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CLAUDE.md

Project Overview

pratdiff is a colorful diff CLI tool in Rust implementing the Patience Diff algorithm (with a histogram extension for non-unique lines). It supports line-level and token-level colorization for files and directory trees.

Architecture

src/
├── lib.rs          - Core Patience Diff algorithm
├── bin/pratdiff.rs - CLI entry point (clap-based)
├── diff.rs         - Core data structures: DiffItem, Hunk, Diffs
├── files.rs        - File/directory I/O and diff dispatch
├── printer.rs      - Output formatting and colorization
└── style.rs        - Color style definitions (owo_colors)

Data flow: bin/pratdiff.rs → files.rs → lib.rs (diff algorithm) → printer.rs (render)

Build & Test

cargo build --release
cargo test                    # 12 unit tests in lib.rs + integration tests
cargo test <test_name>        # Run a specific test

Key Design Decisions

  • Token-level diffs: tokenize_lines() in lib.rs applies the same patience diff recursively at the token level for changed lines. Tokens include: whitespace, numbers, identifiers, and symbols.
  • Byte-oriented diff core: lib.rs operates directly on &[u8] slices. Both line-level and token-level diffing use the same concrete diff(&[&[u8]], &[&[u8]]) function.
  • Histogram fallback: When no unique lines exist for patience diff, falls back to histogram diff (counts occurrences, prefers rarer lines).
  • Common prefix stripping: --verbose-paths disables common path prefix removal in output headers.

Notable Behaviors

  • - as filename means stdin
  • Binary files (non-UTF-8) are detected and reported but not diffed
  • Unix inode checks prevent diffing a file against itself
  • Color output auto-detects terminal; controllable via --color=always|never|auto