obj.Pos(), "illegal cycle in declaration of %s", obj.Name)
+				x.expr = e
+				x.typ = Typ[Invalid]
+				return // don't goto Error - need x.mode == typexpr
+			}
+		case ast.Var:
+			x.mode = variable
+		case ast.Fun:
+			x.mode = value
+		default:
+			unreachable()
+		}
+		x.typ = obj.Type.(Type)
+
+	case *ast.BasicLit:
+		x.setConst(e.Kind, e.Value)
+		if x.mode == invalid {
+			check.invalidAST(e.Pos(), "invalid literal %v", e.Value)
+			goto Error
+		}
+
+	case *ast.FuncLit:
+		x.mode = value
+		x.typ = check.typ(e.Type, false)
+		check.stmt(e.Body)
+
+	case *ast.CompositeLit:
+		// TODO(gri)
+		//	- determine element type if nil
+		//	- deal with map elements
+		for _, e := range e.Elts {
+			var x operand
+			check.expr(&x, e, hint, iota)
+			// TODO(gri) check assignment compatibility to element type
+		}
+		x.mode = value // TODO(gri) composite literals are addressable
+
+	case *ast.ParenExpr:
+		check.exprOrType(x, e.X, hint, iota, cycleOk)
+
+	case *ast.SelectorExpr:
+		// If the identifier refers to a package, handle everything here
+		// so we don't need a "package" mode for operands: package names
+		// can only appear in qualified identifiers which are mapped to
+		// selector expressions.
+		if ident, ok := e.X.(*ast.Ident); ok {
+			if obj := ident.Obj; obj != nil && obj.Kind == ast.Pkg {
+				exp := obj.Data.(*ast.Scope).Lookup(e.Sel.Name)
+				if exp == nil {
+					check.errorf(e.Sel.Pos(), "cannot refer to unexported %s", e.Sel.Name)
+					goto Error
+				}
+				// simplified version of the code for *ast.Idents:
+				// imported objects are always fully initialized
+				switch exp.Kind {
+				case ast.Con:
+					assert(exp.Data != nil)
+					x.mode = constant
+					x.val = exp.Data
+				case ast.Typ:
+					x.mode = typexpr
+				case ast.Var:
+					x.mode = variable
+				case ast.Fun:
+					x.mode = value
+				default:
+					unreachable()
+				}
+				x.expr = e
+				x.typ = exp.Type.(Type)
+				return
+			}
+		}
+
+		// TODO(gri) lots of checks missing below - just raw outline
+		check.expr(x, e.X, hint, iota)
+		switch typ := x.typ.(type) {
+		case *Struct:
+			if fld := lookupField(typ, e.Sel.Name); fld != nil {
+				// TODO(gri) only variable if struct is variable 
+				x.mode = variable
+				x.expr = e
+				x.typ = fld.Type
+				return
+			}
+		case *Interface:
+			unimplemented()
+		case *NamedType:
+			unimplemented()
+		}
+		check.invalidOp(e.Pos(), "%s has no field or method %s", x.typ, e.Sel.Name)
+		goto Error
+
+	case *ast.IndexExpr:
+		var index operand
+		check.expr(x, e.X, hint, iota)
+		switch typ := underlying(x.typ).(type) {
+		case *Array:
+			check.index(&index, e.Index, iota)
+			if x.mode == constant {
+				// TODO(gri) range check
+			}
+			// TODO(gri) only variable if array is variable
+			x.mode = variable
+			x.typ = typ.Elt
+
+		case *Slice:
+			check.index(&index, e.Index, iota)
+			x.mode = variable
+			x.typ = typ.Elt
+
+		case *Map:
+			// TODO(gri) check index type
+			x.mode = variable
+			x.typ = typ.Elt
+
+		default:
+			check.invalidOp(e.Pos(), "cannot index %s", x.typ)
+			goto Error
+		}
+
+	case *ast.SliceExpr:
+		var lo, hi operand
+		check.expr(x, e.X, hint, iota)
+		if e.Low != nil {
+			check.index(&lo, e.Low, iota)
+		} else {
+			lo.mode = constant
+			lo.expr = nil // TODO(gri) should not use nil here
+			lo.typ = Typ[UntypedInt]
+			lo.val = zeroConst
+		}
+		if e.High != nil {
+			check.index(&hi, e.High, iota)
+		} else {
+			unimplemented()
+		}
+		switch typ := x.typ.(type) {
+		case *Array:
+			unimplemented()
+		case *Slice:
+			assert(x.mode == variable)
+			// x.typ does not change
+		case *Pointer:
+			if typ, ok := underlying(typ.Base).(*Array); ok {
+				// TODO(gri) array slice
+				_ = typ
+			}
+			unimplemented()
+		default:
+			check.invalidOp(e.Pos(), "cannot slice %s", x.typ)
+			goto Error
+		}
+
+	case *ast.TypeAssertExpr:
+		check.expr(x, e.X, hint, iota)
+		if _, ok := x.typ.(*Interface); !ok {
+			check.invalidOp(e.X.Pos(), "non-interface type %s in type assertion", x.typ)
+			// ok to continue
+		}
+		// TODO(gri) some type asserts are compile-time decidable
+		x.mode = valueok
+		x.expr = e
+		x.typ = check.typ(e.Type, false)
+
+	case *ast.CallExpr:
+		check.exprOrType(x, e.Fun, nil, iota, false)
+		if x.mode == typexpr {
+			check.conversion(x, e, x.typ, iota)
+
+		} else if sig, ok := underlying(x.typ).(*Signature); ok {
+			// check parameters
+			// TODO(gri) complete this
+			// - deal with various forms of calls
+			// - handle variadic calls
+			if len(sig.Params) == len(e.Args) {
+				var z, x operand
+				z.mode = variable
+				for i, arg := range e.Args {
+					z.expr = nil                      // TODO(gri) can we do better here?
+					z.typ = sig.Params[i].Type.(Type) // TODO(gri) should become something like checkObj(&z, ...) eventually
+					check.expr(&x, arg, z.typ, iota)
+					if x.mode == invalid {
+						goto Error
+					}
+					check.assignOperand(&z, &x)
+				}
+			}
+
+			// determine result
+			x.mode = value
+			if len(sig.Results) == 1 {
+				x.typ = sig.Results[0].Type.(Type)
+			} else {
+				// TODO(gri) change Signature representation to use tuples,
+				//           then this conversion is not required
+				list := make([]Type, len(sig.Results))
+				for i, obj := range sig.Results {
+					list[i] = obj.Type.(Type)
+				}
+				x.typ = &tuple{list: list}
+			}
+
+		} else if bin, ok := x.typ.(*builtin); ok {
+			check.builtin(x, e, bin, iota)
+
+		} else {
+			check.invalidOp(x.pos(), "cannot call non-function %s", x)
+			goto Error
+		}
+
+	case *ast.StarExpr:
+		check.exprOrType(x, e.X, hint, iota, true)
+		switch x.mode {
+		case novalue:
+			check.errorf(x.pos(), "%s used as value or type", x)
+			goto Error
+		case typexpr:
+			x.typ = &Pointer{Base: x.typ}
+		default:
+			if typ, ok := x.typ.(*Pointer); ok {
+				x.mode = variable
+				x.typ = typ.Base
+			} else {
+				check.invalidOp(x.pos(), "cannot indirect %s", x)
+				goto Error
+			}
+		}
+
+	case *ast.UnaryExpr:
+		check.expr(x, e.X, hint, iota)
+		check.unary(x, e.Op)
+
+	case *ast.BinaryExpr:
+		var y operand
+		check.expr(x, e.X, hint, iota)
+		check.expr(&y, e.Y, hint, iota)
+		check.binary(x, &y, e.Op, hint)
+
+	case *ast.KeyValueExpr:
+		unimplemented()
+
+	case *ast.ArrayType:
+		if e.Len != nil {
+			check.expr(x, e.Len, nil, 0)
+			if x.mode == invalid {
+				goto Error
+			}
+			var n int64 = -1
+			if x.mode == constant {
+				if i, ok := x.val.(int64); ok && i == int64(int(i)) {
+					n = i
+				}
+			}
+			if n < 0 {
+				check.errorf(e.Len.Pos(), "invalid array bound %s", e.Len)
+				// ok to continue
+				n = 0
+			}
+			x.typ = &Array{Len: n, Elt: check.typ(e.Elt, cycleOk)}
+		} else {
+			x.typ = &Slice{Elt: check.typ(e.Elt, true)}
+		}
+		x.mode = typexpr
+
+	case *ast.StructType:
+		x.mode = typexpr
+		x.typ = &Struct{Fields: check.collectStructFields(e.Fields, cycleOk)}
+
+	case *ast.FuncType:
+		params, _, isVariadic := check.collectFields(token.FUNC, e.Params, true)
+		results, _, _ := check.collectFields(token.FUNC, e.Results, true)
+		x.mode = typexpr
+		x.typ = &Signature{Recv: nil, Params: params, Results: results, IsVariadic: isVariadic}
+
+	case *ast.InterfaceType:
+		methods, _, _ := check.collectFields(token.INTERFACE, e.Methods, cycleOk)
+		methods.Sort()
+		x.mode = typexpr
+		x.typ = &Interface{Methods: methods}
+
+	case *ast.MapType:
+		x.mode = typexpr
+		x.typ = &Map{Key: check.typ(e.Key, true), Elt: check.typ(e.Value, true)}
+
+	case *ast.ChanType:
+		x.mode = typexpr
+		x.typ = &Chan{Dir: e.Dir, Elt: check.typ(e.Value, true)}
+
+	default:
+		check.dump("e = %s", e)
+		unreachable()
+	}
+
+	// everything went well
+	x.expr = e
+	return
+
+Error:
+	x.mode = invalid
+	x.expr = e
+}
+
+// expr is like exprOrType but also checks that e represents a value (rather than a type).
+func (check *checker) expr(x *operand, e ast.Expr, hint Type, iota int) {
+	check.exprOrType(x, e, hint, iota, false)
+	switch x.mode {
+	case novalue:
+		check.errorf(x.pos(), "%s used as value", x)
+		x.mode = invalid
+	case typexpr:
+		check.errorf(x.pos(), "%s is not an expression", x)
+		x.mode = invalid
+	}
+}
+
+// typ is like exprOrType but also checks that e represents a type (rather than a value).
+// If an error occured, the result is Typ[Invalid].
+//
+func (check *checker) typ(e ast.Expr, cycleOk bool) Type {
+	var x operand
+	check.exprOrType(&x, e, nil, -1, cycleOk)
+	switch {
+	case x.mode == novalue:
+		check.errorf(x.pos(), "%s used as type", &x)
+		x.typ = Typ[Invalid]
+	case x.mode != typexpr:
+		check.errorf(x.pos(), "%s is not a type", &x)
+		x.typ = Typ[Invalid]
+	}
+	return x.typ
+}

src/pkg/exp/types/staging/stmt.go

@@ -0,0 +1,465 @@
+// Copyright 2012 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// This file implements typechecking of statements.
+
+package types
+
+import (
+	"go/ast"
+	"go/token"
+)
+
+func (check *checker) assignOperand(z, x *operand) {
+	if t, ok := x.typ.(*tuple); ok {
+		// TODO(gri) elsewhere we use "assignment count mismatch" (consolidate)
+		check.errorf(x.pos(), "%d-valued expression %s used as single value", len(t.list), x)
+		x.mode = invalid
+		return
+	}
+
+	check.convertUntyped(x, z.typ)
+
+	if !x.isAssignable(z.typ) {
+		check.errorf(x.pos(), "cannot assign %s to %s", x, z)
+		x.mode = invalid
+	}
+}
+
+// assignment typechecks a single assignment of the form lhs := x. If decl is set,
+// the lhs operand must be an identifier. If its type is not set, it is deduced
+// from the type or value of x.
+//
+func (check *checker) assignment(lhs ast.Expr, x *operand, decl bool) {
+	if decl {
+		ident, ok := lhs.(*ast.Ident)
+		if !ok {
+			check.errorf(lhs.Pos(), "cannot declare %s", lhs)
+			return
+		}
+
+		obj := ident.Obj
+		if obj.Type == nil {
+			// determine type from rhs expression
+			var typ Type = Typ[Invalid]
+			if x.mode != invalid {
+				typ = x.typ
+				// determine the default type for variables
+				if obj.Kind == ast.Var && isUntyped(typ) {
+					typ = defaultType(typ)
+				}
+			}
+			obj.Type = typ
+		}
+
+		var z operand
+		switch obj.Kind {
+		case ast.Con:
+			z.mode = constant
+		case ast.Var:
+			z.mode = variable
+		default:
+			unreachable()
+		}
+		z.expr = ident
+		z.typ = obj.Type.(Type)
+
+		check.assignOperand(&z, x)
+
+		// for constants, set the constant value
+		if obj.Kind == ast.Con {
+			assert(obj.Data == nil)
+			if x.mode != invalid && x.mode != constant {
+				check.errorf(x.pos(), "%s is not constant", x) // TODO(gri) better error position
+				x.mode = invalid
+			}
+			if x.mode == constant {
+				obj.Data = x.val
+			} else {
+				// set the constant to the type's zero value to reduce spurious errors
+				// TODO(gri) factor this out - useful elsewhere
+				switch typ := underlying(obj.Type.(Type)); {
+				case typ == Typ[Invalid]:
+					// ignore
+				case isBoolean(typ):
+					obj.Data = false
+				case isNumeric(typ):
+					obj.Data = int64(0)
+				case isString(typ):
+					obj.Data = ""
+				default:
+					check.dump("%s: typ(%s) = %s", obj.Pos(), obj.Name, typ)
+					unreachable()
+				}
+			}
+		}
+
+		return
+	}
+
+	// regular assignment
+	var z operand
+	check.expr(&z, lhs, nil, -1)
+	check.assignOperand(&z, x)
+	if x.mode != invalid && z.mode == constant {
+		check.errorf(x.pos(), "cannot assign %s to %s", x, z)
+	}
+}
+
+func (check *checker) assign1to1(lhs, rhs ast.Expr, decl bool, iota int) {
+	if !decl {
+		// regular assignment - start with lhs[0] to obtain a type hint
+		var z operand
+		check.expr(&z, lhs, nil, -1)
+		if z.mode == invalid {
+			z.typ = nil // so we can proceed with rhs
+		}
+
+		var x operand
+		check.expr(&x, rhs, z.typ, -1)
+		if x.mode == invalid {
+			return
+		}
+
+		check.assignOperand(&z, &x)
+		return
+	}
+
+	// declaration - rhs may or may not be typed yet
+	ident, ok := lhs.(*ast.Ident)
+	if !ok {
+		check.errorf(lhs.Pos(), "cannot declare %s", lhs)
+		return
+	}
+
+	obj := ident.Obj
+	var typ Type
+	if obj.Type != nil {
+		typ = obj.Type.(Type)
+	}
+
+	var x operand
+	check.expr(&x, rhs, typ, iota)
+	if x.mode == invalid {
+		return
+	}
+
+	if typ == nil {
+		// determine lhs type from rhs expression;
+		// for variables, convert untyped types to
+		// default types
+		typ = x.typ
+		if obj.Kind == ast.Var && isUntyped(typ) {
+			// TODO(gri) factor this out
+			var k BasicKind
+			switch typ.(*Basic).Kind {
+			case UntypedBool:
+				k = Bool
+			case UntypedRune:
+				k = Rune
+			case UntypedInt:
+				k = Int
+			case UntypedFloat:
+				k = Float64
+			case UntypedComplex:
+				k = Complex128
+			case UntypedString:
+				k = String
+			default:
+				unreachable()
+			}
+			typ = Typ[k]
+		}
+		obj.Type = typ
+	}
+
+	var z operand
+	switch obj.Kind {
+	case ast.Con:
+		z.mode = constant
+	case ast.Var:
+		z.mode = variable
+	default:
+		unreachable()
+	}
+	z.expr = ident
+	z.typ = typ
+
+	check.assignOperand(&z, &x)
+
+	// for constants, set their value
+	if obj.Kind == ast.Con {
+		assert(obj.Data == nil)
+		if x.mode != constant {
+			check.errorf(x.pos(), "%s is not constant", x)
+			// set the constant to the type's zero value to reduce spurious errors
+			// TODO(gri) factor this out - useful elsewhere
+			switch typ := underlying(typ); {
+			case typ == Typ[Invalid]:
+				// ignore
+			case isBoolean(typ):
+				obj.Data = false
+			case isNumeric(typ):
+				obj.Data = int64(0)
+			case isString(typ):
+				obj.Data = ""
+			default:
+				unreachable()
+			}
+			return
+		}
+		obj.Data = x.val
+	}
+}
+
+// assignNtoM typechecks a general assignment. If decl is set, the lhs operands
+// must be identifiers. If their types are not set, they are deduced from the
+// types of the corresponding rhs expressions. iota >= 0 indicates that the
+// "assignment" is part of a constant declaration.
+// Precondition: len(lhs) > 0 .
+//
+func (check *checker) assignNtoM(lhs, rhs []ast.Expr, decl bool, iota int) {
+	assert(len(lhs) >= 1)
+
+	if len(lhs) == len(rhs) {
+		for i, e := range rhs {
+			check.assign1to1(lhs[i], e, decl, iota)
+		}
+		return
+	}
+
+	if len(rhs) == 1 {
+		// len(lhs) >= 2; therefore a correct rhs expression
+		// cannot be a shift and we don't need a type hint -
+		// ok to evaluate rhs first
+		var x operand
+		check.expr(&x, rhs[0], nil, iota)
+		if x.mode == invalid {
+			return
+		}
+
+		if t, ok := x.typ.(*tuple); ok && len(lhs) == len(t.list) {
+			// function result
+			x.mode = value
+			for i, typ := range t.list {
+				x.expr = nil // TODO(gri) should do better here
+				x.typ = typ
+				check.assignment(lhs[i], &x, decl)
+			}
+			return
+		}
+
+		if x.mode == valueok && len(lhs) == 2 {
+			// comma-ok expression
+			x.mode = value
+			check.assignment(lhs[0], &x, decl)
+
+			x.mode = value
+			x.typ = Typ[UntypedBool]
+			check.assignment(lhs[1], &x, decl)
+			return
+		}
+	}
+
+	check.errorf(lhs[0].Pos(), "assignment count mismatch: %d = %d", len(lhs), len(rhs))
+
+	// avoid checking the same declaration over and over
+	// again for each lhs identifier that has no type yet
+	if iota >= 0 {
+		// declaration
+		for _, e := range lhs {
+			if ident, ok := e.(*ast.Ident); ok {
+				ident.Obj.Type = Typ[Invalid]
+			}
+		}
+	}
+}
+
+func (check *checker) optionalStmt(s ast.Stmt) {
+	if s != nil {
+		check.stmt(s)
+	}
+}
+
+func (check *checker) stmtList(list []ast.Stmt) {
+	for _, s := range list {
+		check.stmt(s)
+	}
+}
+
+// stmt typechecks statement s.
+func (check *checker) stmt(s ast.Stmt) {
+	switch s := s.(type) {
+	case *ast.BadStmt, *ast.EmptyStmt:
+		// ignore
+
+	case *ast.DeclStmt:
+		unimplemented()
+
+	case *ast.LabeledStmt:
+		unimplemented()
+
+	case *ast.ExprStmt:
+		var x operand
+		used := false
+		switch e := unparen(s.X).(type) {
+		case *ast.CallExpr:
+			// function calls are permitted
+			used = true
+			// but some builtins are excluded
+			check.expr(&x, e.Fun, nil, -1)
+			if x.mode != invalid {
+				if b, ok := x.typ.(*builtin); ok && !b.isStatement {
+					used = false
+				}
+			}
+		case *ast.UnaryExpr:
+			// receive operations are permitted
+			if e.Op == token.ARROW {
+				used = true
+			}
+		}
+		if !used {
+			check.errorf(s.Pos(), "%s not used", s.X)
+			// ok to continue
+		}
+		check.exprOrType(&x, s.X, nil, -1, false)
+		if x.mode == typexpr {
+			check.errorf(x.pos(), "%s is not an expression", x)
+		}
+
+	case *ast.SendStmt:
+		var ch, x operand
+		check.expr(&ch, s.Chan, nil, -1)
+		check.expr(&x, s.Value, nil, -1)
+		if ch.mode == invalid || x.mode == invalid {
+			return
+		}
+		if tch, ok := underlying(ch.typ).(*Chan); !ok || tch.Dir&ast.SEND == 0 || !x.isAssignable(tch.Elt) {
+			check.invalidOp(ch.pos(), "cannot send %s to channel %s", &x, &ch)
+		}
+
+	case *ast.IncDecStmt:
+		unimplemented()
+
+	case *ast.AssignStmt:
+		switch s.Tok {
+		case token.ASSIGN, token.DEFINE:
+			if len(s.Lhs) == 0 {
+				check.invalidAST(s.Pos(), "missing lhs in assignment")
+				return
+			}
+			check.assignNtoM(s.Lhs, s.Rhs, s.Tok == token.DEFINE, -1)
+		default:
+			// assignment operations
+			if len(s.Lhs) != 1 || len(s.Rhs) != 1 {
+				check.errorf(s.TokPos, "assignment operation %s requires single-valued expressions", s.Tok)
+				return
+			}
+			// TODO(gri) make this conversion more efficient
+			var op token.Token
+			switch s.Tok {
+			case token.ADD_ASSIGN:
+				op = token.ADD
+			case token.SUB_ASSIGN:
+				op = token.SUB
+			case token.MUL_ASSIGN:
+				op = token.MUL
+			case token.QUO_ASSIGN:
+				op = token.QUO
+			case token.REM_ASSIGN:
+				op = token.REM
+			case token.AND_ASSIGN:
+				op = token.AND
+			case token.OR_ASSIGN:
+				op = token.OR
+			case token.XOR_ASSIGN:
+				op = token.XOR
+			case token.SHL_ASSIGN:
+				op = token.SHL
+			case token.SHR_ASSIGN:
+				op = token.SHR
+			case token.AND_NOT_ASSIGN:
+				op = token.AND_NOT
+			}
+			var x, y operand
+			check.expr(&x, s.Lhs[0], nil, -1)
+			check.expr(&y, s.Rhs[0], nil, -1)
+			check.binary(&x, &y, op, nil)
+			check.assignment(s.Lhs[0], &x, false)
+		}
+
+	case *ast.GoStmt:
+		unimplemented()
+
+	case *ast.DeferStmt:
+		unimplemented()
+
+	case *ast.ReturnStmt:
+		unimplemented()
+
+	case *ast.BranchStmt:
+		unimplemented()
+
+	case *ast.BlockStmt:
+		check.stmtList(s.List)
+
+	case *ast.IfStmt:
+		check.optionalStmt(s.Init)
+		var x operand
+		check.expr(&x, s.Cond, nil, -1)
+		if !isBoolean(x.typ) {
+			check.errorf(s.Cond.Pos(), "non-boolean condition in if statement")
+		}
+		check.stmt(s.Body)
+		check.optionalStmt(s.Else)
+
+	case *ast.SwitchStmt:
+		check.optionalStmt(s.Init)
+		var x operand
+		if s.Tag != nil {
+			check.expr(&x, s.Tag, nil, -1)
+		} else {
+			x.mode = constant
+			x.typ = Typ[UntypedBool]
+			x.val = true
+		}
+		for _, s := range s.Body.List {
+			if clause, ok := s.(*ast.CaseClause); ok {
+				for _, expr := range clause.List {
+					var y operand
+					check.expr(&y, expr, nil, -1)
+					// TODO(gri) x and y must be comparable
+				}
+				check.stmtList(clause.Body)
+			} else {
+				check.errorf(s.Pos(), "invalid AST: case clause expected")
+			}
+		}
+
+	case *ast.TypeSwitchStmt:
+		unimplemented()
+
+	case *ast.SelectStmt:
+		unimplemented()
+
+	case *ast.ForStmt:
+		check.optionalStmt(s.Init)
+		if s.Cond != nil {
+			var x operand
+			check.expr(&x, s.Cond, nil, -1)
+			if !isBoolean(x.typ) {
+				check.errorf(s.Cond.Pos(), "non-boolean condition in for statement")
+			}
+		}
+		check.optionalStmt(s.Post)
+		check.stmt(s.Body)
+
+	case *ast.RangeStmt:
+		unimplemented()
+
+	default:
+		check.errorf(s.Pos(), "invalid statement")
+	}
+}

src/pkg/exp/types/staging/stubs.go

@@ -1,55 +0,0 @@
-// Copyright 2012 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-// This file contains unimplemented stubs so that the
-// code in exp/types/staging compiles.
-
-package types
-
-import "go/ast"
-
-// expr typechecks expression e and initializes x with the expression
-// value or type. If an error occured, x.mode is set to invalid.
-// A hint != nil is used as operand type for untyped shifted operands;
-// iota >= 0 indicates that the expression is part of a constant declaration.
-// cycleOk indicates whether it is ok for a type expression to refer to itself.
-//
-func (check *checker) exprOrType(x *operand, e ast.Expr, hint Type, iota int, cycleOk bool) {
-	unimplemented()
-}
-
-// expr is like exprOrType but also checks that e represents a value (rather than a type).
-func (check *checker) expr(x *operand, e ast.Expr, hint Type, iota int) {
-	unimplemented()
-}
-
-// typ is like exprOrType but also checks that e represents a type (rather than a value).
-// If an error occured, the result is Typ[Invalid].
-//
-func (check *checker) typ(e ast.Expr, cycleOk bool) Type {
-	unimplemented()
-	return nil
-}
-
-// assignNtoM typechecks a general assignment. If decl is set, the lhs operands
-// must be identifiers. If their types are not set, they are deduced from the
-// types of the corresponding rhs expressions. iota >= 0 indicates that the
-// "assignment" is part of a constant declaration.
-//
-func (check *checker) assignNtoM(lhs, rhs []ast.Expr, decl bool, iota int) {
-	unimplemented()
-}
-
-// assignment typechecks a single assignment of the form lhs := x. If decl is set,
-// the lhs operand must be an identifier. If its type is not set, it is deduced
-// from the type or value of x.
-//
-func (check *checker) assignment(lhs ast.Expr, x *operand, decl bool) {
-	unimplemented()
-}
-
-// stmt typechecks statement s.
-func (check *checker) stmt(s ast.Stmt) {
-	unimplemented()
-}

src/pkg/exp/types/staging/testdata/const0.src

@@ -0,0 +1,209 @@
+// Copyright 2012 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// constant declarations
+
+package const0
+
+// constants declarations must be initialized by constants
+var x = 0
+const c0 = x /* ERROR "not constant" */
+
+// untyped constants
+const (
+	// boolean values
+	ub0 = false
+	ub1 = true
+	ub2 = 2 < 1
+	ub3 = ui1 == uf1
+	ub4 = true /* ERROR "cannot convert" */ == 0
+
+	// integer values
+	ui0 = 0
+	ui1 = 1
+	ui2 = 42
+	ui3 = 3141592653589793238462643383279502884197169399375105820974944592307816406286
+	ui4 = -10
+
+	ui5 = ui0 + ui1
+	ui6 = ui1 - ui1
+	ui7 = ui2 * ui1
+	ui8 = ui3 / ui3
+	ui9 = ui3 % ui3
+
+	ui10 = 1 / 0 /* ERROR "division by zero" */
+	ui11 = ui1 / 0 /* ERROR "division by zero" */
+	ui12 = ui3 / ui0 /* ERROR "division by zero" */
+	ui13 = 1 % 0 /* ERROR "division by zero" */
+	ui14 = ui1 % 0 /* ERROR "division by zero" */
+	ui15 = ui3 % ui0 /* ERROR "division by zero" */
+
+	ui16 = ui2 & ui3
+	ui17 = ui2 | ui3
+	ui18 = ui2 ^ ui3
+
+	// floating point values
+	uf0 = 0.
+	uf1 = 1.
+	uf2 = 4.2e1
+	uf3 = 3.141592653589793238462643383279502884197169399375105820974944592307816406286
+	uf4 = 1e-1
+
+	uf5 = uf0 + uf1
+	uf6 = uf1 - uf1
+	uf7 = uf2 * uf1
+	uf8 = uf3 / uf3
+	uf9 = uf3 /* ERROR "not defined" */ % uf3
+
+	uf10 = 1 / 0 /* ERROR "division by zero" */
+	uf11 = uf1 / 0 /* ERROR "division by zero" */
+	uf12 = uf3 / uf0 /* ERROR "division by zero" */
+
+	uf16 = uf2 /* ERROR "not defined" */ & uf3
+	uf17 = uf2 /* ERROR "not defined" */ | uf3
+	uf18 = uf2 /* ERROR "not defined" */ ^ uf3
+
+	// complex values
+	uc0 = 0.i
+	uc1 = 1.i
+	uc2 = 4.2e1i
+	uc3 = 3.141592653589793238462643383279502884197169399375105820974944592307816406286i
+	uc4 = 1e-1i
+
+	uc5 = uc0 + uc1
+	uc6 = uc1 - uc1
+	uc7 = uc2 * uc1
+	uc8 = uc3 / uc3
+	uc9 = uc3 /* ERROR "not defined" */ % uc3
+
+	uc10 = 1 / 0 /* ERROR "division by zero" */
+	uc11 = uc1 / 0 /* ERROR "division by zero" */
+	uc12 = uc3 / uc0 /* ERROR "division by zero" */
+
+	uc16 = uc2 /* ERROR "not defined" */ & uc3
+	uc17 = uc2 /* ERROR "not defined" */ | uc3
+	uc18 = uc2 /* ERROR "not defined" */ ^ uc3
+)
+
+type (
+	mybool bool
+	myint int
+	myfloat float64
+	mycomplex complex128
+)
+
+// typed constants
+const (
+	// boolean values
+	tb0 bool = false
+	tb1 bool = true
+	tb2 mybool = 2 < 1
+	tb3 mybool = ti1 /* ERROR "cannot compare" */ == tf1
+
+	// integer values
+	ti0 int8 = ui0
+	ti1 int32 = ui1
+	ti2 int64 = ui2
+	ti3 myint = ui3 /* ERROR "overflows" */
+	ti4 myint = ui4
+
+	ti5 = ti0 /* ERROR "mismatched types" */ + ti1
+	ti6 = ti1 - ti1
+	ti7 = ti2 /* ERROR "mismatched types" */ * ti1
+	//ti8 = ti3 / ti3 // TODO(gri) enable this
+	//ti9 = ti3 % ti3 // TODO(gri) enable this
+
+	ti10 = 1 / 0 /* ERROR "division by zero" */
+	ti11 = ti1 / 0 /* ERROR "division by zero" */
+	ti12 = ti3 /* ERROR "mismatched types" */ / ti0
+	ti13 = 1 % 0 /* ERROR "division by zero" */
+	ti14 = ti1 % 0 /* ERROR "division by zero" */
+	ti15 = ti3 /* ERROR "mismatched types" */ % ti0
+
+	ti16 = ti2 /* ERROR "mismatched types" */ & ti3
+	ti17 = ti2 /* ERROR "mismatched types" */ | ti4
+	ti18 = ti2 ^ ti5 // no mismatched types error because the type of ti5 is unknown
+
+	// floating point values
+	tf0 float32 = 0.
+	tf1 float32 = 1.
+	tf2 float64 = 4.2e1
+	tf3 myfloat = 3.141592653589793238462643383279502884197169399375105820974944592307816406286
+	tf4 myfloat = 1e-1
+
+	tf5 = tf0 + tf1
+	tf6 = tf1 - tf1
+	tf7 = tf2 /* ERROR "mismatched types" */ * tf1
+	// tf8 = tf3 / tf3 // TODO(gri) enable this
+	tf9 = tf3 /* ERROR "not defined" */ % tf3
+
+	tf10 = 1 / 0 /* ERROR "division by zero" */
+	tf11 = tf1 / 0 /* ERROR "division by zero" */
+	tf12 = tf3 /* ERROR "mismatched types" */ / tf0
+
+	tf16 = tf2 /* ERROR "mismatched types" */ & tf3
+	tf17 = tf2 /* ERROR "mismatched types" */ | tf3
+	tf18 = tf2 /* ERROR "mismatched types" */ ^ tf3
+
+	// complex values
+	tc0 = 0.i
+	tc1 = 1.i
+	tc2 = 4.2e1i
+	tc3 = 3.141592653589793238462643383279502884197169399375105820974944592307816406286i
+	tc4 = 1e-1i
+
+	tc5 = tc0 + tc1
+	tc6 = tc1 - tc1
+	tc7 = tc2 * tc1
+	tc8 = tc3 / tc3
+	tc9 = tc3 /* ERROR "not defined" */ % tc3
+
+	tc10 = 1 / 0 /* ERROR "division by zero" */
+	tc11 = tc1 / 0 /* ERROR "division by zero" */
+	tc12 = tc3 / tc0 /* ERROR "division by zero" */
+
+	tc16 = tc2 /* ERROR "not defined" */ & tc3
+	tc17 = tc2 /* ERROR "not defined" */ | tc3
+	tc18 = tc2 /* ERROR "not defined" */ ^ tc3
+)
+
+// initialization cycles
+const (
+	a /* ERROR "cycle" */ = a
+	b /* ERROR "cycle" */ , c /* ERROR "cycle" */, d, e = e, d, c, b // TODO(gri) should only have one cycle error
+	f float64 = d
+)
+
+// multiple initialization
+const (
+	a1, a2, a3 = 7, 3.1415926, "foo"
+	b1, b2, b3 = b3, b1, 42
+	_p0 = assert(a1 == 7)
+	_p1 = assert(a2 == 3.1415926)
+	_p2 = assert(a3 == "foo")
+	_p3 = assert(b1 == 42)
+	_p4 = assert(b2 == 42)
+	_p5 = assert(b3 == 42)
+)
+
+// iota
+const (
+	iota0 = iota
+	iota1 = iota
+	iota2 = iota*2
+	_a0 = assert(iota0 == 0)
+	_a1 = assert(iota1 == 1)
+	_a2 = assert(iota2 == 4)
+	iota6 = iota*3
+
+	iota7
+	iota8
+	_a3 = assert(iota7 == 21)
+	_a4 = assert(iota8 == 24)
+)
+
+const (
+	_b0 = iota
+	_b1 = assert(iota + iota2 == 5)
+)

src/pkg/exp/types/staging/testdata/conversions.src

@@ -0,0 +1,18 @@
+// Copyright 2012 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// conversions
+
+package conversions
+
+// argument count
+var (
+	_v0 = int /* ERROR "one argument" */ ()
+	_v1 = int /* ERROR "one argument" */ (1, 2)
+)
+
+//
+var (
+	_v2 = int8(0)
+)

src/pkg/exp/types/staging/testdata/decls0.src

@@ -0,0 +1,168 @@
+// Copyright 2011 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// type declarations
+
+package decls0
+
+import (
+	"unsafe"
+	// we can have multiple blank imports (was bug)
+	_ "math"
+	_ "net/rpc"
+)
+
+const pi = 3.1415
+
+type (
+	N undeclared /* ERROR "undeclared" */ /* ERROR "not a type" */
+	B bool
+	I int32
+	A [10]P
+	T struct {
+		x, y P
+	}
+	P *T
+	R (*R)
+	F func(A) I
+	Y interface {
+		f(A) I
+	}
+	S [](((P)))
+	M map[I]F
+	C chan<- I
+
+	// blank types must be typechecked
+	_ pi /* ERROR "not a type" */
+	_ struct{}
+	_ struct{ pi /* ERROR "not a type" */ }
+)
+
+
+type (
+	p1 pi /* ERROR "no field or method foo" */ /* ERROR "not a type" */ .foo
+	p2 unsafe.Pointer
+)
+
+
+type (
+	Pi pi /* ERROR "not a type" */
+
+	a /* ERROR "illegal cycle" */ a
+	a /* ERROR "redeclared" */ int
+
+	// where the cycle error appears depends on the
+	// order in which declarations are processed
+	// (which depends on the order in which a map
+	// is iterated through)
+	b /* ERROR "illegal cycle" */ c
+	c d
+	d e
+	e b
+
+	t *t
+
+	U V
+	V *W
+	W U
+
+	P1 *S2
+	P2 P1
+
+	S0 struct {
+	}
+	S1 struct {
+		a, b, c int
+		u, v, a /* ERROR "redeclared" */ float32
+	}
+	S2 struct {
+		U // anonymous field
+		// TODO(gri) recognize double-declaration below
+		// U /* ERROR "redeclared" */ int
+	}
+	S3 struct {
+		x S2
+	}
+	S4/* ERROR "illegal cycle" */ struct {
+		S4
+	}
+	S5 /* ERROR "illegal cycle" */ struct {
+		S6
+	}
+	S6 struct {
+		field S7
+	}
+	S7 struct {
+		S5
+	}
+
+	L1 []L1
+	L2 []int
+
+	A1 [10.0]int
+	A2 /* ERROR "illegal cycle" */ [10]A2
+	A3 /* ERROR "illegal cycle" */ [10]struct {
+		x A4
+	}
+	A4 [10]A3
+
+	F1 func()
+	F2 func(x, y, z float32)
+	F3 func(x, y, x /* ERROR "redeclared" */ float32)
+	F4 func() (x, y, x /* ERROR "redeclared" */ float32)
+	F5 func(x int) (x /* ERROR "redeclared" */ float32)
+	F6 func(x ...int)
+
+	I1 interface{}
+	I2 interface {
+		m1()
+	}
+	I3 interface {
+		m1()
+		m1 /* ERROR "redeclared" */ ()
+	}
+	I4 interface {
+		m1(x, y, x /* ERROR "redeclared" */ float32)
+		m2() (x, y, x /* ERROR "redeclared" */ float32)
+		m3(x int) (x /* ERROR "redeclared" */ float32)
+	}
+	I5 interface {
+		m1(I5)
+	}
+	I6 interface {
+		S0 /* ERROR "non-interface" */
+	}
+	I7 interface {
+		I1
+		I1
+	}
+	I8 /* ERROR "illegal cycle" */ interface {
+		I8
+	}
+	// Use I09 (rather than I9) because it appears lexically before
+	// I10 so that we get the illegal cycle here rather then in the
+	// declaration of I10. If the implementation sorts by position
+	// rather than name, the error message will still be here.
+	I09 /* ERROR "illegal cycle" */ interface {
+		I10
+	}
+	I10 interface {
+		I11
+	}
+	I11 interface {
+		I09
+	}
+
+	C1 chan int
+	C2 <-chan int
+	C3 chan<- C3
+	C4 chan C5
+	C5 chan C6
+	C6 chan C4
+
+	M1 map[Last]string
+	M2 map[string]M2
+
+	Last int
+)

src/pkg/exp/types/staging/testdata/decls1.src

@@ -0,0 +1,123 @@
+// Copyright 2012 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// variable declarations
+
+package decls1
+
+import (
+	"math"
+)
+
+// Global variables without initialization
+var (
+	a, b bool
+	c byte
+	d uint8
+	r rune
+	i int
+	j, k, l int
+	x, y float32
+	xx, yy float64
+	u, v complex64
+	uu, vv complex128
+	s, t string
+	array []byte
+	iface interface{}
+	
+	blank _ /* ERROR "cannot use _" */ /* ERROR "not a type" */
+)
+
+// Global variables with initialization
+var (
+	s1 = i + j
+	s2 = i /* ERROR "mismatched types" */ + x
+	s3 = c + d
+	s4 = s + t
+	s5 = s /* ERROR "invalid operation" */ / t
+	s6 = array[t1]
+	s7 = array[x /* ERROR "array index" */]
+	s8 = &a
+	s10 = &42 /* ERROR "cannot take address" */
+	s11 = &v
+	s12 = -(u + *t11) / *&v
+	s13 = a /* ERROR "shifted operand" */ << d
+	s14 = i << j /* ERROR "must be unsigned" */ 
+	s18 = math.Pi * 10.0
+	s19 = s1 /* ERROR "cannot call" */ ()
+ 	s20 = f0 /* ERROR "used as single value" */ ()
+	s21 = f6(1, s1, i)
+	s22 = f6(1, s1, uu /* ERROR "cannot assign" */ )
+	
+	t1 int = i + j
+	t2 int = i /* ERROR "mismatched types" */ + x
+	t3 int = c /* ERROR "cannot assign" */ + d
+	t4 string = s + t
+	t5 string = s /* ERROR "invalid operation" */ / t
+	t6 byte = array[t1]
+	t7 byte = array[x /* ERROR "array index" */]
+	t8 *int = & /* ERROR "cannot assign" */ a
+	t10 *int = &42 /* ERROR "cannot take address" */
+	t11 *complex64 = &v
+	t12 complex64 = -(u + *t11) / *&v
+	t13 int = a /* ERROR "shifted operand" */ << d
+	t14 int = i << j /* ERROR "must be unsigned" */ 
+	t15 math /* ERROR "not in selector" */ /* ERROR "not a type" */
+	t16 math /* ERROR "not a type" */ .xxx /* ERROR "unexported" */
+	t17 math /* ERROR "not a type" */ .Pi
+	t18 float64 = math.Pi * 10.0
+	t19 int = t1 /* ERROR "cannot call" */ ()
+	t20 int = f0 /* ERROR "used as single value" */ ()
+)
+
+// Various more complex expressions
+var (
+	u1 = x /* ERROR "non-interface type" */ .(int)
+	u2 = iface.([]int)
+	u3 = iface.(a /* ERROR "not a type" */ )
+	u4, ok = iface.(int)
+	u5 /* ERROR "assignment count mismatch" */ , ok2, ok3 = iface.(int)
+)
+
+// Constant expression initializations
+var (
+	v1 = 1 /* ERROR "cannot convert" */ + "foo"
+	v2 = c + 255
+	v3 = c + 256 /* ERROR "overflows" */
+	v4 = r + 2147483647
+	v5 = r + 2147483648 /* ERROR "overflows" */
+	v6 = 42
+	v7 = v6 + 2147483647
+	v8 = v6 + 2147483648 /* ERROR "overflows" */
+	v9 = i + 1 << 10
+	v10 byte = 1024 /* ERROR "overflows" */
+	v11 = xx/yy*yy - xx
+	v12 = true && false
+)
+
+// Multiple assignment expressions
+var (
+	m1a, m1b = 1, 2
+	m2a /* ERROR "assignment count mismatch" */ , m2b, m2c = 1, 2
+	m3a /* ERROR "assignment count mismatch" */ , m3b = 1, 2, 3
+)
+
+// Declaration of parameters and results
+func f0() {}
+func f1(a /* ERROR "not a type" */) {}
+func f2(a, b, c d /* ERROR "not a type" */) {}
+
+func f3() int {}
+func f4() a /* ERROR "not a type" */ {}
+func f5() (a, b, c d /* ERROR "not a type" */) {}
+
+func f6(a, b, c int) complex128 { return 0 }
+
+// Declaration of receivers
+type T struct{}
+
+func (T) m0() {}
+func (*T) m1() {}
+func (x T) m2() {}
+func (x *T) m3() {}

src/pkg/exp/types/staging/testdata/decls2a.src

@@ -0,0 +1,66 @@
+// Copyright 2012 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// method declarations
+
+package decls2
+
+import "time"
+
+// T1 declared before its methods.
+type T1 struct{
+	f int
+}
+
+func (T1) m() {}
+func (T1) m /* ERROR "redeclared" */ () {}
+func (x *T1) f /* ERROR "field and method" */ () {}
+
+// T2's method declared before the type.
+func (*T2) f /* ERROR "field and method" */ () {}
+
+type T2 struct {
+	f int
+}
+
+// Methods declared without a declared type.
+func (undeclared /* ERROR "undeclared" */) m() {}
+func (x *undeclared /* ERROR "undeclared" */) m() {}
+
+func (pi /* ERROR "not a type" */) m1() {}
+func (x pi /* ERROR "not a type" */) m2() {}
+func (x *pi /* ERROR "not a type" */) m3() {}
+
+// Blank types.
+type _ struct { m int }
+type _ struct { m int }
+
+// TODO(gri) blank idents not fully checked - disabled for now
+// func (_ /* ERROR "cannot use _" */) m() {}
+// func (_ /* ERROR "cannot use _" */) m() {}
+
+// Methods with receiver base type declared in another file.
+func (T3) m1() {}
+func (*T3) m2() {}
+func (x T3) m3() {}
+func (x *T3) f /* ERROR "field and method" */ () {}
+
+// Methods of non-struct type.
+type T4 func()
+
+func (self T4) m() func() { return self }
+
+// Methods associated with an interface.
+type T5 interface {
+	m() int
+}
+
+func (T5 /* ERROR "invalid receiver" */) m1() {}
+func (T5 /* ERROR "invalid receiver" */) m2() {}
+
+// Methods associated with non-local or unnamed types.
+// func (int) m() {} TODO(gri) check for methods associated with external (not package-local) types
+func ([ /* ERROR "expected" */ ]int) m() {}
+func (time /* ERROR "expected" */ .Time) m() {}
+func (x interface /* ERROR "expected" */ {}) m() {}

src/pkg/exp/types/staging/testdata/decls2b.src

@@ -0,0 +1,15 @@
+// Copyright 2012 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// method declarations
+
+package decls2
+
+const pi = 3.1415
+
+func (T1) m /* ERROR "redeclared" */ () {}
+
+type T3 struct {
+	f *T3
+}

src/pkg/exp/types/staging/testdata/expr0.src

@@ -0,0 +1,135 @@
+// Copyright 2012 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// unary expressions
+
+package expr0 
+
+var (
+	// bool
+	b0 = true
+	b1 bool = b0
+	b2 = !true
+	b3 = !b1
+	b4 bool = !true
+	b5 bool = !b4
+	b6 = +b0 /* ERROR "not defined" */
+	b7 = -b0 /* ERROR "not defined" */
+	b8 = ^b0 /* ERROR "not defined" */
+	b9 = *b0 /* ERROR "cannot indirect" */
+	b10 = &true /* ERROR "cannot take address" */
+	b11 = &b0
+	b12 = <-b0 /* ERROR "not defined" */
+
+	// int
+	i0 = 1
+	i1 int = i0
+	i2 = +1
+	i3 = +i0
+	i4 int = +1
+	i5 int = +i4
+	i6 = -1
+	i7 = -i0
+	i8 int = -1
+	i9 int = -i4
+	i10 = !i0 /* ERROR "not defined" */
+	i11 = ^1
+	i12 = ^i0
+	i13 int = ^1
+	i14 int = ^i4
+	i15 = *i0 /* ERROR "cannot indirect" */
+	i16 = &i0
+	i17 = *i16
+	i18 = <-i16 /* ERROR "not defined" */
+
+	// uint
+	u0 = uint(1)
+	u1 uint = u0
+	u2 = +1
+	u3 = +u0
+	u4 uint = +1
+	u5 uint = +u4
+	u6 = -1
+	u7 = -u0
+	u8 uint = - /* ERROR "overflows" */ 1
+	u9 uint = -u4
+	u10 = !u0 /* ERROR "not defined" */
+	u11 = ^1
+	u12 = ^i0
+	u13 uint = ^ /* ERROR "overflows" */ 1
+	u14 uint = ^u4
+	u15 = *u0 /* ERROR "cannot indirect" */
+	u16 = &u0
+	u17 = *u16
+	u18 = <-u16 /* ERROR "not defined" */
+
+	// float64
+	f0 = float64(1)
+	f1 float64 = f0
+	f2 = +1
+	f3 = +f0
+	f4 float64 = +1
+	f5 float64 = +f4 /* ERROR not defined */
+	f6 = -1
+	f7 = -f0
+	f8 float64 = -1
+	f9 float64 = -f4
+	f10 = !f0 /* ERROR "not defined" */
+	f11 = ^1
+	f12 = ^i0
+	f13 float64 = ^1
+	f14 float64 = ^f4 /* ERROR "not defined" */
+	f15 = *f0 /* ERROR "cannot indirect" */
+	f16 = &f0
+	f17 = *u16
+	f18 = <-u16 /* ERROR "not defined" */
+
+	// complex128
+	c0 = complex128(1)
+	c1 complex128 = c0
+	c2 = +1
+	c3 = +c0
+	c4 complex128 = +1
+	c5 complex128 = +c4 /* ERROR not defined */
+	c6 = -1
+	c7 = -c0
+	c8 complex128 = -1
+	c9 complex128 = -c4
+	c10 = !c0 /* ERROR "not defined" */
+	c11 = ^1
+	c12 = ^i0
+	c13 complex128 = ^1
+	c14 complex128 = ^c4 /* ERROR "not defined" */
+	c15 = *c0 /* ERROR "cannot indirect" */
+	c16 = &c0
+	c17 = *u16
+	c18 = <-u16 /* ERROR "not defined" */
+
+	// string
+	s0 = "foo"
+	s1 = +"foo" /* ERROR "not defined" */
+	s2 = -s0 /* ERROR "not defined" */
+	s3 = !s0 /* ERROR "not defined" */
+	s4 = ^s0 /* ERROR "not defined" */
+	s5 = *s4 /* ERROR "cannot indirect" */
+	s6 = &s4
+	s7 = *s6
+	s8 = <-s7  /* ERROR "not defined" */
+
+	// channel
+	ch chan int
+	rc <-chan float64
+	sc chan <- string
+	ch0 = +ch /* ERROR "not defined" */
+	ch1 = -ch /* ERROR "not defined" */
+	ch2 = !ch /* ERROR "not defined" */
+	ch3 = ^ch /* ERROR "not defined" */
+	ch4 = *ch /* ERROR "cannot indirect" */
+	ch5 = &ch
+	ch6 = *ch5
+	ch7 = <-ch
+	ch8 = <-rc
+	ch9 = <-sc /* ERROR "not defined" */
+
+)

src/pkg/exp/types/staging/testdata/expr1.src

@@ -0,0 +1,7 @@
+// Copyright 2012 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// binary expressions
+
+package expr1

src/pkg/exp/types/staging/testdata/expr2.src

@@ -0,0 +1,7 @@
+// Copyright 2012 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// comparisons
+
+package expr2

src/pkg/exp/types/staging/testdata/expr3.src

@@ -0,0 +1,43 @@
+// Copyright 2012 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// shifts
+
+package expr3
+
+var (
+	i0 int
+	u0 uint
+)
+
+var (
+	v0 = 1<<0
+	v1 = 1<<i0 /* ERROR "must be unsigned" */
+	v2 = 1<<u0
+	v3 = 1<<"foo" /* ERROR "must be unsigned" */
+	v4 = 1<<- /* ERROR "stupid shift" */ 1
+	v5 = 1<<1025 /* ERROR "stupid shift" */
+	v6 = 1 /* ERROR "overflows" */ <<100
+
+	v10 uint = 1 << 0
+	v11 uint = 1 << u0
+	v12 float32 = 1 /* ERROR "must be integer" */ << u0
+)
+
+// TODO(gri) enable commented out tests below.
+
+// from the spec
+var (
+	s uint = 33
+	i = 1<<s           // 1 has type int
+	j int32 = 1<<s     // 1 has type int32; j == 0
+	k = uint64(1<<s)   // 1 has type uint64; k == 1<<33
+	m int = 1.0<<s     // 1.0 has type int
+//	n = 1.0<<s != 0    // 1.0 has type int; n == false if ints are 32bits in size
+	o = 1<<s == 2<<s   // 1 and 2 have type int; o == true if ints are 32bits in size
+//	p = 1<<s == 1 /* ERROR "overflows" */ <<33  // illegal if ints are 32bits in size: 1 has type int, but 1<<33 overflows int
+	u = 1.0 /* ERROR "must be integer" */ <<s         // illegal: 1.0 has type float64, cannot shift
+	v float32 = 1 /* ERROR "must be integer" */ <<s   // illegal: 1 has type float32, cannot shift
+	w int64 = 1.0<<33  // 1.0<<33 is a constant shift expression
+)

src/pkg/exp/types/staging/testdata/stmt0.src

@@ -0,0 +1,42 @@
+// Copyright 2012 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// statements
+
+package stmt0
+
+func _() {
+	b, i, f, c, s := false, 1, 1.0, 1i, "foo"
+	b = i /* ERROR "cannot assign" */
+	i = f /* ERROR "cannot assign" */
+	f = c /* ERROR "cannot assign" */
+	c = s /* ERROR "cannot assign" */
+	s = b /* ERROR "cannot assign" */
+
+	v0 /* ERROR "mismatch" */, v1, v2 := 1, 2, 3, 4
+
+	b = true
+
+	i += 1
+	i += "foo" /* ERROR "cannot convert.*int" */
+
+	f -= 1
+	f -= "foo" /* ERROR "cannot convert.*float64" */
+
+	c *= 1
+	c /= 0 /* ERROR "division by zero" */
+
+	s += "bar"
+	s += 1 /* ERROR "cannot convert.*string" */
+}
+
+func _sends() {
+	var ch chan int
+	var rch <-chan int
+	var x int
+	x /* ERROR "cannot send" */ <- x
+	rch /* ERROR "cannot send" */ <- x
+	ch /* ERROR "cannot send" */ <- "foo"
+	ch <- x
+}