go/types/call.go - tools - Git at Google

 // Copyright 2013 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 call and selector expressions.

 package types

 import (
 	"go/ast"
 	"go/token"
 )

 func (check *checker) call(x *operand, e *ast.CallExpr) {
 	check.exprOrType(x, e.Fun)
 	if x.mode == invalid {
 		// We don't have a valid call or conversion but we have a list of arguments.
 		// Typecheck them independently for better partial type information in
 		// the presence of type errors.
 		for _, arg := range e.Args {
 			check.expr(x, arg)
 		}
 		x.mode = invalid
 		x.expr = e
 		return
 	}

 	if x.mode == typexpr {
 		check.conversion(x, e, x.typ)
 		return
 	}

 	if sig, ok := x.typ.Underlying().(*Signature); ok {
 		// function/method call

 		passSlice := false
 		if e.Ellipsis.IsValid() {
 			// last argument is of the form x...
 			if sig.isVariadic {
 				passSlice = true
 			} else {
 				check.errorf(e.Ellipsis, "cannot use ... in call to non-variadic %s", e.Fun)
 				// ok to continue
 			}
 		}

 		// evaluate arguments
 		n := len(e.Args) // argument count
 		if n == 1 {
 			// single argument but possibly a multi-valued function call
 			arg := e.Args[0]
 			check.expr(x, arg)
 			if x.mode != invalid {
 				if t, ok := x.typ.(*Tuple); ok {
 					// argument is multi-valued function call
 					n = t.Len()
 					for i := 0; i < n; i++ {
 						x.mode = value
 						x.expr = arg
 						x.typ = t.At(i).typ
 						check.argument(sig, i, x, passSlice && i == n-1)
 					}
 				} else {
 					// single value
 					check.argument(sig, 0, x, passSlice)
 				}
 			} else {
 				n = sig.params.Len() // avoid additional argument length errors below
 			}
 		} else {
 			// zero or multiple arguments
 			for i, arg := range e.Args {
 				check.expr(x, arg)
 				if x.mode != invalid {
 					check.argument(sig, i, x, passSlice && i == n-1)
 				}
 			}
 		}

 		// check argument count
 		if sig.isVariadic {
 			// a variadic function accepts an "empty"
 			// last argument: count one extra
 			n++
 		}
 		if n < sig.params.Len() {
 			check.errorf(e.Fun.Pos(), "too few arguments in call to %s", e.Fun)
 			// ok to continue
 		}

 		// determine result
 		switch sig.results.Len() {
 		case 0:
 			x.mode = novalue
 		case 1:
 			x.mode = value
 			x.typ = sig.results.vars[0].typ // unpack tuple
 		default:
 			x.mode = value
 			x.typ = sig.results
 		}
 		x.expr = e
 		return
 	}

 	if bin, ok := x.typ.(*Builtin); ok {
 		check.builtin(x, e, bin)
 		return
 	}

 	check.invalidOp(x.pos(), "cannot call non-function %s", x)
 	x.mode = invalid
 	x.expr = e
 }

 // argument checks passing of argument x to the i'th parameter of the given signature.
 // If passSlice is set, the argument is followed by ... in the call.
 func (check *checker) argument(sig *Signature, i int, x *operand, passSlice bool) {
 	n := sig.params.Len()

 	// determine parameter type
 	var typ Type
 	switch {
 	case i < n:
 		typ = sig.params.vars[i].typ
 	case sig.isVariadic:
 		typ = sig.params.vars[n-1].typ
 		if debug {
 			if _, ok := typ.(*Slice); !ok {
 				check.dump("%s: expected slice type, got %s", sig.params.vars[n-1].Pos(), typ)
 			}
 		}
 	default:
 		check.errorf(x.pos(), "too many arguments")
 		return
 	}

 	if passSlice {
 		// argument is of the form x...
 		if i != n-1 {
 			check.errorf(x.pos(), "can only use ... with matching parameter")
 			return
 		}
 		if _, ok := x.typ.(*Slice); !ok {
 			check.errorf(x.pos(), "cannot use %s as parameter of type %s", x, typ)
 			return
 		}
 	} else if sig.isVariadic && i >= n-1 {
 		// use the variadic parameter slice's element type
 		typ = typ.(*Slice).elt
 	}

 	if !check.assignment(x, typ) && x.mode != invalid {
 		check.errorf(x.pos(), "cannot pass argument %s to parameter of type %s", x, typ)
 	}
 }

 func (check *checker) selector(x *operand, e *ast.SelectorExpr) {
 	// these must be declared before the "goto Error" statements
 	var (
 		obj      Object
 		index    []int
 		indirect bool
 	)

 	sel := e.Sel.Name
 	// 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 pkg, ok := check.topScope.LookupParent(ident.Name).(*Package); ok {
 			check.recordObject(ident, pkg)
 			exp := pkg.scope.Lookup(sel)
 			if exp == nil {
 				check.errorf(e.Pos(), "%s not declared by package %s", sel, ident)
 				goto Error
 			} else if !exp.IsExported() {
 				// gcimported package scopes contain non-exported
 				// objects such as types used in partially exported
 				// objects - do not accept them
 				check.errorf(e.Pos(), "%s not exported by package %s", sel, ident)
 				goto Error
 			}
 			check.recordObject(e.Sel, exp)
 			// Simplified version of the code for *ast.Idents:
 			// - imported packages use types.Scope and types.Objects
 			// - imported objects are always fully initialized
 			switch exp := exp.(type) {
 			case *Const:
 				assert(exp.Val != nil)
 				x.mode = constant
 				x.typ = exp.typ
 				x.val = exp.val
 			case *TypeName:
 				x.mode = typexpr
 				x.typ = exp.typ
 			case *Var:
 				x.mode = variable
 				x.typ = exp.typ
 			case *Func:
 				x.mode = value
 				x.typ = exp.typ
 			default:
 				unreachable()
 			}
 			x.expr = e
 			return
 		}
 	}

 	check.exprOrType(x, e.X)
 	if x.mode == invalid {
 		goto Error
 	}

 	obj, index, indirect = LookupFieldOrMethod(x.typ, check.pkg, sel)
 	if obj == nil {
 		if index != nil {
 			// TODO(gri) should provide actual type where the conflict happens
 			check.invalidOp(e.Pos(), "ambiguous selector %s", sel)
 		} else {
 			check.invalidOp(e.Pos(), "%s has no field or method %s", x, sel)
 		}
 		goto Error
 	}

 	// TODO(gri) don't create a lookupResult if no Objects map exists
 	check.recordObject(e.Sel, lookupResult(x.typ, obj, index, indirect))

 	if x.mode == typexpr {
 		// method expression
 		m, _ := obj.(*Func)
 		if m == nil {
 			check.invalidOp(e.Pos(), "%s has no method %s", x, sel)
 			goto Error
 		}

 		// verify that m is in the method set of x.typ
 		if !indirect && ptrRecv(m) {
 			check.invalidOp(e.Pos(), "%s is not in method set of %s", sel, x.typ)
 			goto Error
 		}

 		// the receiver type becomes the type of the first function
 		// argument of the method expression's function type
 		var params []*Var
 		sig := m.typ.(*Signature)
 		if sig.params != nil {
 			params = sig.params.vars
 		}
 		x.mode = value
 		x.typ = &Signature{
 			params:     NewTuple(append([]*Var{NewVar(token.NoPos, check.pkg, "", x.typ)}, params...)...),
 			results:    sig.results,
 			isVariadic: sig.isVariadic,
 		}

 	} else {
 		// regular selector
 		switch obj := obj.(type) {
 		case *Var:
 			x.mode = variable
 			x.typ = obj.typ

 		case *Func:
 			// TODO(gri) This code appears elsewhere, too. Factor!
 			// verify that obj is in the method set of x.typ (or &(x.typ) if x is addressable)
 			//
 			// spec: "A method call x.m() is valid if the method set of (the type of) x
 			//        contains m and the argument list can be assigned to the parameter
 			//        list of m. If x is addressable and &x's method set contains m, x.m()
 			//        is shorthand for (&x).m()".
 			if !indirect && x.mode != variable && ptrRecv(obj) {
 				check.invalidOp(e.Pos(), "%s is not in method set of %s", sel, x)
 				goto Error
 			}

 			if debug {
 				// Verify that LookupFieldOrMethod and MethodSet.Lookup agree.
 				typ := x.typ
 				if x.mode == variable {
 					// If typ is not an (unnamed) pointer, use *typ instead,
 					// because the method set of *typ includes the methods
 					// of typ.
 					// Variables are addressable, so we can always take their
 					// address.
 					if _, isPtr := typ.(*Pointer); !isPtr {
 						typ = &Pointer{base: typ}
 					}
 				}
 				// If we created a synthetic pointer type above, we will throw
 				// away the method set computed here after use.
 				// TODO(gri) Consider also using a method set cache for the lifetime
 				// of checker once we rely on MethodSet lookup instead of individual
 				// lookup.
 				mset := typ.MethodSet()
 				if m := mset.Lookup(check.pkg, sel); m == nil || m.Func != obj {
 					check.dump("%s: (%s).%v -> %s", e.Pos(), typ, obj.name, m)
 					check.dump("%s\n", mset)
 					panic("method sets and lookup don't agree")
 				}
 			}

 			x.mode = value
 			x.typ = obj.typ

 		default:
 			unreachable()
 		}
 	}

 	// everything went well
 	x.expr = e
 	return

 Error:
 	x.mode = invalid
 	x.expr = e
 }
	// Copyright 2013 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 call and selector expressions.

	package types

	import (
	"go/ast"
	"go/token"
	)

	func (check checker) call(x operand, e *ast.CallExpr) {
	check.exprOrType(x, e.Fun)
	if x.mode == invalid {
	// We don't have a valid call or conversion but we have a list of arguments.
	// Typecheck them independently for better partial type information in
	// the presence of type errors.
	for _, arg := range e.Args {
	check.expr(x, arg)
	}
	x.mode = invalid
	x.expr = e
	return
	}

	if x.mode == typexpr {
	check.conversion(x, e, x.typ)
	return
	}

	if sig, ok := x.typ.Underlying().(*Signature); ok {
	// function/method call

	passSlice := false
	if e.Ellipsis.IsValid() {
	// last argument is of the form x...
	if sig.isVariadic {
	passSlice = true
	} else {
	check.errorf(e.Ellipsis, "cannot use ... in call to non-variadic %s", e.Fun)
	// ok to continue
	}
	}

	// evaluate arguments
	n := len(e.Args) // argument count
	if n == 1 {
	// single argument but possibly a multi-valued function call
	arg := e.Args[0]
	check.expr(x, arg)
	if x.mode != invalid {
	if t, ok := x.typ.(*Tuple); ok {
	// argument is multi-valued function call
	n = t.Len()
	for i := 0; i < n; i++ {
	x.mode = value
	x.expr = arg
	x.typ = t.At(i).typ
	check.argument(sig, i, x, passSlice && i == n-1)
	}
	} else {
	// single value
	check.argument(sig, 0, x, passSlice)
	}
	} else {
	n = sig.params.Len() // avoid additional argument length errors below
	}
	} else {
	// zero or multiple arguments
	for i, arg := range e.Args {
	check.expr(x, arg)
	if x.mode != invalid {
	check.argument(sig, i, x, passSlice && i == n-1)
	}
	}
	}

	// check argument count
	if sig.isVariadic {
	// a variadic function accepts an "empty"
	// last argument: count one extra
	n++
	}
	if n < sig.params.Len() {
	check.errorf(e.Fun.Pos(), "too few arguments in call to %s", e.Fun)
	// ok to continue
	}

	// determine result
	switch sig.results.Len() {
	case 0:
	x.mode = novalue
	case 1:
	x.mode = value
	x.typ = sig.results.vars[0].typ // unpack tuple
	default:
	x.mode = value
	x.typ = sig.results
	}
	x.expr = e
	return
	}

	if bin, ok := x.typ.(*Builtin); ok {
	check.builtin(x, e, bin)
	return
	}

	check.invalidOp(x.pos(), "cannot call non-function %s", x)
	x.mode = invalid
	x.expr = e
	}

	// argument checks passing of argument x to the i'th parameter of the given signature.
	// If passSlice is set, the argument is followed by ... in the call.
	func (check checker) argument(sig Signature, i int, x *operand, passSlice bool) {
	n := sig.params.Len()

	// determine parameter type
	var typ Type
	switch {
	case i < n:
	typ = sig.params.vars[i].typ
	case sig.isVariadic:
	typ = sig.params.vars[n-1].typ
	if debug {
	if _, ok := typ.(*Slice); !ok {
	check.dump("%s: expected slice type, got %s", sig.params.vars[n-1].Pos(), typ)
	}
	}
	default:
	check.errorf(x.pos(), "too many arguments")
	return
	}

	if passSlice {
	// argument is of the form x...
	if i != n-1 {
	check.errorf(x.pos(), "can only use ... with matching parameter")
	return
	}
	if _, ok := x.typ.(*Slice); !ok {
	check.errorf(x.pos(), "cannot use %s as parameter of type %s", x, typ)
	return
	}
	} else if sig.isVariadic && i >= n-1 {
	// use the variadic parameter slice's element type
	typ = typ.(*Slice).elt
	}

	if !check.assignment(x, typ) && x.mode != invalid {
	check.errorf(x.pos(), "cannot pass argument %s to parameter of type %s", x, typ)
	}
	}

	func (check checker) selector(x operand, e *ast.SelectorExpr) {
	// these must be declared before the "goto Error" statements
	var (
	obj Object
	index []int
	indirect bool
	)

	sel := e.Sel.Name
	// 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 pkg, ok := check.topScope.LookupParent(ident.Name).(*Package); ok {
	check.recordObject(ident, pkg)
	exp := pkg.scope.Lookup(sel)
	if exp == nil {
	check.errorf(e.Pos(), "%s not declared by package %s", sel, ident)
	goto Error
	} else if !exp.IsExported() {
	// gcimported package scopes contain non-exported
	// objects such as types used in partially exported
	// objects - do not accept them
	check.errorf(e.Pos(), "%s not exported by package %s", sel, ident)
	goto Error
	}
	check.recordObject(e.Sel, exp)
	// Simplified version of the code for *ast.Idents:
	// - imported packages use types.Scope and types.Objects
	// - imported objects are always fully initialized
	switch exp := exp.(type) {
	case *Const:
	assert(exp.Val != nil)
	x.mode = constant
	x.typ = exp.typ
	x.val = exp.val
	case *TypeName:
	x.mode = typexpr
	x.typ = exp.typ
	case *Var:
	x.mode = variable
	x.typ = exp.typ
	case *Func:
	x.mode = value
	x.typ = exp.typ
	default:
	unreachable()
	}
	x.expr = e
	return
	}
	}

	check.exprOrType(x, e.X)
	if x.mode == invalid {
	goto Error
	}

	obj, index, indirect = LookupFieldOrMethod(x.typ, check.pkg, sel)
	if obj == nil {
	if index != nil {
	// TODO(gri) should provide actual type where the conflict happens
	check.invalidOp(e.Pos(), "ambiguous selector %s", sel)
	} else {
	check.invalidOp(e.Pos(), "%s has no field or method %s", x, sel)
	}
	goto Error
	}

	// TODO(gri) don't create a lookupResult if no Objects map exists
	check.recordObject(e.Sel, lookupResult(x.typ, obj, index, indirect))

	if x.mode == typexpr {
	// method expression
	m, _ := obj.(*Func)
	if m == nil {
	check.invalidOp(e.Pos(), "%s has no method %s", x, sel)
	goto Error
	}

	// verify that m is in the method set of x.typ
	if !indirect && ptrRecv(m) {
	check.invalidOp(e.Pos(), "%s is not in method set of %s", sel, x.typ)
	goto Error
	}

	// the receiver type becomes the type of the first function
	// argument of the method expression's function type
	var params []*Var
	sig := m.typ.(*Signature)
	if sig.params != nil {
	params = sig.params.vars
	}
	x.mode = value
	x.typ = &Signature{
	params: NewTuple(append([]*Var{NewVar(token.NoPos, check.pkg, "", x.typ)}, params...)...),
	results: sig.results,
	isVariadic: sig.isVariadic,
	}

	} else {
	// regular selector
	switch obj := obj.(type) {
	case *Var:
	x.mode = variable
	x.typ = obj.typ

	case *Func:
	// TODO(gri) This code appears elsewhere, too. Factor!
	// verify that obj is in the method set of x.typ (or &(x.typ) if x is addressable)
	//
	// spec: "A method call x.m() is valid if the method set of (the type of) x
	// contains m and the argument list can be assigned to the parameter
	// list of m. If x is addressable and &x's method set contains m, x.m()
	// is shorthand for (&x).m()".
	if !indirect && x.mode != variable && ptrRecv(obj) {
	check.invalidOp(e.Pos(), "%s is not in method set of %s", sel, x)
	goto Error
	}

	if debug {
	// Verify that LookupFieldOrMethod and MethodSet.Lookup agree.
	typ := x.typ
	if x.mode == variable {
	// If typ is not an (unnamed) pointer, use *typ instead,
	// because the method set of *typ includes the methods
	// of typ.
	// Variables are addressable, so we can always take their
	// address.
	if _, isPtr := typ.(*Pointer); !isPtr {
	typ = &Pointer{base: typ}
	}
	}
	// If we created a synthetic pointer type above, we will throw
	// away the method set computed here after use.
	// TODO(gri) Consider also using a method set cache for the lifetime
	// of checker once we rely on MethodSet lookup instead of individual
	// lookup.
	mset := typ.MethodSet()
	if m := mset.Lookup(check.pkg, sel); m == nil \|\| m.Func != obj {
	check.dump("%s: (%s).%v -> %s", e.Pos(), typ, obj.name, m)
	check.dump("%s\n", mset)
	panic("method sets and lookup don't agree")
	}
	}

	x.mode = value
	x.typ = obj.typ

	default:
	unreachable()
	}
	}

	// everything went well
	x.expr = e
	return

	Error:
	x.mode = invalid
	x.expr = e
	}