Code awareness

A parse tree for twenty languages

bi ships twenty grammars: Rust, C, C++, C3, Go, Python, Lua, Bash, CSS, GLSL, HLSL, Slang, HCL/Terraform, Dockerfile, CMake, TOML, YAML, JSON, INI and Markdown. The grammar is picked by the file name and reparsed incrementally on every keystroke, and only the visible rows are highlighted, so a large file costs no more than a small one.

When the name lies — a script with no extension, a .txt that is really JSON — tell bi what to read it as:

A name bi has no grammar for is refused by name rather than silently leaving the buffer plain.

Which block am I in

A closing brace says nothing. bi repeats the line that opened the block around the cursor after the line that closes it, behind the language’s comment marker, and when that opening line has scrolled off the top it draws it over the pane’s first row instead.

lstring.c What block am I in 1 / 3 play

1. start The cursor is inside the while. After its closing brace bi repeats the line that opened it, dimmed — it is not in the file.
2. 1 :set context_depth 3Enter context_depth walks further out: the for and the function get their closers annotated too.
3. 2 Ctrl-E ×8 Scroll the function’s first line off the top: it is drawn over the top row instead.

Nothing is shown while the cursor is on the opening line itself — it is right there already.

Symbols

:symbols (or :sym) lists the modules, functions, types and methods tree-sitter found in the buffer. It is a walk of the tree that is already there: no index, no tags file, nothing to go stale after an edit.

lstring.c Jump to a declaration 1 / 4 play

1. start lstring.c, from the top.
2. 1 :symbolsEnter Every declaration tree-sitter found, in file order.
3. 2 resize Type to filter.
4. 3 Enter Enter lands on the name itself, not on column zero.

A file with no declarations says so; a file bi has no grammar for says that instead — which is what :set syntax is for.

Split and join lists

:tssplit breaks the bracketed list around the cursor — call arguments, parameters, arrays, struct literals, a { } block — onto one line per element. :tsjoin puts it back. “Element” means what the grammar says, not what a regex guessed, so a comma inside a nested call stays where it is.

lstring.c Split an argument list 1 / 3 play

1. start The cursor is inside the arguments of luaM_reallocvector.
2. 1 :tssplitEnter One argument per line, reindented the way = would.
3. 2 :tsjoinEnter Back onto one line. Either is one u away.

No trailing comma is added on split; one pressed against the closer is removed on join.

Reflow and reindent

gq is an operator: gqip rewraps a paragraph to textwidth, keeping the indentation and the comment leader (///, //, #, --, *, > …) on every line. Inside code, name the lines — gq3j — so the paragraph does not run on into the function below. = reindents by what the brackets say.

src/color.rs Reflow a comment 1 / 3 play

1. start A doc comment that grew a sentence in the middle and went ragged.
2. 1 :set textwidth 60Enter gq folds to textwidth — 80 by default.
3. 2 gq3j gq3j rewraps the four lines. Each keeps its /// and indent.

Marks on the text

A few things are drawn over the text without being in it. Each is an option you can switch off, globally or per filetype.

Indent guides

A thin vertical line at every indentation step, never over the text itself. A blank line keeps the guides of the block it sits in. :set indent_guides false.

TODO: and friends

TODO:, FIX:, HACK:, WARN:, PERF:, NOTE: and TEST: get five theme colours — FIXME, BUG, XXX, OPTIM and the rest are aliases. Uppercase, on a word boundary, colon required, TODO(name): included. They are matched anywhere, not only in comments, because a Markdown list or a YAML file is exactly where people write them. :set todo_comments false.

Colour swatches

#fb4934, #f94, rgb(251,73,52), rgba(…) and the shader spelling rgb(0.5f,0.1f,0.1) are painted in the colour they name, with black or white text chosen by contrast. A colour must be a whole token, so #define is not one. :set color_swatches false.

src/theme.rs Tags and swatches 1 / 1 play

1. start TODO:, FIX:, HACK: and NOTE: each get their colour; every hex colour is drawn in the colour it names.

Showing the whitespace

:whitespace (:ws) toggles a literal view of every blank: · for a space, → for a tab at the column it starts, ¶ for a newline and ␣ for a non-breaking space. Indent guides stand down while it is on.

lstring.c See every blank 1 / 2 play

1. start Line 28 lines its value up with a tab. You cannot tell from here.
2. 1 :whitespaceEnter Spaces are ·, the tab is → where it starts, newlines are ¶.

Git signs

One cell to the left of the line numbers is held open for signs. For every line that differs from what git add would take, git draws ▎ (added or changed) or ▁ (lines removed under this row), and the focused window’s status row carries a +3 ~1 -2 numstat. The diff is against the index and follows the buffer as you type — nothing has to be saved.

lstring.c Git signs 1 / 4 play

1. start A clean file from the repository: no signs, no numstat.
2. 1 dd Delete a line: ▁ marks where it was.
3. 2 jA /* grows */Esc Change one: ▎ in the change colour, and the status row starts counting.
4. 3 o /* one more line */Esc Add one. +1 ~1 -1 counts against the index, before anything is saved.

A diagnostic’s • wins the cell when both want it. Untracked files and directories outside a repository simply show nothing.

A flash on yank

yy is the one command whose effect is invisible, so what it read lights up for yank_flash milliseconds — charwise, linewise, or one span per row of a rectangle. Deletes and pastes do not flash; you can already see those.

lstring.c A flash on yank 1 / 2 play

1. start yank_flash is stretched to four seconds here so the frame can catch it — 150 ms by default.
2. 1 yi( yi( yanks the arguments. Nothing moved, so what was read lights up.