ast: implement String() for ast.Position

ast/position.go

@@ -20,13 +20,23 @@
 
 package ast
 
+import "strconv"
+
 // Position represents a position in the parsed document.
 // Line and column numbers are 1-based.
 type Position struct {
 	Line   int
 	Column int
 }
 
+func (p Position) String() string {
+	s := strconv.Itoa(p.Line)
+	if c := p.Column; c > 0 {
+		s += ":" + strconv.Itoa(c)
+	}
+	return s
+}
+
 // Pos attempts to return the position of a Node in the parsed document.
 // For most use cases, prefer to use idl.Info to access positional information.
 func Pos(n Node) (Position, bool) {

idl/error.go

@@ -56,7 +56,7 @@ func (pe *ParseError) Error() string {
 	var buffer bytes.Buffer
 	buffer.WriteString("parse error\n")
 	for _, pe := range pe.Errors {
-		buffer.WriteString(fmt.Sprintf("  line %d:%d: %s\n", pe.Pos.Line, pe.Pos.Column, pe.Err))
+		buffer.WriteString(fmt.Sprintf("  line %s: %s\n", pe.Pos, pe.Err))
 	}
 	return buffer.String()
 }