rustc: Fix a number of stability lint holes

There are a number of holes that the stability lint did not previously cover,
including:

* Types
* Bounds on type parameters on functions and impls
* Where clauses
* Imports
* Patterns (structs and enums)

These holes have all been fixed by overriding the `visit_path` function on the
AST visitor instead of a few specialized cases. This change also necessitated a
few stability changes:

* The `collections::fmt` module is now stable (it was already supposed to be).
* The `thread_local::imp::Key` type is now stable (it was already supposed to
  be).
* The `std::rt::{begin_unwind, begin_unwind_fmt}` functions are now stable.
  These are required via the `panic!` macro.
* The `std::old_io::stdio::{println, println_args}` functions are now stable.
  These are required by the `print!` and `println!` macros.
* The `ops::{FnOnce, FnMut, Fn}` traits are now `#[stable]`. This is required to
  make bounds with these traits stable. Note that manual implementations of
  these traits are still gated by default, this stability only allows bounds
  such as `F: FnOnce()`.

Additionally, the compiler now has special logic to ignore its own generated
`__test` module for the `--test` harness in terms of stability.

Closes #8962
Closes #16360
Closes #20327

[breaking-change]

1 files changed, 7 insertions, 0 deletions

diff --git a/src/libstd/thread_local/mod.rs b/src/libstd/thread_local/mod.rs
index 9de5fd1c770..0ec241a65e2 100644
--- a/src/libstd/thread_local/mod.rs
+++ b/src/libstd/thread_local/mod.rs
@@ -335,6 +335,7 @@ mod imp {
     use ptr;
 
     #[doc(hidden)]
+    #[stable(since = "1.0.0", feature = "rust1")]
     pub struct Key<T> {
         // Place the inner bits in an `UnsafeCell` to currently get around the
         // "only Sync statics" restriction. This allows any type to be placed in
@@ -342,11 +343,14 @@ mod imp {
         //
         // Note that all access requires `T: 'static` so it can't be a type with
         // any borrowed pointers still.
+        #[stable(since = "1.0.0", feature = "rust1")]
         pub inner: UnsafeCell<T>,
 
         // Metadata to keep track of the state of the destructor. Remember that
         // these variables are thread-local, not global.
+        #[stable(since = "1.0.0", feature = "rust1")]
         pub dtor_registered: UnsafeCell<bool>, // should be Cell
+        #[stable(since = "1.0.0", feature = "rust1")]
         pub dtor_running: UnsafeCell<bool>, // should be Cell
     }
 
@@ -468,12 +472,15 @@ mod imp {
     use sys_common::thread_local::StaticKey as OsStaticKey;
 
     #[doc(hidden)]
+    #[stable(since = "1.0.0", feature = "rust1")]
     pub struct Key<T> {
         // Statically allocated initialization expression, using an `UnsafeCell`
         // for the same reasons as above.
+        #[stable(since = "1.0.0", feature = "rust1")]
         pub inner: UnsafeCell<T>,
 
         // OS-TLS key that we'll use to key off.
+        #[stable(since = "1.0.0", feature = "rust1")]
         pub os: OsStaticKey,
     }