Rollup merge of #135003 - RalfJung:deprecate-allowed-through-unstable, r=davidtwco

deprecate `std::intrinsics::transmute` etc, use `std::mem::*` instead

The `rustc_allowed_through_unstable_modules` attribute lets users call `std::mem::transmute` as `std::intrinsics::transmute`. The former is a reexport of the latter, and for a long time we didn't properly check stability for reexports, so making this a hard error now would be a breaking change for little gain. But at the same time, `std::intrinsics::transmute` is not the intended path for this function, so I think it is a good idea to show a deprecation warning when that path is used. This PR implements that, for all the functions in `std::intrinsics` that carry the attribute.

I assume this will need ``@rust-lang/libs-api`` FCP.

5 files changed, 25 insertions, 3 deletions

diff --git a/tests/ui/stability-attribute/accidental-stable-in-unstable.rs b/tests/ui/stability-attribute/accidental-stable-in-unstable.rs
index 86a9d2066eb..a36a78ee442 100644
--- a/tests/ui/stability-attribute/accidental-stable-in-unstable.rs
+++ b/tests/ui/stability-attribute/accidental-stable-in-unstable.rs
@@ -8,3 +8,4 @@ use core::unicode::UNICODE_VERSION; //~ ERROR use of unstable library feature `u
 // Known accidental stabilizations with known users
 // fully stable @ core::mem::transmute
 use core::intrinsics::transmute; // depended upon by rand_core
+//~^WARN deprecated
diff --git a/tests/ui/stability-attribute/accidental-stable-in-unstable.stderr b/tests/ui/stability-attribute/accidental-stable-in-unstable.stderr
index 9943e6d7ac6..16e3676aa65 100644
--- a/tests/ui/stability-attribute/accidental-stable-in-unstable.stderr
+++ b/tests/ui/stability-attribute/accidental-stable-in-unstable.stderr
@@ -7,6 +7,14 @@ LL | use core::unicode::UNICODE_VERSION;
    = help: add `#![feature(unicode_internals)]` to the crate attributes to enable
    = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
 
-error: aborting due to 1 previous error
+warning: use of deprecated module `std::intrinsics`: import this function via `std::mem` instead
+  --> $DIR/accidental-stable-in-unstable.rs:10:23
+   |
+LL | use core::intrinsics::transmute; // depended upon by rand_core
+   |                       ^^^^^^^^^
+   |
+   = note: `#[warn(deprecated)]` on by default
+
+error: aborting due to 1 previous error; 1 warning emitted
 
 For more information about this error, try `rustc --explain E0658`.
diff --git a/tests/ui/stability-attribute/allowed-through-unstable.rs b/tests/ui/stability-attribute/allowed-through-unstable.rs
index 29911a70be9..e03417a4dae 100644
--- a/tests/ui/stability-attribute/allowed-through-unstable.rs
+++ b/tests/ui/stability-attribute/allowed-through-unstable.rs
@@ -6,4 +6,5 @@
 extern crate allowed_through_unstable_core;
 
 use allowed_through_unstable_core::unstable_module::OldStableTraitAllowedThoughUnstable;
+use allowed_through_unstable_core::unstable_module::OldStableTraitAllowedThoughUnstableWithDeprecation; //~WARN use of deprecated module `allowed_through_unstable_core::unstable_module`: use the new path instead
 use allowed_through_unstable_core::unstable_module::NewStableTraitNotAllowedThroughUnstable; //~ ERROR use of unstable library feature `unstable_test_feature`
diff --git a/tests/ui/stability-attribute/allowed-through-unstable.stderr b/tests/ui/stability-attribute/allowed-through-unstable.stderr
index 00eea9f730d..8d07b0cf9e8 100644
--- a/tests/ui/stability-attribute/allowed-through-unstable.stderr
+++ b/tests/ui/stability-attribute/allowed-through-unstable.stderr
@@ -1,5 +1,13 @@
+warning: use of deprecated module `allowed_through_unstable_core::unstable_module`: use the new path instead
+  --> $DIR/allowed-through-unstable.rs:9:53
+   |
+LL | use allowed_through_unstable_core::unstable_module::OldStableTraitAllowedThoughUnstableWithDeprecation;
+   |                                                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: `#[warn(deprecated)]` on by default
+
 error[E0658]: use of unstable library feature `unstable_test_feature`
-  --> $DIR/allowed-through-unstable.rs:9:5
+  --> $DIR/allowed-through-unstable.rs:10:5
    |
 LL | use allowed_through_unstable_core::unstable_module::NewStableTraitNotAllowedThroughUnstable;
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -8,6 +16,6 @@ LL | use allowed_through_unstable_core::unstable_module::NewStableTraitNotAllowe
    = help: add `#![feature(unstable_test_feature)]` to the crate attributes to enable
    = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
 
-error: aborting due to 1 previous error
+error: aborting due to 1 previous error; 1 warning emitted
 
 For more information about this error, try `rustc --explain E0658`.
diff --git a/tests/ui/stability-attribute/auxiliary/allowed-through-unstable-core.rs b/tests/ui/stability-attribute/auxiliary/allowed-through-unstable-core.rs
index b597009a309..9dfbb451d04 100644
--- a/tests/ui/stability-attribute/auxiliary/allowed-through-unstable-core.rs
+++ b/tests/ui/stability-attribute/auxiliary/allowed-through-unstable-core.rs
@@ -10,5 +10,9 @@ pub mod unstable_module {
     pub trait OldStableTraitAllowedThoughUnstable {}
 
     #[stable(feature = "stable_test_feature", since = "1.2.0")]
+    #[rustc_allowed_through_unstable_modules = "use the new path instead"]
+    pub trait OldStableTraitAllowedThoughUnstableWithDeprecation {}
+
+    #[stable(feature = "stable_test_feature", since = "1.2.0")]
     pub trait NewStableTraitNotAllowedThroughUnstable {}
 }