Why are doctests exempted from conditional compilation for tests?

Let's look at the following code. It defines a single constant ARGON2_MEMORY_COST using conditional compilation: If we're testing, then set it small, otherwise set it large. Below that constant, we have both a unit test, as well as a doctest. Both types of tests have assert_eq!(ARGON2_MEMORY_COST, 1024). However, only the unit test passes. The doctest has somehow been compiled under the non-test code, as we will later see.

#![allow(dead_code)]

#[cfg(test)]
pub const ARGON2_MEMORY_COST: u32 = 1024; // smaller for faster tests
#[cfg(not(test))]
pub const ARGON2_MEMORY_COST: u32 = 65536; // larger for enhanced security

#[cfg(test)]
mod tests {
    use super::*;
    #[test]
    fn memory_cost_is_small() {
        assert_eq!(ARGON2_MEMORY_COST, 1024);
    }
}

/// Placeholder struct just so we can show an example of a doctest.
/// 
/// # Examples
/// ```rust
/// use doctests_conditional_compilation::ARGON2_MEMORY_COST;
/// 
/// assert_eq!(ARGON2_MEMORY_COST, 1024);
/// ```
struct UnitStruct;

This is the output for the unit test:

running 1 test
test tests::memory_cost_is_small ... ok

test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s

On the other hand, this is the output for the doctest:

   Doc-tests doctests_conditional_compilation

running 1 test
test src/lib.rs - UnitStruct (line 20) ... FAILED

failures:

---- src/lib.rs - UnitStruct (line 20) stdout ----
Test executable failed (exit status: 101).

stderr:

thread 'main' panicked at /tmp/rustdoctestCdCfPy/doctest_bundle_2024.rs:8:1:
assertion `left == right` failed
  left: 65536
 right: 1024
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace



failures:
    src/lib.rs - UnitStruct (line 20)

test result: FAILED. 0 passed; 1 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s

So, why are doctests excluded like this from conditional compilation which is explicitly aimed at test cases? And how can I configure the conditional compilation to include doctests in my testing code?

Any insight would be appreciated.

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