go index 源码
golang index 代码
文件路径：/src/cmd/compile/internal/types2/index.go
// Copyright 2021 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 index/slice expressions.
package types2
import (
"cmd/compile/internal/syntax"
"go/constant"
)
// If e is a valid function instantiation, indexExpr returns true.
// In that case x represents the uninstantiated function value and
// it is the caller's responsibility to instantiate the function.
func (check *Checker) indexExpr(x *operand, e *syntax.IndexExpr) (isFuncInst bool) {
check.exprOrType(x, e.X, true)
// x may be generic
switch x.mode {
case invalid:
check.use(e.Index)
return false
case typexpr:
// type instantiation
x.mode = invalid
// TODO(gri) here we re-evaluate e.X - try to avoid this
x.typ = check.varType(e)
if x.typ != Typ[Invalid] {
x.mode = typexpr
}
return false
case value:
if sig, _ := under(x.typ).(*Signature); sig != nil && sig.TypeParams().Len() > 0 {
// function instantiation
return true
}
}
// x should not be generic at this point, but be safe and check
check.nonGeneric(x)
if x.mode == invalid {
return false
}
// ordinary index expression
valid := false
length := int64(-1) // valid if >= 0
switch typ := under(x.typ).(type) {
case *Basic:
if isString(typ) {
valid = true
if x.mode == constant_ {
length = int64(len(constant.StringVal(x.val)))
}
// an indexed string always yields a byte value
// (not a constant) even if the string and the
// index are constant
x.mode = value
x.typ = universeByte // use 'byte' name
}
case *Array:
valid = true
length = typ.len
if x.mode != variable {
x.mode = value
}
x.typ = typ.elem
case *Pointer:
if typ, _ := under(typ.base).(*Array); typ != nil {
valid = true
length = typ.len
x.mode = variable
x.typ = typ.elem
}
case *Slice:
valid = true
x.mode = variable
x.typ = typ.elem
case *Map:
index := check.singleIndex(e)
if index == nil {
x.mode = invalid
return false
}
var key operand
check.expr(&key, index)
check.assignment(&key, typ.key, "map index")
// ok to continue even if indexing failed - map element type is known
x.mode = mapindex
x.typ = typ.elem
x.expr = e
return false
case *Interface:
if !isTypeParam(x.typ) {
break
}
// TODO(gri) report detailed failure cause for better error messages
var key, elem Type // key != nil: we must have all maps
mode := variable // non-maps result mode
// TODO(gri) factor out closure and use it for non-typeparam cases as well
if typ.typeSet().underIs(func(u Type) bool {
l := int64(-1) // valid if >= 0
var k, e Type // k is only set for maps
switch t := u.(type) {
case *Basic:
if isString(t) {
e = universeByte
mode = value
}
case *Array:
l = t.len
e = t.elem
if x.mode != variable {
mode = value
}
case *Pointer:
if t, _ := under(t.base).(*Array); t != nil {
l = t.len
e = t.elem
}
case *Slice:
e = t.elem
case *Map:
k = t.key
e = t.elem
}
if e == nil {
return false
}
if elem == nil {
// first type
length = l
key, elem = k, e
return true
}
// all map keys must be identical (incl. all nil)
// (that is, we cannot mix maps with other types)
if !Identical(key, k) {
return false
}
// all element types must be identical
if !Identical(elem, e) {
return false
}
// track the minimal length for arrays, if any
if l >= 0 && l < length {
length = l
}
return true
}) {
// For maps, the index expression must be assignable to the map key type.
if key != nil {
index := check.singleIndex(e)
if index == nil {
x.mode = invalid
return false
}
var k operand
check.expr(&k, index)
check.assignment(&k, key, "map index")
// ok to continue even if indexing failed - map element type is known
x.mode = mapindex
x.typ = elem
x.expr = e
return false
}
// no maps
valid = true
x.mode = mode
x.typ = elem
}
}
if !valid {
check.errorf(e.Pos(), invalidOp+"cannot index %s", x)
x.mode = invalid
return false
}
index := check.singleIndex(e)
if index == nil {
x.mode = invalid
return false
}
// In pathological (invalid) cases (e.g.: type T1 [][[]T1{}[0][0]]T0)
// the element type may be accessed before it's set. Make sure we have
// a valid type.
if x.typ == nil {
x.typ = Typ[Invalid]
}
check.index(index, length)
return false
}
func (check *Checker) sliceExpr(x *operand, e *syntax.SliceExpr) {
check.expr(x, e.X)
if x.mode == invalid {
check.use(e.Index[:]...)
return
}
valid := false
length := int64(-1) // valid if >= 0
switch u := coreString(x.typ).(type) {
case nil:
check.errorf(x, invalidOp+"cannot slice %s: %s has no core type", x, x.typ)
x.mode = invalid
return
case *Basic:
if isString(u) {
if e.Full {
at := e.Index[2]
if at == nil {
at = e // e.Index[2] should be present but be careful
}
check.error(at, invalidOp+"3-index slice of string")
x.mode = invalid
return
}
valid = true
if x.mode == constant_ {
length = int64(len(constant.StringVal(x.val)))
}
// spec: "For untyped string operands the result
// is a non-constant value of type string."
if isUntyped(x.typ) {
x.typ = Typ[String]
}
}
case *Array:
valid = true
length = u.len
if x.mode != variable {
check.errorf(x, invalidOp+"%s (slice of unaddressable value)", x)
x.mode = invalid
return
}
x.typ = &Slice{elem: u.elem}
case *Pointer:
if u, _ := under(u.base).(*Array); u != nil {
valid = true
length = u.len
x.typ = &Slice{elem: u.elem}
}
case *Slice:
valid = true
// x.typ doesn't change
}
if !valid {
check.errorf(x, invalidOp+"cannot slice %s", x)
x.mode = invalid
return
}
x.mode = value
// spec: "Only the first index may be omitted; it defaults to 0."
if e.Full && (e.Index[1] == nil || e.Index[2] == nil) {
check.error(e, invalidAST+"2nd and 3rd index required in 3-index slice")
x.mode = invalid
return
}
// check indices
var ind [3]int64
for i, expr := range e.Index {
x := int64(-1)
switch {
case expr != nil:
// The "capacity" is only known statically for strings, arrays,
// and pointers to arrays, and it is the same as the length for
// those types.
max := int64(-1)
if length >= 0 {
max = length + 1
}
if _, v := check.index(expr, max); v >= 0 {
x = v
}
case i == 0:
// default is 0 for the first index
x = 0
case length >= 0:
// default is length (== capacity) otherwise
x = length
}
ind[i] = x
}
// constant indices must be in range
// (check.index already checks that existing indices >= 0)
L:
for i, x := range ind[:len(ind)-1] {
if x > 0 {
for j, y := range ind[i+1:] {
if y >= 0 && y < x {
// The value y corresponds to the expression e.Index[i+1+j].
// Because y >= 0, it must have been set from the expression
// when checking indices and thus e.Index[i+1+j] is not nil.
check.errorf(e.Index[i+1+j], "invalid slice indices: %d < %d", y, x)
break L // only report one error, ok to continue
}
}
}
}
}
// singleIndex returns the (single) index from the index expression e.
// If the index is missing, or if there are multiple indices, an error
// is reported and the result is nil.
func (check *Checker) singleIndex(e *syntax.IndexExpr) syntax.Expr {
index := e.Index
if index == nil {
check.errorf(e, invalidAST+"missing index for %s", e.X)
return nil
}
if l, _ := index.(*syntax.ListExpr); l != nil {
if n := len(l.ElemList); n <= 1 {
check.errorf(e, invalidAST+"invalid use of ListExpr for index expression %v with %d indices", e, n)
return nil
}
// len(l.ElemList) > 1
check.error(l.ElemList[1], invalidOp+"more than one index")
index = l.ElemList[0] // continue with first index
}
return index
}
// index checks an index expression for validity.
// If max >= 0, it is the upper bound for index.
// If the result typ is != Typ[Invalid], index is valid and typ is its (possibly named) integer type.
// If the result val >= 0, index is valid and val is its constant int value.
func (check *Checker) index(index syntax.Expr, max int64) (typ Type, val int64) {
typ = Typ[Invalid]
val = -1
var x operand
check.expr(&x, index)
if !check.isValidIndex(&x, "index", false) {
return
}
if x.mode != constant_ {
return x.typ, -1
}
if x.val.Kind() == constant.Unknown {
return
}
v, ok := constant.Int64Val(x.val)
assert(ok)
if max >= 0 && v >= max {
check.errorf(&x, invalidArg+"index %s out of bounds [0:%d]", x.val.String(), max)
return
}
// 0 <= v [ && v < max ]
return x.typ, v
}
// isValidIndex checks whether operand x satisfies the criteria for integer
// index values. If allowNegative is set, a constant operand may be negative.
// If the operand is not valid, an error is reported (using what as context)
// and the result is false.
func (check *Checker) isValidIndex(x *operand, what string, allowNegative bool) bool {
if x.mode == invalid {
return false
}
// spec: "a constant index that is untyped is given type int"
check.convertUntyped(x, Typ[Int])
if x.mode == invalid {
return false
}
// spec: "the index x must be of integer type or an untyped constant"
if !allInteger(x.typ) {
check.errorf(x, invalidArg+"%s %s must be integer", what, x)
return false
}
if x.mode == constant_ {
// spec: "a constant index must be non-negative ..."
if !allowNegative && constant.Sign(x.val) < 0 {
check.errorf(x, invalidArg+"%s %s must not be negative", what, x)
return false
}
// spec: "... and representable by a value of type int"
if !representableConst(x.val, check, Typ[Int], &x.val) {
check.errorf(x, invalidArg+"%s %s overflows int", what, x)
return false
}
}
return true
}
// indexElts checks the elements (elts) of an array or slice composite literal
// against the literal's element type (typ), and the element indices against
// the literal length if known (length >= 0). It returns the length of the
// literal (maximum index value + 1).
func (check *Checker) indexedElts(elts []syntax.Expr, typ Type, length int64) int64 {
visited := make(map[int64]bool, len(elts))
var index, max int64
for _, e := range elts {
// determine and check index
validIndex := false
eval := e
if kv, _ := e.(*syntax.KeyValueExpr); kv != nil {
if typ, i := check.index(kv.Key, length); typ != Typ[Invalid] {
if i >= 0 {
index = i
validIndex = true
} else {
check.errorf(e, "index %s must be integer constant", kv.Key)
}
}
eval = kv.Value
} else if length >= 0 && index >= length {
check.errorf(e, "index %d is out of bounds (>= %d)", index, length)
} else {
validIndex = true
}
// if we have a valid index, check for duplicate entries
if validIndex {
if visited[index] {
check.errorf(e, "duplicate index %d in array or slice literal", index)
}
visited[index] = true
}
index++
if index > max {
max = index
}
// check element against composite literal element type
var x operand
check.exprWithHint(&x, eval, typ)
check.assignment(&x, typ, "array or slice literal")
}
return max
}
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