cmd/compile: make duplicate index error distinguish arrays and slices

Fixes #35291

Change-Id: I11ae367b6e972cd9e7a22bbc2cb23d32f4d72b98
Reviewed-on: https://go-review.googlesource.com/c/go/+/204617
Run-TryBot: Cuong Manh Le <cuong.manhle.vn@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

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

@@ -2782,7 +2782,7 @@ func typecheckcomplit(n *Node) (res *Node) {
 		}
 		elemType := n.Right.Right.Type
 
-		length := typecheckarraylit(elemType, -1, n.List.Slice())
+		length := typecheckarraylit(elemType, -1, n.List.Slice(), "array literal")
 
 		n.Op = OARRAYLIT
 		n.Type = types.NewArray(elemType, length)
@@ -2804,12 +2804,12 @@ func typecheckcomplit(n *Node) (res *Node) {
 		n.Type = nil
 
 	case TARRAY:
-		typecheckarraylit(t.Elem(), t.NumElem(), n.List.Slice())
+		typecheckarraylit(t.Elem(), t.NumElem(), n.List.Slice(), "array literal")
 		n.Op = OARRAYLIT
 		n.Right = nil
 
 	case TSLICE:
-		length := typecheckarraylit(t.Elem(), -1, n.List.Slice())
+		length := typecheckarraylit(t.Elem(), -2, n.List.Slice(), "slice literal")
 		n.Op = OSLICELIT
 		n.Right = nodintconst(length)
 
@@ -2960,7 +2960,8 @@ func typecheckcomplit(n *Node) (res *Node) {
 	return n
 }
 
-func typecheckarraylit(elemType *types.Type, bound int64, elts []*Node) int64 {
+// typecheckarraylit type-checks a sequence of slice/array literal elements.
+func typecheckarraylit(elemType *types.Type, bound int64, elts []*Node, ctx string) int64 {
 	// 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
@@ -2995,12 +2996,12 @@ func typecheckarraylit(elemType *types.Type, bound int64, elts []*Node) int64 {
 		r := *vp
 		r = pushtype(r, elemType)
 		r = typecheck(r, ctxExpr)
-		*vp = assignconv(r, elemType, "array or slice literal")
+		*vp = assignconv(r, elemType, ctx)
 
 		if key >= 0 {
 			if indices != nil {
 				if indices[key] {
-					yyerror("duplicate index in array literal: %d", key)
+					yyerror("duplicate index in %s: %d", ctx, key)
 				} else {
 					indices[key] = true
 				}

test/fixedbugs/issue13365.go

@@ -19,7 +19,7 @@ func main() {
 	_ = [10]int{100: 0} // ERROR "array index 100 out of bounds"
 	_ = [...]int{100: 0}
 
-	_ = []int{t}    // ERROR "cannot use .* as type int in array or slice literal"
-	_ = [10]int{t}  // ERROR "cannot use .* as type int in array or slice literal"
-	_ = [...]int{t} // ERROR "cannot use .* as type int in array or slice literal"
+	_ = []int{t}    // ERROR "cannot use .* as type int in slice literal"
+	_ = [10]int{t}  // ERROR "cannot use .* as type int in array literal"
+	_ = [...]int{t} // ERROR "cannot use .* as type int in array literal"
 }

test/fixedbugs/issue35291.go

@@ -0,0 +1,14 @@
+// errorcheck
+
+// Copyright 2019 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.
+
+// Check error message for duplicated index in slice literal
+
+package p
+
+var s = []string{
+	1: "dup",
+	1: "dup", // ERROR "duplicate index in slice literal: 1"
+}

test/fixedbugs/issue7153.go

@@ -8,4 +8,4 @@
 
 package p
 
-var _ = []int{a: true, true} // ERROR "undefined: a" "cannot use true \(type untyped bool\) as type int in array or slice literal"
+var _ = []int{a: true, true} // ERROR "undefined: a" "cannot use true \(type untyped bool\) as type int in slice literal"