[ruby/prism] Raise `void value expression` in begin clauses

In some cases Prism was either not raising an appropriate `void value
expression` error, or raising that error when the syntax is considered
valid.

To fix this Prism needs to check whether we have other clauses on the
`begin` rather than just returning `cast->statements`.

* If the `cast->statements` are null and the `cast->ensure_clause` is
not null, set the code to `cast->ensure_clause`
* else
  * If there is a `cast->rescue_clause`
    * Check if `cast->statements` are null and `cast->rescue_clause->statements`
    are null, and return `NULL`
    * Check if there is an `else_clause`, and set the node to
      `cast->else_clause`.
    * Otherwise return `cast->statements` as the node
  * return `cast->statements` as the node

See tests for test cases. Note I took these directly from CRuby so if
desired I can delete them since the test will now pass. This only fixes
one test in the `test_parse` file, taking failures from 14 to 13.

This fixes `TestParse#test_void_value_in_rhs` and is related to
issue #2791.

https://github.com/ruby/prism/commit/398152b412

1 files changed, 35 insertions, 0 deletions

diff --git a/test/prism/errors_test.rb b/test/prism/errors_test.rb
index 50417e476e..5f4acb0120 100644
--- a/test/prism/errors_test.rb
+++ b/test/prism/errors_test.rb
@@ -1630,6 +1630,41 @@ module Prism
       ]
     end
 
+    def test_void_value_expression_in_begin_statement
+      source = <<~RUBY
+        x = return 1
+        x = return, 1
+        x = 1, return
+        x, y = return
+        x = begin return ensure end
+        x = begin ensure return end
+        x = begin return ensure return end
+        x = begin return; rescue; return end
+        x = begin return; rescue; return; else return end
+        x = begin; return; rescue; retry; end
+      RUBY
+
+      message = 'unexpected void value expression'
+      assert_errors expression(source), source, [
+        [message, 4..12],
+        [message, 17..23],
+        [message, 34..40],
+        [message, 48..54],
+        [message, 65..71],
+        [message, 100..106],
+        [message, 121..127],
+        [message, 156..162],
+        [message, 222..228],
+        [message, 244..250],
+      ]
+
+      refute_error_messages("x = begin return; rescue; end")
+      refute_error_messages("x = begin return; rescue; return; else end")
+      refute_error_messages("x = begin; rescue; retry; end")
+      refute_error_messages("x = begin 1; rescue; retry; ensure; end")
+      refute_error_messages("x = begin 1; rescue; return; end")
+    end
+
     def test_void_value_expression_in_def
       source = <<~RUBY
         def (return).x