go.tools/oracle: address reviewer suggestions from CL 9502043

(I made these changes in the wrong workspace.)

R=crawshaw
CC=golang-dev
https://golang.org/cl/13328044

oracle/oracle.go

@@ -87,7 +87,7 @@ func Main(args []string, mode, pos string, ptalog, out io.Writer, buildContext *
 		if mode == "" {
 			return errors.New("You must specify a -mode to perform.")
 		}
-		return fmt.Errorf("Invalid mode type '%s'.", mode)
+		return fmt.Errorf("Invalid mode type: %q.", mode)
 	}
 
 	var loader importer.SourceLoader

oracle/peers.go

@@ -21,22 +21,10 @@ import (
 // or the implicit receive in "for v := range ch".
 //
 func peers(o *oracle) (queryResult, error) {
-	// Determine the enclosing send/receive op for the specified position.
-	var arrowPos token.Pos
-	for _, n := range o.queryPath {
-		switch n := n.(type) {
-		case *ast.UnaryExpr:
-			if n.Op == token.ARROW {
-				arrowPos = n.OpPos
-				goto found
-			}
-		case *ast.SendStmt:
-			arrowPos = n.Arrow
-			goto found
-		}
-	}
+	arrowPos := findArrow(o)
+	if arrowPos == token.NoPos {
 		return nil, o.errorf(o.queryPath[0], "there is no send/receive here")
-found:
+	}
 
 	buildSSA(o)
 
@@ -90,6 +78,23 @@ found:
 	}, nil
 }
 
+// findArrow returns the position of the enclosing send/receive op
+// (<-) for the query position, or token.NoPos if not found.
+//
+func findArrow(o *oracle) token.Pos {
+	for _, n := range o.queryPath {
+		switch n := n.(type) {
+		case *ast.UnaryExpr:
+			if n.Op == token.ARROW {
+				return n.OpPos
+			}
+		case *ast.SendStmt:
+			return n.Arrow
+		}
+	}
+	return token.NoPos
+}
+
 // chanOp abstracts an ssa.Send, ssa.Unop(ARROW), or a SelectState.
 type chanOp struct {
 	ch  ssa.Value