Move fn_to_numeric_cast to its own module

Author: Y-Nak

clippy_lints/src/casts/fn_to_numeric_cast.rs

@@ -0,0 +1,37 @@
+use rustc_errors::Applicability;
+use rustc_hir::Expr;
+use rustc_lint::LateContext;
+use rustc_middle::ty::{self, Ty, UintTy};
+
+use crate::utils::{snippet_with_applicability, span_lint_and_sugg};
+
+use super::{utils, FN_TO_NUMERIC_CAST};
+
+pub(super) fn check(cx: &LateContext<'_>, expr: &Expr<'_>, cast_expr: &Expr<'_>, cast_from: Ty<'_>, cast_to: Ty<'_>) {
+    // We only want to check casts to `ty::Uint` or `ty::Int`
+    match cast_to.kind() {
+        ty::Uint(_) | ty::Int(..) => { /* continue on */ },
+        _ => return,
+    }
+
+    match cast_from.kind() {
+        ty::FnDef(..) | ty::FnPtr(_) => {
+            let mut applicability = Applicability::MaybeIncorrect;
+            let from_snippet = snippet_with_applicability(cx, cast_expr.span, "x", &mut applicability);
+            let to_nbits = utils::int_ty_to_nbits(cast_to, cx.tcx);
+
+            if (to_nbits >= cx.tcx.data_layout.pointer_size.bits()) && (*cast_to.kind() != ty::Uint(UintTy::Usize)) {
+                span_lint_and_sugg(
+                    cx,
+                    FN_TO_NUMERIC_CAST,
+                    expr.span,
+                    &format!("casting function pointer `{}` to `{}`", from_snippet, cast_to),
+                    "try",
+                    format!("{} as usize", from_snippet),
+                    applicability,
+                );
+            }
+        },
+        _ => {},
+    }
+}

clippy_lints/src/casts/mod.rs

@@ -3,6 +3,7 @@ mod cast_possible_truncation;
 mod cast_possible_wrap;
 mod cast_precision_loss;
 mod cast_sign_loss;
+mod fn_to_numeric_cast;
 mod unnecessary_cast;
 mod utils;
 
@@ -301,6 +302,8 @@ impl<'tcx> LateLintPass<'tcx> for Casts {
             if unnecessary_cast::check(cx, expr, cast_expr, cast_from, cast_to) {
                 return;
             }
+
+            fn_to_numeric_cast::check(cx, expr, cast_expr, cast_from, cast_to);
             lint_fn_to_numeric_cast(cx, expr, cast_expr, cast_from, cast_to);
             lint_cast_ptr_alignment(cx, expr, cast_from, cast_to);
             if cast_from.is_numeric() && cast_to.is_numeric() && !in_external_macro(cx.sess(), expr.span) {
@@ -386,16 +389,6 @@ fn lint_fn_to_numeric_cast(
                     format!("{} as usize", from_snippet),
                     applicability,
                 );
-            } else if *cast_to.kind() != ty::Uint(UintTy::Usize) {
-                span_lint_and_sugg(
-                    cx,
-                    FN_TO_NUMERIC_CAST,
-                    expr.span,
-                    &format!("casting function pointer `{}` to `{}`", from_snippet, cast_to),
-                    "try",
-                    format!("{} as usize", from_snippet),
-                    applicability,
-                );
             }
         },
         _ => {},