Rollup merge of rust-lang#125951 - slanterns:error_in_core_stabilizat…

…ion, r=Amanieu

Stabilize `error_in_core`

Closes: rust-lang#103765.

`@rustbot` label: +T-libs-api

r? libs-api

tests/ui/std_instead_of_core.fixed

@@ -45,8 +45,8 @@ fn std_instead_of_core() {
 
     let _ = std::env!("PATH");
 
-    // do not lint until `error_in_core` is stable
-    use std::error::Error;
+    use core::error::Error;
+    //~^ ERROR: used import from `std` instead of `core`
 
     // lint items re-exported from private modules, `core::iter::traits::iterator::Iterator`
     use core::iter::Iterator;

tests/ui/std_instead_of_core.rs

@@ -45,8 +45,8 @@ fn std_instead_of_core() {
 
     let _ = std::env!("PATH");
 
-    // do not lint until `error_in_core` is stable
     use std::error::Error;
+    //~^ ERROR: used import from `std` instead of `core`
 
     // lint items re-exported from private modules, `core::iter::traits::iterator::Iterator`
     use std::iter::Iterator;

tests/ui/std_instead_of_core.stderr

@@ -49,6 +49,12 @@ error: used import from `std` instead of `core`
 LL |     let cell_absolute = ::std::cell::Cell::new(8u32);
    |                           ^^^ help: consider importing the item from `core`: `core`
 
+error: used import from `std` instead of `core`
+  --> tests/ui/std_instead_of_core.rs:48:9
+   |
+LL |     use std::error::Error;
+   |         ^^^ help: consider importing the item from `core`: `core`
+
 error: used import from `std` instead of `core`
   --> tests/ui/std_instead_of_core.rs:52:9
    |
@@ -79,5 +85,5 @@ LL |     use alloc::slice::from_ref;
    = note: `-D clippy::alloc-instead-of-core` implied by `-D warnings`
    = help: to override `-D warnings` add `#[allow(clippy::alloc_instead_of_core)]`
 
-error: aborting due to 12 previous errors
+error: aborting due to 13 previous errors