Don't lint unstable moves in std_instead_of_core

Such as the currently unstable `core::error`

Author: Alexendoo

clippy_lints/src/std_instead_of_core.rs

@@ -1,6 +1,8 @@
 use clippy_utils::diagnostics::span_lint_and_help;
+use rustc_hir::def_id::DefId;
 use rustc_hir::{def::Res, HirId, Path, PathSegment};
 use rustc_lint::{LateContext, LateLintPass};
+use rustc_middle::ty::DefIdTree;
 use rustc_session::{declare_tool_lint, impl_lint_pass};
 use rustc_span::{sym, symbol::kw, Span};
 
@@ -94,6 +96,7 @@ impl<'tcx> LateLintPass<'tcx> for StdReexports {
     fn check_path(&mut self, cx: &LateContext<'tcx>, path: &Path<'tcx>, _: HirId) {
         if let Res::Def(_, def_id) = path.res
             && let Some(first_segment) = get_first_segment(path)
+            && is_stable(cx, def_id)
         {
             let (lint, msg, help) = match first_segment.ident.name {
                 sym::std => match cx.tcx.crate_name(def_id.krate) {
@@ -146,3 +149,22 @@ fn get_first_segment<'tcx>(path: &Path<'tcx>) -> Option<&'tcx PathSegment<'tcx>>
         _ => None,
     }
 }
+
+/// Checks if all ancestors of `def_id` are stable, to avoid linting
+/// [unstable moves](https://github.com/rust-lang/rust/pull/95956)
+fn is_stable(cx: &LateContext<'_>, mut def_id: DefId) -> bool {
+    loop {
+        if cx
+            .tcx
+            .lookup_stability(def_id)
+            .map_or(false, |stability| stability.is_unstable())
+        {
+            return false;
+        }
+
+        match cx.tcx.opt_parent(def_id) {
+            Some(parent) => def_id = parent,
+            None => return true,
+        }
+    }
+}

tests/ui/std_instead_of_core.rs

@@ -24,6 +24,12 @@ fn std_instead_of_core() {
     let cell_absolute = ::std::cell::Cell::new(8u32);
 
     let _ = std::env!("PATH");
+
+    // do not lint until `error_in_core` is stable
+    use std::error::Error;
+
+    // lint items re-exported from private modules, `core::iter::traits::iterator::Iterator`
+    use std::iter::Iterator;
 }
 
 #[warn(clippy::std_instead_of_alloc)]

tests/ui/std_instead_of_core.stderr

@@ -63,31 +63,39 @@ LL |     let cell_absolute = ::std::cell::Cell::new(8u32);
    |
    = help: consider importing the item from `core`
 
-error: used import from `std` instead of `alloc`
+error: used import from `std` instead of `core`
   --> $DIR/std_instead_of_core.rs:32:9
    |
+LL |     use std::iter::Iterator;
+   |         ^^^^^^^^^^^^^^^^^^^
+   |
+   = help: consider importing the item from `core`
+
+error: used import from `std` instead of `alloc`
+  --> $DIR/std_instead_of_core.rs:38:9
+   |
 LL |     use std::vec;
    |         ^^^^^^^^
    |
    = note: `-D clippy::std-instead-of-alloc` implied by `-D warnings`
    = help: consider importing the item from `alloc`
 
 error: used import from `std` instead of `alloc`
-  --> $DIR/std_instead_of_core.rs:33:9
+  --> $DIR/std_instead_of_core.rs:39:9
    |
 LL |     use std::vec::Vec;
    |         ^^^^^^^^^^^^^
    |
    = help: consider importing the item from `alloc`
 
 error: used import from `alloc` instead of `core`
-  --> $DIR/std_instead_of_core.rs:38:9
+  --> $DIR/std_instead_of_core.rs:44:9
    |
 LL |     use alloc::slice::from_ref;
    |         ^^^^^^^^^^^^^^^^^^^^^^
    |
    = note: `-D clippy::alloc-instead-of-core` implied by `-D warnings`
    = help: consider importing the item from `core`
 
-error: aborting due to 11 previous errors
+error: aborting due to 12 previous errors