[ruby-core:106638] [Ruby master Bug#18396] An unexpected "hash value omission" syntax error when without parentheses call expr follows

Issue #18396 has been updated by mame (Yusuke Endoh).


I think this patch will change the meaning of `p x:` as matz said.

```diff
diff --git a/parse.y b/parse.y
index 0ff3ddbb4e..d92decfc1c 100644
--- a/parse.y
+++ b/parse.y
@@ -9290,7 +9290,7 @@ parser_yylex(struct parser_params *p)
        p->token_seen = token_seen;
        c = (IS_lex_state(EXPR_BEG|EXPR_CLASS|EXPR_FNAME|EXPR_DOT) &&
             !IS_lex_state(EXPR_LABELED));
-       if (c || IS_lex_state_all(EXPR_ARG|EXPR_LABELED)) {
+       if (c || (IS_lex_state_all(EXPR_ARG|EXPR_LABELED) && p->lex.paren_nest)) {
             if (!fallthru) {
                 dispatch_scan_event(p, tIGNORED_NL);
             }
```

Example:

```
x = 1
p x:
2

#=> {:x=>2}  # before the patch
#=> {:x=>1}  # after the patch
```

If the expression is within parentheses, the behavior is be changed.

```
x = 1
p(x:
2
)

#=> {:x=>2}  # not changed
```

Before introducing this change, we definitely need to prepare migration path. The following patch will keep the current behavior and print a warning against code that will be changed. This can be used to estimate the impact of the compatibility.

```diff
diff --git a/parse.y b/parse.y
index 0ff3ddbb4e..73deae8627 100644
--- a/parse.y
+++ b/parse.y
@@ -9291,6 +9291,9 @@ parser_yylex(struct parser_params *p)
        c = (IS_lex_state(EXPR_BEG|EXPR_CLASS|EXPR_FNAME|EXPR_DOT) &&
             !IS_lex_state(EXPR_LABELED));
        if (c || IS_lex_state_all(EXPR_ARG|EXPR_LABELED)) {
+            if (IS_lex_state_all(EXPR_ARG|EXPR_LABELED) && !p->lex.paren_nest) {
+               rb_warn0("keyword label followed by newline without parentheses will be changed in Ruby 3.3");
+            }
             if (!fallthru) {
                 dispatch_scan_event(p, tIGNORED_NL);
             }
```

----------------------------------------
Bug #18396: An unexpected "hash value omission" syntax error when without parentheses call expr follows
https://bugs.ruby-lang.org/issues/18396#change-95310

* Author: koic (Koichi ITO)
* Status: Open
* Priority: Normal
* ruby -v: ruby 3.1.0dev (2021-12-07T23:18:11Z master 4a3e7984bf) [x86_64-darwin19]
* Backport: 2.6: UNKNOWN, 2.7: UNKNOWN, 3.0: UNKNOWN
----------------------------------------
## Summary

I encountered an unexpected "hash value omission" syntax error when parentheses call expression follows:

```ruby
% cat example.rb
foo key:
foo arg
```

```console
% ruby -cv /tmp/b.rb
ruby 3.1.0dev (2021-12-07T23:18:11Z master 4a3e7984bf) [x86_64-darwin19]
example.rb:2: syntax error, unexpected local variable or method, expecting `do' or '{' or '('
foo arg
```

## Additional Information

The following is a traditional usage.

```ruby
# No errors.
foo key: key
foo arg
```

A syntax error is unexpectedly raised when hash value omission argument without parentheses is followed by a method call without parentheses.

```ruby
# No errors is expected, but syntax error is raised.
foo key:
foo arg
```

No error occurs if any of the calls have parentheses.

```ruby
# No errors.
foo(key:)
foo arg
```

```ruby
# Also no errors.
foo key:
foo(arg)
```

No error occurs when calling alone.

```ruby
# No errors.
foo key:
```

I encountered this error while trying to apply hash value omission to  RSpec code of a real-world application (proprietary) .
But this is a new Ruby 3.1 syntax and may not be supported yet. Thank you.



-- 
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