Watch Mode

Builder can automatically rebuild your package when source files change using the -watch flag. This is useful during active development to see changes immediately without manually running the build command.

⚠️ Warning: this feature is vibe-coded, sorry.

Usage

builder -watch
builder -watch -input srcr -output R

How It Works

When watch mode is enabled:

Builder performs an initial build (with cleaning unless -noclean is specified)
Sets up file system monitoring on the input directory
Waits for file changes (create, modify, delete)
Automatically rebuilds when changes are detected
Repeats until interrupted with Ctrl+C

Example

$ builder -watch
[INFO] Watch mode enabled, monitoring srcr
[INFO] Cleaning: R/ and testthat/
[INFO] Copying srcr/main.R to R/main.R
[INFO] Waiting for changes...

# Edit srcr/main.R in your editor...

[INFO] Change detected, rebuilding...
[INFO] Copying srcr/main.R to R/main.R
[INFO] Waiting for changes...

# Press Ctrl+C to exit

Options

Flag	Description
`-watch`	Enable watch mode
`-noclean`	Skip cleaning on initial build

Behavior

Initial build: Cleans output directory (unless -noclean)
Subsequent rebuilds: Skip cleaning to preserve any manual changes
Error handling: Build errors are reported but don’t stop watching
Exit: Press Ctrl+C to stop watching

Technical Details

Watch mode uses Linux’s inotify API to efficiently monitor file changes. It watches for:

File saves (close after write)
File renames/moves (vim-style atomic saves)
File deletions

A 100ms debounce prevents multiple rebuilds from rapid successive saves.

Limitations

Only the input directory (-input) is monitored
Imported header files (-import) are not watched; restart watch mode if headers change
Linux only (uses inotify); macOS support would require kqueue