Rollup merge of #72380 - lcnr:const_context, r=estebank

Fix `is_const_context`, update `check_for_cast`

A better version of #71477

Adds `fn enclosing_body_owner` and uses it in `is_const_context`.
`is_const_context` now uses the same mechanism as `mir_const_qualif` as it was previously incorrect.
Renames `is_const_context` to `is_inside_const_context`.

I also updated `check_for_cast` in the second commit, so r? @estebank

(I removed one lvl of indentation, so it might be easier to review by hiding whitespace changes)

src/test/ui/consts/enum-discr-type-err.stderr

@@ -11,10 +11,6 @@ LL | | }
    | |_- in this macro invocation
    |
    = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
-help: you can convert an `i32` to `isize` and panic if the converted value wouldn't fit
-   |
-LL |             $( $v = $s::V.try_into().unwrap(), )*
-   |                     ^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error[E0308]: mismatched types
   --> $DIR/enum-discr-type-err.rs:18:21
@@ -29,10 +25,6 @@ LL | | }
    | |_- in this macro invocation
    |
    = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
-help: you can convert an `i32` to `isize` and panic if the converted value wouldn't fit
-   |
-LL |             $( $v = $s::V.try_into().unwrap(), )*
-   |                     ^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: aborting due to 2 previous errors
 

src/test/ui/issues/issue-31910.stderr

@@ -3,11 +3,6 @@ error[E0308]: mismatched types
    |
 LL |     X = Trait::Number,
    |         ^^^^^^^^^^^^^ expected `isize`, found `i32`
-   |
-help: you can convert an `i32` to `isize` and panic if the converted value wouldn't fit
-   |
-LL |     X = Trait::Number.try_into().unwrap(),
-   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: aborting due to previous error
 

src/test/ui/numeric/const-scope.stderr

@@ -3,6 +3,11 @@ error[E0308]: mismatched types
    |
 LL | const C: i32 = 1i8;
    |                ^^^ expected `i32`, found `i8`
+   |
+help: change the type of the numeric literal from `i8` to `i32`
+   |
+LL | const C: i32 = 1i32;
+   |                ^^^^
 
 error[E0308]: mismatched types
   --> $DIR/const-scope.rs:2:15
@@ -17,6 +22,11 @@ LL |     let c: i32 = 1i8;
    |            ---   ^^^ expected `i32`, found `i8`
    |            |
    |            expected due to this
+   |
+help: change the type of the numeric literal from `i8` to `i32`
+   |
+LL |     let c: i32 = 1i32;
+   |                  ^^^^
 
 error[E0308]: mismatched types
   --> $DIR/const-scope.rs:6:17

src/test/ui/repeat_count.rs

@@ -22,6 +22,9 @@ fn main() {
     let f = [0_usize; -1_isize];
     //~^ ERROR mismatched types
     //~| expected `usize`, found `isize`
+    let f = [0; 4u8];
+    //~^ ERROR mismatched types
+    //~| expected `usize`, found `u8`
     struct G {
         g: (),
     }

src/test/ui/repeat_count.stderr

@@ -29,7 +29,7 @@ LL |     let e = [0; "foo"];
    |                 ^^^^^ expected `usize`, found `&str`
 
 error[E0308]: mismatched types
-  --> $DIR/repeat_count.rs:28:17
+  --> $DIR/repeat_count.rs:31:17
    |
 LL |     let g = [0; G { g: () }];
    |                 ^^^^^^^^^^^ expected `usize`, found struct `main::G`
@@ -39,24 +39,25 @@ error[E0308]: mismatched types
    |
 LL |     let f = [0; -4_isize];
    |                 ^^^^^^^^ expected `usize`, found `isize`
-   |
-help: you can convert an `isize` to `usize` and panic if the converted value wouldn't fit
-   |
-LL |     let f = [0; (-4_isize).try_into().unwrap()];
-   |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error[E0308]: mismatched types
   --> $DIR/repeat_count.rs:22:23
    |
 LL |     let f = [0_usize; -1_isize];
    |                       ^^^^^^^^ expected `usize`, found `isize`
-   |
-help: you can convert an `isize` to `usize` and panic if the converted value wouldn't fit
-   |
-LL |     let f = [0_usize; (-1_isize).try_into().unwrap()];
-   |                       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-error: aborting due to 8 previous errors
+error[E0308]: mismatched types
+  --> $DIR/repeat_count.rs:25:17
+   |
+LL |     let f = [0; 4u8];
+   |                 ^^^ expected `usize`, found `u8`
+   |
+help: change the type of the numeric literal from `u8` to `usize`
+   |
+LL |     let f = [0; 4usize];
+   |                 ^^^^^^
+
+error: aborting due to 9 previous errors
 
 Some errors have detailed explanations: E0308, E0435.
 For more information about an error, try `rustc --explain E0308`.