Systems

Internal building blocks of the fd binary. Each subsystem lives in its own module under src/.

System	Source	Responsibility
CLI parsing	src/cli.rs, src/main.rs	The Opts struct (clap derive), the custom Exec parser, smart-case detection, and the conversion from Opts to Config.
Walker	src/walk.rs	Parallel directory traversal, batching, the buffer-then-stream receiver, and the Ctrl-C handler.
Filters	src/filter/, src/filetypes.rs, src/walk.rs	Per-entry checks: file type, extension, size, modification time, owner, depth, exclude globs, ignore_contain.
Ignore rules	src/walk.rs (configured), ignore crate (implementation)	.gitignore, .ignore, .fdignore, parent ignores, the global ignore, and --exclude overrides.
Command execution	src/exec/	--exec/--exec-batch machinery, CommandSet, CommandTemplate, CommandBuilder, and the per-thread job/batch receivers.
Format templates	src/fmt/	Shared placeholder engine for both --exec/--exec-batch arguments and --format output.
Output	src/output.rs, src/dir_entry.rs, src/hyperlink.rs	Path formatting with colors, custom path separators, OSC 8 hyperlinks, trailing slashes for directories, null vs newline separators.

How they connect

graph LR
    cli[CLI parsing] -->|Opts → Config| walk[Walker]
    walk -->|builds| ignore[Ignore rules]
    walk -->|applies| filter[Filters]
    walk -->|via channel| receive[Receiver]
    receive -->|prints| output[Output]
    receive -->|spawns| exec[Command execution]
    exec -->|placeholders| fmt[Format templates]
    output -->|optional| fmt

Where each subsystem reads Config

The Config struct in src/config.rs is the integration point. Every subsystem reads only the fields it needs:

• Walker reads ignore_*, follow_links, one_file_system, max_depth, min_depth, prune, threads, quit_flag semantics.
• Filters read file_types, extensions, size_constraints, time_constraints, owner_constraint, ignore_contain.
• Receiver reads quiet, max_results, max_buffer_time, command, show_filesystem_errors.
• Output reads ls_colors, hyperlink, format, path_separator, actual_path_separator, null_separator, strip_cwd_prefix.
• Command execution reads command, batch_size, path_separator, null_separator, threads.

This separation keeps each module testable in isolation: most subsystems own their own #[cfg(test)] mod tests block (see how-to-contribute/testing).