Tree Sitter Fortran in Neovim

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1

I’m currently updating my nvim config and have encountered some indentation problems since I installed nvim-treesitter with a Fortran parser.

Does anyone have any experience with nvim and treesitter?

I only used fortrls (LSP) before, and it feels like I had fewer issues without tree-sitter.

Currently, for example, when I type do <enter> the indentation level is zero and messes everything up (no indentation at all) as long as I don’t have an end do.

    ! some code
    ! with indent level 1
do ! as soon as I type the 'o', indent is zero
! indentation is zero instead of +1
    end do ! this magically gets indented correctly
        ! but the next line is indented ???
    ! but only one line, this is fine again

The most relevant settings:

indentexpr=nvim_treesitter#indent()
indent={enable=true}

If someone managed to set tree-sitter-fortran correctly, I would be very happy to see the nvim config.

2

Does nvim also use GitHub - stadelmanma/tree-sitter-fortran: Fortran grammar for tree-sitter like helix? I’m seeing indentation issues when using block ... end block in helix. I suspect the fix is to update the tree-sitter files used to match the updates on github.

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3

I’ve tried tree-sitter on Neovim and ended up disabling it in Fortran because there were a lot of errors, mostly with the more modern constructs. I assume it only handles FORTRAN77 and maybe some parts of Fortran90 and should be updated. In their GitHub (GitHub - nvim-treesitter/nvim-treesitter: Nvim Treesitter configurations and abstraction layer) they say that they support Fortran via the one that @freevryheid said Helix uses

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4

Yes, exactly!

The reason you see this behaviour is because there is no indentation rule for blocks in indents.scm:

[
  (module)
  (submodule)
  (program)
  (subroutine)
  (module_procedure)
  (function)
  ; (interface)
  (if_statement)
  (do_loop_statement)
  (where_statement)
  (derived_type_definition)
  (enum)
] @indent

I guess I will do the same and hope for more updates. Maybe if I find some time I will contribute to it, too.
Did you disable it for everything or just indentation?

5

Yes, I’m thinking on contributing at some time too (but never made up the time to see how Tree-Sitter works). I did disable it for everything because I had other problems that I don’t remember exactly right now, but they were related to syntax highlighting.

Right now I’m just using the indentation that Neovim provides, plus I run fprettify on my files fairly often to fix indentations and spaces (watch out to anyone that runs fprettify! Sometimes it can delete your whole file so always run fprettify --diff first)

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6

Would these tools (tree-sitter, fprettify) not benefit from an AST, that I understand LFortran already provides?

7

I don’t know much about Tree Sitter, but afaik it needs a “grammar” and generates a parser from it.

8

lfortran fmt takes care of formatting, essentially a stand-in for fprettify
lfortran already uses a grammar file that I’m guessing is used by the compiler. Instead of re-inventing the wheel so to speak, why not just “convert” this asdl file to tree-sitter format.

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9

Hey guy, how’s it going?
Try adding the disable part should make it works fun.
indent = { enable = true, disable = { "fortran" } }