Rollup merge of #103964 - clubby789:lint-enclosing-unsafe, r=compiler-errors

Give a specific lint for unsafety not being inherited

In cases like
```rs
static mut FOO: u64 = 0;
fn main() {
    unsafe {static BAR: u64 = FOO;}
}
```
and
```rs
fn foo() {
  unsafe {
    fn bar() {
      unsafe_call();
    }
  }
}
```
Specifically inform the user that the unsafety is not inherited for the seperate enclosing items
Fixes #94077
r? compiler-errors
`@rustbot` label +A-diagnostics

2 files changed, 50 insertions, 0 deletions

diff --git a/src/test/ui/unsafe/unsafe-not-inherited.rs b/src/test/ui/unsafe/unsafe-not-inherited.rs
new file mode 100644
index 00000000000..6d797caa0f9
--- /dev/null
+++ b/src/test/ui/unsafe/unsafe-not-inherited.rs
@@ -0,0 +1,26 @@
+#![allow(unused, dead_code)]
+
+static mut FOO: u64 = 0;
+
+fn static_mod() {
+    unsafe {static BAR: u64 = FOO;}
+    //~^ ERROR: use of mutable static is unsafe
+    //~| NOTE: use of mutable static
+    //~| NOTE: mutable statics can be mutated by multiple threads
+    //~| NOTE: items do not inherit unsafety
+}
+
+unsafe fn unsafe_call() {}
+fn foo() {
+    unsafe {
+    //~^ NOTE: items do not inherit unsafety
+        fn bar() {
+            unsafe_call();
+            //~^ ERROR: call to unsafe function
+            //~| NOTE: call to unsafe function
+            //~| NOTE: consult the function's documentation
+        }
+    }
+}
+
+fn main() {}
diff --git a/src/test/ui/unsafe/unsafe-not-inherited.stderr b/src/test/ui/unsafe/unsafe-not-inherited.stderr
new file mode 100644
index 00000000000..3bc5ca5c9d1
--- /dev/null
+++ b/src/test/ui/unsafe/unsafe-not-inherited.stderr
@@ -0,0 +1,24 @@
+error[E0133]: use of mutable static is unsafe and requires unsafe function or block
+  --> $DIR/unsafe-not-inherited.rs:6:31
+   |
+LL |     unsafe {static BAR: u64 = FOO;}
+   |     ------                    ^^^ use of mutable static
+   |     |
+   |     items do not inherit unsafety from separate enclosing items
+   |
+   = note: mutable statics can be mutated by multiple threads: aliasing violations or data races will cause undefined behavior
+
+error[E0133]: call to unsafe function is unsafe and requires unsafe function or block
+  --> $DIR/unsafe-not-inherited.rs:18:13
+   |
+LL |     unsafe {
+   |     ------ items do not inherit unsafety from separate enclosing items
+...
+LL |             unsafe_call();
+   |             ^^^^^^^^^^^^^ call to unsafe function
+   |
+   = note: consult the function's documentation for information on how to avoid undefined behavior
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0133`.