cmd/compile: clearer error for invalid array/slice literal elements

Fixes #13365.

Change-Id: I5a447ff806dbbb11c8c75e2b5cfa7fd4a845fb92
Reviewed-on: https://go-review.googlesource.com/17206
Run-TryBot: Robert Griesemer <gri@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

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

@@ -2971,9 +2971,8 @@ func typecheckcomplit(np **Node) {
 		}
 		length := int64(0)
 		i := 0
-		var l *Node
 		for ll := n.List; ll != nil; ll = ll.Next {
-			l = ll.N
+			l := ll.N
 			setlineno(l)
 			if l.Op != OKEY {
 				l = Nod(OKEY, Nodintconst(int64(i)), l)
@@ -2986,7 +2985,7 @@ func typecheckcomplit(np **Node) {
 			evconst(l.Left)
 			i = nonnegconst(l.Left)
 			if i < 0 && l.Left.Diag == 0 {
-				Yyerror("array index must be non-negative integer constant")
+				Yyerror("index must be non-negative integer constant")
 				l.Left.Diag = 1
 				i = -(1 << 30) // stay negative for a while
 			}
@@ -3008,7 +3007,7 @@ func typecheckcomplit(np **Node) {
 			pushtype(r, t.Type)
 			typecheck(&r, Erv)
 			defaultlit(&r, t.Type)
-			l.Right = assignconv(r, t.Type, "array element")
+			l.Right = assignconv(r, t.Type, "array or slice literal")
 		}
 
 		if t.Bound == -100 {

test/fixedbugs/issue13365.go

@@ -0,0 +1,25 @@
+// errorcheck
+
+// Copyright 2015 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.
+
+// issue 13365: confusing error message (array vs slice)
+
+package main
+
+var t struct{}
+
+func main() {
+	_ = []int{-1: 0}    // ERROR "index must be non\-negative integer constant"
+	_ = [10]int{-1: 0}  // ERROR "index must be non\-negative integer constant"
+	_ = [...]int{-1: 0} // ERROR "index must be non\-negative integer constant"
+
+	_ = []int{100: 0}
+	_ = [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"
+}

test/fixedbugs/issue7150.go

@@ -9,9 +9,9 @@
 package main
 
 func main() {
-	_ = [0]int{-1: 50}              // ERROR "array index must be non-negative integer constant"
-	_ = [0]int{0: 0}                // ERROR "array index 0 out of bounds \[0:0\]"
-	_ = [0]int{5: 25}               // ERROR "array index 5 out of bounds \[0:0\]"
-	_ = [10]int{2: 10, 15: 30}      // ERROR "array index 15 out of bounds \[0:10\]"
-	_ = [10]int{5: 5, 1: 1, 12: 12} // ERROR "array index 12 out of bounds \[0:10\]"
+	_ = [0]int{-1: 50}              // ERROR "index must be non-negative integer constant"
+	_ = [0]int{0: 0}                // ERROR "index 0 out of bounds \[0:0\]"
+	_ = [0]int{5: 25}               // ERROR "index 5 out of bounds \[0:0\]"
+	_ = [10]int{2: 10, 15: 30}      // ERROR "index 15 out of bounds \[0:10\]"
+	_ = [10]int{5: 5, 1: 1, 12: 12} // ERROR "index 12 out of bounds \[0:10\]"
 }

test/fixedbugs/issue7153.go

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