errors: fix caret position on lines with tabs

vlib/v/util/errors.v

@@ -65,16 +65,17 @@ pub fn formated_error(kind string /*error or warn*/, emsg string, filepath strin
 				break
 			}
 		}
-		column = pos.pos - p
+		column = util.imax(0, pos.pos - p - 1)
 	}
 	position := '${path}:${pos.line_nr+1}:$column:'
 	//
-	bline := pos.line_nr - error_context_before
-	aline := pos.line_nr + error_context_after
+	bline := util.imax(0, pos.line_nr - error_context_before)
+	aline := util.imin(source_lines.len-1, pos.line_nr + error_context_after)
 	mut clines := []string
-	for iline, sline in source_lines {
-		if iline >= bline && iline <= aline {
-			mut cline := '${iline+1:5d}| $sline'
+	tab_spaces := '    '
+	for iline := bline; iline <= aline; iline++ {
+		sline := source_lines[iline]
+		mut cline := '${iline+1:5d}| ' + sline.replace('\t', tab_spaces)
 		if iline == pos.line_nr && emanager.support_color {
 			cline = term.red( cline )
 		}
@@ -86,17 +87,21 @@ pub fn formated_error(kind string /*error or warn*/, emsg string, filepath strin
 			// where it is needed. That is the reason we can not just
 			// use strings.repeat(` `, col) to form it.
 			mut pointerline := []string
-				for i, c in cline {
+			for i, c in sline {
 				if i < column {
-						x := if c.is_space() { c } else { ` ` }
+					mut x := c
+					if x == `\t` {
+						pointerline << tab_spaces
+					}else{
+						x = if x.is_space() { c } else { ` ` }
 						pointerline << x.str()
+					}
 					continue
 				}
 				pointerline << if emanager.support_color { term.bold(term.blue('^')) } else { '^' }
 				break
 			}
-				clines << '      ' + pointerline.join('')
-			}
+			clines << '${0:5d}| ' + pointerline.join('')
 		}
 	}
 	source_context += clines.join('\n')

vlib/v/util/util.v

@@ -174,3 +174,14 @@ pub fn read_file(file_path string) ?string {
 	}
 	return raw_text
 }
+
+
+[inline]
+fn imin(a, b int) int {
+    return if a < b { a } else { b }
+}
+
+[inline]
+fn imax(a, b int) int {
+    return if a > b { a } else { b }
+}