limit eval const items to the current local crate

Author: tesuji

clippy_lints/src/casts/cast_possible_truncation.rs

@@ -80,7 +80,20 @@ fn apply_reductions(cx: &LateContext<'_>, nbits: u64, expr: &Expr<'_>, signed: b
                 nbits
             }
         },
-        ExprKind::Path(ref _qpath) => get_constant_bits(cx, expr).unwrap_or(nbits),
+        ExprKind::Path(QPath::Resolved(
+            None,
+            rustc_hir::Path {
+                res: Res::Def(DefKind::Const | DefKind::AssocConst, def_id),
+                ..
+            },
+        ))
+        // NOTE(@Jarcho): A constant from another crate might not have the same value
+        // for all versions of the crate. This isn't a problem for constants in the
+        // current crate since a crate can't compile against multiple versions of itself.
+        if def_id.is_local() => {
+            // `constant()` already checks if a const item is based on `cfg!`.
+            get_constant_bits(cx, expr).unwrap_or(nbits)
+        },
         // mem::size_of::<T>();
         ExprKind::Call(func, []) => {
             if let ExprKind::Path(ref func_qpath) = func.kind

tests/ui/cast.rs

@@ -509,5 +509,7 @@ pub fn issue_7486() -> u8 {
 pub fn issue_9613() {
     const CHUNK: usize = 64;
     CHUNK as u32;
+    u64::MIN as u32;
+    //~^ ERROR: casting `u64` to `u32` may truncate the value
     core::mem::size_of::<String>() as u32;
 }

tests/ui/cast.stderr

@@ -731,5 +731,17 @@ help: ... or use `try_from` and handle the error accordingly
 LL |     u8::try_from(255 % 999999u64);
    |     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
-error: aborting due to 92 previous errors
+error: casting `u64` to `u32` may truncate the value
+  --> tests/ui/cast.rs:510:5
+   |
+LL |     u64::MIN 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(u64::MIN);
+   |     ~~~~~~~~~~~~~~~~~~~~~~~
+
+error: aborting due to 93 previous errors