Bug #21139: Prism and parse.y parses `it = it` differently

• Status: Assigned
• Assignee: prism
• Target version: -
• ruby -v: ruby 3.5.0dev (2025-02-14T16:49:52Z master ee181d1bb7) +PRISM [x86_64-linux]
• Backport: 3.1: UNKNOWN, 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN

[tompng (tomoya ishida)]

# ruby --parser=parse.y -e "42.tap { it = it; p it }"
nil
# ruby --parser=prism -e "42.tap { it = it; p it }"
42

[matz (Yukihiro Matsumoto)]

Assignment to it should be prohibited in the long run. Temporarily, I vote for Prism behavior.

Matz.

By the way, how can I clear assignee of the issue on Redmine?

[nobu (Nobuyoshi Nakada)]

matz (Yukihiro Matsumoto) wrote in #note-1:

Assignment to it should be prohibited in the long run. Temporarily, I vote for Prism behavior.

1. Currently, it is an ordinary local variable if assigned syntactically.
2. And a local variable is nil before assigned, even in its RHS, at the runtime.

The behavior in parse.y obeys above principles.

Do you want to change the rule 1, make it always special?

[nobu (Nobuyoshi Nakada)]

• Related to Bug #21137: Compound assignment operator with "it" parsed differently between parse.y and prism added

[nobu (Nobuyoshi Nakada)]

• Related to Bug #21138: The modifier expression with "it" is parsed differently in parse.y and Prism, which is unexpected in both. added