Do not remove cast if it would make the expression type uncertain

Author: samueltardieu

clippy_lints/src/casts/unnecessary_cast.rs

@@ -1,6 +1,7 @@
 use clippy_utils::diagnostics::span_lint_and_sugg;
 use clippy_utils::numeric_literal::NumericLiteral;
 use clippy_utils::source::{SpanRangeExt, snippet_opt};
+use clippy_utils::ty::expr_type_is_certain;
 use clippy_utils::visitors::{Visitable, for_each_expr_without_closures};
 use clippy_utils::{get_parent_expr, is_hir_ty_cfg_dependant, is_ty_alias, path_to_local};
 use rustc_ast::{LitFloatType, LitIntType, LitKind};
@@ -143,7 +144,10 @@ pub(super) fn check<'tcx>(
         }
     }
 
-    if cast_from.kind() == cast_to.kind() && !expr.span.in_external_macro(cx.sess().source_map()) {
+    if cast_from.kind() == cast_to.kind()
+        && !expr.span.in_external_macro(cx.sess().source_map())
+        && expr_type_is_certain(cx, cast_expr)
+    {
         enum MaybeParenOrBlock {
             Paren,
             Block,
@@ -167,7 +171,7 @@ pub(super) fn check<'tcx>(
                 sym::assert_ne_macro,
                 sym::debug_assert_ne_macro,
             ];
-            matches!(expr.span.ctxt().outer_expn_data().macro_def_id, Some(def_id) if 
+            matches!(expr.span.ctxt().outer_expn_data().macro_def_id, Some(def_id) if
                 cx.tcx.get_diagnostic_name(def_id).is_some_and(|sym| ALLOWED_MACROS.contains(&sym)))
         }
 

tests/ui/unnecessary_cast.fixed

@@ -6,6 +6,7 @@
     clippy::no_effect,
     clippy::nonstandard_macro_braces,
     clippy::unnecessary_operation,
+    clippy::double_parens,
     nonstandard_style,
     unused
 )]
@@ -283,4 +284,24 @@ mod fixable {
         let _ = 5i32 as i64;
         //~^ unnecessary_cast
     }
+
+    fn issue_14366(i: u32) {
+        // Do not remove the cast if it helps determining the type
+        let _ = ((1.0 / 8.0) as f64).powf(i as f64);
+
+        // But remove useless casts anyway
+        let _ = (((1.0 / 8.0) as f64)).powf(i as f64);
+        //~^ unnecessary_cast
+    }
+
+    fn ambiguity() {
+        pub trait T {}
+        impl T for u32 {}
+        impl T for String {}
+        fn f(_: impl T) {}
+
+        f((1 + 2) as u32);
+        f(((1 + 2u32)));
+        //~^ unnecessary_cast
+    }
 }

tests/ui/unnecessary_cast.rs

@@ -6,6 +6,7 @@
     clippy::no_effect,
     clippy::nonstandard_macro_braces,
     clippy::unnecessary_operation,
+    clippy::double_parens,
     nonstandard_style,
     unused
 )]
@@ -283,4 +284,24 @@ mod fixable {
         let _ = 5i32 as i64 as i64;
         //~^ unnecessary_cast
     }
+
+    fn issue_14366(i: u32) {
+        // Do not remove the cast if it helps determining the type
+        let _ = ((1.0 / 8.0) as f64).powf(i as f64);
+
+        // But remove useless casts anyway
+        let _ = (((1.0 / 8.0) as f64) as f64).powf(i as f64);
+        //~^ unnecessary_cast
+    }
+
+    fn ambiguity() {
+        pub trait T {}
+        impl T for u32 {}
+        impl T for String {}
+        fn f(_: impl T) {}
+
+        f((1 + 2) as u32);
+        f((1 + 2u32) as u32);
+        //~^ unnecessary_cast
+    }
 }