Now that statements can be matched and replaced (#6587) some usecases
require expressions to be replaced with statements as well. This happens
when something that can ambiguously be an expression or statement like
`if` and loop blocks appear in the last position of a block, as trailing
expression. In this case a replacement pattern of the form `if
foo(){$a();}==>>$a();` will only substitute `if` blocks in the list of
statements but not if they (implicitly) end up in the trailing
expression, where they are not wrapped by an EXPR_STMT (but the pattern
and template are, as parsing only succeeds for the `stmt ==>> stmt`
case).
Instead of adding two rules that match an expression - and emit
duplicate matching errors - allow the template for expressions to be a
statement if it fails to parse as an expression.
We might want to provide more efficient impls for check if usages
exist, limiting the search, filtering and cancellation, so let's
violate YAGNI a bit here.
5758: SSR: Explicitly autoderef and ref placeholders as needed r=matklad a=davidlattimore
Structural search replace now inserts *, & and &mut in the replacement to match any auto[de]ref in the matched code.
e.g. `$a.foo() ==>> bar($a)` might convert `x.foo()` to `bar(&mut x)`
Co-authored-by: David Lattimore <dml@google.com>
