Switch from govendor to go modules. (#587)

Thanks to @BenoitKnecht for leading the way on this.

vendor/github.com/tdewolff/parse/position.go

@@ -0,0 +1,79 @@
+package parse
+
+import (
+	"fmt"
+	"io"
+	"strings"
+
+	"github.com/tdewolff/parse/buffer"
+)
+
+// Position returns the line and column number for a certain position in a file. It is useful for recovering the position in a file that caused an error.
+// It only treates \n, \r, and \r\n as newlines, which might be different from some languages also recognizing \f, \u2028, and \u2029 to be newlines.
+func Position(r io.Reader, offset int) (line, col int, context string, err error) {
+	l := buffer.NewLexer(r)
+
+	line = 1
+	for {
+		c := l.Peek(0)
+		if c == 0 {
+			col = l.Pos() + 1
+			context = positionContext(l, line, col)
+			err = l.Err()
+			if err == nil {
+				err = io.EOF
+			}
+			return
+		}
+
+		if offset == l.Pos() {
+			col = l.Pos() + 1
+			context = positionContext(l, line, col)
+			return
+		}
+
+		if c == '\n' {
+			l.Move(1)
+			line++
+			offset -= l.Pos()
+			l.Skip()
+		} else if c == '\r' {
+			if l.Peek(1) == '\n' {
+				if offset == l.Pos()+1 {
+					l.Move(1)
+					continue
+				}
+				l.Move(2)
+			} else {
+				l.Move(1)
+			}
+			line++
+			offset -= l.Pos()
+			l.Skip()
+		} else {
+			l.Move(1)
+		}
+	}
+}
+
+func positionContext(l *buffer.Lexer, line, col int) (context string) {
+	for {
+		c := l.Peek(0)
+		if c == 0 && l.Err() != nil || c == '\n' || c == '\r' {
+			break
+		}
+		l.Move(1)
+	}
+
+	// replace unprintable characters by a space
+	b := l.Lexeme()
+	for i, c := range b {
+		if c < 0x20 || c == 0x7F {
+			b[i] = ' '
+		}
+	}
+
+	context += fmt.Sprintf("%5d: %s\n", line, string(b))
+	context += fmt.Sprintf("%s^", strings.Repeat(" ", col+6))
+	return
+}