Fix inference of literals when the expectation is Castable

I followed the compiler: https://github.com/rust-lang/rust/blob/5bce6d48ff09dcb2613278ec93013795718478ef/compiler/rustc_hir_typeck/src/fn_ctxt/checks.rs#L1560-L1579.

Author: ChayimFriedman2

src/tools/rust-analyzer/crates/hir-ty/src/infer/expr.rs

@@ -895,21 +895,52 @@ impl InferenceContext<'_> {
                         TyKind::Scalar(Scalar::Int(primitive::int_ty_from_builtin(*int_ty)))
                             .intern(Interner)
                     }
-                    None => self.table.new_integer_var(),
+                    None => {
+                        let expected_ty = expected.to_option(&mut self.table);
+                        let opt_ty = match expected_ty.as_ref().map(|it| it.kind(Interner)) {
+                            Some(TyKind::Scalar(Scalar::Int(_) | Scalar::Uint(_))) => expected_ty,
+                            Some(TyKind::Scalar(Scalar::Char)) => {
+                                Some(TyKind::Scalar(Scalar::Uint(UintTy::U8)).intern(Interner))
+                            }
+                            Some(TyKind::Raw(..) | TyKind::FnDef(..) | TyKind::Function(..)) => {
+                                Some(TyKind::Scalar(Scalar::Uint(UintTy::Usize)).intern(Interner))
+                            }
+                            _ => None,
+                        };
+                        opt_ty.unwrap_or_else(|| self.table.new_integer_var())
+                    }
                 },
                 Literal::Uint(_v, ty) => match ty {
                     Some(int_ty) => {
                         TyKind::Scalar(Scalar::Uint(primitive::uint_ty_from_builtin(*int_ty)))
                             .intern(Interner)
                     }
-                    None => self.table.new_integer_var(),
+                    None => {
+                        let expected_ty = expected.to_option(&mut self.table);
+                        let opt_ty = match expected_ty.as_ref().map(|it| it.kind(Interner)) {
+                            Some(TyKind::Scalar(Scalar::Int(_) | Scalar::Uint(_))) => expected_ty,
+                            Some(TyKind::Scalar(Scalar::Char)) => {
+                                Some(TyKind::Scalar(Scalar::Uint(UintTy::U8)).intern(Interner))
+                            }
+                            Some(TyKind::Raw(..) | TyKind::FnDef(..) | TyKind::Function(..)) => {
+                                Some(TyKind::Scalar(Scalar::Uint(UintTy::Usize)).intern(Interner))
+                            }
+                            _ => None,
+                        };
+                        opt_ty.unwrap_or_else(|| self.table.new_integer_var())
+                    }
                 },
                 Literal::Float(_v, ty) => match ty {
                     Some(float_ty) => {
                         TyKind::Scalar(Scalar::Float(primitive::float_ty_from_builtin(*float_ty)))
                             .intern(Interner)
                     }
-                    None => self.table.new_float_var(),
+                    None => {
+                        let opt_ty = expected.to_option(&mut self.table).filter(|ty| {
+                            matches!(ty.kind(Interner), TyKind::Scalar(Scalar::Float(_)))
+                        });
+                        opt_ty.unwrap_or_else(|| self.table.new_float_var())
+                    }
                 },
             },
             Expr::Underscore => {

src/tools/rust-analyzer/crates/hir-ty/src/tests/coercion.rs

@@ -49,7 +49,7 @@ fn let_stmt_coerce() {
 //- minicore: coerce_unsized
 fn test() {
     let x: &[isize] = &[1];
-                   // ^^^^ adjustments: Deref(None), Borrow(Ref('?3, Not)), Pointer(Unsize)
+                   // ^^^^ adjustments: Deref(None), Borrow(Ref('?2, Not)), Pointer(Unsize)
     let x: *const [isize] = &[1];
                          // ^^^^ adjustments: Deref(None), Borrow(RawPtr(Not)), Pointer(Unsize)
 }
@@ -148,7 +148,7 @@ fn foo<T>(x: &[T]) -> &[T] { x }
 fn test(i: i32) {
     let x = match i {
         2 => foo(&[2]),
-              // ^^^^ adjustments: Deref(None), Borrow(Ref('?10, Not)), Pointer(Unsize)
+              // ^^^^ adjustments: Deref(None), Borrow(Ref('?8, Not)), Pointer(Unsize)
         1 => &[1],
         _ => &[3],
     };

src/tools/rust-analyzer/crates/hir-ty/src/tests/simple.rs

@@ -917,7 +917,7 @@ fn test(a: A<i32>) {
             278..279 'A': extern "rust-call" A<i32>(*mut i32) -> A<i32>
             278..292 'A(0 as *mut _)': A<i32>
             278..307 'A(0 as...B(a)))': &'? i32
-            280..281 '0': i32
+            280..281 '0': usize
             280..291 '0 as *mut _': *mut i32
             297..306 '&&B(B(a))': &'? &'? B<B<A<i32>>>
             298..306 '&B(B(a))': &'? B<B<A<i32>>>

src/tools/rust-analyzer/crates/ide-diagnostics/src/handlers/invalid_cast.rs

@@ -441,16 +441,16 @@ fn main() {
   //^^^^^^^^^^^^^^^^^ error: cannot cast thin pointer `*const i32` to fat pointer `*const [i32]`
 
     let t: *mut (dyn Trait + 'static) = 0 as *mut _;
-                                      //^^^^^^^^^^^ error: cannot cast `i32` to a fat pointer `*mut _`
+                                      //^^^^^^^^^^^ error: cannot cast `usize` to a fat pointer `*mut _`
     let mut fail: *const str = 0 as *const str;
-                             //^^^^^^^^^^^^^^^ error: cannot cast `i32` to a fat pointer `*const str`
+                             //^^^^^^^^^^^^^^^ error: cannot cast `usize` to a fat pointer `*const str`
     let mut fail2: *const str = 0isize as *const str;
                               //^^^^^^^^^^^^^^^^^^^^ error: cannot cast `isize` to a fat pointer `*const str`
 }
 
 fn foo<T: ?Sized>() {
     let s = 0 as *const T;
-          //^^^^^^^^^^^^^ error: cannot cast `i32` to a fat pointer `*const T`
+          //^^^^^^^^^^^^^ error: cannot cast `usize` to a fat pointer `*const T`
 }
 "#,
             &["E0308", "unused_variables"],
@@ -1100,4 +1100,15 @@ where
 "#,
         );
     }
+
+    #[test]
+    fn cast_literal_to_char() {
+        check_diagnostics(
+            r#"
+fn foo() {
+    0 as char;
+}
+            "#,
+        );
+    }
 }