Auto merge of rust-lang#7396 - ranweiler:zero-offset, r=Manishearth

Fix invocation of `zst_offset` lint

The `zst_offset` lint was broken by a refactoring regression in 2108387. In the invocation of the `zst_offset` check [here](rust-lang/rust-clippy@2108387#diff-7f73f6fe28c04b654223c09c42fe02937d2351fc58a91d21ab812aaf6f9b185dR1927), we shadow the already-destructured receiver `recv`, and accidentally pass the first argument of the method as if it were the receiver.

This was not caught because the UI test expectation was never correct (a bad cast obscured the actual test result).

This PR:
- Fixes the existing test expectation
- Tests both `const` and `mut` raw pointers
- Passes the actual receiver to the lint's implementation

Fixes rust-lang#7395.

changelog: Fix [`zst_offset`] invocation and test

clippy_lints/src/methods/mod.rs

@@ -2036,7 +2036,7 @@ impl<'tcx> LateLintPass<'tcx> for Methods {
 fn check_methods<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>, msrv: Option<&RustcVersion>) {
     if let Some((name, [recv, args @ ..], span)) = method_call!(expr) {
         match (name, args) {
-            ("add" | "offset" | "sub" | "wrapping_offset" | "wrapping_add" | "wrapping_sub", [recv, _]) => {
+            ("add" | "offset" | "sub" | "wrapping_offset" | "wrapping_add" | "wrapping_sub", [_arg]) => {
                 zst_offset::check(cx, expr, recv);
             },
             ("and_then", [arg]) => {

tests/ui/zero_offset.rs

@@ -1,12 +1,18 @@
 fn main() {
     unsafe {
-        let x = &() as *const ();
-        x.offset(0);
-        x.wrapping_add(0);
-        x.sub(0);
-        x.wrapping_sub(0);
+        let m = &mut () as *mut ();
+        m.offset(0);
+        m.wrapping_add(0);
+        m.sub(0);
+        m.wrapping_sub(0);
 
-        let y = &1 as *const u8;
-        y.offset(0);
+        let c = &() as *const ();
+        c.offset(0);
+        c.wrapping_add(0);
+        c.sub(0);
+        c.wrapping_sub(0);
+
+        let sized = &1 as *const i32;
+        sized.offset(0);
     }
 }

tests/ui/zero_offset.stderr

@@ -1,9 +1,52 @@
-error[E0606]: casting `&i32` as `*const u8` is invalid
-  --> $DIR/zero_offset.rs:9:17
+error: offset calculation on zero-sized value
+  --> $DIR/zero_offset.rs:4:9
    |
-LL |         let y = &1 as *const u8;
-   |                 ^^^^^^^^^^^^^^^
+LL |         m.offset(0);
+   |         ^^^^^^^^^^^
+   |
+   = note: `#[deny(clippy::zst_offset)]` on by default
+
+error: offset calculation on zero-sized value
+  --> $DIR/zero_offset.rs:5:9
+   |
+LL |         m.wrapping_add(0);
+   |         ^^^^^^^^^^^^^^^^^
+
+error: offset calculation on zero-sized value
+  --> $DIR/zero_offset.rs:6:9
+   |
+LL |         m.sub(0);
+   |         ^^^^^^^^
+
+error: offset calculation on zero-sized value
+  --> $DIR/zero_offset.rs:7:9
+   |
+LL |         m.wrapping_sub(0);
+   |         ^^^^^^^^^^^^^^^^^
+
+error: offset calculation on zero-sized value
+  --> $DIR/zero_offset.rs:10:9
+   |
+LL |         c.offset(0);
+   |         ^^^^^^^^^^^
+
+error: offset calculation on zero-sized value
+  --> $DIR/zero_offset.rs:11:9
+   |
+LL |         c.wrapping_add(0);
+   |         ^^^^^^^^^^^^^^^^^
+
+error: offset calculation on zero-sized value
+  --> $DIR/zero_offset.rs:12:9
+   |
+LL |         c.sub(0);
+   |         ^^^^^^^^
+
+error: offset calculation on zero-sized value
+  --> $DIR/zero_offset.rs:13:9
+   |
+LL |         c.wrapping_sub(0);
+   |         ^^^^^^^^^^^^^^^^^
 
-error: aborting due to previous error
+error: aborting due to 8 previous errors
 
-For more information about this error, try `rustc --explain E0606`.