exp/types/staging: support for typechecking (most) builtins

This code relies on some functions that are not yet in staging,
but it get's harder to keep all this in sync in a piece-meal
fashion.

R=rsc
CC=golang-dev
https://golang.org/cl/6492124

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

+// 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 builtin function calls.
+
+package types
+
+import (
+	"go/ast"
+	"go/token"
+)
+
+// builtin typechecks a built-in call. The built-in type is bin, and iota is the current
+// value of iota or -1 if iota doesn't have a value in the current context. The result
+// of the call is returned via x. If the call has type errors, the returned x is marked
+// as invalid (x.mode == invalid).
+//
+func (check *checker) builtin(x *operand, call *ast.CallExpr, bin *builtin, iota int) {
+	args := call.Args
+	id := bin.id
+
+	// declare before goto's
+	var arg0 ast.Expr
+	var typ0 Type
+
+	// check argument count
+	n := len(args)
+	msg := ""
+	if n < bin.nargs {
+		msg = "not enough"
+	} else if !bin.isVariadic && n > bin.nargs {
+		msg = "too many"
+	}
+	if msg != "" {
+		check.invalidOp(call.Pos(), msg+"arguments for %s (expected %d, found %d)", call, bin.nargs, n)
+		goto Error
+	}
+
+	// common case: evaluate first argument if present;
+	// if it is an expression, x has the expression value
+	if n > 0 {
+		arg0 = args[0]
+		switch id {
+		case _Make, _New:
+			// argument must be a type
+			typ0 = underlying(check.typ(arg0, false))
+			if typ0 == Typ[Invalid] {
+				goto Error
+			}
+		case _Trace:
+			// _Trace implementation does the work
+		default:
+			// argument must be an expression
+			check.expr(x, arg0, nil, iota)
+			if x.mode == invalid {
+				goto Error
+			}
+			typ0 = underlying(x.typ)
+		}
+	}
+
+	switch id {
+	case _Append:
+		s, ok := typ0.(*Slice)
+		if !ok {
+			check.invalidArg(x.pos(), "%s is not a typed slice", x)
+			goto Error
+		}
+		for _, arg := range args[1:] {
+			check.expr(x, arg, nil, iota)
+			if x.mode == invalid {
+				goto Error
+			}
+			// TODO(gri) check assignability
+		}
+		x.mode = value
+		x.typ = s
+
+	case _Cap, _Len:
+		mode := invalid
+		var val interface{}
+		switch typ := implicitDeref(typ0).(type) {
+		case *Basic:
+			if isString(typ) && id == _Len {
+				if x.mode == constant {
+					mode = constant
+					val = int64(len(x.val.(string)))
+				} else {
+					mode = value
+				}
+			}
+
+		case *Array:
+			mode = value
+			if !containsCallsOrReceives(arg0) {
+				mode = constant
+				val = typ.Len
+			}
+
+		case *Slice, *Chan:
+			mode = value
+
+		case *Map:
+			if id == _Len {
+				mode = value
+			}
+		}
+
+		if mode == invalid {
+			check.invalidArg(x.pos(), "%s for %s", x, bin.name)
+			goto Error
+		}
+		x.mode = mode
+		x.typ = Typ[Int]
+		x.val = val
+
+	case _Close:
+		ch, ok := typ0.(*Chan)
+		if !ok {
+			check.invalidArg(x.pos(), "%s is not a channel", x)
+			goto Error
+		}
+		if ch.Dir&ast.SEND == 0 {
+			check.invalidArg(x.pos(), "%s must not be a receive-only channel", x)
+			goto Error
+		}
+		x.mode = novalue
+
+	case _Complex:
+		var y operand
+		check.expr(&y, args[1], nil, iota)
+		if y.mode == invalid {
+			goto Error
+		}
+		// TODO(gri) handle complex(a, b) like (a + toImag(b))
+		unimplemented()
+
+	case _Copy:
+		// TODO(gri) implements checks
+		unimplemented()
+		x.mode = value
+		x.typ = Typ[Int]
+
+	case _Delete:
+		m, ok := typ0.(*Map)
+		if !ok {
+			check.invalidArg(x.pos(), "%s is not a map", x)
+			goto Error
+		}
+		check.expr(x, args[1], nil, iota)
+		if x.mode == invalid {
+			goto Error
+		}
+		if !x.isAssignable(m.Key) {
+			check.invalidArg(x.pos(), "%s is not assignable to %s", x, m.Key)
+			goto Error
+		}
+		x.mode = novalue
+
+	case _Imag, _Real:
+		if !isComplex(typ0) {
+			check.invalidArg(x.pos(), "%s must be a complex number", x)
+			goto Error
+		}
+		if x.mode == constant {
+			// nothing to do for x.val == 0
+			if !isZeroConst(x.val) {
+				c := x.val.(complex)
+				if id == _Real {
+					x.val = c.re
+				} else {
+					x.val = c.im
+				}
+			}
+		} else {
+			x.mode = value
+		}
+		k := Invalid
+		switch typ0.(*Basic).Kind {
+		case Complex64:
+			k = Float32
+		case Complex128:
+			k = Float64
+		case UntypedComplex:
+			k = UntypedFloat
+		default:
+			unreachable()
+		}
+		x.typ = Typ[k]
+
+	case _Make:
+		var min int // minimum number of arguments
+		switch typ0.(type) {
+		case *Slice:
+			min = 2
+		case *Map, *Chan:
+			min = 1
+		default:
+			check.invalidArg(arg0.Pos(), "cannot make %s; type must be slice, map, or channel", arg0)
+			goto Error
+		}
+		if n := len(args); n < min || min+1 < n {
+			check.errorf(call.Pos(), "%s expects %d or %d arguments; found %d", call, min, min+1, n)
+			goto Error
+		}
+		for _, arg := range args[1:] {
+			check.expr(x, arg, nil, iota)
+			if !x.isInteger() {
+				check.invalidArg(x.pos(), "%s must be an integer", x)
+				// safe to continue
+			}
+		}
+		x.mode = variable
+		x.typ = typ0
+
+	case _New:
+		x.mode = variable
+		x.typ = &Pointer{Base: typ0}
+
+	case _Panic, _Print, _Println:
+		x.mode = novalue
+
+	case _Recover:
+		x.mode = value
+		x.typ = emptyInterface
+
+	case _Alignof:
+		x.mode = constant
+		x.typ = Typ[Uintptr]
+		// For now we return 1 always as it satisfies the spec's alignment guarantees.
+		// TODO(gri) Extend typechecker API so that platform-specific values can be
+		//           provided.
+		x.val = int64(1)
+
+	case _Offsetof:
+		if _, ok := unparen(x.expr).(*ast.SelectorExpr); !ok {
+			check.invalidArg(x.pos(), "%s is not a selector", x)
+			goto Error
+		}
+		x.mode = constant
+		x.typ = Typ[Uintptr]
+		// because of the size guarantees for basic types (> 0 for some),
+		// returning 0 is only correct if two distinct non-zero size
+		// structs can have the same address (the spec permits that)
+		x.val = int64(0)
+
+	case _Sizeof:
+		// basic types with specified sizes have size guarantees; for all others we use 0
+		var size int64
+		if typ, ok := typ0.(*Basic); ok {
+			size = typ.Size
+		}
+		x.mode = constant
+		x.typ = Typ[Uintptr]
+		x.val = size
+
+	case _Assert:
+		// assert(pred) causes a typechecker error if pred is false.
+		// The result of assert is the value of pred if there is no error.
+		// Note: assert is only available in self-test mode.
+		if x.mode != constant || !isBoolean(typ0) {
+			check.invalidArg(x.pos(), "%s is not a boolean constant", x)
+			goto Error
+		}
+		pred, ok := x.val.(bool)
+		if !ok {
+			check.errorf(x.pos(), "internal error: value of %s should be a boolean constant", x)
+			goto Error
+		}
+		if !pred {
+			check.errorf(call.Pos(), "%s failed", call)
+			// compile-time assertion failure - safe to continue
+		}
+
+	case _Trace:
+		// trace(x, y, z, ...) dumps the positions, expressions, and
+		// values of its arguments. The result of trace is the value
+		// of the first argument.
+		// Note: trace is only available in self-test mode.
+		if len(args) == 0 {
+			check.dump("%s: trace() without arguments", call.Pos())
+			x.mode = novalue
+			x.expr = call
+			return
+		}
+		var t operand
+		x1 := x
+		for _, arg := range args {
+			check.exprOrType(x1, arg, nil, iota, true) // permit trace for types, e.g.: new(trace(T))
+			check.dump("%s: %s", x1.pos(), x1)
+			x1 = &t // use incoming x only for first argument
+		}
+
+	default:
+		check.invalidAST(call.Pos(), "unknown builtin id %d", id)
+		goto Error
+	}
+
+	x.expr = call
+	return
+
+Error:
+	x.mode = invalid
+	x.expr = call
+}
+
+// implicitDeref returns A if typ is of the form *A and A is an array;
+// otherwise it returns typ.
+//
+func implicitDeref(typ Type) Type {
+	if p, ok := typ.(*Pointer); ok {
+		if a, ok := underlying(p.Base).(*Array); ok {
+			return a
+		}
+	}
+	return typ
+}
+
+// containsCallsOrReceives returns true if the expression x contains
+// function calls or channel receives; it returns false otherwise.
+//
+func containsCallsOrReceives(x ast.Expr) bool {
+	res := false
+	ast.Inspect(x, func(x ast.Node) bool {
+		switch x := x.(type) {
+		case *ast.CallExpr:
+			res = true
+			return false
+		case *ast.UnaryExpr:
+			if x.Op == token.ARROW {
+				res = true
+				return false
+			}
+		}
+		return true
+	})
+	return res
+}
+
+// unparen removes any parentheses surrounding an expression and returns
+// the naked expression.
+//
+func unparen(x ast.Expr) ast.Expr {
+	if p, ok := x.(*ast.ParenExpr); ok {
+		return unparen(p.X)
+	}
+	return x
+}

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

+// 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.
+
+// builtin calls
+
+package builtins
+
+import "unsafe"
+
+func _append() {
+	var x int
+	var s []byte
+	_0 := append /* ERROR "argument" */ ()
+	_1 := append("foo" /* ERROR "not a typed slice" */)
+	_2 := append(nil /* ERROR "not a typed slice" */, s)
+	_3 := append(x /* ERROR "not a typed slice" */, s)
+	_4 := append(s)
+	append /* ERROR "not used" */ (s)
+}
+
+func _cap() {
+	var a [10]bool
+	var p *[20]int
+	var s []int
+	var c chan string
+	_0 := cap /* ERROR "argument" */ ()
+	_1 := cap /* ERROR "argument" */ (1, 2)
+	_2 := cap(42 /* ERROR "invalid" */)
+	const _3 = cap(a)
+	assert(_3 == 10)
+	const _4 = cap(p)
+	assert(_4 == 20)
+	_5 := cap(c)
+	cap /* ERROR "not used" */ (c)
+}
+
+func _close() {
+	var c chan int
+	var r <-chan int
+	close /* ERROR "argument" */ ()
+	close /* ERROR "argument" */ (1, 2)
+	close(42 /* ERROR "not a channel" */)
+	close(r /* ERROR "receive-only channel" */)
+	close(c)
+}
+
+func _complex() {
+	_0 := complex /* ERROR "argument" */ ()
+	_1 := complex /* ERROR "argument" */ (1)
+	_2 := complex(1, 2)
+	// TODO(gri) add tests checking types
+	complex /* ERROR "not used" */ (1, 2)
+}
+
+func _delete() {
+	var m map[string]int
+	var s string
+	delete /* ERROR "argument" */ ()
+	delete /* ERROR "argument" */ (1)
+	delete /* ERROR "argument" */ (1, 2, 3)
+	delete(m, 0 /* ERROR "not assignable" */)
+	delete(m, s)
+}
+
+func _imag() {
+	var f32 float32
+	var f64 float64
+	var c64 complex64
+	var c128 complex128
+	_0 := imag /* ERROR "argument" */ ()
+	_1 := imag /* ERROR "argument" */ (1, 2)
+	_2 := imag(10 /* ERROR "must be a complex number" */)
+	_3 := imag(2.7182818 /* ERROR "must be a complex number" */)
+	_4 := imag("foo" /* ERROR "must be a complex number" */)
+	const _5 = imag(1 + 2i)
+	assert(_5 == 2)
+	f32 = _5
+	f64 = _5
+	const _6 = imag(0i)
+	assert(_6 == 0)
+	f32 = imag(c64)
+	f64 = imag(c128)
+	f32 = imag /* ERROR "cannot assign" */ (c128)
+	f64 = imag /* ERROR "cannot assign" */ (c64)
+	imag /* ERROR "not used" */ (c64)
+}
+
+func _len() {
+	const c = "foobar"
+	var a [10]bool
+	var p *[20]int
+	var s []int
+	var m map[string]complex128
+	_0 := len /* ERROR "argument" */ ()
+	_1 := len /* ERROR "argument" */ (1, 2)
+	_2 := len(42 /* ERROR "invalid" */)
+	const _3 = len(c)
+	assert(_3 == 6)
+	const _4 = len(a)
+	assert(_4 == 10)
+	const _5 = len(p)
+	assert(_5 == 20)
+	_6 := len(m)
+	len /* ERROR "not used" */ (c)
+
+	// esoteric case
+	var t string
+	var hash map[interface{}][]*[10]int
+	const n = len /* ERROR "not constant" */ (hash[recover()][len(t)])
+	assert /* ERROR "failed" */ (n == 10)
+	var ch <-chan int
+	const nn = len /* ERROR "not constant" */ (hash[<-ch][len(t)])
+	_7 := nn // TODO(gri) remove this once unused constants get type-checked
+}
+
+func _make() {
+	n := 0
+
+	_0 := make /* ERROR "argument" */ ()
+	_1 := make(1 /* ERROR "not a type" */)
+	_2 := make(int /* ERROR "cannot make" */)
+
+	// slices
+	_3 := make/* ERROR "arguments" */ ([]int)
+	_4 := make/* ERROR "arguments" */ ([]int, 2, 3, 4)
+	_5 := make([]int, int /* ERROR "not an expression" */)
+	_6 := make([]int, 10, float32 /* ERROR "not an expression" */)
+	_7 := make([]int, "foo" /* ERROR "must be an integer" */)
+	_8 := make([]int, 10, 2.3 /* ERROR "must be an integer" */)
+	_9 := make([]int, 5, 10.0)
+	_10 := make([]int, 0i)
+	_11 := make([]int, -1, 1<<100) // out-of-range constants lead to run-time errors
+
+	// maps
+	_12 := make /* ERROR "arguments" */ (map[int]string, 10, 20)
+	_13 := make(map[int]float32, int /* ERROR "not an expression" */)
+	_14 := make(map[int]float32, "foo" /* ERROR "must be an integer" */)
+	_15 := make(map[int]float32, 10)
+	_16 := make(map[int]float32, n)
+	_17 := make(map[int]float32, int64(n))
+
+	// channels
+	_22 := make /* ERROR "arguments" */ (chan int, 10, 20)
+	_23 := make(chan int, int /* ERROR "not an expression" */)
+	_24 := make(chan<- int, "foo" /* ERROR "must be an integer" */)
+	_25 := make(<-chan float64, 10)
+	_26 := make(chan chan int, n)
+	_27 := make(chan string, int64(n))
+
+	make /* ERROR "not used" */ ([]int, 10)
+}
+
+func _new() {
+	_0 := new /* ERROR "argument" */ ()
+	_1 := new /* ERROR "argument" */ (1, 2)
+	_3 := new("foo" /* ERROR "not a type" */)
+	_4 := new(float64)
+	_5 := new(struct{ x, y int })
+	_6 := new(*float64)
+	_7 := *_4 == **_6
+	new /* ERROR "not used" */ (int)
+}
+
+func _real() {
+	var f32 float32
+	var f64 float64
+	var c64 complex64
+	var c128 complex128
+	_0 := real /* ERROR "argument" */ ()
+	_1 := real /* ERROR "argument" */ (1, 2)
+	_2 := real(10 /* ERROR "must be a complex number" */)
+	_3 := real(2.7182818 /* ERROR "must be a complex number" */)
+	_4 := real("foo" /* ERROR "must be a complex number" */)
+	const _5 = real(1 + 2i)
+	assert(_5 == 1)
+	f32 = _5
+	f64 = _5
+	const _6 = real(0i)
+	assert(_6 == 0)
+	f32 = real(c64)
+	f64 = real(c128)
+	f32 = real /* ERROR "cannot assign" */ (c128)
+	f64 = real /* ERROR "cannot assign" */ (c64)
+	real /* ERROR "not used" */ (c64)
+}
+
+func _recover() {
+	_0 := recover()
+	_1 := recover /* ERROR "argument" */ (10)
+	recover()
+}
+
+func _Alignof() {
+	var x int
+	_0 := unsafe /* ERROR "argument" */ .Alignof()
+	_1 := unsafe /* ERROR "argument" */ .Alignof(1, 2)
+	_3 := unsafe.Alignof(int /* ERROR "not an expression" */)
+	_4 := unsafe.Alignof(42)
+	_5 := unsafe.Alignof(new(struct{}))
+	unsafe /* ERROR "not used" */ .Alignof(x)
+}
+
+func _Offsetof() {
+	var x struct{ f int }
+	_0 := unsafe /* ERROR "argument" */ .Offsetof()
+	_1 := unsafe /* ERROR "argument" */ .Offsetof(1, 2)
+	_2 := unsafe.Offsetof(int /* ERROR "not an expression" */)
+	_3 := unsafe.Offsetof(x /* ERROR "not a selector" */)
+	_4 := unsafe.Offsetof(x.f)
+	_5 := unsafe.Offsetof((x.f))
+	_6 := unsafe.Offsetof((((((((x))).f)))))
+	unsafe /* ERROR "not used" */ .Offsetof(x.f)
+}
+
+func _Sizeof() {
+	var x int
+	_0 := unsafe /* ERROR "argument" */ .Sizeof()
+	_1 := unsafe /* ERROR "argument" */ .Sizeof(1, 2)
+	_2 := unsafe.Sizeof(int /* ERROR "not an expression" */)
+	_3 := unsafe.Sizeof(42)
+	_4 := unsafe.Sizeof(new(complex128))
+	unsafe /* ERROR "not used" */ .Sizeof(x)
+
+	// basic types have size guarantees
+	assert(unsafe.Sizeof(byte(0)) == 1)
+	assert(unsafe.Sizeof(uint8(0)) == 1)
+	assert(unsafe.Sizeof(int8(0)) == 1)
+	assert(unsafe.Sizeof(uint16(0)) == 2)
+	assert(unsafe.Sizeof(int16(0)) == 2)
+	assert(unsafe.Sizeof(uint32(0)) == 4)
+	assert(unsafe.Sizeof(int32(0)) == 4)
+	assert(unsafe.Sizeof(float32(0)) == 4)
+	assert(unsafe.Sizeof(uint64(0)) == 8)
+	assert(unsafe.Sizeof(int64(0)) == 8)
+	assert(unsafe.Sizeof(float64(0)) == 8)
+	assert(unsafe.Sizeof(complex64(0)) == 8)
+	assert(unsafe.Sizeof(complex128(0)) == 16)
+}
+
+// self-testing only
+func _assert() {
+	var x int
+	assert /* ERROR "argument" */ ()
+	assert /* ERROR "argument" */ (1, 2)
+	assert("foo" /* ERROR "boolean constant" */ )
+	assert(x /* ERROR "boolean constant" */)
+	assert(true)
+	assert /* ERROR "failed" */ (false) 
+}
+
+// self-testing only
+func _trace() {
+	// Uncomment the code below to test trace - will produce console output
+	// _0 := trace /* ERROR "no value" */ ()
+	// _1 := trace(1)
+	// _2 := trace(true, 1.2, '\'', "foo", 42i, "foo" <= "bar")
+}