fmt: only insert a space after // if the 3rd char is alphanumeric (#7330)

vlib/v/fmt/fmt.v

@@ -1204,16 +1204,19 @@ pub fn (mut f Fmt) comment(node ast.Comment, options CommentsOptions) {
 	if !node.text.contains('\n') {
 		is_separate_line := !options.inline || node.text.starts_with('\x01')
 		mut s := if node.text.starts_with('\x01') { node.text[1..] } else { node.text }
-		if s == '' {
-			s = '//'
-		} else {
-			s = '// ' + s
+		mut out_s := '//'
+		if s != '' {
+			match s[0] {
+				`a`...`z`, `A`...`Z`, `0`...`9` { out_s += ' ' }
+				else {}
+			}
+			out_s += s
 		}
 		if !is_separate_line && f.indent > 0 {
 			f.remove_new_line() // delete the generated \n
 			f.write(' ')
 		}
-		f.write(s)
+		f.write(out_s)
 		return
 	}
 	lines := node.text.split_into_lines()

vlib/v/fmt/tests/comments_keep.vv

@@ -30,6 +30,9 @@ fn main() {
 	a := 123 // comment after assign
 	b := 'foo' // also comment after assign
 	c := true
-	// between two assigns
+	// Between two assigns
 	d := false
+	//////
+	// /
+	// 123
 }

vlib/v/scanner/scanner.v

@@ -926,7 +926,7 @@ fn (mut s Scanner) text_scan() token.Token {
 					}
 					if s.should_parse_comment() {
 						s.line_comment = s.text[start + 1..comment_line_end]
-						mut comment := s.line_comment.trim_space()
+						mut comment := s.line_comment
 						// Find out if this comment is on its own line (for vfmt)
 						mut is_separate_line_comment := true
 						for j := start - 2; j >= 0 && s.text[j] != `\n`; j-- {