Replace directive

The godebug directive in go.mod or go.work sets default GODEBUG environment variable values for a module or workspace, overriding toolchain defaults based on the Go version.

// In go.mod or go.work
godebug (
    default=go1.21
    panicnil=1
    asynctimerchan=0
)

Alternatively, use //go:debug comments at the top of a main package source file to set defaults for that specific package:

//go:debug default=go1.21
//go:debug panicnil=1
package main

The default key specifies a Go version to inherit unspecified settings from, while other keys explicitly enable or disable specific behaviors like panicnil or asynctimerchan.

The godebug directive lets you control specific Go runtime behaviors, like how errors are handled or which security checks are active, directly in your project configuration. It acts like a switchboard that lets you opt-in to older or newer behaviors regardless of the Go version you are using. This ensures your code runs consistently across different environments without needing to change environment variables manually.