Fix collapsible_if FP on block stmt before expr

[profetia]

Closes #14722

changelog: [collapsible_if] fix FP on block stmt before expr

[rustbot]

r? @dswij

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[Alexendoo]

Nominating this to be in the same release as #14481 if needed

[samueltardieu]

Nominating this to be in the same release as #14481 if needed

Thanks, this was indeed introduced (and not caught by existing checks) during the conversion into a late lint.

[samueltardieu]

r? @samueltardieu

[samueltardieu]

The fix looks complicated. It looks like there is a guard missing in expr_block(), adding it may be enough to fix the problem and would greatly simplify this PR:

     match block.stmts {
         [] => block.expr,
-        [stmt] => {
+        [stmt] if block.expr.is_none() => {

[profetia]

Thanks. Im changing it back now.

[samueltardieu]

LGTM, thanks

[flip1995]

Same as: #14733 (comment)

The likelihood of a beta backport right after the release increases.