feat(snippets.default): filter_snippets function for disabling certain snippet files

[stefanboca]

This can be used with eg.

filter_snippets = function(ft, file)
  return not (string.match(file, "friendly.snippets") and string.match(file, "framework"))
end,

to disable friendly-snippets frameworks.

Closes #291

Also removes the ignored_filetypes option, which is redundant now that users can filter snippets with more control.

[saghen]

Long term I think we should move the settings for the registry into the top level snippets (maybe under snippets.registry), and make the snippets source options generic to all snippet providers (luasnip, mini.snippets, default). Just something to think about

[GeoDaoyu]

This can be used with eg.

filter_snippets = function(ft, file)
  return not (string.match(file, "friendly.snippets") and string.match(file, "framework"))
end,

to disable friendly-snippets frameworks.

Closes #291

Also removes the ignored_filetypes option, which is redundant now that users can filter snippets with more control.

Thanks for your feature~
Where should I write [filter_snippets] config? and there is a not used 'ft'?
I try to set filter_snippets under snippets,such as follow, but it throw error on config.

      snippets = {
        preset = "luasnip",
        filter_snippets = function(_, file)
          return not (string.match(file, "friendly.snippets") and string.match(file, "framework"))
        end,
      },

[stefanboca]

filter_snippets should be in snippets.opts:

providers = {
  snippets = {
    opts = {
      filter_snippets = function(ft, file)
        return not (string.match(file, "friendly.snippets") and string.match(file, "framework"))
      end,
    },
  },
}

You're right that there is a ft parameter (filetype) that is unused in this example, in order to allow disable snippets based on filetype. For instance, you could write

filter_snippets = function(ft, file)
  return ft == "rust" or not (string.match(file, "friendly.snippets") and string.match(file, "framework"))
end,

in order to disable friendly-snippet frameworks, except for in rust.

[sneha-afk]

@stefanboca Could you update the documentation since there are still references to ignored_filetypes, I was stuck until I found your PR. Thank you so much for this feature!

[noidilin]

It also takes me some time to find this thread.

Here is a use case that

• disable only javascript snippet from friendly-snippet
• when the file extension is js, ts, jsx, tsx
• but keep other snippet from friendly-snippet alive (e.g global.json snippet)

snippet config

sources = {
  providers = {
    snippets = {
      opts = {
        -- disable friendly-snippet frameworks, except for in rust.
        filter_snippets = function(ft, file)
          local disabled_fts = {
            javascript = true,
            javascriptreact = true, -- .jsx
            typescript = true,
            typescriptreact = true, -- .tsx
          }

          -- check if the snippet file path contains 'friendly-snippet' or 'javascript'
          if
            disabled_fts[ft]
            and string.match(file, "friendly.snippets")
            and string.match(file, "javascript")
          then
            return false
          end

          -- allow everything else by default
          return true
        end,
      },
    },
  },
},

The snippet file path can be referenced from friendly-snippet repo.
Hope this example shed some light on the usage of filter_snippets to other people.