fix: alloc_instead_of_core FP when alloc is an alias

Author: profetia

clippy_lints/src/std_instead_of_core.rs

@@ -1,7 +1,7 @@
 use clippy_config::Conf;
 use clippy_utils::diagnostics::{span_lint_and_help, span_lint_and_sugg};
-use clippy_utils::is_from_proc_macro;
 use clippy_utils::msrvs::Msrv;
+use clippy_utils::{is_from_proc_macro, is_res_crate};
 use rustc_errors::Applicability;
 use rustc_hir::def::{DefKind, Res};
 use rustc_hir::def_id::DefId;
@@ -126,6 +126,7 @@ impl<'tcx> LateLintPass<'tcx> for StdReexports {
             && !is_from_proc_macro(cx, &first_segment.ident)
             && !matches!(def_kind, DefKind::Macro(_))
             && let Some(last_segment) = path.segments.last()
+            && is_res_crate(first_segment.res)
         {
             let (lint, used_mod, replace_with) = match first_segment.ident.name {
                 sym::std => match cx.tcx.crate_name(def_id.krate) {

clippy_utils/src/lib.rs

@@ -3664,3 +3664,8 @@ pub fn is_expr_async_block(expr: &Expr<'_>) -> bool {
         })
     )
 }
+
+/// Checks if a `Res` refers to a crate
+pub fn is_res_crate(res: Res) -> bool {
+    matches!(res, Res::Def(DefKind::Mod, def_id) if def_id.is_crate_root() && !def_id.is_local())
+}

tests/ui/std_instead_of_core.fixed

@@ -89,3 +89,10 @@ fn msrv_1_76(_: std::net::IpAddr) {}
 #[clippy::msrv = "1.77"]
 fn msrv_1_77(_: core::net::IpAddr) {}
 //~^ std_instead_of_core
+
+#[warn(clippy::alloc_instead_of_core)]
+fn issue15579() {
+    use std::alloc;
+
+    let layout = alloc::Layout::new::<u8>();
+}

tests/ui/std_instead_of_core.rs

@@ -89,3 +89,10 @@ fn msrv_1_76(_: std::net::IpAddr) {}
 #[clippy::msrv = "1.77"]
 fn msrv_1_77(_: std::net::IpAddr) {}
 //~^ std_instead_of_core
+
+#[warn(clippy::alloc_instead_of_core)]
+fn issue15579() {
+    use std::alloc;
+
+    let layout = alloc::Layout::new::<u8>();
+}