codex/prs/bolinfest/study/PR-2864-study.md

DOs

• Bold the core idea: Gate debug-only commands with #[cfg(debug_assertions)] everywhere they’re referenced.

// enum definition
enum SlashCommand {
    Diff,
    Mention,
    Status,
    Mcp,
    Quit,
    #[cfg(debug_assertions)]
    TestApproval,
}

// usage
impl SlashCommand {
    fn is_public(&self) -> bool {
        match self {
            SlashCommand::Diff
            | SlashCommand::Mention
            | SlashCommand::Status
            | SlashCommand::Mcp
            | SlashCommand::Quit => true,

            #[cfg(debug_assertions)]
            SlashCommand::TestApproval => true,
        }
    }
}

• Bold the core idea: Keep user-facing commands (e.g., Diff) enabled in release builds.

// Good: `Diff` is always available; no cfg guard
SlashCommand::Diff
| SlashCommand::Mention
| SlashCommand::Status
| SlashCommand::Mcp
| SlashCommand::Quit => true,

• Bold the core idea: Match cfg attributes on arms with the enum’s cfg to avoid missing-variant errors in release.

// Variant is debug-only…
#[cfg(debug_assertions)]
SlashCommand::TestApproval => true;
// …so there is no arm for it when not(debug_assertions)

• Bold the core idea: If a variant exists in all builds but behavior differs, provide both arms so matches stay exhaustive.

#[cfg(debug_assertions)]
SlashCommand::TestApproval => true,
#[cfg(not(debug_assertions))]
SlashCommand::TestApproval => false,

• Bold the core idea: Validate both debug and release to catch cfg mistakes early.

# Debug (default)
cargo build -p codex-tui
cargo test -p codex-tui

# Release (CI parity)
cargo build --release -p codex-tui

DON’Ts

• Bold the core idea: Don’t disable the wrong command; don’t gate Diff to “fix” release—gate the test-only command.

// Bad: gating a user command
#[cfg(debug_assertions)]
SlashCommand::Diff => true;

• Bold the core idea: Don’t reference a debug-only variant without guarding it.

// Bad: breaks in release if `TestApproval` is not compiled in
SlashCommand::TestApproval => true;

// Good
#[cfg(debug_assertions)]
SlashCommand::TestApproval => true,

• Bold the core idea: Don’t leave variants unmatched under some cfg; ensure exhaustiveness in all configurations.

// Bad: `TestApproval` removed from enum in release, but arm remains
SlashCommand::TestApproval => true; // compile error in release

• Bold the core idea: Don’t duplicate the same variant across arms without cfg separation.

// Bad: conflicting arms (unreachable/ambiguous)
SlashCommand::Diff => true,
SlashCommand::Diff => false,

// Good: use cfg to separate build-specific behavior
#[cfg(debug_assertions)]
SlashCommand::TestApproval => true,
#[cfg(not(debug_assertions))]
SlashCommand::TestApproval => false,