cmd/compile: do not report error for invalid constant

Invalid constant was already reported by noder, so don't re-check in
typecheck, which lead to compiler crashing.

Updates #43311

Change-Id: I48e2f540601cef725c1ff628c066ed15d848e771
Reviewed-on: https://go-review.googlesource.com/c/go/+/298713
Trust: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Run-TryBot: Cuong Manh Le <cuong.manhle.vn@gmail.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

src/cmd/compile/internal/noder/noder.go

@@ -689,7 +689,7 @@ func (p *noder) expr(expr syntax.Expr) ir.Node {
 		if expr.Kind == syntax.RuneLit {
 			n.SetType(types.UntypedRune)
 		}
-		n.SetDiag(expr.Bad) // avoid follow-on errors if there was a syntax error
+		n.SetDiag(expr.Bad || n.Val().Kind() == constant.Unknown) // avoid follow-on errors if there was a syntax error
 		return n
 	case *syntax.CompositeLit:
 		n := ir.NewCompLitExpr(p.pos(expr), ir.OCOMPLIT, p.typeExpr(expr.Type), nil)

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

@@ -482,8 +482,10 @@ func typecheck1(n ir.Node, top int) ir.Node {
 
 	case ir.OLITERAL:
 		if n.Sym() == nil && n.Type() == nil {
+			if !n.Diag() {
 				base.Fatalf("literal missing type: %v", n)
 			}
+		}
 		return n
 
 	case ir.ONIL:

test/char_lit1.go

@@ -1,4 +1,4 @@
-// errorcheck
+// errorcheck -d=panic
 
 // Copyright 2009 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style

test/fixedbugs/issue20232.go

@@ -1,4 +1,4 @@
-// errorcheck
+// errorcheck -d=panic
 
 // Copyright 2017 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style