Limit local ADT types to size_of

Require all fields to be local

Author: tesuji

clippy_lints/src/casts/cast_possible_truncation.rs

@@ -8,7 +8,7 @@ use rustc_errors::{Applicability, Diag, SuggestionStyle};
 use rustc_hir::def::{DefKind, Res};
 use rustc_hir::{BinOpKind, Expr, ExprKind, QPath};
 use rustc_lint::LateContext;
-use rustc_middle::ty::{self, FloatTy, Ty};
+use rustc_middle::ty::{self, FloatTy, Ty, TyCtxt};
 use rustc_span::symbol::sym;
 use rustc_span::Span;
 use rustc_target::abi::IntegerType;
@@ -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(cx.tcx, ty)
                 && let Ok(layout) = cx.tcx.layout_of(cx.param_env.and(ty))
             {
                 let size: u64 = layout.layout.size().bytes();
@@ -228,3 +229,23 @@ 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>(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>) -> bool {
+    if ty.is_primitive_ty() || ty.is_any_ptr() || ty.is_box() || ty.is_slice() {
+        return true;
+    }
+    if let ty::Adt(def, args) = ty.kind()
+        && def.did().is_local()
+    {
+        def.all_fields().all(|field| {
+            let ty = field.ty(tcx, args);
+            is_valid_sizeof(tcx, ty)
+        })
+    } else {
+        false
+    }
+}

tests/ui/cast.rs

@@ -511,5 +511,11 @@ pub fn issue_9613() {
     CHUNK as u32;
     u64::MIN as u32;
     //~^ ERROR: casting `u64` to `u32` may truncate the value
+    struct Foo(usize, u32);
+    struct Bar(usize, String);
+    core::mem::size_of::<Foo>() as u32;
+    core::mem::size_of::<Bar>() as u32;
+    //~^ ERROR: casting `usize` to `u32` may truncate
     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 +743,29 @@ 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:517:5
+   |
+LL |     core::mem::size_of::<Bar>() 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::<Bar>());
+   |     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+error: casting `usize` to `u32` may truncate the value on targets with 64-bit wide pointers
+  --> tests/ui/cast.rs:519:5
+   |
+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 95 previous errors