Nightfury

• automatic language-independent autocompletion engine relying on EBNF syntax

Project Goal

The primary goal is to minimise the time programmers spent on typing syntax. Its aim is not to (fully) replace LSP, but to work alongside it.

Concept

For instance, take this variable declaration in Java: double PI;. You would start typing this by first pressing the letter 'd'. Nightfury sees that and compares it against an internal data structure. If only the token double is possible at the location in the code, it'll automatically autocomplete it for you. But what now? The Java syntax demands a variable name here, a string which the programmer is free to choose themselves. Nightfury can't (and won't) interfere with that, instead quietly listening for a token that terminates the identifier, a semicolon in this case.

To at least try to be language-independent, the project uses the ebnf parser crate as well as a custom translator to convert conventional EBNF-diagrams into its internal data structure.

Features

• EBNF-based tree generator
• IDE-independent client-server architecture
• lots of customization-potential

Running

cargo run # debug build, very verbose logging

cargo run --release # release build, almost no logging (i.e. what you should use)

Reading the FSM

Run the cli with the dbg subcommand. This will print the FSM nightfury generated from the provided ebnf. It currently supports three types of nodes:

• Keyword: some keyword, has two important fields: expanded (the actual keyword) and short (the character sequence you need to type for it to be autocompleted)
  • Note: if nightfury can definitely determine what keyword should be inserted before you finish typing the entire short-sequence, it will insert it without needing you to finish typing the short sequence
• UserDefinedCombo: section for a user-defined token, e.g. identifiers. Consists of a regex (used for deciding which branch to take) and an array of characters called "final_tokens" (used to determine when the userdefined token is completed)
• Null: placeholder node, used to either combine paths or split them apart

The indentation shows you the general flow of the graph. If you see a "Cycle to ", then that means there is a node link that cannot cleanly be displayed in the tree-like view (e.g. cycles)

Architecture

• nightfury: the main lib crate; provides the main API for completions
• nightfury-server: server frontend that can take commands in JSON-Format over a UNIX socket and manipulate the internal FSMs
• nightfury-cli: cli containing helper methods for generating nightfury fsms as well as server debugging
• nightfury-vscode: source code for the visual studio integration extension