// relative info
		if got := pos.RelFilename(); got != test.relFilename {
			t.Errorf("%s: got relFilename %q; want %q", test.string, got, test.relFilename)
		}
		if got := pos.RelLine(); got != test.relLine {
			t.Errorf("%s: got relLine %d; want %d", test.string, got, test.relLine)
		}
		if got := pos.RelCol(); got != test.relCol {
			t.Errorf("%s: got relCol %d; want %d", test.string, got, test.relCol)
		}
	}
}

	b := pos.base
	for b != nil && b != b.pos.base {
		b = b.pos.base
	}
	// b == nil || b == b.pos.base
	return b
}

func (pos Pos) RelFilename() string { return pos.base.Filename() }

func (pos Pos) RelLine() uint {
	b := pos.base
	if b.Line() == 0 {
		// base line is unknown => relative line is unknown
		return 0
	}
	return b.Line() + (pos.Line() - b.Pos().Line())
}

func (pos Pos) RelCol() uint {

// etc).
func (ctxt *Link) getFileIndexAndLine(xpos src.XPos) (int, int32) {
	pos := ctxt.InnermostPos(xpos)
	if !pos.IsKnown() {
		pos = src.Pos{}
	}
	return pos.FileIndex(), int32(pos.RelLine())