lsp-tree-sitter

A core library to support language servers.

I write many language servers and they share some same code so I extract the shared code to this library.

I’ve had enough of writing many DSLs in my editor without any LSP support (completion, hover, …). So I decide to sacrifice my time to do this work.

Language servers

• termux-language-server: for some specific bash scripts:

  • build.sh

  • PKGBUILD

  • *.ebuild

  • …

• mutt-language-server: for (neo)mutt’s (neo)muttrc

• More

What does this library provide

Schema

A Trie to convert a file to a json, then you can use json schema to validate it to get diagnostics.

Take termux-language-server as an example.

PKGBUILD:

pkgname=hello
pkgver=0.0.1
pkgrel=1
pkgdesc="hello"
arch=(wrong_arch)
license=(GPL3)

build() {
    cat <<EOF > hello
#!/usr/bin/env sh
echo hello
EOF
}

package() {
    install -D hello -t $pkgdir/usr/bin
}

termux-language-server --convert PKGBUILD

{
  "pkgname": "hello",
  "pkgver": "0.0.1",
  "pkgrel": "1",
  "pkgdesc": "hello",
  "arch": [
    "wrong_arch"
  ],
  "license": [
    "GPL3"
  ],
  "build": 0,
  "package": 0
}

So, we can validate the json by a json schema:

$ termux-language-server --check PKGBUILD
PKGBUILD:5:7-5:17:error: 'wrong_arch' is not one of ['any', 'pentium4', 'i486', 'i686', 'x86_64', 'x86_64_v3', 'arm', 'armv6h', 'armv7h', 'armv8', 'aarch64']

Sometimes it will be more complicated:

neomuttrc:

set allow_ansi=yes sleep_time = no ispell = aspell
set query_command = 'mutt_ldap_query.pl %s'

mutt-language-server --convert neomuttrc

{
  "set": {
    "allow_ansi": "yes",
    "sleep_time": "no",
    "ispell": "aspell",
    "query_command": "mutt_ldap_query.pl %s"
  }
}

$ mutt-language-server --check neomuttrc
neomuttrc:1:33-1:35:error: 'no' is not of type 'number'

We put the result to the json’s .set not . just in order to reserve the other keys for other usages.

Finders

Some finders to find the required node in tree-sitter’s AST. Such as, if you want to get the node under the cursor:

@self.feature(TEXT_DOCUMENT_COMPLETION)
def completions(params: CompletionParams) -> CompletionList:
    document = self.workspace.get_document(params.text_document.uri)
    uni = PositionFinder(params.position, right_equal=True).find(
        document.uri, self.trees[document.uri]
    )
    # ...

UNI (Universal Node Identifier) is URI + node.

Utilities

This library also provides many utility functions. Such as converting man page to markdown and tokenizing it in order to generate the json schema.

mutt-language-server --generate-schema neomuttrc

{
  "$id": "https://github.com/neomutt/mutt-language-server/blob/main/src/termux_language_server/assets/json/neomuttrc.json",
  "$schema": "http://json-schema.org/draft-07/schema#",
  "$comment": "Don't edit this file directly! It is generated by `mutt-language-server --generate-schema=neomuttrc`.",
  "type": "object",
  "properties": {
    "account-hook": {
      "description": "```neomuttrc\naccount-hook regex command\n```\nThis hook is executed whenever you access a remote mailbox. Useful to adjust configuration settings to different IMAP or POP servers."
    },
    "$comment": "..."
  }
}

References

• some Chinese blogs about how I write these language servers

• tree-sitter

• language server protocol

• json schema