Further improve diagnostics for expressions in pattern position
Follow-up of #118625, see #121697.
```rs
fn main() {
match 'b' {
y.0.0.1.z().f()? as u32 => {},
}
}
```
Before:
```
error: expected one of `=>`, ``@`,` `if`, or `|`, found `.`
--> src/main.rs:3:10
|
3 | y.0.0.1.z().f()? as u32 => {},
| ^ expected one of `=>`, ``@`,` `if`, or `|`
```
After:
```
error: expected a pattern, found an expression
--> src/main.rs:3:9
|
3 | y.0.0.1.z().f()? as u32 => {},
| ^^^^^^^^^^^^^^^^^^^^^^^ arbitrary expressions are not allowed in patterns
|
help: consider moving the expression to a match arm guard
|
3 | val if val == y.0.0.1.z().f()? as u32 => {},
| ~~~ +++++++++++++++++++++++++++++++++
help: consider extracting the expression into a `const`
|
2 + const VAL: /* Type */ = y.0.0.1.z().f()? as u32;
3 ~ match 'b' {
4 ~ VAL => {},
|
help: consider wrapping the expression in an inline `const` (requires `#![feature(inline_const_pat)]`)
|
3 | const { y.0.0.1.z().f()? as u32 } => {},
| +++++++ +
```
---
r? fmease
`@rustbot` label +A-diagnostics +A-parser +A-patterns +C-enhancement
df7f77811c