bug#61017: 29.0.60; ruby-ts-mode indents class between two lines incorrectly

[Dmitry Gutov]

On 24/01/2023 16:17, Aaron Jensen wrote:
> On Mon, Jan 23, 2023 at 4:28 PM Dmitry Gutov <dgutov@yandex.ru> wrote:
> > Hi!
> >
> > On 23/01/2023 06:33, Aaron Jensen wrote:
> > > Start with a buffer in ruby-ts-mode like:
> > >
> > > a
> > >
> > > b
> > >
> > > Between the two lines, type "class Foo", then press enter
> > >
> > > You should get this:
> > >
> > > a
> > >
> > >     class Foo
> > >
> > > b
> > >
> > > But this is expected:
> > >
> > > a
> > >
> > > class Foo
> > >
> > > b
> > >
> > > Note that reindenting after adding the "end" will indent correctly, so
> > > it's only an issue with electric indent
> >
> > Thanks for the report, the problem here is that such examples parse into
> > a malformed syntax tree:
> >
> >     (program (identifier)
> >      (ERROR class (constant) (identifier)))
> >
> > Another example would be:
> >
> >     class C
> >       def foo
> >
> > which parses as
> >
> >     (ERROR class (constant) def (identifier))
> >
> > We can try to anticipate such cases and infer the implied structure
> > somehow, or just disable indentation for specific cases. See the
> > attached patch for the latter.
> >
> > Is it enough of an improvement?
>
> That seems to make indentation after an open def not happen:
>
> def foo
> bar
> end

Not sure what you mean. Is that an example with an "open def"? "end" 
seems to be closing it. In the final state, it indents correctly here.

> I applied the patch manually though, so maybe you can confirm that you
> see the same thing?

If I have a buffer with just the first line:

  def foo

then it indeed doesn't indent. But I think that happens with or without 
this patch?

It's a slightly different problem: the grammar parses this code example 
without ERROR nodes, like a full method, for some reason:

  (program
   (method def body: (identifier) end))

And the end position of the "virtual" end node stays at the previous 
line, so our code doesn't know it's inside the method.

I suppose we could add some tricky predicate like (is the previous node 
a method with an "end" child that is 0 characters long), but the grammar 
might change (we should look for any previous reported issues about this 
behavior, or maybe ones that resulted in it), and it only happen this 
way when there is nothing after "def xyz" in the buffer.

Because in the more common case, like

  class C
    def foo
      |
  end

the last "end" is parsed like the closer for the method, the method node 
spans until it, and the line with "|" indents correctly.

WDYT?