`try_validation` unconditionally adds semicolons

[jyn514]

I tried this code (https://github.com/rust-lang/rust/blob/0da6d42f297642a60f2640ec313b879b376b9ad8/compiler/rustc_mir/src/interpret/validity.rs#L78-L96):

macro_rules! try_validation {
    ($e:expr, $where:expr,
     $( $( $p:pat )|+ => { $( $what_fmt:expr ),+ } $( expected { $( $expected_fmt:expr ),+ } )? ),+ $(,)?
    ) => {{
        match $e {
            Ok(x) => x,
            // We catch the error and turn it into a validation failure. We are okay with
            // allocation here as this can only slow down builds that fail anyway.
            $( $( Err(InterpErrorInfo { kind: $p, .. }) )|+ =>
                throw_validation_failure!(
                    $where,
                    { $( $what_fmt ),+ } $( expected { $( $expected_fmt ),+ } )?
                ),
            )+
            #[allow(unreachable_patterns)]
            Err(e) => Err::<!, _>(e)?,
        }
    }};
}

I expected to see this happen: The Err(e)? is replaced with return Err(e).

Instead, this happened: It's replaced with return Err(e);, causing a syntax error since this is an expression context.

error: expected one of `)`, `,`, `.`, `?`, or an operator, found `;`
   --> compiler/rustc_mir/src/interpret/validity.rs:97:18
    |
78  |  / macro_rules! try_validation {
79  |  |     ($e:expr, $where:expr,
80  |  |      $( $( $p:pat )|+ => { $( $what_fmt:expr ),+ } $( expected { $( $expected_fmt:expr ),+ } )? ),+ $(,)?
81  |  |     ) => {{
...    |
93  |  |             Err(e) => return Err(try_validation!(
    |  |__________________________________-
94  | ||                     self.ecx.memory.read_bytes(mplace.ptr, Size::from_bytes(len)),
95  | ||                     self.path,
96  | ||                     err_ub!(InvalidUninitBytes(..)) => { "uninitialized data in `str`" },
97  | ||                 );),
    | ||                 -^ expected one of `)`, `,`, `.`, `?`, or an operator
    | ||_________________|
    |  |                 in this macro invocation (#2)
98  |  |         }
99  |  |     }};
100 |  | }
    |  | -
    |  | |
    |  |_in this expansion of `try_validation!` (#1)
    |    in this expansion of `try_validation!` (#2)
...
341 | /                  try_validation!(
342 | |                      self.ecx.read_size_and_align_from_vtable(vtable),
343 | |                      self.path,
344 | |                      err_unsup!(ReadPointerAsBytes) => { "invalid size or align in vtable" },
345 | |                  );
    | |___________________- in this macro invocation (#1)

warning: returning an `Err(_)` with the `?` operator
   --> compiler/rustc_mir/src/interpret/validity.rs:93:23
    |
78  | / macro_rules! try_validation {
79  | |     ($e:expr, $where:expr,
80  | |      $( $( $p:pat )|+ => { $( $what_fmt:expr ),+ } $( expected { $( $expected_fmt:expr ),+ } )? ),+ $(,)?
81  | |     ) => {{
...   |
93  | |             Err(e) => Err::<!, _>(e)?,
    | |                       ^^^^^^^^^^^^^^^
94  | |         }
95  | |     }};
96  | | }
    | |_- in this expansion of `try_validation!`
...
310 | /                 try_validation!(
311 | |                     self.ecx.memory.check_ptr_access_align(
312 | |                         vtable,
313 | |                         3 * self.ecx.tcx.data_layout.pointer_size, // drop, size, align
...   |
325 | |                         { "too small vtable" },
326 | |                 );
    | |__________________- in this macro invocation
    |
    = note: `#[warn(clippy::try_err)]` on by default
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#try_err
help: try this
    |
93  |             Err(e) => return Err(try_validation!(
94  |                     self.ecx.memory.check_ptr_access_align(
95  |                         vtable,
96  |                         3 * self.ecx.tcx.data_layout.pointer_size, // drop, size, align
97  |                         Some(self.ecx.tcx.data_layout.pointer_align.abi),
98  |                         CheckInAllocMsg::InboundsTest,
  ...

Meta

• cargo clippy -V: clippy 0.0.212 (ffa2e7a 2020-10-24)

[jyn514]

Actually I think this is the same issue as #6234, clippy is expanding e to $e. But that seems really weird because e is a variable and not a macro parameter.