cmd/compile, go/types: omit needless word in error message

CL 21462 and CL 21463 made this message say explicitly that the problem
was a struct field in a map, but the word "directly" is unnecessary,
sounds wrong, and makes the error long.

Change-Id: I2fb68cdaeb8bd94776b8022cf3eae751919ccf6f
Reviewed-on: https://go-review.googlesource.com/23373
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: David Chase <drchase@google.com>

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

@@ -3153,7 +3153,7 @@ func checkassign(stmt *Node, n *Node) {
 	}
 
 	if n.Op == ODOT && n.Left.Op == OINDEXMAP {
-		Yyerror("cannot directly assign to struct field %v in map", n)
+		Yyerror("cannot assign to struct field %v in map", n)
 		return
 	}
 

src/go/types/assignments.go

@@ -183,7 +183,7 @@ func (check *Checker) assignVar(lhs ast.Expr, x *operand) Type {
 			var op operand
 			check.expr(&op, sel.X)
 			if op.mode == mapindex {
-				check.errorf(z.pos(), "cannot directly assign to struct field %s in map", ExprString(z.expr))
+				check.errorf(z.pos(), "cannot assign to struct field %s in map", ExprString(z.expr))
 				return nil
 			}
 		}

src/go/types/testdata/stmt0.src

@@ -137,7 +137,7 @@ func issue6487() {
 
 	type M map[string]S
 	var m M
-	m /* ERROR "cannot directly assign to struct field" */ ["foo"].x = 0
+	m /* ERROR "cannot assign to struct field" */ ["foo"].x = 0
 	_ = &( /* ERROR "cannot take address" */ m["foo"].x)
 	_ = &m /* ERROR "cannot take address" */ ["foo"].x
 }

test/fixedbugs/issue13779.go

@@ -11,5 +11,5 @@ package main
 func main() {
 	type person struct{ age, weight, height int }
 	students := map[string]person{"sally": person{12, 50, 32}}
-	students["sally"].age = 3 // ERROR "cannot directly assign to struct field .* in map"
+	students["sally"].age = 3 // ERROR "cannot assign to struct field .* in map"
 }