Logging can be expensive for programs deployed to Solana or logs may contain sensitive information that should not be available during the normal operation of a program.

In these scenarios, we miss having different log levels, as we are used to with other application frameworks. In this micro-post, we will implement this feature for both Anchor and plain Solana applications.

We will try to keep things simple: introduce a macro that includes or omits logs based on a Cargo feature.

Anchor

The debug macro, for Anchor programs, is implemented as below:

#[macro_export]
macro_rules! debug {
    ($($rest:tt)*) => {
        #[cfg(feature="verbose")]
        anchor_lang::prelude::msg!($($rest)*)
    };
}

The macro checks for the verbose Cargo feature and includes the logging statement if it is enabled.

For this to work, you will need to declare a verbose feature in the program's Cargo.toml:

[features]
...
verbose = []
...

Now you can use this feature in your code:

debug!("some super detailed info");
debug!("the secret is {}", secret);

We can build binaries with or without debug logging using the following Anchor commands:

# with debug logging
anchor build -- --features verbose
# without debug logging
anchor build

Unfortunately, both anchor build and anchor test run Cargo builds with --release flag so we have to be explicit about enabling the feature.

Solana

The differences are minimal between Anchor and non-Anchor versions.

The debug macro is defined as below:

#[macro_export]
macro_rules! debug {
    ($($rest:tt)*) => {
        #[cfg(debug_assertions)]
        solana_program::msg!($($rest)*)
    };
}

Here we use the standard debug_assertions conditional compilation instead. This removes the need for defining custom features and can be controlled by the standard Cargo profiles.

And cargo commands are used for the build:

# with debug logging
cargo build
# without debug logging
cargo build --release