fmt: keep interface comments between methods (#7650)

vlib/v/ast/ast.v

@@ -312,6 +312,7 @@ pub mut:
 	stmts           []Stmt
 	return_type     table.Type
 	comments        []Comment // comments *after* the header, but *before* `{`; used for InterfaceDecl
+	next_comments   []Comment // coments that are one line after the decl; used for InterfaceDecl
 	source_file     &File = 0
 	scope           &Scope
 }

vlib/v/fmt/fmt.v

@@ -715,6 +715,7 @@ pub fn (mut f Fmt) interface_decl(node ast.InterfaceDecl) {
 		f.write(method.stringify(f.table, f.cur_mod, f.mod2alias).after('fn '))
 		f.comments(method.comments, inline: true, has_nl: false, level: .indent)
 		f.writeln('')
+		f.comments(method.next_comments, inline: false, has_nl: true, level: .indent)
 	}
 	f.writeln('}\n')
 }

vlib/v/fmt/tests/interface_declaration_comments_keep.vv

@@ -2,3 +2,30 @@ pub interface ReaderWriter {
 	read(mut buf []byte) ?int // from Reader
 	write(buf []byte) ?int // from Writer
 }
+
+interface Speaker {
+	// first
+	speak() string
+	// between
+	foo() string
+	foo2() string
+	// last
+}
+
+interface Baz {
+	// first
+	speak() string
+	// comment
+	// more between
+	foo() string
+	foo2() string
+	// last
+}
+
+interface Bar {
+	speak() string // after
+	foo() string
+	speak2() string // also after
+	// and between
+	foo2() string
+}

vlib/v/parser/struct.v

@@ -455,8 +455,10 @@ fn (mut p Parser) interface_decl() ast.InterfaceDecl {
 		if p.tok.kind.is_start_of_type() && p.tok.line_nr == line_nr {
 			method.return_type = p.parse_type()
 		}
-		mcomments := p.eat_comments()
+		mcomments := p.eat_line_end_comments()
+		mnext_comments := p.eat_comments()
 		method.comments = mcomments
+		method.next_comments = mnext_comments
 		methods << method
 		// println('register method $name')
 		ts.register_method(name: name, params: args, return_type: method.return_type, is_pub: true)