E0308 arising from unary/binary `-` grammar ambiguity

Code

fn f(x: bool)->i32 {
    if x { 5 } else { 10 } - 3
}

Current output

Compiling playground v0.0.1 (/playground)
error[E0308]: mismatched types
 --> src/main.rs:2:12
  |
2 |     if x { 5 } else { 10 } - 3
  |     -------^--------------
  |     |      |
  |     |      expected `()`, found integer
  |     expected this to be `()`
  |
help: you might have meant to return this value
  |
2 |     if x { return 5; } else { 10 } - 3
  |            ++++++  +

error[E0308]: mismatched types
 --> src/main.rs:2:23
  |
2 |     if x { 5 } else { 10 } - 3
  |     ------------------^^--
  |     |                 |
  |     |                 expected `()`, found integer
  |     expected this to be `()`
  |
help: you might have meant to return this value
  |
2 |     if x { 5 } else { return 10; } - 3
  |                       ++++++   +

For more information about this error, try `rustc --explain E0308`.
error: could not compile `playground` (bin "playground") due to 2 previous errors

Desired output

help: parentheses are required to parse this as an expression
  |
2 |     (if x { 5 } else { 10 }) - 3
  |     +                      +

help: a semicolon is required to discard this value
  |
2 |     if x { 5 } else { 10 }; - 3
  |                           +

Rationale and extra context

This arises from a grammar ambiguity regarding block expressions and unary vs. binary -.

A brief search of open issues found #116128 which arises from a similar ambiguity between boolean or and an empty closure parameter list.

This issue was discovered during an URLO conversation

Other cases

If another operator, like '+', is used, a help message about adding parens is already emitted:

fn f(x: bool)->i32 {
    if x { 5 } else { 10 } + 3
}

Partial output:

error: leading `+` is not supported
 --> src/main.rs:2:28
  |
2 |     if x { 5 } else { 10 } + 3
  |                            ^ unexpected `+`
  |
help: parentheses are required to parse this as an expression
  |
2 |     (if x { 5 } else { 10 }) + 3
  |     +                      +

error[E0308]: mismatched types
 --> src/main.rs:2:12
  |
2 |     if x { 5 } else { 10 } + 3
  |     -------^--------------
  |     |      |
  |     |      expected `()`, found integer
  |     expected this to be `()`
  |
help: you might have meant to return this value
  |
2 |     if x { return 5; } else { 10 } + 3
  |            ++++++  +

error[E0308]: mismatched types
 --> src/main.rs:2:23
  |
2 |     if x { 5 } else { 10 } + 3
  |     ------------------^^--
  |     |                 |
  |     |                 expected `()`, found integer
  |     expected this to be `()`
  |
help: you might have meant to return this value
  |
2 |     if x { 5 } else { return 10; } + 3
  |                       ++++++   +

Anything else?

No response

Reproduce the example in src/main.rs and compare its diagnostics with the '+' variant, which already emits the parentheses suggestion. Trace the rustc diagnostic path for E0308 and make the '-' case produce the requested parentheses and semicolon-help output, then verify both examples.