use integer_sign_cast

Author: bend-n

compiler/rustc_mir_transform/src/check_redundant_transmutes.rs

@@ -62,11 +62,10 @@ impl<'a, 'tcx> RedundantTransmutesChecker<'a, 'tcx> {
                 span,
             });
         }
-        return match input.kind() {
+        match input.kind() {
             // char → u32
-            Char => matches!(fn_sig.output().kind(), Uint(UintTy::U32)).then(|| {
-                errors::RedundantTransmute { sugg: format!("({arg}) as u32"), help: None, span }
-            }),
+            Char => matches!(fn_sig.output().kind(), Uint(UintTy::U32))
+                .then(|| errors::RedundantTransmute::new(format!("({arg}) as u32"), span)),
             // u32 → char
             Uint(UintTy::U32) if *fn_sig.output().kind() == Char => {
                 Some(errors::RedundantTransmute {
@@ -75,19 +74,26 @@ impl<'a, 'tcx> RedundantTransmutesChecker<'a, 'tcx> {
                     span,
                 })
             }
-            // bool → (uNN ↔ iNN)
-            Bool | Uint(..) | Int(..) => {
-                matches!(fn_sig.output().kind(), Int(..) | Uint(..)).then(|| {
-                    // FIXME: suggest `cast_unsigned`/ `cast_signed` when `integer_sign_cast` stabilizes
-                    errors::RedundantTransmute {
-                        sugg: format!("({arg}) as {}", fn_sig.output()),
-                        help: None,
-                        span,
-                    }
-                })
+            // uNN → iNN
+            Uint(ty) if matches!(fn_sig.output().kind(), Int(..)) => {
+                Some(errors::RedundantTransmute::new(
+                    format!("{}::cast_signed({arg})", ty.name_str()),
+                    span,
+                ))
             }
+            // iNN → uNN
+            Int(ty) if matches!(fn_sig.output().kind(), Uint(..)) => {
+                Some(errors::RedundantTransmute::new(
+                    format!("{}::cast_unsigned({arg})", ty.name_str()),
+                    span,
+                ))
+            }
+            // bool → { uNN, iNN }
+            Bool if matches!(fn_sig.output().kind(), Int(..) | Uint(..)) => Some(
+                errors::RedundantTransmute::new(format!("({arg}) as {}", fn_sig.output()), span),
+            ),
             _ => None,
-        };
+        }
     }
 }
 

compiler/rustc_mir_transform/src/errors.rs

@@ -164,6 +164,12 @@ pub(crate) struct RedundantTransmute {
     pub help: Option<&'static str>,
 }
 
+impl RedundantTransmute {
+    pub(crate) fn new(sugg: String, span: Span) -> Self {
+        Self { span, sugg, help: None }
+    }
+}
+
 // Needed for def_path_str
 impl<'a> LintDiagnostic<'a, ()> for RedundantTransmute {
     fn decorate_lint<'b>(self, diag: &'b mut rustc_errors::Diag<'a, ()>) {