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

Author: WaterWhisperer

clippy_lints/src/main_recursion.rs

@@ -1,6 +1,6 @@
 use clippy_utils::diagnostics::span_lint_and_help;
+use clippy_utils::is_entrypoint_fn;
 use clippy_utils::source::snippet;
-use clippy_utils::{is_entrypoint_fn, is_no_std_crate};
 use rustc_hir::{Expr, ExprKind, QPath};
 use rustc_lint::{LateContext, LateLintPass};
 use rustc_session::impl_lint_pass;
@@ -26,22 +26,12 @@ declare_clippy_lint! {
 }
 
 #[derive(Default)]
-pub struct MainRecursion {
-    has_no_std_attr: bool,
-}
+pub struct MainRecursion;
 
 impl_lint_pass!(MainRecursion => [MAIN_RECURSION]);
 
 impl LateLintPass<'_> for MainRecursion {
-    fn check_crate(&mut self, cx: &LateContext<'_>) {
-        self.has_no_std_attr = is_no_std_crate(cx);
-    }
-
     fn check_expr_post(&mut self, cx: &LateContext<'_>, expr: &Expr<'_>) {
-        if self.has_no_std_attr {
-            return;
-        }
-
         if let ExprKind::Call(func, []) = &expr.kind
             && let ExprKind::Path(QPath::Resolved(_, path)) = &func.kind
             && let Some(def_id) = path.res.opt_def_id()

tests/ui/crate_level_checks/entrypoint_recursion.rs

@@ -1,12 +1,11 @@
-//@check-pass
 //@ignore-target: apple
-
 #![feature(rustc_attrs)]
-
 #[warn(clippy::main_recursion)]
 #[allow(unconditional_recursion)]
 #[rustc_main]
 fn a() {
-    println!("Hello, World!");
     a();
+    //~^ main_recursion
 }
+
+fn main() {}

tests/ui/crate_level_checks/entrypoint_recursion.stderr

@@ -0,0 +1,12 @@
+error: recursing into entrypoint `a`
+  --> tests/ui/crate_level_checks/entrypoint_recursion.rs:7:5
+   |
+LL |     a();
+   |     ^
+   |
+   = help: consider using another function for this recursion
+   = note: `-D clippy::main-recursion` implied by `-D warnings`
+   = help: to override `-D warnings` add `#[allow(clippy::main_recursion)]`
+
+error: aborting due to 1 previous error
+

tests/ui/crate_level_checks/no_std_main_recursion.rs

@@ -0,0 +1,13 @@
+//@compile-flags: -Cpanic=abort
+#![no_std]
+#[warn(clippy::main_recursion)]
+#[allow(unconditional_recursion)]
+fn main() {
+    main();
+    //~^ main_recursion
+}
+
+#[panic_handler]
+fn panic(_info: &core::panic::PanicInfo) -> ! {
+    loop {}
+}

tests/ui/crate_level_checks/no_std_main_recursion.stderr

@@ -0,0 +1,12 @@
+error: recursing into entrypoint `main`
+  --> tests/ui/crate_level_checks/no_std_main_recursion.rs:6:5
+   |
+LL |     main();
+   |     ^^^^
+   |
+   = help: consider using another function for this recursion
+   = note: `-D clippy::main-recursion` implied by `-D warnings`
+   = help: to override `-D warnings` add `#[allow(clippy::main_recursion)]`
+
+error: aborting due to 1 previous error
+