cmd/compile: silence unnecessary unsafe error

If n.Type==nil after typechecking, then we should have already
reported a more useful error somewhere else. Just return 0 in
evalunsafe without trying to do anything else that's likely to cause
problems.

Also, further split out issue7525.go into more test files, because
cmd/compile reports at most one typechecking loop per compilation
unit.

Fixes #22351.

Change-Id: I3ebf505f72c48fcbfef5ec915606224406026597
Reviewed-on: https://go-review.googlesource.com/72251
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Daniel Martí <mvdan@mvdan.cc>
Reviewed-by: Robert Griesemer <gri@golang.org>

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

@@ -12,7 +12,6 @@ func evalunsafe(n *Node) int64 {
 		n.Left = defaultlit(n.Left, nil)
 		tr := n.Left.Type
 		if tr == nil {
-			yyerror("invalid expression %v", n)
 			return 0
 		}
 		dowidth(tr)
@@ -35,6 +34,9 @@ func evalunsafe(n *Node) int64 {
 		base := n.Left.Left
 
 		n.Left = typecheck(n.Left, Erv)
+		if n.Left.Type == nil {
+			return 0
+		}
 		switch n.Left.Op {
 		case ODOT, ODOTPTR:
 			break

test/fixedbugs/issue22351.go

@@ -0,0 +1,11 @@
+// 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 main
+
+import "unsafe"
+
+const _ = uint64(unsafe.Offsetof(T{}.F)) // ERROR "undefined"

test/fixedbugs/issue7525.go

@@ -11,7 +11,5 @@ 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"
 }

test/fixedbugs/issue7525d.go

@@ -0,0 +1,15 @@
+// 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
+
+import "unsafe"
+
+var x struct {
+	b [unsafe.Offsetof(x.b)]int // ERROR "array bound|typechecking loop|invalid array"
+}

test/fixedbugs/issue7525e.go

@@ -0,0 +1,15 @@
+// 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
+
+import "unsafe"
+
+var x struct {
+	c [unsafe.Alignof(x.c)]int // ERROR "array bound|typechecking loop|invalid array"
+}