ltk/code_style_guide.md

Code Style Guide

This project follows a Modified Allman brace and formatting style, applied to Rust. It prioritizes visual clarity, symmetry, and logical separation of blocks over strict line compactness.

This file is the canonical style reference; the style bullets in CONTRIBUTING.md are a summary of it.

---

Key principles

• Indentation with tabs (width = 4).
• Opening braces { start on their own line — for fn, impl, struct, enum, trait, mod, if, for, while, loop and match.
• } else { and } else if … { stay on the same line for compact flow.
• Spaces inside parentheses only when non-empty:
  • ( arg1, arg2 )
  • main()
• Spaces inside attribute brackets only when non-empty: #[ derive( Clone, Debug ) ], #[ cfg( test ) ].
• No spaces inside generics: Vec<String>, Option<i32>, Element<Msg>.
• Types, traits, and enum variants: PascalCase.
• Functions, methods, variables, and modules: snake_case (the Rust convention; rustc warns on anything else).
• Constants and statics: UPPER_CASE_WITH_UNDERSCORES.
• Aligned columns in consecutive struct fields, match arms, or let groups where it aids scanning.
• Comments in English, only where the code cannot say it itself.

---

Examples

if / else structure

if condition
{
	do_something();
} else if other_condition {
	do_other_thing();
} else {
	do_something_else( arg1, arg2 );
}

match structure

match points.len()
{
	0 => None,
	1 => Some( points[0].value ),
	n => Some( total / n as f32 ),
}

Error handling

Rust has no try / catch; recoverable errors travel as Result and propagate with ?. The block style applies to the match when a result is handled in place:

fn load_config( path: &Path ) -> Result<Config, ConfigError>
{
	let text = std::fs::read_to_string( path )?;
	match toml::from_str( &text )
	{
		Ok( cfg ) => Ok( cfg ),
		Err( e )  => Err( ConfigError::Parse( e ) ),
	}
}

if let follows the same brace rules as if:

if let Some( ( rgba, w, h ) ) = icon( "general/right" )
{
	it = it.trailing_icon( rgba, w, h );
}

Structs, impls, and attributes

#[ derive( Clone, Debug ) ]
pub struct DataPoint
{
	value: f32,
	label: String,
}

impl DataPoint
{
	pub fn new( value: f32, label: impl Into<String> ) -> Self
	{
		Self
		{
			value,
			label: label.into(),
		}
	}

	pub fn scaled( &self, factor: f32 ) -> f32
	{
		if factor <= 0.0
		{
			self.value
		} else {
			self.value * factor
		}
	}
}

main() function

fn main()
{
	let analyzer = DataAnalyzer::new( "results.csv" );

	if let Err( e ) = analyzer.process_and_report()
	{
		eprintln!( "Error: {e}" );
		std::process::exit( 1 );
	}
}

---

Tooling: do not run cargo fmt

rustfmt cannot express this style, so never run cargo fmt on this codebase — it would rewrite every file into the default style. Specifically:

• There is no rustfmt option for spaces inside parentheses or attribute brackets (the historical spaces_within_parens options were removed from rustfmt).
• The item brace styles (brace_style, control_brace_style) are unstable, nightly-only options.
• Even on nightly, the combination of Allman opening braces with a compact } else { is not representable: control_brace_style = "AlwaysNextLine" also pushes else onto its own line.

The repository ships a rustfmt.toml containing only disable_all_formatting = true, so an accidental cargo fmt — or an editor with format-on-save wired to rustfmt — is a no-op instead of a 40 000-line diff. Style is enforced by review, not by a formatter.