fix: main_recursion enable lint in no_std crates and fix broken tests

[WaterWhisperer]

fixes the main_recursion lint which was previously skipping all no_std crates. It also fixes existing UI tests that were "testing nothing" because they were either marked as //@check-pass while missing expected errors, or were being compiled as libraries (which have no entrypoints).

• Lint Change: Removed the has_no_std_attr check in MainRecursion. The is_entrypoint_fn utility is now robust enough to handle entrypoint detection correctly without this manual skip.
• Test Fixes:
  • Updated entrypoint_recursion.rs by adding a dummy main function to force the compiler to treat it as a binary crate, allowing #[rustc_main] to be recognized as an entrypoint.
  • Added no_std_main_recursion.rs to specifically verify the lint works in #![no_std] environments.

Fixes #11034

• Added passing UI tests (including committed .stderr file)
• cargo test passes locally
• Executed cargo dev update_lints
• Run cargo dev fmt

changelog: [main_recursion]: now works in no_std crates and fixed broken tests

[rustbot]

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[samueltardieu]

Isn't the lint expected to ignore no_std entry points? The lint description contains:

Why is this bad?

Apart from special setups (which we could detect following attributes like #![no_std]),
recursing into main() seems like an unintuitive anti-pattern we should be able to detect.

[WaterWhisperer]

Isn't the lint expected to ignore no_std entry points? The lint description contains:

Why is this bad?

Apart from special setups (which we could detect following attributes like #![no_std]),
recursing into main() seems like an unintuitive anti-pattern we should be able to detect.

Thanks for the review! You are absolutely right. I misread the documentation. I have reverted the change that enabled the lint for no_std crates.