cmd/compile: report the struct type in invalid number of initializer values

Fixes #23732

Disambiguate "too few" or "too many" values in struct
initializer messages by reporting the name of the literal.

After:
issue23732.go:27:3: too few values in Foo literal
issue23732.go:34:12: too many values in Bar literal
issue23732.go:40:6: too few values in Foo literal
issue23732.go:40:12: too many values in Bar literal

Change-Id: Ieca37298441d907ac78ffe960c5ab55741a362ef
Reviewed-on: https://go-review.googlesource.com/93277
Run-TryBot: Emmanuel Odeke <emm.odeke@gmail.com>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

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

@@ -3030,7 +3030,7 @@ func typecheckcomplit(n *Node) *Node {
 				ls[i] = n1
 				if i >= t.NumFields() {
 					if !errored {
-						yyerror("too many values in struct initializer")
+						yyerror("too many values in %v", n)
 						errored = true
 					}
 					continue
@@ -3048,7 +3048,7 @@ func typecheckcomplit(n *Node) *Node {
 				ls[i] = n1
 			}
 			if len(ls) < t.NumFields() {
-				yyerror("too few values in struct initializer")
+				yyerror("too few values in %v", n)
 			}
 		} else {
 			hash := make(map[string]bool)

test/fixedbugs/issue23732.go

+// errorcheck
+
+// Copyright 2018 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 23732: Give better details about which struct
+// initializer has the wrong number of values.
+
+package main
+
+type Foo struct {
+	A int
+	B int
+	C interface{}
+	Bar
+}
+
+type Bar struct {
+	A string
+}
+
+func main() {
+	_ = Foo{
+		1,
+		2,
+		3, // ERROR "too few values in Foo literal"
+	}
+
+	_ = Foo{
+		1,
+		2,
+		3,
+		Bar{"A", "B"}, // ERROR "too many values in Bar literal"
+	}
+
+	_ = Foo{
+		1,
+		2,
+		Bar{"A", "B"}, // ERROR "too many values in Bar literal" "too few values in Foo literal"
+	}
+}