Note expr being cast when encounter NonScalar cast error

Signed-off-by: xizheyin <[email protected]>

Author: xizheyin

compiler/rustc_hir_typeck/src/cast.rs

@@ -408,6 +408,15 @@ impl<'a, 'tcx> CastCheck<'tcx> {
                     self.expr_ty,
                     fcx.ty_to_string(self.cast_ty)
                 );
+
+                if let Ok(snippet) = fcx.tcx.sess.source_map().span_to_snippet(self.expr_span) {
+                    err.note(format!(
+                        "casting expr `{}` as `{}`",
+                        snippet,
+                        fcx.ty_to_string(self.cast_ty)
+                    ));
+                }
+
                 let mut sugg = None;
                 let mut sugg_mutref = false;
                 if let ty::Ref(reg, cast_ty, mutbl) = *self.cast_ty.kind() {

tests/ui/cast/cast-from-nil.stderr

@@ -3,6 +3,8 @@ error[E0605]: non-primitive cast: `()` as `u32`
    |
 LL | fn main() { let u = (assert!(true) as u32); }
    |                     ^^^^^^^^^^^^^^^^^^^^^^ an `as` expression can only be used to convert between primitive types or to coerce to a specific trait object
+   |
+   = note: casting expr `assert!(true)` as `u32`
 
 error: aborting due to 1 previous error
 

tests/ui/cast/cast-to-bare-fn.stderr

@@ -3,12 +3,16 @@ error[E0605]: non-primitive cast: `fn(isize) {foo}` as `extern "C" fn() -> isize
    |
 LL |     let x = foo as extern "C" fn() -> isize;
    |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ invalid cast
+   |
+   = note: casting expr `foo` as `extern "C" fn() -> isize`
 
 error[E0605]: non-primitive cast: `u64` as `fn(isize) -> (isize, isize)`
   --> $DIR/cast-to-bare-fn.rs:7:13
    |
 LL |     let y = v as extern "Rust" fn(isize) -> (isize, isize);
    |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ invalid cast
+   |
+   = note: casting expr `v` as `fn(isize) -> (isize, isize)`
 
 error: aborting due to 2 previous errors
 

tests/ui/cast/cast-to-nil.stderr

@@ -3,6 +3,8 @@ error[E0605]: non-primitive cast: `u32` as `()`
    |
 LL | fn main() { let u = 0u32 as (); }
    |                     ^^^^^^^^^^ an `as` expression can only be used to convert between primitive types or to coerce to a specific trait object
+   |
+   = note: casting expr `0u32` as `()`
 
 error: aborting due to 1 previous error
 

tests/ui/cast/enum-to-numeric-cast.stderr

@@ -4,6 +4,7 @@ error[E0605]: non-primitive cast: `NotUnitOnlyOrFieldless` as `isize`
 LL |     let _ = not_unit_only_or_fieldless as isize;
    |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ an `as` expression can be used to convert enum types to numeric types only if the enum type is unit-only or field-less
    |
+   = note: casting expr `not_unit_only_or_fieldless` as `isize`
    = note: see https://doc.rust-lang.org/reference/items/enumerations.html#casting for more information
 
 error[E0605]: non-primitive cast: `NotUnitOnlyOrFieldless` as `i32`
@@ -12,6 +13,7 @@ error[E0605]: non-primitive cast: `NotUnitOnlyOrFieldless` as `i32`
 LL |     let _ = not_unit_only_or_fieldless as i32;
    |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ an `as` expression can be used to convert enum types to numeric types only if the enum type is unit-only or field-less
    |
+   = note: casting expr `not_unit_only_or_fieldless` as `i32`
    = note: see https://doc.rust-lang.org/reference/items/enumerations.html#casting for more information
 
 error[E0605]: non-primitive cast: `NotUnitOnlyOrFieldless` as `usize`
@@ -20,6 +22,7 @@ error[E0605]: non-primitive cast: `NotUnitOnlyOrFieldless` as `usize`
 LL |     let _ = not_unit_only_or_fieldless as usize;
    |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ an `as` expression can be used to convert enum types to numeric types only if the enum type is unit-only or field-less
    |
+   = note: casting expr `not_unit_only_or_fieldless` as `usize`
    = note: see https://doc.rust-lang.org/reference/items/enumerations.html#casting for more information
 
 error[E0605]: non-primitive cast: `NotUnitOnlyOrFieldless` as `u32`
@@ -28,6 +31,7 @@ error[E0605]: non-primitive cast: `NotUnitOnlyOrFieldless` as `u32`
 LL |     let _ = not_unit_only_or_fieldless as u32;
    |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ an `as` expression can be used to convert enum types to numeric types only if the enum type is unit-only or field-less
    |
+   = note: casting expr `not_unit_only_or_fieldless` as `u32`
    = note: see https://doc.rust-lang.org/reference/items/enumerations.html#casting for more information
 
 error: aborting due to 4 previous errors

tests/ui/cast/fat-ptr-cast.stderr

@@ -35,6 +35,8 @@ error[E0605]: non-primitive cast: `Box<[i32]>` as `usize`
    |
 LL |     b as usize;
    |     ^^^^^^^^^^ an `as` expression can only be used to convert between primitive types or to coerce to a specific trait object
+   |
+   = note: casting expr `b` as `usize`
 
 error[E0606]: casting `*const [i32]` as `usize` is invalid
   --> $DIR/fat-ptr-cast.rs:15:5

tests/ui/cast/func-pointer-issue-140491.stderr

@@ -3,6 +3,8 @@ error[E0605]: non-primitive cast: `&for<'a, 'b> fn(&'a Event<'b>) {my_fn}` as `&
    |
 LL | ..._>) = &my_fn as _;
    |          ^^^^^^^^^^^ an `as` expression can only be used to convert between primitive types or to coerce to a specific trait object
+   |
+   = note: casting expr `&my_fn` as `&for<'a, 'b> fn(&'a Event<'b>)`
 
 error: aborting due to 1 previous error
 

tests/ui/cast/issue-106883-is-empty.stderr

@@ -16,6 +16,7 @@ error[E0605]: non-primitive cast: `String` as `bool`
 LL |     let _ = String::from("foo") as bool;
    |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^ an `as` expression can only be used to convert between primitive types or to coerce to a specific trait object
    |
+   = note: casting expr `String::from("foo")` as `bool`
 note: this expression `Deref`s to `str` which implements `is_empty`
   --> $DIR/issue-106883-is-empty.rs:17:13
    |
@@ -33,6 +34,7 @@ error[E0605]: non-primitive cast: `Foo` as `bool`
 LL |     let _ = Foo as bool;
    |             ^^^^^^^^^^^ an `as` expression can only be used to convert between primitive types or to coerce to a specific trait object
    |
+   = note: casting expr `Foo` as `bool`
 note: this expression `Deref`s to `[u8]` which implements `is_empty`
   --> $DIR/issue-106883-is-empty.rs:20:13
    |

tests/ui/cast/issue-10991.stderr

@@ -3,6 +3,8 @@ error[E0605]: non-primitive cast: `()` as `usize`
    |
 LL |     let _t = nil as usize;
    |              ^^^^^^^^^^^^ an `as` expression can only be used to convert between primitive types or to coerce to a specific trait object
+   |
+   = note: casting expr `nil` as `usize`
 
 error: aborting due to 1 previous error
 

tests/ui/cast/issue-84213.stderr

@@ -4,6 +4,7 @@ error[E0605]: non-primitive cast: `Something` as `*const Something`
 LL |     let _pointer_to_something = something as *const Something;
    |                                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ invalid cast
    |
+   = note: casting expr `something` as `*const Something`
 help: consider borrowing the value
    |
 LL |     let _pointer_to_something = &something as *const Something;
@@ -15,6 +16,7 @@ error[E0605]: non-primitive cast: `Something` as `*mut Something`
 LL |     let _mut_pointer_to_something = something as *mut Something;
    |                                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^ invalid cast
    |
+   = note: casting expr `something` as `*mut Something`
 help: consider borrowing the value
    |
 LL |     let _mut_pointer_to_something = &mut something as *mut Something;

tests/ui/cast/issue-88621.stderr

@@ -4,6 +4,7 @@ error[E0605]: non-primitive cast: `Kind2` as `u8`
 LL |     let _ = Kind2::Foo() as u8;
    |             ^^^^^^^^^^^^^^^^^^ an `as` expression can be used to convert enum types to numeric types only if the enum type is unit-only or field-less
    |
+   = note: casting expr `Kind2::Foo()` as `u8`
    = note: see https://doc.rust-lang.org/reference/items/enumerations.html#casting for more information
 
 error: aborting due to 1 previous error

tests/ui/cast/issue-89497.stderr

@@ -4,6 +4,7 @@ error[E0605]: non-primitive cast: `*const i32` as `&'static i32`
 LL |     let _reference: &'static i32 = unsafe { pointer as *const i32 as &'static i32 };
    |                                             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ invalid cast
    |
+   = note: casting expr `pointer as *const i32` as `&'static i32`
 help: consider borrowing the value
    |
 LL -     let _reference: &'static i32 = unsafe { pointer as *const i32 as &'static i32 };

tests/ui/closures/closure-no-fn-3.stderr

@@ -4,6 +4,7 @@ error[E0605]: non-primitive cast: `{closure@$DIR/closure-no-fn-3.rs:6:28: 6:30}`
 LL |     let baz: fn() -> u8 = (|| { b }) as fn() -> u8;
    |                           ^^^^^^^^^^^^^^^^^^^^^^^^ invalid cast
    |
+   = note: casting expr `(|| { b })` as `fn() -> u8`
 note: closures can only be coerced to `fn` types if they do not capture any variables
   --> $DIR/closure-no-fn-3.rs:6:33
    |

tests/ui/coercion/coerce-to-bang-cast.stderr

@@ -3,12 +3,16 @@ error[E0605]: non-primitive cast: `i32` as `!`
    |
 LL |     let y = {return; 22} as !;
    |             ^^^^^^^^^^^^^^^^^ an `as` expression can only be used to convert between primitive types or to coerce to a specific trait object
+   |
+   = note: casting expr `{return; 22}` as `!`
 
 error[E0605]: non-primitive cast: `i32` as `!`
   --> $DIR/coerce-to-bang-cast.rs:9:13
    |
 LL |     let y = 22 as !;
    |             ^^^^^^^ an `as` expression can only be used to convert between primitive types or to coerce to a specific trait object
+   |
+   = note: casting expr `22` as `!`
 
 error: aborting due to 2 previous errors
 

tests/ui/coercion/issue-73886.stderr

@@ -3,13 +3,16 @@ error[E0605]: non-primitive cast: `&&[i32; 1]` as `&[_]`
    |
 LL |     let _ = &&[0] as &[_];
    |             ^^^^^^^^^^^^^ an `as` expression can only be used to convert between primitive types or to coerce to a specific trait object
+   |
+   = note: casting expr `&&[0]` as `&[_]`
 
 error[E0605]: non-primitive cast: `u32` as `Option<_>`
   --> $DIR/issue-73886.rs:4:13
    |
 LL |     let _ = 7u32 as Option<_>;
    |             ^^^^^^^^^^^^^^^^^
    |
+   = note: casting expr `7u32` as `Option<_>`
    = note: an `as` expression can only be used to convert between primitive types or to coerce to a specific trait object
 help: consider using the `From` trait instead
    |

tests/ui/coercion/non-primitive-cast-135412.stderr

@@ -4,6 +4,7 @@ error[E0605]: non-primitive cast: `u32` as `Option<_>`
 LL |     let _ = 7u32 as Option<_>;
    |             ^^^^^^^^^^^^^^^^^
    |
+   = note: casting expr `7u32` as `Option<_>`
    = note: an `as` expression can only be used to convert between primitive types or to coerce to a specific trait object
 help: consider using the `From` trait instead
    |
@@ -17,6 +18,7 @@ error[E0605]: non-primitive cast: `&'static str` as `Arc<str>`
 LL |     let _ = "String" as Arc<str>;
    |             ^^^^^^^^^^^^^^^^^^^^
    |
+   = note: casting expr `"String"` as `Arc<str>`
    = note: an `as` expression can only be used to convert between primitive types or to coerce to a specific trait object
 help: consider using the `From` trait instead
    |

tests/ui/const-generics/generic_const_exprs/opaque_type.stderr

@@ -15,6 +15,8 @@ error[E0605]: non-primitive cast: `usize` as `Foo`
    |
 LL |     let _: [u8; (N / 2) as Foo] = [0; (N / 2) as usize];
    |                 ^^^^^^^^^^^^^^ an `as` expression can only be used to convert between primitive types or to coerce to a specific trait object
+   |
+   = note: casting expr `(N / 2)` as `Foo`
 
 error: aborting due to 2 previous errors
 

tests/ui/dyn-star/dyn-to-rigid.stderr

@@ -3,6 +3,8 @@ error[E0605]: non-primitive cast: `(dyn* Tr + 'static)` as `usize`
    |
 LL |     x as usize
    |     ^^^^^^^^^^ an `as` expression can only be used to convert between primitive types or to coerce to a specific trait object
+   |
+   = note: casting expr `x` as `usize`
 
 error: aborting due to 1 previous error
 

tests/ui/dyn-star/unsize-into-ref-dyn-star.stderr

@@ -3,6 +3,8 @@ error[E0605]: non-primitive cast: `i32` as `&dyn* Debug`
    |
 LL |     let i = 42 as &dyn* Debug;
    |             ^^^^^^^^^^^^^^^^^ an `as` expression can only be used to convert between primitive types or to coerce to a specific trait object
+   |
+   = note: casting expr `42` as `&dyn* Debug`
 
 error: aborting due to 1 previous error
 

tests/ui/error-codes/E0605.stderr

@@ -3,13 +3,16 @@ error[E0605]: non-primitive cast: `u8` as `Vec<u8>`
    |
 LL |     x as Vec<u8>;
    |     ^^^^^^^^^^^^ an `as` expression can only be used to convert between primitive types or to coerce to a specific trait object
+   |
+   = note: casting expr `x` as `Vec<u8>`
 
 error[E0605]: non-primitive cast: `*const u8` as `&u8`
   --> $DIR/E0605.rs:6:5
    |
 LL |     v as &u8;
    |     ^^^^^^^^ invalid cast
    |
+   = note: casting expr `v` as `&u8`
 help: consider borrowing the value
    |
 LL -     v as &u8;

tests/ui/error-emitter/error-festival.stderr

@@ -68,6 +68,8 @@ error[E0605]: non-primitive cast: `u8` as `Vec<u8>`
    |
 LL |     x as Vec<u8>;
    |     ^^^^^^^^^^^^ an `as` expression can only be used to convert between primitive types or to coerce to a specific trait object
+   |
+   = note: casting expr `x` as `Vec<u8>`
 
 error[E0054]: cannot cast `{integer}` as `bool`
   --> $DIR/error-festival.rs:35:24

tests/ui/force-inlining/cast.stderr

@@ -19,6 +19,8 @@ error[E0605]: non-primitive cast: `fn(isize) -> usize {callee}` as `fn(isize) ->
    |
 LL |     let _ = callee as fn(isize) -> usize;
    |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ invalid cast
+   |
+   = note: casting expr `callee` as `fn(isize) -> usize`
 
 error[E0308]: cannot coerce functions which must be inlined to function pointers
   --> $DIR/cast.rs:21:9

tests/ui/issues/issue-16048.rs

@@ -23,6 +23,7 @@ impl<'a> NoLifetime for Foo<'a> {
     //~| NOTE lifetimes do not match method in trait
         return *self as T;
         //~^ ERROR non-primitive cast: `Foo<'a>` as `T`
+        //~| NOTE casting expr `*self` as `T`
         //~| NOTE an `as` expression can only be used to convert between primitive types
     }
 }

tests/ui/issues/issue-16048.stderr

@@ -13,6 +13,7 @@ error[E0605]: non-primitive cast: `Foo<'a>` as `T`
 LL |         return *self as T;
    |                ^^^^^^^^^^ help: consider using the `From` trait instead: `T::from(*self)`
    |
+   = note: casting expr `*self` as `T`
    = note: an `as` expression can only be used to convert between primitive types or to coerce to a specific trait object
 
 error: aborting due to 2 previous errors

tests/ui/issues/issue-22289.stderr

@@ -4,6 +4,7 @@ error[E0605]: non-primitive cast: `i32` as `&(dyn Any + 'static)`
 LL |     0 as &dyn std::any::Any;
    |     ^^^^^^^^^^^^^^^^^^^^^^^ invalid cast
    |
+   = note: casting expr `0` as `&(dyn Any + 'static)`
 help: consider borrowing the value
    |
 LL |     &0 as &dyn std::any::Any;

tests/ui/issues/issue-22312.stderr

@@ -4,6 +4,7 @@ error[E0605]: non-primitive cast: `Self` as `&dyn Index<usize, Output = <Self as
 LL |         let indexer = &(*self as &dyn Index<usize, Output = <Self as Index<usize>>::Output>);
    |                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ invalid cast
    |
+   = note: casting expr `*self` as `&dyn Index<usize, Output = <Self as Index<usize>>::Output>`
 help: consider borrowing the value
    |
 LL |         let indexer = &(&*self as &dyn Index<usize, Output = <Self as Index<usize>>::Output>);

tests/ui/issues/issue-2995.stderr

@@ -4,6 +4,7 @@ error[E0605]: non-primitive cast: `*const isize` as `&isize`
 LL |     let _q: &isize = p as &isize;
    |                      ^^^^^^^^^^^ invalid cast
    |
+   = note: casting expr `p` as `&isize`
 help: consider borrowing the value
    |
 LL -     let _q: &isize = p as &isize;

tests/ui/mismatched_types/cast-rfc0401.stderr

@@ -26,6 +26,7 @@ error[E0605]: non-primitive cast: `*const u8` as `&u8`
 LL |     let _ = v as &u8;
    |             ^^^^^^^^ invalid cast
    |
+   = note: casting expr `v` as `&u8`
 help: consider borrowing the value
    |
 LL -     let _ = v as &u8;
@@ -37,24 +38,32 @@ error[E0605]: non-primitive cast: `*const u8` as `E`
    |
 LL |     let _ = v as E;
    |             ^^^^^^ an `as` expression can only be used to convert between primitive types or to coerce to a specific trait object
+   |
+   = note: casting expr `v` as `E`
 
 error[E0605]: non-primitive cast: `*const u8` as `fn()`
   --> $DIR/cast-rfc0401.rs:31:13
    |
 LL |     let _ = v as fn();
    |             ^^^^^^^^^ invalid cast
+   |
+   = note: casting expr `v` as `fn()`
 
 error[E0605]: non-primitive cast: `*const u8` as `(u32,)`
   --> $DIR/cast-rfc0401.rs:32:13
    |
 LL |     let _ = v as (u32,);
    |             ^^^^^^^^^^^ an `as` expression can only be used to convert between primitive types or to coerce to a specific trait object
+   |
+   = note: casting expr `v` as `(u32,)`
 
 error[E0605]: non-primitive cast: `Option<&*const u8>` as `*const u8`
   --> $DIR/cast-rfc0401.rs:33:13
    |
 LL |     let _ = Some(&v) as *const u8;
    |             ^^^^^^^^^^^^^^^^^^^^^ an `as` expression can only be used to convert between primitive types or to coerce to a specific trait object
+   |
+   = note: casting expr `Some(&v)` as `*const u8`
 
 error[E0606]: casting `*const u8` as `f32` is invalid
   --> $DIR/cast-rfc0401.rs:35:13

tests/ui/mismatched_types/issue-26480.stderr

@@ -29,6 +29,7 @@ LL |     ($x:expr) => ($x as ())
 LL |     cast!(2);
    |     -------- in this macro invocation
    |
+   = note: casting expr `2` as `()`
    = note: this error originates in the macro `cast` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: aborting due to 2 previous errors

tests/ui/nonscalar-cast.stderr

@@ -4,6 +4,7 @@ error[E0605]: non-primitive cast: `Foo` as `isize`
 LL |     println!("{}", Foo { x: 1 } as isize);
    |                    ^^^^^^^^^^^^^^^^^^^^^ help: consider using the `From` trait instead: `isize::from(Foo { x: 1 })`
    |
+   = note: casting expr `Foo { x: 1 }` as `isize`
    = note: an `as` expression can only be used to convert between primitive types or to coerce to a specific trait object
 
 error: aborting due to 1 previous error

tests/ui/reachable/expr_cast.stderr

@@ -18,6 +18,8 @@ error[E0605]: non-primitive cast: `()` as `!`
    |
 LL |     let x = {return} as !;
    |             ^^^^^^^^^^^^^ an `as` expression can only be used to convert between primitive types or to coerce to a specific trait object
+   |
+   = note: casting expr `{return}` as `!`
 
 error: aborting due to 2 previous errors
 

tests/ui/rfcs/rfc-1623-static/rfc1623-3.stderr

@@ -28,6 +28,8 @@ error[E0605]: non-primitive cast: `for<'a, 'b> fn(&'a u8, &'b u8) -> &'a u8 {non
    |
 LL |     &(non_elidable as fn(&u8, &u8) -> &u8);
    |      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ invalid cast
+   |
+   = note: casting expr `non_elidable` as `for<'a, 'b> fn(&'a u8, &'b u8) -> &u8`
 
 error: aborting due to 3 previous errors