Trait Theme

pub trait Theme: Debug {
    // Required methods
    fn equal_prefix<'this>(&self) -> Cow<'this, str>;
    fn delete_prefix<'this>(&self) -> Cow<'this, str>;
    fn insert_prefix<'this>(&self) -> Cow<'this, str>;
    fn header<'this>(&self) -> Cow<'this, str>;

    // Provided methods
    fn highlight_insert<'this>(&self, input: &'this str) -> Cow<'this, str> { ... }
    fn highlight_delete<'this>(&self, input: &'this str) -> Cow<'this, str> { ... }
    fn equal_content<'this>(&self, input: &'this str) -> Cow<'this, str> { ... }
    fn delete_content<'this>(&self, input: &'this str) -> Cow<'this, str> { ... }
    fn insert_line<'this>(&self, input: &'this str) -> Cow<'this, str> { ... }
    fn line_end<'this>(&self) -> Cow<'this, str> { ... }
    fn trailing_lf_marker<'this>(&self) -> Cow<'this, str> { ... }
}

A Theme for customizing the appearance of diffs

This trait allows you to control how diffs are displayed without having to parse the diff output yourself. You can customize prefixes, highlighting, and formatting for different types of changes.

Implementing a Custom Theme

To create a custom theme, you must implement at minimum:

• equal_prefix: Prefix for unchanged lines
• delete_prefix: Prefix for removed lines
• insert_prefix: Prefix for added lines
• header: Header text displayed at the top of the diff

All other methods have default implementations that you can override as needed.

Example

use std::borrow::Cow;
use termdiff::Theme;

#[derive(Debug)]
struct MyCustomTheme {}

impl Theme for MyCustomTheme {
    // Required methods
    fn equal_prefix<'this>(&self) -> Cow<'this, str> {
        " ".into()  // Space for unchanged lines
    }

    fn delete_prefix<'this>(&self) -> Cow<'this, str> {
        "[-]".into()  // Custom prefix for removed lines
    }

    fn insert_prefix<'this>(&self) -> Cow<'this, str> {
        "[+]".into()  // Custom prefix for added lines
    }

    fn header<'this>(&self) -> Cow<'this, str> {
        "=== DIFF RESULTS ===\n".into()  // Custom header
    }

    // Optional overrides for customizing content formatting
    fn delete_content<'this>(&self, input: &'this str) -> Cow<'this, str> {
        format!("REMOVED: {}", input).into()  // Custom formatting for removed content
    }

    fn insert_line<'this>(&self, input: &'this str) -> Cow<'this, str> {
        format!("ADDED: {}", input).into()  // Custom formatting for added content
    }
}

Required Methods

fn equal_prefix<'this>(&self) -> Cow<'this, str>

The prefix to display before lines that are unchanged

This is typically a space or other character that indicates the line is unchanged. This method is required for all theme implementations.

fn delete_prefix<'this>(&self) -> Cow<'this, str>

The prefix to display before lines that are being removed

This is typically a character like ‘-’ that indicates the line is being removed. This method is required for all theme implementations.

fn insert_prefix<'this>(&self) -> Cow<'this, str>

The prefix to display before lines that are being added

This is typically a character like ‘+’ that indicates the line is being added. This method is required for all theme implementations.

fn header<'this>(&self) -> Cow<'this, str>

The header text to display at the top of the diff

This is typically a line explaining the diff format. This method is required for all theme implementations.

Provided Methods

fn highlight_insert<'this>(&self, input: &'this str) -> Cow<'this, str>

How to format the text when highlighting specific changes in inserted lines

This is used to highlight the specific parts of text that have changed within an inserted line. By default, it returns the input unchanged.

Example

fn highlight_insert<'this>(&self, input: &'this str) -> Cow<'this, str> {
    format!("**{}**", input).into()  // Bold the inserted text
}

fn highlight_delete<'this>(&self, input: &'this str) -> Cow<'this, str>

How to format the text when highlighting specific changes in deleted lines

This is used to highlight the specific parts of text that have changed within a deleted line. By default, it returns the input unchanged.

fn equal_content<'this>(&self, input: &'this str) -> Cow<'this, str>

How to format unchanged content

This method is called for content that exists in both the old and new text. By default, it returns the input unchanged.

fn delete_content<'this>(&self, input: &'this str) -> Cow<'this, str>

How to format content that is being removed

This method is called for content that exists only in the old text. By default, it returns the input unchanged.

fn insert_line<'this>(&self, input: &'this str) -> Cow<'this, str>

How to format content that is being added

This method is called for content that exists only in the new text. By default, it returns the input unchanged.

fn line_end<'this>(&self) -> Cow<'this, str>

The string to append when a diff line doesn’t end with a newline

By default, this adds a newline character.

fn trailing_lf_marker<'this>(&self) -> Cow<'this, str>

The marker to show when one string has a trailing newline and the other doesn’t

When one of the two strings ends with a newline and the other doesn’t, this character is inserted before the newline to make the difference visible. By default, this uses the Unicode character ‘␊’ (U+240A).

Implementors

impl Theme for ArrowsColorTheme

impl Theme for ArrowsTheme

impl Theme for SignsColorTheme

impl Theme for SignsTheme