`bynk-fmt`

Bynk’s formatter. There is one implementation, in the bynk-fmt crate — a leaf over bynk-syntax that never links the compiler; the CLI (via bynk-driver) and the language server both drive that one copy. You invoke it as bynkc fmt (or bynk fmt) — see the how-to Format your code with bynk-fmt for usage.

What it does

format_source(source, &FormatOptions) tokenises and parses the source, then re-prints the AST in canonical form. It is idempotent — formatting formatted code is a no-op — and it returns a FormatError (carrying the parse diagnostics) if the source does not parse.

Options

FormatOptions controls the output:

Field	Type	Default
indent	IndentStyle (Tab or Spaces(n))	Tab
max_line_width	u32	100
trailing_comma	bool	true

Three sources feed them, each overriding the one before:

1. the defaults above;
2. the project’s [fmt] section in bynk.toml (indent, indent_width, max_line_width, trailing_comma), resolved from the nearest manifest at or above the file being formatted;
3. the flags a CLI run passes — --indent tab|spaces, --indent-width N, --max-line-width COLUMNS, --trailing-comma / --no-trailing-comma.

Step 2 goes through bynk_fmt::FmtConfig, which both the CLI and the language server call, so a manifest they can both read is interpreted identically. --no-config drops step 2 for a run.

A manifest that does not read is where they differ: the CLI reports the error and formats nothing; the language server falls back to the canonical style, since it cannot refuse to serve. A typo therefore shows up as an editor that quietly stops honouring the section and a bynkc fmt that fails loudly.

Canonical style

• Tab indentation, one tab per nesting level.
• K&R braces — the opening brace stays on the construct’s line.
• Trailing commas in multi-line records, sums, list literals and exports clauses. Parameter and argument lists never carry one — the grammar rejects it.
• One blank line between top-level declarations; none inside record/sum/parameter lists or between match arms.
• A doc block sits directly above its declaration, with no blank line between.
• One space around binary operators and after commas; no padding inside parentheses.
• A soft 100-column width. A construct that would overrun it wraps vertically — one entry per line for records, lists and argument lists; a break before each &&/||; a break before each call of a long .-chain. A line whose overflow sits inside a single token (a long string literal) is left long rather than mangled.

Programmatic use

use bynk_fmt::{format_source, FormatOptions};

let formatted = format_source(source, &FormatOptions::default())?;

This is exactly what bynkc fmt and the language server’s formatting requests call, and both resolve their FormatOptions through the same [fmt] reader, so editor format-on-save and CLI formatting agree on any project whose manifest parses.