exp/types: checking of type switches and range clauses

Also:
- better handling of type assertions
- implemented built-in error type
- first cut at handling variadic function signatures
- several bug fixes

R=rsc, rogpeppe
CC=golang-dev
https://golang.org/cl/6846131

src/pkg/exp/types/check.go

@@ -188,10 +188,13 @@ func (check *checker) object(obj *ast.Object, cycleOk bool) {
 
 	case ast.Fun:
 		fdecl := obj.Decl.(*ast.FuncDecl)
-		check.collectParams(fdecl.Recv) // ensure method base is type-checked
+		check.collectParams(fdecl.Recv, false) // ensure method base is type-checked
 		ftyp := check.typ(fdecl.Type, cycleOk).(*Signature)
 		obj.Type = ftyp
-		check.function(ftyp, fdecl.Body)
+		// functions implemented elsewhere (say in assembly) have no body
+		if fdecl.Body != nil {
+			check.function(ftyp, fdecl.Body)
+		}
 
 	default:
 		panic("unreachable")

src/pkg/exp/types/const.go

@@ -278,7 +278,7 @@ func isRepresentableConst(x interface{}, as BasicKind) bool {
 		return as == String || as == UntypedString
 
 	case nilType:
-		return as == UntypedNil
+		return as == UntypedNil || as == UnsafePointer
 
 	default:
 		unreachable()

src/pkg/exp/types/expr.go

@@ -12,20 +12,36 @@ import (
 	"strconv"
 )
 
-// TODO(gri)
+// TODO(gri) Cleanups
 // - 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?
 // - rethink error handling: should all callers check if x.mode == valid after making a call?
+// - at the moment, iota is passed around almost everywhere - in many places we know it cannot be used
 
-func (check *checker) collectParams(list *ast.FieldList) (params ObjList, isVariadic bool) {
+// TODO(gri) API issues
+// - clients need access to result type information (tuples)
+// - clients need access to constant values
+// - clients need access to built-in type information
+
+// TODO(gri) Bugs
+// - expression hints are (correctly) used untyped for composite literal components, but also
+//   in possibly overlapping use as hints for shift expressions - investigate
+
+func (check *checker) collectParams(list *ast.FieldList, variadicOk bool) (params ObjList, isVariadic bool) {
 	if list == nil {
 		return
 	}
-	for _, field := range list.List {
+	var last *ast.Object
+	for i, field := range list.List {
 		ftype := field.Type
-		if t, ok := ftype.(*ast.Ellipsis); ok {
+		if t, _ := ftype.(*ast.Ellipsis); t != nil {
 			ftype = t.Elt
-			isVariadic = true
+			if variadicOk && i == len(list.List)-1 {
+				isVariadic = true
+			} else {
+				check.invalidAST(field.Pos(), "... not permitted")
+				// ok to continue
+			}
 		}
 		// the parser ensures that f.Tag is nil and we don't
 		// care if a constructed AST contains a non-nil tag
@@ -36,14 +52,26 @@ func (check *checker) collectParams(list *ast.FieldList) (params ObjList, isVari
 				obj := name.Obj
 				obj.Type = typ
 				params = append(params, obj)
+				last = obj
 			}
 		} else {
 			// anonymous parameter
 			obj := ast.NewObj(ast.Var, "")
 			obj.Type = typ
 			params = append(params, obj)
+			last = obj
 		}
 	}
+	// For a variadic function, change the last parameter's object type
+	// from T to []T (this is the type used inside the function), but
+	// keep a copy of the object with the original type T in the params
+	// list (this is the externally visible type).
+	if isVariadic {
+		// if isVariadic is set, last must exist and len(params) > 0
+		copy := *last
+		last.Type = &Slice{Elt: last.Type.(Type)}
+		params[len(params)-1] = &copy
+	}
 	return
 }
 
@@ -118,9 +146,9 @@ func (check *checker) collectFields(list *ast.FieldList, cycleOk bool) (fields [
 			// anonymous field
 			switch t := deref(typ).(type) {
 			case *Basic:
-				fields = append(fields, &StructField{t.Name, t, tag, true})
+				fields = append(fields, &StructField{t.Name, typ, tag, true})
 			case *NamedType:
-				fields = append(fields, &StructField{t.Obj.Name, t, tag, true})
+				fields = append(fields, &StructField{t.Obj.Name, typ, tag, true})
 			default:
 				if typ != Typ[Invalid] {
 					check.invalidAST(f.Type.Pos(), "anonymous field type %s must be named", typ)
@@ -198,7 +226,7 @@ func (check *checker) unary(x *operand, op token.Token) {
 		}
 		// Typed constants must be representable in
 		// their type after each constant operation.
-		check.isRepresentable(x, x.typ.(*Basic))
+		check.isRepresentable(x, underlying(x.typ).(*Basic))
 		return
 	}
 
@@ -526,7 +554,30 @@ func (check *checker) indexedElts(elts []ast.Expr, typ Type, length int64, iota
 	return max
 }
 
-func (check *checker) callRecord(x *operand) {
+func (check *checker) argument(sig *Signature, i int, arg ast.Expr) {
+	var par *ast.Object
+	if n := len(sig.Params); i < n {
+		par = sig.Params[i]
+	} else if sig.IsVariadic {
+		par = sig.Params[n-1]
+	} else {
+		check.errorf(arg.Pos(), "too many arguments")
+		return
+	}
+
+	// TODO(gri) deal with ... last argument
+	var z, x operand
+	z.mode = variable
+	z.expr = nil            // TODO(gri) can we do better here?
+	z.typ = par.Type.(Type) // TODO(gri) should become something like checkObj(&z, ...) eventually
+	check.expr(&x, arg, z.typ, -1)
+	if x.mode == invalid {
+		return // ignore this argument
+	}
+	check.assignOperand(&z, &x)
+}
+
+func (check *checker) recordType(x *operand) {
 	if x.mode != invalid {
 		check.mapf(x.expr, x.typ)
 	}
@@ -545,7 +596,7 @@ func (check *checker) rawExpr(x *operand, e ast.Expr, hint Type, iota int, cycle
 	}
 
 	if check.mapf != nil {
-		defer check.callRecord(x)
+		defer check.recordType(x)
 	}
 
 	switch e := e.(type) {
@@ -856,6 +907,14 @@ func (check *checker) rawExpr(x *operand, e ast.Expr, hint Type, iota int, cycle
 			}
 			x.typ = typ.Elt
 
+		case *Pointer:
+			if typ, _ := underlying(typ.Base).(*Array); typ != nil {
+				valid = true
+				length = typ.Len
+				x.mode = variable
+				x.typ = typ.Elt
+			}
+
 		case *Slice:
 			valid = true
 			x.mode = variable
@@ -870,6 +929,7 @@ func (check *checker) rawExpr(x *operand, e ast.Expr, hint Type, iota int, cycle
 			}
 			x.mode = valueok
 			x.typ = typ.Elt
+			x.expr = e
 			return
 		}
 
@@ -915,6 +975,14 @@ func (check *checker) rawExpr(x *operand, e ast.Expr, hint Type, iota int, cycle
 			}
 			x.typ = &Slice{Elt: typ.Elt}
 
+		case *Pointer:
+			if typ, _ := underlying(typ.Base).(*Array); typ != nil {
+				valid = true
+				length = typ.Len + 1 // +1 for slice
+				x.mode = variable
+				x.typ = &Slice{Elt: typ.Elt}
+			}
+
 		case *Slice:
 			valid = true
 			x.mode = variable
@@ -945,14 +1013,36 @@ func (check *checker) rawExpr(x *operand, e ast.Expr, hint Type, iota int, cycle
 
 	case *ast.TypeAssertExpr:
 		check.expr(x, e.X, hint, iota)
-		if _, ok := underlying(x.typ).(*Interface); !ok {
-			check.invalidOp(e.X.Pos(), "non-interface type %s in type assertion", x.typ)
+		if x.mode == invalid {
+			goto Error
+		}
+		var T *Interface
+		if T, _ = underlying(x.typ).(*Interface); T == nil {
+			check.invalidOp(x.pos(), "%s is not an interface", x)
+			goto Error
+		}
+		// x.(type) expressions are handled explicitly in type switches
+		if e.Type == nil {
+			check.errorf(e.Pos(), "use of .(type) outside type switch")
+			goto Error
+		}
+		typ := check.typ(e.Type, false)
+		if typ == Typ[Invalid] {
+			goto Error
+		}
+		if method, wrongType := missingMethod(typ, T); method != nil {
+			var msg string
+			if wrongType {
+				msg = "%s cannot have dynamic type %s (wrong type for method %s)"
+			} else {
+				msg = "%s cannot have dynamic type %s (missing method %s)"
+			}
+			check.errorf(e.Type.Pos(), msg, x, typ, method.Name)
 			// 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)
+		x.typ = typ
 
 	case *ast.CallExpr:
 		check.exprOrType(x, e.Fun, nil, iota, false)
@@ -962,21 +1052,11 @@ func (check *checker) rawExpr(x *operand, e ast.Expr, hint Type, iota int, cycle
 			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)
-				}
+			// TODO(gri)
+			// - deal with single multi-valued function arguments: f(g())
+			// - variadic functions only partially addressed
+			for i, arg := range e.Args {
+				check.argument(sig, i, arg)
 			}
 
 			// determine result
@@ -1061,8 +1141,8 @@ func (check *checker) rawExpr(x *operand, e ast.Expr, hint Type, iota int, cycle
 		x.typ = &Struct{Fields: check.collectFields(e.Fields, cycleOk)}
 
 	case *ast.FuncType:
-		params, isVariadic := check.collectParams(e.Params)
-		results, _ := check.collectParams(e.Results)
+		params, isVariadic := check.collectParams(e.Params, true)
+		results, _ := check.collectParams(e.Results, false)
 		x.mode = typexpr
 		x.typ = &Signature{Recv: nil, Params: params, Results: results, IsVariadic: isVariadic}
 
@@ -1114,10 +1194,7 @@ func (check *checker) expr(x *operand, e ast.Expr, hint Type, iota int) {
 	}
 }
 
-// expr is like rawExpr but reports an error if e doesn't represents a type.
-// It returns e's type, or Typ[Invalid] if an error occured.
-//
-func (check *checker) typ(e ast.Expr, cycleOk bool) Type {
+func (check *checker) rawTyp(e ast.Expr, cycleOk, nilOk bool) Type {
 	var x operand
 	check.rawExpr(&x, e, nil, -1, cycleOk)
 	switch x.mode {
@@ -1127,8 +1204,27 @@ func (check *checker) typ(e ast.Expr, cycleOk bool) Type {
 		check.errorf(x.pos(), "%s used as type", &x)
 	case typexpr:
 		return x.typ
+	case constant:
+		if nilOk && x.isNil() {
+			return nil
+		}
+		fallthrough
 	default:
 		check.errorf(x.pos(), "%s is not a type", &x)
 	}
 	return Typ[Invalid]
 }
+
+// typOrNil is like rawExpr but reports an error if e doesn't represents a type or the predeclared value nil.
+// It returns e's type, nil, or Typ[Invalid] if an error occured.
+//
+func (check *checker) typOrNil(e ast.Expr, cycleOk bool) Type {
+	return check.rawTyp(e, cycleOk, true)
+}
+
+// typ is like rawExpr but reports an error if e doesn't represents a type.
+// It returns e's type, or Typ[Invalid] if an error occured.
+//
+func (check *checker) typ(e ast.Expr, cycleOk bool) Type {
+	return check.rawTyp(e, cycleOk, false)
+}

src/pkg/exp/types/operand.go

@@ -119,25 +119,6 @@ func (x *operand) setConst(tok token.Token, lit string) {
 	}
 }
 
-// implements reports whether x implements interface T.
-func (x *operand) implements(T *Interface) bool {
-	if x.mode == invalid {
-		return true // avoid spurious errors
-	}
-
-	// x implements T if it implements all methods of T.
-	// TODO(gri): distinguish pointer and non-pointer receivers
-	for _, m := range T.Methods {
-		mode, typ := lookupField(x.typ, m.Name)
-		if mode == invalid || !isIdentical(typ, m.Type.(Type)) {
-			// TODO(gri) should report which method is missing
-			return false
-		}
-	}
-
-	return true
-}
-
 // isNil reports whether x is the predeclared nil constant.
 func (x *operand) isNil() bool {
 	return x.mode == constant && x.val == nilConst
@@ -170,8 +151,10 @@ func (x *operand) isAssignable(T Type) bool {
 	}
 
 	// T is an interface type and x implements T
-	if Ti, ok := Tu.(*Interface); ok && x.implements(Ti) {
-		return true
+	if Ti, ok := Tu.(*Interface); ok {
+		if m, _ := missingMethod(x.typ, Ti); m == nil {
+			return true
+		}
 	}
 
 	// x is a bidirectional channel value, T is a channel

src/pkg/exp/types/predicates.go

@@ -6,6 +6,8 @@
 
 package types
 
+import "go/ast"
+
 func isNamed(typ Type) bool {
 	if _, ok := typ.(*Basic); ok {
 		return ok
@@ -247,3 +249,34 @@ func defaultType(typ Type) Type {
 	}
 	return typ
 }
+
+// missingMethod returns (nil, false) if typ implements T, otherwise
+// it returns the first missing method required by T and whether it
+// is missing or simply has the wrong type.
+//
+func missingMethod(typ Type, T *Interface) (method *ast.Object, wrongType bool) {
+	// TODO(gri): distinguish pointer and non-pointer receivers
+	// an interface type implements T if it has no methods with conflicting signatures
+	// Note: This is stronger than the current spec. Should the spec require this?
+	if ityp, _ := underlying(typ).(*Interface); ityp != nil {
+		for _, m := range T.Methods {
+			mode, sig := lookupField(ityp, m.Name) // TODO(gri) no need to go via lookupField
+			if mode != invalid && !isIdentical(sig, m.Type.(Type)) {
+				return m, true
+			}
+		}
+		return
+	}
+
+	// a concrete type implements T if it implements all methods of T.
+	for _, m := range T.Methods {
+		mode, sig := lookupField(typ, m.Name)
+		if mode == invalid {
+			return m, false
+		}
+		if !isIdentical(sig, m.Type.(Type)) {
+			return m, true
+		}
+	}
+	return
+}

src/pkg/exp/types/stmt.go

@@ -27,8 +27,8 @@ func (check *checker) assignOperand(z, x *operand) {
 	}
 }
 
-// assign1to1 typechecks a single assignment of the form lhs := rhs (if rhs != nil),
-// or lhs := x (if rhs == nil). If decl is set, the lhs operand must be an identifier.
+// assign1to1 typechecks a single assignment of the form lhs = rhs (if rhs != nil),
+// or lhs = x (if rhs == nil). 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. If lhs has a
 // type it is used as a hint when evaluating rhs, if present.
 //
@@ -226,19 +226,36 @@ func (check *checker) stmtList(list []ast.Stmt) {
 	}
 }
 
-func (check *checker) call(c ast.Expr) {
-	call, _ := c.(*ast.CallExpr)
-	if call == nil {
-		// For go/defer, the parser makes sure that we have a function call,
-		// so if we don't, the AST was created incorrectly elsewhere.
-		// TODO(gri) consider removing the checks from the parser.
-		check.invalidAST(c.Pos(), "%s is not a function call", c)
-		return
-	}
+func (check *checker) call(call *ast.CallExpr) {
 	var x operand
 	check.rawExpr(&x, call, nil, -1, false) // don't check if value is used
-	// TODO(gri) If a builtin is called, the builtin must be valid in statement
-	//           context. However, the spec doesn't say that explicitly.
+	// TODO(gri) If a builtin is called, the builtin must be valid in statement context.
+}
+
+func (check *checker) multipleDefaults(list []ast.Stmt) {
+	var first ast.Stmt
+	for _, s := range list {
+		var d ast.Stmt
+		switch c := s.(type) {
+		case *ast.CaseClause:
+			if len(c.List) == 0 {
+				d = s
+			}
+		case *ast.CommClause:
+			if c.Comm == nil {
+				d = s
+			}
+		default:
+			check.invalidAST(s.Pos(), "case/communication clause expected")
+		}
+		if d != nil {
+			if first != nil {
+				check.errorf(d.Pos(), "multiple defaults (first at %s)", first.Pos())
+			} else {
+				first = d
+			}
+		}
+	}
 }
 
 // stmt typechecks statement s.
@@ -280,7 +297,7 @@ func (check *checker) stmt(s ast.Stmt) {
 		}
 		check.rawExpr(&x, s.X, nil, -1, false)
 		if x.mode == typexpr {
-			check.errorf(x.pos(), "%s is not an expression", x)
+			check.errorf(x.pos(), "%s is not an expression", &x)
 		}
 
 	case *ast.SendStmt:
@@ -418,31 +435,122 @@ func (check *checker) stmt(s ast.Stmt) {
 			x.typ = Typ[UntypedBool]
 			x.val = true
 		}
+
+		check.multipleDefaults(s.Body.List)
 		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")
+			clause, _ := s.(*ast.CaseClause)
+			if clause == nil {
+				continue // error reported before
 			}
+			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)
 		}
 
 	case *ast.TypeSwitchStmt:
-		unimplemented()
+		check.optionalStmt(s.Init)
+
+		// A type switch guard must be of the form:
+		//
+		//     TypeSwitchGuard = [ identifier ":=" ] PrimaryExpr "." "(" "type" ")" .
+		//
+		// The parser is checking syntactic correctness;
+		// remaining syntactic errors are considered AST errors here.
+		// TODO(gri) better factoring of error handling (invalid ASTs)
+		//
+		var lhs *ast.Object // lhs identifier object or nil
+		var rhs ast.Expr
+		switch guard := s.Assign.(type) {
+		case *ast.ExprStmt:
+			rhs = guard.X
+		case *ast.AssignStmt:
+			if len(guard.Lhs) != 1 || guard.Tok != token.DEFINE || len(guard.Rhs) != 1 {
+				check.invalidAST(s.Pos(), "incorrect form of type switch guard")
+				return
+			}
+			ident, _ := guard.Lhs[0].(*ast.Ident)
+			if ident == nil {
+				check.invalidAST(s.Pos(), "incorrect form of type switch guard")
+				return
+			}
+			lhs = ident.Obj
+			rhs = guard.Rhs[0]
+		default:
+			check.invalidAST(s.Pos(), "incorrect form of type switch guard")
+			return
+		}
+
+		// rhs must be of the form: expr.(type) and expr must be an interface
+		expr, _ := rhs.(*ast.TypeAssertExpr)
+		if expr == nil || expr.Type != nil {
+			check.invalidAST(s.Pos(), "incorrect form of type switch guard")
+			return
+		}
+		var x operand
+		check.expr(&x, expr.X, nil, -1)
+		if x.mode == invalid {
+			return
+		}
+		var T *Interface
+		if T, _ = underlying(x.typ).(*Interface); T == nil {
+			check.errorf(x.pos(), "%s is not an interface", &x)
+			return
+		}
+
+		check.multipleDefaults(s.Body.List)
+		for _, s := range s.Body.List {
+			clause, _ := s.(*ast.CaseClause)
+			if clause == nil {
+				continue // error reported before
+			}
+			// Check each type in this type switch case.
+			var typ Type
+			for _, expr := range clause.List {
+				typ = check.typOrNil(expr, false)
+				if typ != nil && typ != Typ[Invalid] {
+					if method, wrongType := missingMethod(typ, T); method != nil {
+						var msg string
+						if wrongType {
+							msg = "%s cannot have dynamic type %s (wrong type for method %s)"
+						} else {
+							msg = "%s cannot have dynamic type %s (missing method %s)"
+						}
+						check.errorf(expr.Pos(), msg, &x, typ, method.Name)
+						// ok to continue
+					}
+				}
+			}
+			// If lhs exists, set its type for each clause.
+			if lhs != nil {
+				// In clauses with a case listing exactly one type, the variable has that type;
+				// otherwise, the variable has the type of the expression in the TypeSwitchGuard.
+				if len(clause.List) != 1 || typ == nil {
+					typ = x.typ
+				}
+				lhs.Type = typ
+			}
+			check.stmtList(clause.Body)
+		}
+
+		// There is only one object (lhs) associated with a lhs identifier, but that object
+		// assumes different types for different clauses. Set it to nil when we are done so
+		// that the type cannot be used by mistake.
+		if lhs != nil {
+			lhs.Type = nil
+		}
 
 	case *ast.SelectStmt:
+		check.multipleDefaults(s.Body.List)
 		for _, s := range s.Body.List {
-			c, ok := s.(*ast.CommClause)
-			if !ok {
-				check.invalidAST(s.Pos(), "communication clause expected")
-				continue
+			clause, _ := s.(*ast.CommClause)
+			if clause == nil {
+				continue // error reported before
 			}
-			check.optionalStmt(c.Comm) // TODO(gri) check correctness of c.Comm (must be Send/RecvStmt)
-			check.stmtList(c.Body)
+			check.optionalStmt(clause.Comm) // TODO(gri) check correctness of c.Comm (must be Send/RecvStmt)
+			check.stmtList(clause.Body)
 		}
 
 	case *ast.ForStmt:
@@ -458,7 +566,79 @@ func (check *checker) stmt(s ast.Stmt) {
 		check.stmt(s.Body)
 
 	case *ast.RangeStmt:
-		unimplemented()
+		// check expression to iterate over
+		decl := s.Tok == token.DEFINE
+		var x operand
+		check.expr(&x, s.X, nil, -1)
+		if x.mode == invalid {
+			// if we don't have a declaration, we can still check the loop's body
+			if !decl {
+				check.stmt(s.Body)
+			}
+			return
+		}
+
+		// determine key/value types
+		var key, val Type
+		switch typ := underlying(x.typ).(type) {
+		case *Basic:
+			if isString(typ) {
+				key = Typ[UntypedInt]
+				val = Typ[UntypedRune]
+			}
+		case *Array:
+			key = Typ[UntypedInt]
+			val = typ.Elt
+		case *Slice:
+			key = Typ[UntypedInt]
+			val = typ.Elt
+		case *Pointer:
+			if typ, _ := underlying(typ.Base).(*Array); typ != nil {
+				key = Typ[UntypedInt]
+				val = typ.Elt
+			}
+		case *Map:
+			key = typ.Key
+			val = typ.Elt
+		case *Chan:
+			key = typ.Elt
+			if typ.Dir&ast.RECV == 0 {
+				check.errorf(x.pos(), "cannot range over send-only channel %s", &x)
+				// ok to continue
+			}
+			if s.Value != nil {
+				check.errorf(s.Value.Pos(), "iteration over %s permits only one iteration variable", &x)
+				// ok to continue
+			}
+		}
+
+		if key == nil {
+			check.errorf(x.pos(), "cannot range over %s", &x)
+			// if we don't have a declaration, we can still check the loop's body
+			if !decl {
+				check.stmt(s.Body)
+			}
+			return
+		}
+
+		// check assignment to/declaration of iteration variables
+		// TODO(gri) The error messages/positions are not great here,
+		//           they refer to the expression in the range clause.
+		//           Should give better messages w/o too much code
+		//           duplication (assignment checking).
+		if s.Key != nil {
+			x.typ = key
+			check.assign1to1(s.Key, nil, &x, decl, -1)
+		} else {
+			check.invalidAST(s.Pos(), "range clause requires index iteration variable")
+			// ok to continue
+		}
+		if s.Value != nil {
+			x.typ = val
+			check.assign1to1(s.Value, nil, &x, decl, -1)
+		}
+
+		check.stmt(s.Body)
 
 	default:
 		check.errorf(s.Pos(), "invalid statement")

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

@@ -73,7 +73,7 @@ var (
 
 // Various more complex expressions
 var (
-	u1 = x /* ERROR "non-interface type" */ .(int)
+	u1 = x /* ERROR "not an interface" */ .(int)
 	u2 = iface.([]int)
 	u3 = iface.(a /* ERROR "not a type" */ )
 	u4, ok = iface.(int)

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

@@ -75,6 +75,17 @@ func indexes() {
 	_ = a[: 11 /* ERROR "index .* out of bounds" */ ]
 	_ = a[: 1 /* ERROR "stupid index" */ <<100]
 
+	pa := &a
+	_ = pa[9]
+	_ = pa[10 /* ERROR "index .* out of bounds" */ ]
+	_ = pa[1 /* ERROR "stupid index" */ <<100]
+	_ = pa[10:]
+	_ = pa[:10]
+	_ = pa[10:10]
+	_ = pa[11 /* ERROR "index .* out of bounds" */ :]
+	_ = pa[: 11 /* ERROR "index .* out of bounds" */ ]
+	_ = pa[: 1 /* ERROR "stupid index" */ <<100]
+
 	var b [0]int
 	_ = b[0 /* ERROR "index .* out of bounds" */ ]
 	_ = b[:]
@@ -206,6 +217,15 @@ func array_literals() {
 
 	a4 := [...]complex128{0, 1, 2, 1<<10-2: -1i, 1i, 400: 10, 12, 14}
 	assert(len(a4) == 1024)
+
+	// from the spec
+	type Point struct { x, y float32 }
+	_ = [...]Point{Point{1.5, -3.5}, Point{0, 0}}
+	_ = [...]Point{{1.5, -3.5}, {0, 0}}
+	_ = [][]int{[]int{1, 2, 3}, []int{4, 5}}
+	_ = [][]int{{1, 2, 3}, {4, 5}}
+	_ = [...]*Point{&Point{1.5, -3.5}, &Point{0, 0}}
+	_ = [...]*Point{{1.5, -3.5}, {0, 0}}
 }
 
 func slice_literals() {
@@ -237,3 +257,32 @@ func map_literals() {
 	_ = M0{"foo": "bar" /* ERROR "cannot use .* as int value" */ }
 	_ = M0{"foo": 1, "bar": 2, "foo" /* ERROR "duplicate key" */ : 3 }
 }
+
+type I interface {
+	m()
+}
+
+type I2 interface {
+	m(int)
+}
+
+type T1 struct{}
+type T2 struct{}
+
+func (T2) m(int) {}
+
+func type_asserts() {
+	var x int
+	_ = x /* ERROR "not an interface" */ .(int)
+
+	var e interface{}
+	var ok bool
+	x, ok = e.(int)
+
+	var t I
+	_ = t /* ERROR "use of .* outside type switch" */ .(type)
+	_ = t.(T)
+	_ = t.(T1 /* ERROR "missing method m" */ )
+	_ = t.(T2 /* ERROR "wrong type for method m" */ )
+	_ = t.(I2 /* ERROR "wrong type for method m" */ )
+}

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

@@ -71,6 +71,10 @@ func _selects() {
 		x = t
 	case <-sc /* ERROR "cannot receive from send-only channel" */ :
 	}
+	select {
+	default:
+	default /* ERROR "multiple defaults" */ :
+	}
 }
 
 func _gos() {
@@ -88,3 +92,149 @@ func _defers() {
 	defer close(c)
 	defer len(c) // TODO(gri) this should not be legal
 }
+
+func _switches() {
+	var x int
+
+	switch x {
+	default:
+	default /* ERROR "multiple defaults" */ :
+	}
+
+	// TODO(gri) more tests
+}
+
+type I interface {
+	m()
+}
+
+type I2 interface {
+	m(int)
+}
+
+type T struct{}
+type T1 struct{}
+type T2 struct{}
+
+func (T) m() {}
+func (T2) m(int) {}
+
+func _typeswitches() {
+	var i int
+	var x interface{}
+
+	switch x.(type) {}
+	switch (x /* ERROR "outside type switch" */ .(type)) {}
+
+	switch x.(type) {
+	default:
+	default /* ERROR "multiple defaults" */ :
+	}
+
+	switch x := x.(type) {}
+
+	switch x := x.(type) {
+	case int:
+		var y int = x
+	}
+
+	switch x := i /* ERROR "not an interface" */ .(type) {}
+
+	switch t := x.(type) {
+	case nil:
+		var v bool = t /* ERROR "cannot assign" */
+	case int:
+		var v int = t
+	case float32, complex64:
+		var v float32 = t /* ERROR "cannot assign" */
+	default:
+		var v float32 = t /* ERROR "cannot assign" */
+	}
+
+	var t I
+	switch t.(type) {
+	case T:
+	case T1 /* ERROR "missing method m" */ :
+	case T2 /* ERROR "wrong type for method m" */ :
+	case I2 /* ERROR "wrong type for method m" */ :
+	}
+}
+
+func _rangeloops() {
+	var (
+		x int
+		a [10]float32
+		b []string
+		p *[10]complex128
+		pp **[10]complex128
+		s string
+		m map[int]bool
+		c chan int
+		sc chan<- int
+		rc <-chan int
+	)
+
+	for _ = range x /* ERROR "cannot range over" */ {}
+	for i := range x /* ERROR "cannot range over" */ {}
+
+	for i := range a {
+		var ii int
+		ii = i
+	}
+	for i, x := range a {
+		var ii int
+		ii = i
+		var xx float64
+		xx = x /* ERROR "cannot assign" */
+	}
+	var ii int
+	var xx float32
+	for ii, xx := range a {}
+
+	for i := range b {
+		var ii int
+		ii = i
+	}
+	for i, x := range b {
+		var ii int
+		ii = i
+		var xx string
+		xx = x
+	}
+
+	for i := range s {
+		var ii int
+		ii = i
+	}
+	for i, x := range s {
+		var ii int
+		ii = i
+		var xx rune
+		xx = x
+	}
+
+	for _, x := range p {
+		var xx complex128
+		xx = x
+	}
+
+	for _, x := range pp /* ERROR "cannot range over" */ {}
+
+	for k := range m {
+		var kk int32
+		kk = k /* ERROR "cannot assign" */
+	}
+	for k, v := range m {
+		var kk int
+		kk = k
+		if v {}
+	}
+
+	for _, _ /* ERROR "only one iteration variable" */ = range c {}
+	for e := range c {
+		var ee int
+		ee = e
+	}
+	for _ = range sc /* ERROR "cannot range over send-only channel" */ {}
+	for _ = range rc {}
+}

src/pkg/exp/types/universe.go

@@ -116,10 +116,12 @@ func init() {
 
 	// error type
 	{
+		res := ast.NewObj(ast.Var, "")
+		res.Type = Typ[String]
+		err := ast.NewObj(ast.Fun, "Error")
+		err.Type = &Signature{Results: ObjList{res}}
 		obj := def(ast.Typ, "error")
-		// TODO(gri) set up correct interface type
-		typ := &NamedType{Underlying: &Interface{}, Obj: obj}
-		obj.Type = typ
+		obj.Type = &NamedType{Underlying: &Interface{Methods: ObjList{err}}, Obj: obj}
 	}
 
 	// predeclared constants

src/pkg/go/parser/parser.go

@@ -1803,7 +1803,7 @@ func (p *parser) parseSwitchStmt() ast.Stmt {
 				//
 				//	switch t := 0; t := x.(T) { ... }
 				//
-				// (this code is not valid Go because the first t will
+				// (this code is not valid Go because the first t
 				// cannot be accessed and thus is never used, the extra
 				// scope is needed for the correct error message).
 				//