Language servers

Servers start by themselves

Open a file and bi looks up the server for its filetype, walks up from the file to the nearest root marker, and starts the server there. One server process per (server, root), shared by every buffer under it. Nothing to install in bi — only the server itself has to be on your PATH.

No root marker found means the file’s own directory is the root.

:lsp says where the buffer stands — the server, its state, the root, the position encoding, how many diagnostics it holds, and what it is busy with.

Where an ecosystem has no one-line installer (clangd, lua-language-server, c3-lsp), :lsp install prints the hint instead of downloading anything.

A server is a config section, and yours patches bi’s field by field:

[lsp.servers.rust-analyzer]
command = ["rust-analyzer"]
filetypes = ["rust"]
roots = ["Cargo.toml"]

[lsp]
enabled = true          # false turns the whole client off

Diagnostics

Every diagnostic is drawn three ways: the range is recoloured and underlined in its severity’s colour, the sign column gets a • (it wins over a git sign), and the first line of the message sits at the end of the cursor’s line — only the cursor’s, so the screen does not shout.

What arrives, and when, is the server’s call. rust-analyzer’s compiler errors come from cargo check, which it runs when the file is saved — so the first :w is when they land.

src/main.rs Diagnostics 1 / 5 play

1. start rust-analyzer started by itself when main.rs opened. mix is called on an Option, which has no such method.
2. 1 :wEnter Save. rust-analyzer runs cargo check: the call is underlined in the error colour and • marks the line.
3. 2 :lspEnter :lsp names the server, its root, the encoding and how many diagnostics it holds.
4. 3 ]d ]d jumps to the next one. Its message sits at the end of the line and on the status line.
5. 4 :diagsEnter :diags lists every open buffer’s diagnostics in a pane. Enter jumps.

The :diags pane is the same pane :find fills: j/k to move, Enter to jump, Ctrl-^ back to the file, :results to reopen it later.

Moving through code

Each key is short for an ex command, so every one of them is typeable without the key and rebindable by name.

Every jump goes on the jump list, so Ctrl-O is the way back.

src/main.rs Definition and references 1 / 5 play

1. start The cursor is on vesper, defined in another file.
2. 1 gd gd opens theme.rs on the definition.
3. 2 Ctrl-O Ctrl-O comes back — it was a jump.
4. 3 7G/to_hexEnter Put the cursor on to_hex…
5. 4 gr …and gr lists every reference in a results pane. Enter opens one.

:peek answers “what is that” without leaving: the definition opens beside the call site, and Ctrl-W q is the whole way back.

src/main.rs Peek 1 / 2 play

1. start The cursor is on lookup.
2. 1 :peekEnter The definition opens in a split beside you; the call site stays put. Ctrl-W q closes it.

Hover

K floats what the server knows about the cursor — type, signature, doc comment — above the line. Code blocks in the answer are highlighted with the buffer’s own grammar. Any next key dismisses it.

src/main.rs Hover 1 / 2 play

1. start The cursor is on luminance.
2. 1 K K floats what the server knows: signature and doc comment.

Completion and signatures

Completion opens by itself in insert mode, as you type an identifier or one of the server’s trigger characters (., ::). Filtering happens locally as the word grows: prefix matches first, then subsequence matches.

Type ( in a call and the signature floats above the cursor, the parameter you are on underlined. It follows you from comma to comma and leaves when the call does. Both floats can be up at once: the signature above, the menu below.

src/main.rs Completion and signatures 1 / 6 play

1. start The end of main.
2. 1 olet bg = theme. Type . after a name and the menu opens by itself with what Theme has.
3. 2 ba Typing narrows it. Ctrl-N and Ctrl-P move through what is left.
4. 3 Tab Tab or Enter accepts.
5. 4 ();Enterlet deep = bg.mix( Type ( in a call: the signature floats above the cursor, the parameter you are on underlined.
6. 5 bg, Past the comma the highlight moves on to t.

Code actions and formatting

<leader><leader> (:actions) asks the server what it can do at the cursor — the quickfix under a diagnostic, a missing import, a refactor — and shows the answer as a picker. In visual mode the selection is what it asks about.

:format (:fmt) reformats the whole file as one undo step. A dedicated tool wins where one is configured (clang-format for C/C++, c3fmt for C3); otherwise the server formats.

src/main.rs Code actions and format 1 / 4 play

1. start The cursor is on accent.
2. 1 SpaceSpace <leader><leader> asks the server what it can do here, as a picker.
3. 2 Esc7G describe was written on one line.
4. 3 :formatEnter :format reformats the file as one undo step.

[fmt.tools.clang-format]
command   = ["clang-format", "--style=file", "--fallback-style=LLVM"]
filetypes = ["c", "cpp"]