`@single_line_no_indent` adds extra blank line

[Tuupertunut]

Environment

• OS: Ubuntu 22.04
• Topiary: 0.6.1

Describe the bug

My grammar has C-like macros and I'm trying to make the macros not indented while the code around them is indented. However if I add a formatting rule like (macro) @single_line_no_indent, it will also add an extra blank line before it. Normally this isn't noticeable because extra blank lines get removed, but if I also want to allow blank lines before macros with (macro) @allow_blank_line_before, there will be a blank line before every macro. If there already was a blank line before the macro in the input, there will now be two blank lines.

To Reproduce

1. Take any grammar and find some rule that is usually in their own line, such as (macro) in the SQF grammar.
2. Create a Topiary formatter with the following rules (or equivalent in your grammar):

   "{" @append_indent_start
   "}" @prepend_indent_end
   
   [
       "{"
       "}"
       ";"
       (macro)
   ] @append_hardline
   
   (macro) @single_line_no_indent @allow_blank_line_before
   

3. Try formatting a file with the content (or equivalent):

   {
       a = 1 + 1;
       #define macro b
       c = 2 + 2;
   
       #define macro d
       e = 3 + 3;
   }
   

4. See how it formats into

   {
       a = 1 + 1;
   
   #define macro b
       c = 2 + 2;
   
   
   #define macro d
       e = 3 + 3;
   }
   

Expected behavior

I would expect it to format into

{
    a = 1 + 1;
#define macro b
    c = 2 + 2;

#define macro d
    e = 3 + 3;
}

without the added blank lines. @single_line_no_indent sounds like it should only remove indentation for that node but not add any lines.

Workarounds

One could rewrite the @append_hardline rule to ignore cases where the following node is (macro), like this:

"{" @append_indent_start
"}" @prepend_indent_end

(
    [
        "{"
        "}"
        ";"
        (macro)
    ]
    .
    (macro)? @do_nothing
) @append_hardline

(macro) @single_line_no_indent @allow_blank_line_before

This will help for the single blank line case but still not for the two blank lines case. The file now formats into

{
    a = 1 + 1;
#define macro b
    c = 2 + 2;


#define macro d
    e = 3 + 3;
}

[Xophmeister]

Thanks, @Tuupertunut, for your issue report.

I'm able to replicate this problem with the Bash grammar. The following query manifests the issue:

"{" @append_indent_start
"}" @prepend_indent_end

[
  "{"
  "}"
  (command)
  (variable_assignment)
] @append_hardline

; Spaces between command arguments
(command
  _ @append_space
)

(variable_assignment) @leaf @allow_blank_line_before @single_line_no_indent

Observe:

Input	Output
{ cat a b c a=123 echo foo }	{ cat a b c a=123 echo foo }
{ cat a b c a=123 echo foo }	{ cat a b c a=123 echo foo }
{ cat a b c a=123 echo foo }	{ cat a b c a=123 echo foo }

Looking at the rendering code, it looks like an explicit line break is added into the output stream when single_line_no_indent is true for leaf nodes, before writing its contents:

topiary/topiary-core/src/pretty.rs

Lines 50 to 54 in 66686bd

	if *single_line_no_indent {
	// The line break after the content has been previously added
	// as a `Hardline` in the atom stream.
	writeln!(buffer)?;
	}

I think this is probably the source of the problem. Whereas, the comment about the hardline is implemented in the atom collection code, where a hardline is inserted to the atom stream after @single_line_no_indent nodes:

topiary/topiary-core/src/atom_collection.rs

Lines 399 to 415 in 66686bd

	// Mark a leaf to be printed on an single line, with no indentation
	"single_line_no_indent" => {
	for a in &mut self.atoms {
	if let Atom::Leaf {
	id,
	single_line_no_indent,
	..
	} = a
	{
	if *id == node.id() {
	*single_line_no_indent = true;
	}
	}
	}
	self.append(Atom::Hardline, node, predicates);
	}

---

The thing is, the only place this capture is used in our supported queries is for OCaml line number directives...and it appears to work correctly. In fact, the passing test case seems to show the opposite behaviour: Topiary swallows the blank line, rather than adding a new one:

Input	Expected
topiary/topiary-cli/tests/samples/input/ocaml.ml Lines 978 to 983 in 66686bd (* Showcase usage of line number directive. Line breaks could be improved. *) module Foo = struct val bar # 1 "v1/pervasives.mli" end	topiary/topiary-cli/tests/samples/expected/ocaml.ml Lines 1026 to 1030 in 66686bd (* Showcase usage of line number directive. Line breaks could be improved. *) module Foo = struct val bar # 1 "v1/pervasives.mli" end

@nbacquey Do you have any ideas on this one?

[Tuupertunut]

In that OCaml query file (line_number_directive) is not marked as @allow_blank_line_before, that's why the blank line disappears. (also mentioned in a comment in #298 )

[Tuupertunut]

I found another usage for @single_line_no_indent in this fork of Topiary that has Erlang formatting queries.
https://github.com/cfclavijo/topiary/blob/main/topiary-queries/queries/erlang.scm
The (pp_define) nodes are marked as both @single_line_no_indent and @allow_blank_line_before so they probably suffer from the same issue. The use case is also the same as mine: not indenting macros.