move char_lit_as_u8 under the explicit-cast case (#15477)

allows reusing `cast_from_expr` and `cast_to`

also make the test files a bit more.. standard

changelog: none

Author: Jarcho

clippy_lints/src/casts/char_lit_as_u8.rs

@@ -4,18 +4,17 @@ use rustc_ast::LitKind;
 use rustc_errors::Applicability;
 use rustc_hir::{Expr, ExprKind};
 use rustc_lint::LateContext;
-use rustc_middle::ty::{self, UintTy};
+use rustc_middle::ty::{self, Ty, UintTy};
 
 use super::CHAR_LIT_AS_U8;
 
-pub(super) fn check(cx: &LateContext<'_>, expr: &Expr<'_>) {
-    if let ExprKind::Cast(e, _) = &expr.kind
-        && let ExprKind::Lit(l) = &e.kind
+pub(super) fn check(cx: &LateContext<'_>, expr: &Expr<'_>, cast_from_expr: &Expr<'_>, cast_to: Ty<'_>) {
+    if let ExprKind::Lit(l) = &cast_from_expr.kind
         && let LitKind::Char(c) = l.node
-        && ty::Uint(UintTy::U8) == *cx.typeck_results().expr_ty(expr).kind()
+        && ty::Uint(UintTy::U8) == *cast_to.kind()
     {
         let mut applicability = Applicability::MachineApplicable;
-        let snippet = snippet_with_applicability(cx, e.span, "'x'", &mut applicability);
+        let snippet = snippet_with_applicability(cx, cast_from_expr.span, "'x'", &mut applicability);
 
         span_lint_and_then(
             cx,

clippy_lints/src/casts/mod.rs

@@ -871,6 +871,7 @@ impl<'tcx> LateLintPass<'tcx> for Casts {
             if !expr.span.from_expansion() && unnecessary_cast::check(cx, expr, cast_from_expr, cast_from, cast_to) {
                 return;
             }
+            char_lit_as_u8::check(cx, expr, cast_from_expr, cast_to);
             cast_slice_from_raw_parts::check(cx, expr, cast_from_expr, cast_to, self.msrv);
             ptr_cast_constness::check(cx, expr, cast_from_expr, cast_from, cast_to, self.msrv);
             as_ptr_cast_mut::check(cx, expr, cast_from_expr, cast_to);
@@ -911,7 +912,6 @@ impl<'tcx> LateLintPass<'tcx> for Casts {
             borrow_as_ptr::check_implicit_cast(cx, expr);
         }
         cast_ptr_alignment::check(cx, expr);
-        char_lit_as_u8::check(cx, expr);
         ptr_as_ptr::check(cx, expr, self.msrv);
         cast_slice_different_sizes::check(cx, expr, self.msrv);
         ptr_cast_constness::check_null_ptr_cast_method(cx, expr);

tests/ui/char_lit_as_u8_suggestions.fixed renamed to tests/ui/char_lit_as_u8.fixed

@@ -1,7 +1,12 @@
 #![warn(clippy::char_lit_as_u8)]
 
 fn main() {
-    // no suggestion, since a byte literal won't work.
-    let _ = '❤' as u8;
+    let _ = 'a' as u8;
+    //~^ char_lit_as_u8
+    let _ = '\n' as u8;
+    //~^ char_lit_as_u8
+    let _ = '\0' as u8;
+    //~^ char_lit_as_u8
+    let _ = '\x01' as u8;
     //~^ char_lit_as_u8
 }

tests/ui/char_lit_as_u8.rs

@@ -1,12 +1,36 @@
 error: casting a character literal to `u8` truncates
-  --> tests/ui/char_lit_as_u8.rs:5:13
+  --> tests/ui/char_lit_as_u8.rs:4:13
    |
-LL |     let _ = '❤' as u8;
-   |             ^^^^^^^^^
+LL |     let _ = 'a' as u8;
+   |             ^^^^^^^^^ help: use a byte literal instead: `b'a'`
    |
    = note: `char` is four bytes wide, but `u8` is a single byte
    = note: `-D clippy::char-lit-as-u8` implied by `-D warnings`
    = help: to override `-D warnings` add `#[allow(clippy::char_lit_as_u8)]`
 
-error: aborting due to 1 previous error
+error: casting a character literal to `u8` truncates
+  --> tests/ui/char_lit_as_u8.rs:6:13
+   |
+LL |     let _ = '\n' as u8;
+   |             ^^^^^^^^^^ help: use a byte literal instead: `b'\n'`
+   |
+   = note: `char` is four bytes wide, but `u8` is a single byte
+
+error: casting a character literal to `u8` truncates
+  --> tests/ui/char_lit_as_u8.rs:8:13
+   |
+LL |     let _ = '\0' as u8;
+   |             ^^^^^^^^^^ help: use a byte literal instead: `b'\0'`
+   |
+   = note: `char` is four bytes wide, but `u8` is a single byte
+
+error: casting a character literal to `u8` truncates
+  --> tests/ui/char_lit_as_u8.rs:10:13
+   |
+LL |     let _ = '\x01' as u8;
+   |             ^^^^^^^^^^^^ help: use a byte literal instead: `b'\x01'`
+   |
+   = note: `char` is four bytes wide, but `u8` is a single byte
+
+error: aborting due to 4 previous errors
 

tests/ui/char_lit_as_u8.stderr

@@ -0,0 +1,8 @@
+//@no-rustfix
+#![warn(clippy::char_lit_as_u8)]
+
+fn main() {
+    // no suggestion, since a byte literal won't work.
+    let _ = '❤' as u8;
+    //~^ char_lit_as_u8
+}

tests/ui/char_lit_as_u8_suggestions.rs

@@ -0,0 +1,12 @@
+error: casting a character literal to `u8` truncates
+  --> tests/ui/char_lit_as_u8_unfixable.rs:6:13
+   |
+LL |     let _ = '❤' as u8;
+   |             ^^^^^^^^^
+   |
+   = note: `char` is four bytes wide, but `u8` is a single byte
+   = note: `-D clippy::char-lit-as-u8` implied by `-D warnings`
+   = help: to override `-D warnings` add `#[allow(clippy::char_lit_as_u8)]`
+
+error: aborting due to 1 previous error
+