cmd/compile: only allow integer expressions as keys in array literals

Fixes #16439
Updates #16679

Change-Id: Idff4b313f29351866b1a649786501adee85fd580
Reviewed-on: https://go-review.googlesource.com/29011
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>

src/cmd/compile/internal/gc/const.go

@@ -1513,37 +1513,33 @@ func smallintconst(n *Node) bool {
 			return true
 
 		case TIDEAL, TINT64, TUINT64, TPTR64:
-			if n.Val().U.(*Mpint).Cmp(minintval[TINT32]) < 0 || n.Val().U.(*Mpint).Cmp(maxintval[TINT32]) > 0 {
-				break
+			v, ok := n.Val().U.(*Mpint)
+			if ok && v.Cmp(minintval[TINT32]) > 0 && v.Cmp(maxintval[TINT32]) < 0 {
+				return true
 			}
-			return true
 		}
 	}
 
 	return false
 }
 
-func nonnegconst(n *Node) int {
-	if n.Op == OLITERAL && n.Type != nil {
-		switch simtype[n.Type.Etype] {
-		// check negative and 2^31
-		case TINT8,
-			TUINT8,
-			TINT16,
-			TUINT16,
-			TINT32,
-			TUINT32,
-			TINT64,
-			TUINT64,
-			TIDEAL:
-			if n.Val().U.(*Mpint).Cmp(minintval[TUINT32]) < 0 || n.Val().U.(*Mpint).Cmp(maxintval[TINT32]) > 0 {
-				break
-			}
-			return int(n.Int64())
-		}
+// nonnegintconst checks if Node n contains a constant expression
+// representable as a non-negative small integer, and returns its
+// (integer) value if that's the case. Otherwise, it returns -1.
+func nonnegintconst(n *Node) int64 {
+	if n.Op != OLITERAL {
+		return -1
 	}
 
-	return -1
+	// toint will leave n.Val unchanged if it's not castable to an
+	// Mpint, so we still have to guard the conversion.
+	v := toint(n.Val())
+	vi, ok := v.U.(*Mpint)
+	if !ok || vi.Val.Sign() < 0 || vi.Cmp(maxintval[TINT32]) > 0 {
+		return -1
+	}
+
+	return vi.Int64()
 }
 
 // convert x to type et and back to int64

src/cmd/compile/internal/gc/sinit.go

@@ -1226,10 +1226,11 @@ func initplan(n *Node) {
 
 	case OARRAYLIT, OSLICELIT:
 		for _, a := range n.List.Slice() {
-			if a.Op != OKEY || !smallintconst(a.Left) {
+			index := nonnegintconst(a.Left)
+			if a.Op != OKEY || index < 0 {
 				Fatalf("initplan fixedlit")
 			}
-			addvalue(p, n.Type.Elem().Width*a.Left.Int64(), a.Right)
+			addvalue(p, index*n.Type.Elem().Width, a.Right)
 		}
 
 	case OSTRUCTLIT:

src/cmd/compile/internal/gc/typecheck.go

@@ -2781,19 +2781,6 @@ func keydup(n *Node, hash map[uint32][]*Node) {
 	hash[h] = append(hash[h], orign)
 }
 
-func indexdup(n *Node, hash map[int64]*Node) {
-	if n.Op != OLITERAL {
-		Fatalf("indexdup: not OLITERAL")
-	}
-
-	v := n.Int64()
-	if hash[v] != nil {
-		yyerror("duplicate index in array literal: %d", v)
-		return
-	}
-	hash[v] = n
-}
-
 // iscomptype reports whether type t is a composite literal type
 // or a pointer to one.
 func iscomptype(t *Type) bool {
@@ -2890,16 +2877,17 @@ func typecheckcomplit(n *Node) *Node {
 		n.Type = nil
 
 	case TARRAY, TSLICE:
-		// Only allocate hash if there are some key/value pairs.
-		var hash map[int64]*Node
+		// If there are key/value pairs, create a map to keep seen
+		// keys so we can check for duplicate indices.
+		var indices map[int64]bool
 		for _, n1 := range n.List.Slice() {
 			if n1.Op == OKEY {
-				hash = make(map[int64]*Node)
+				indices = make(map[int64]bool)
 				break
 			}
 		}
-		length := int64(0)
-		i := 0
+
+		var length, i int64
 		checkBounds := t.IsArray() && !t.isDDDArray()
 		for i2, n2 := range n.List.Slice() {
 			l := n2
@@ -2913,19 +2901,25 @@ func typecheckcomplit(n *Node) *Node {
 
 			l.Left = typecheck(l.Left, Erv)
 			evconst(l.Left)
-			i = nonnegconst(l.Left)
+
+			i = nonnegintconst(l.Left)
 			if i < 0 && l.Left.Diag == 0 {
 				yyerror("index must be non-negative integer constant")
 				l.Left.Diag = 1
 				i = -(1 << 30) // stay negative for a while
 			}
 
-			if i >= 0 && hash != nil {
-				indexdup(l.Left, hash)
+			if i >= 0 && indices != nil {
+				if indices[i] {
+					yyerror("duplicate index in array literal: %d", i)
+				} else {
+					indices[i] = true
+				}
 			}
+
 			i++
-			if int64(i) > length {
-				length = int64(i)
+			if i > length {
+				length = i
 				if checkBounds && length > t.NumElem() {
 					setlineno(l)
 					yyerror("array index %d out of bounds [0:%d]", length-1, t.NumElem())

test/fixedbugs/issue16439.go

@@ -0,0 +1,18 @@
+// errorcheck
+
+// Copyright 2016 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.
+
+package p
+
+var a []int = []int{1: 1}
+var b []int = []int{-1: 1} // ERROR "must be non-negative integer constant"
+
+var c []int = []int{2.0: 2}
+var d []int = []int{-2.0: 2} // ERROR "must be non-negative integer constant"
+
+var e []int = []int{3 + 0i: 3}
+var f []int = []int{3i: 3} // ERROR "truncated to real"
+
+var g []int = []int{"a": 4} // ERROR "must be non-negative integer constant"