limit local ADT types to size_of

Author: tesuji

clippy_lints/src/casts/cast_possible_truncation.rs

@@ -100,6 +100,7 @@ fn apply_reductions(cx: &LateContext<'_>, nbits: u64, expr: &Expr<'_>, signed: b
                 && let Some(def_id) = cx.qpath_res(func_qpath, func.hir_id).opt_def_id()
                 && cx.tcx.is_diagnostic_item(sym::mem_size_of, def_id)
                 && let Some(ty) = cx.typeck_results().node_args(func.hir_id).types().next()
+                && is_valid_sizeof(ty)
                 && let Ok(layout) = cx.tcx.layout_of(cx.param_env.and(ty))
             {
                 let size: u64 = layout.layout.size().bytes();
@@ -228,3 +229,17 @@ fn offer_suggestion(
         SuggestionStyle::ShowAlways,
     );
 }
+
+// FIXME(@tesuji): May extend this to a validator functions to include:
+// * some ABI-guaranteed STD types,
+// * some non-local crate types suggested in [PR-12962][1].
+// [1]: https://github.com/rust-lang/rust-clippy/pull/12962#discussion_r1661500351
+fn is_valid_sizeof<'tcx>(ty: Ty<'tcx>) -> bool {
+    if ty.is_primitive_ty() || ty.is_any_ptr() || ty.is_box() || ty.is_slice() {
+        return true;
+    }
+    match ty.kind() {
+        ty::Adt(def, ..) if def.did().is_local() => true,
+        _ => false,
+    }
+}

tests/ui/cast.rs

@@ -511,5 +511,8 @@ pub fn issue_9613() {
     CHUNK as u32;
     u64::MIN as u32;
     //~^ ERROR: casting `u64` to `u32` may truncate the value
+    struct Foo(usize, u32);
+    core::mem::size_of::<Foo>() as u32;
     core::mem::size_of::<String>() as u32;
+    //~^ ERROR: casting `usize` to `u32` may truncate
 }

tests/ui/cast.stderr

@@ -732,7 +732,7 @@ LL |     u8::try_from(255 % 999999u64);
    |     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
 error: casting `u64` to `u32` may truncate the value
-  --> tests/ui/cast.rs:510:5
+  --> tests/ui/cast.rs:512:5
    |
 LL |     u64::MIN as u32;
    |     ^^^^^^^^^^^^^^^
@@ -743,5 +743,17 @@ help: ... or use `try_from` and handle the error accordingly
 LL |     u32::try_from(u64::MIN);
    |     ~~~~~~~~~~~~~~~~~~~~~~~
 
-error: aborting due to 93 previous errors
+error: casting `usize` to `u32` may truncate the value on targets with 64-bit wide pointers
+  --> tests/ui/cast.rs:516:5
+   |
+LL |     core::mem::size_of::<String>() as u32;
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = help: if this is intentional allow the lint with `#[allow(clippy::cast_possible_truncation)]` ...
+help: ... or use `try_from` and handle the error accordingly
+   |
+LL |     u32::try_from(core::mem::size_of::<String>());
+   |     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+error: aborting due to 94 previous errors