From: "kddnewton (Kevin Newton) via ruby-core" <ruby-core@...>
Date: 2026-10-15T20:14:59+00:00
Subject: [ruby-core:127131] [Ruby Bug#22447] parse.y `-> do ... end` COND state

Issue #22447 has been reported by kddnewton (Kevin Newton).

----------------------------------------
Bug #22447: parse.y `-> do ... end` COND state
https://bugs.ruby-lang.org/issues/22447

* Author: kddnewton (Kevin Newton)
* Status: Open
* Backport: 3.3: UNKNOWN, 3.4: UNKNOWN, 4.0: UNKNOWN
----------------------------------------
With parse.y, `do`-blocks inside a `-> do ... end` lambda body are rejected when the lambda appears in a `while`/`until`/`for` condition:

```ruby
while -> do foo do end end; end
# => syntax error, unexpected 'do' for condition, expecting 'end' or dummy end
```

The same body is accepted outside a condition, and with brace delimiters inside one:

```ruby
-> do foo do end end                  # OK
while -> { foo do end }; end          # OK
while (foo do end); end               # OK
while def m; foo do end; end; end     # OK
while -> do foo do end end; end       # SyntaxError
until -> do foo do end end; end       # SyntaxError
for x in -> do foo do end end do end  # SyntaxError
```

Nesting a `-> do` lambda in an unparenthesized lambda parameter default also triggers it:

```ruby
while -> a = -> do foo do end end do end; end  # SyntaxError
```

Pretty much everywhere this kind of thing happens there is a pair of `CMDARG_PUSH(0)` and `COND_PUSH(0)`, but lambda is missing the latter. I think that's really all that needs to change to make this work:

```diff
--- a/parse.y
+++ b/parse.y
@@ lambda           : tLAMBDA[lpar]
                   f_larglist[args]
                     {
                         CMDARG_PUSH(0);
+                        COND_PUSH(0);
                     }
                   lambda_body[body]
                     {
@@
                         restore_block_exit(p, $al
+                        COND_POP();
                         CMDARG_POP();
```

It looks like this was fixed in other places (test_methoddef_in_cond and test_classdef_in_cond both test this kind of thing).



-- 
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