fmt: better newline handling in block comments (#8325)

vlib/v/fmt/comments.v

@@ -44,9 +44,8 @@ pub fn (mut f Fmt) comment(node ast.Comment, options CommentsOptions) {
 		mut s := node.text.trim_left('\x01')
 		mut out_s := '//'
 		if s != '' {
-			match s[0] {
-				`a`...`z`, `A`...`Z`, `0`...`9` { out_s += ' ' }
-				else {}
+			if is_first_char_alphanumeric(s) {
+				out_s += ' '
 			}
 			out_s += s
 		}
@@ -57,12 +56,21 @@ pub fn (mut f Fmt) comment(node ast.Comment, options CommentsOptions) {
 		f.write(out_s)
 	} else {
 		lines := node.text.trim_space().split_into_lines()
-		f.writeln('/*')
+		expected_line_count := node.pos.last_line - node.pos.line_nr
+		no_new_lines := lines.len > expected_line_count && !is_first_char_alphanumeric(lines[0])
+		f.write('/*')
+		if !no_new_lines {
+			f.writeln('')
+		}
 		for line in lines {
 			f.writeln(line)
 			f.empty_line = false
 		}
+		if no_new_lines {
+			f.remove_new_line()
+		} else {
 			f.empty_line = true
+		}
 		f.write('*/')
 	}
 	if options.level == .indent {
@@ -96,3 +104,10 @@ pub fn (mut f Fmt) comments_after_last_field(comments []ast.Comment) {
 		f.indent--
 	}
 }
+
+fn is_first_char_alphanumeric(s string) bool {
+	return match s[0] {
+		`a`...`z`, `A`...`Z`, `0`...`9` { true }
+		else { false }
+	}
+}

vlib/v/fmt/tests/comments_expected.vv

@@ -64,3 +64,20 @@ fn main() {
 	// empty return
 	return
 }
+
+fn insert_space() {
+	// abc
+}
+
+fn linebreaks_in_block_comments() {
+	/*
+	foo
+	comment goes here!
+	bar
+	*/
+	/*
+	spam
+	spaces make no difference there
+	eggs
+	*/
+}

vlib/v/fmt/tests/comments_input.vv

@@ -52,3 +52,16 @@ fn main() {
 	}
   return // empty return
 }
+
+fn insert_space() {
+	//abc
+}
+
+fn linebreaks_in_block_comments() {
+	/*foo
+	comment goes here!
+	bar*/
+	/*  spam
+	spaces make no difference there
+	eggs */
+}

vlib/v/fmt/tests/comments_keep.vv

@@ -35,16 +35,26 @@ fn main() {
 	_ := User{
 		// Just a comment
 	}
+	//////
+	// /
+	// 123
+}
+
+fn assign_comments() {
 	a := 123 // comment after assign
 	b := 'foo' // also comment after assign
 	c := true
 	// Between two assigns
 	d := false
-	//////
-	// /
-	// 123
+	// at the end
+}
+
+fn linebreaks_in_block_comments() {
 	/*
 	block
 	*/
-	println('hello world')
+	/*****
+	Want a long line of stars?
+	no problem
+	*****/
 }