Basic Formatting Rules

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§1 Indentation

§1.1 Indent Width. Use 4 spaces for indentation by default. This can be modified via the indent_width configuration option.

// Default indentation (4 spaces)
fn foo() {
    let x = 1;
    if x > 0 {
        print(x);
    }
}

// 2-space indentation (indent_width = 2)
fn foo() {
  let x = 1;
  if x > 0 {
    print(x);
  }
}

§1.2 Tab Indentation. When use_tabs = true, use tab characters for indentation. Default is false.

§1.3 Indentation Consistency. Do not mix tabs and spaces within the same file.

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§2 Line Width

§2.1 Maximum Line Width. The default maximum line width is 120 characters. This can be modified via the line_width configuration option.

§2.2 Line Break Strategy. When a line exceeds the maximum line width, it must be broken at an appropriate position. The priority of line break positions is:

1. After low-priority operators (+, -, or, and, =)
2. Function parameter list
3. List/dictionary elements
4. After high-priority operators (*, /, %, ==, !=)

§2.3 Line Break Indentation. Content after a line break must be indented one additional level.

// Line break when exceeding line width
let result = very_long_variable_name + another_long_name + yet_another_long_name;

// After formatting
let result = very_long_variable_name
    + another_long_name
    + yet_another_long_name;

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§3 Operators

§3.1 Operator Spacing. There must be spaces on both sides of a binary operator.

// ✅ Correct
let x = 1 + 2;
let y = a == b;

// ❌ Incorrect
let x = 1+2;
let y = a==b;

§3.2 Unary Operators. No space is added between a unary operator and its operand.

// ✅ Correct (! is a tightly-bound unary operator with no space)
let x = -1;
let y = !flag;
let z = *ptr;

// ❌ Incorrect
let x = - 1;
let y = ! flag;

§3.3 Low-Priority Operator Line Breaks. When an expression exceeds the line width, place the low-priority operator at the beginning of the new line.

// When exceeding line width
let result = first_value + second_value + third_value + fourth_value;

// After formatting
let result = first_value
    + second_value
    + third_value
    + fourth_value;

§3.4 High-Priority Operator Line Breaks. Place the high-priority operator at the beginning of the new line.

// When exceeding line width
let result = first_value * second_value / third_value % fourth_value;

// After formatting
let result = first_value
    * second_value
    / third_value
    % fourth_value;

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§3.5 Variable Reference

§3.5.1 Variable Names. Variable references output the variable name directly, without adding extra spaces.

// ✅ Correct
let x = my_variable;
let y = camelCaseName;

// ❌ Incorrect
let x = my_variable ;  // Extra space
let y = "camelCaseName";  // Should not be quoted

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§6 Code Blocks

§6.1 Code Block Format. Code blocks are enclosed with curly braces {}, with one space before the opening brace.

// ✅ Correct
fn foo() {
    let x = 1;
}

// ❌ Incorrect
fn foo(){
    let x = 1;
}
fn foo()
{
    let x = 1;
}

§6.2 Single-Line Code Block. When a code block contains only one line and the total length does not exceed the line width, the single-line format may be used.

// ✅ Single-line format
fn foo() { 1 }

// ✅ Multi-line format
fn foo() {
    let x = 1;
    let y = 2;
    x + y
}

§6.3 Empty Code Block. Use {} to represent an empty code block.

// ✅ Correct
fn foo() {}

// ❌ Incorrect
fn foo() {
}