Auto merge of #130540 - veera-sivarajan:fix-87525, r=estebank

Add a Lint for Pointer to Integer Transmutes in Consts

Fixes #87525

This PR adds a MirLint for pointer to integer transmutes in const functions and associated consts. The implementation closely follows this comment: https://github.com/rust-lang/rust/pull/85769#issuecomment-880969112. More details about the implementation can be found in the comments.

Note: This could break some sound code as mentioned by RalfJung in https://github.com/rust-lang/rust/pull/85769#issuecomment-886491680:

> ... technically const-code could transmute/cast an int to a ptr and then transmute it back and that would be correct -- so the lint will deny some sound code. Does not seem terribly likely though.

References:
1. https://doc.rust-lang.org/std/mem/fn.transmute.html
2. https://doc.rust-lang.org/reference/items/associated-items.html#associated-constants

2 files changed, 123 insertions, 0 deletions

diff --git a/tests/ui/consts/const-eval/ptr-to-int-transmute-in-consts-issue-87525.rs b/tests/ui/consts/const-eval/ptr-to-int-transmute-in-consts-issue-87525.rs
new file mode 100644
index 00000000000..19c78f019aa
--- /dev/null
+++ b/tests/ui/consts/const-eval/ptr-to-int-transmute-in-consts-issue-87525.rs
@@ -0,0 +1,70 @@
+const fn foo(ptr: *const u8) -> usize {
+    unsafe {
+        std::mem::transmute(ptr)
+        //~^ WARN pointers cannot be transmuted to integers
+    }
+}
+
+trait Human {
+    const ID: usize = {
+        let value = 10;
+        let ptr: *const usize = &value;
+        unsafe {
+            std::mem::transmute(ptr)
+            //~^ WARN pointers cannot be transmuted to integers
+        }
+    };
+
+    fn id_plus_one() -> usize {
+        Self::ID + 1
+    }
+}
+
+struct Type<T>(T);
+
+impl<T> Type<T> {
+    const ID: usize = {
+        let value = 10;
+        let ptr: *const usize = &value;
+        unsafe {
+            std::mem::transmute(ptr)
+            //~^ WARN pointers cannot be transmuted to integers
+        }
+    };
+
+    fn id_plus_one() -> usize {
+        Self::ID + 1
+    }
+}
+
+fn control(ptr: *const u8) -> usize {
+    unsafe {
+        std::mem::transmute(ptr)
+    }
+}
+
+struct ControlStruct;
+
+impl ControlStruct {
+    fn new() -> usize {
+        let value = 10;
+        let ptr: *const i32 = &value;
+        unsafe {
+            std::mem::transmute(ptr)
+        }
+    }
+}
+
+
+const fn zoom(ptr: *const u8) -> usize {
+    unsafe {
+        std::mem::transmute(ptr)
+        //~^ WARN pointers cannot be transmuted to integers
+    }
+}
+
+fn main() {
+    const a: u8 = 10;
+    const value: usize = zoom(&a);
+    //~^ ERROR evaluation of constant value failed
+}
diff --git a/tests/ui/consts/const-eval/ptr-to-int-transmute-in-consts-issue-87525.stderr b/tests/ui/consts/const-eval/ptr-to-int-transmute-in-consts-issue-87525.stderr
new file mode 100644
index 00000000000..ca6ad9408ab
--- /dev/null
+++ b/tests/ui/consts/const-eval/ptr-to-int-transmute-in-consts-issue-87525.stderr
@@ -0,0 +1,53 @@
+warning: pointers cannot be transmuted to integers during const eval
+  --> $DIR/ptr-to-int-transmute-in-consts-issue-87525.rs:61:9
+   |
+LL |         std::mem::transmute(ptr)
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: at compile-time, pointers do not have an integer value
+   = note: avoiding this restriction via `union` or raw pointers leads to compile-time undefined behavior
+   = help: for more information, see https://doc.rust-lang.org/std/mem/fn.transmute.html
+   = note: `#[warn(ptr_to_integer_transmute_in_consts)]` on by default
+
+error[E0080]: evaluation of constant value failed
+  --> $DIR/ptr-to-int-transmute-in-consts-issue-87525.rs:68:26
+   |
+LL |     const value: usize = zoom(&a);
+   |                          ^^^^^^^^ unable to turn pointer into integer
+   |
+   = help: this code performed an operation that depends on the underlying bytes representing a pointer
+   = help: the absolute address of a pointer is not known at compile-time, so such operations are not supported
+
+warning: pointers cannot be transmuted to integers during const eval
+  --> $DIR/ptr-to-int-transmute-in-consts-issue-87525.rs:3:9
+   |
+LL |         std::mem::transmute(ptr)
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: at compile-time, pointers do not have an integer value
+   = note: avoiding this restriction via `union` or raw pointers leads to compile-time undefined behavior
+   = help: for more information, see https://doc.rust-lang.org/std/mem/fn.transmute.html
+
+warning: pointers cannot be transmuted to integers during const eval
+  --> $DIR/ptr-to-int-transmute-in-consts-issue-87525.rs:13:13
+   |
+LL |             std::mem::transmute(ptr)
+   |             ^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: at compile-time, pointers do not have an integer value
+   = note: avoiding this restriction via `union` or raw pointers leads to compile-time undefined behavior
+   = help: for more information, see https://doc.rust-lang.org/std/mem/fn.transmute.html
+
+warning: pointers cannot be transmuted to integers during const eval
+  --> $DIR/ptr-to-int-transmute-in-consts-issue-87525.rs:30:13
+   |
+LL |             std::mem::transmute(ptr)
+   |             ^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: at compile-time, pointers do not have an integer value
+   = note: avoiding this restriction via `union` or raw pointers leads to compile-time undefined behavior
+   = help: for more information, see https://doc.rust-lang.org/std/mem/fn.transmute.html
+
+error: aborting due to 1 previous error; 4 warnings emitted
+
+For more information about this error, try `rustc --explain E0080`.