cmd/compile: skip array bounds errors when type is broken

This avoids false positives
like those found in #19880.

Fixes #19880

Change-Id: I583c16cc3c71e7462a72500db9ea2547c468f8c1
Reviewed-on: https://go-review.googlesource.com/40255
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

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

@@ -369,9 +369,12 @@ OpSwitch:
 			n.Left = indexlit(typecheck(n.Left, Erv))
 			l := n.Left
 			if consttype(l) != CTINT {
-				if l.Type != nil && l.Type.IsInteger() && l.Op != OLITERAL {
+				switch {
+				case l.Type == nil:
+					// Error already reported elsewhere.
+				case l.Type.IsInteger() && l.Op != OLITERAL:
 					yyerror("non-constant array bound %v", l)
-				} else {
+				default:
 					yyerror("invalid array bound %v", l)
 				}
 				n.Type = nil

test/fixedbugs/bug255.go

@@ -11,7 +11,7 @@ var b [1e1]int     // ok
 var c [1.5]int     // ERROR "truncated"
 var d ["abc"]int   // ERROR "invalid array bound|not numeric"
 var e [nil]int     // ERROR "use of untyped nil|invalid array bound|not numeric"
-var f [e]int       // ERROR "invalid array bound|not constant"
+var f [e]int       // ok: error already reported for e
 var g [1 << 65]int // ERROR "array bound is too large|overflows"
 var h [len(a)]int  // ok
 

test/fixedbugs/issue19880.go

+// errorcheck
+
+// Copyright 2017 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
+
+type T struct {
+	f [1]int
+}
+
+func a() {
+	_ = T // ERROR "type T is not an expression"
+}
+
+func b() {
+	var v [len(T{}.f)]int // ok
+	_ = v
+}

test/fixedbugs/issue7525.go

@@ -11,9 +11,7 @@ package main
 import "unsafe"
 
 var x struct {
-	a [unsafe.Sizeof(x.a)]int // ERROR "array bound|typechecking loop|invalid expression"
+	a [unsafe.Sizeof(x.a)]int   // ERROR "array bound|typechecking loop|invalid expression"
 	b [unsafe.Offsetof(x.b)]int // ERROR "array bound"
-	c [unsafe.Alignof(x.c)]int // ERROR "array bound|invalid expression"
-	d [len(x.d)]int // ERROR "array bound|invalid array"
-	e [cap(x.e)]int // ERROR "array bound|invalid array"
+	c [unsafe.Alignof(x.c)]int  // ERROR "array bound|invalid expression"
 }

test/fixedbugs/issue7525b.go

+// errorcheck
+
+// Copyright 2017 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 7525: self-referential array types.
+
+package main
+
+var y struct {
+	d [len(y.d)]int // ERROR "array bound|typechecking loop|invalid array"
+}

test/fixedbugs/issue7525c.go

+// errorcheck
+
+// Copyright 2017 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 7525: self-referential array types.
+
+package main
+
+var z struct {
+	e [cap(z.e)]int // ERROR "array bound|typechecking loop|invalid array"
+}