From: "ko1 (Koichi Sasada) via ruby-core" <ruby-core@...>
Date: 2024-06-07T02:08:54+00:00
Subject: [ruby-core:118225] [Ruby master Bug#20043] `defined?` checks for method existence but only sometimes

Issue #20043 has been updated by ko1 (Koichi Sasada).


Here is a survey which node (in Prism) are used in `defined?(expr)` (the node of `expr`)
https://gist.github.com/ko1/b31517a5037d55bbe50e7f12d79b9fc1

I understand the usage of :constant_read_node, :constant_path_node, :instance_variable_read_node, :call_node,         :global_variable_read_node, :class_variable_read_node, :forwarding_super_node, :numbered_reference_read_node, :yield_node, :super_node, but not sure other nodes.

https://gist.github.com/ko1/fcf98c0fec3aecfdae7f1a4d91ee5626
is a survey of other nodes.

There are misusages like `defined? C ? x : y` (expected `defined?(C) ? x : y` but `defined?(C ? x : y)` which always returns `"expression"`.


----------------------------------------
Bug #20043: `defined?` checks for method existence but only sometimes
https://bugs.ruby-lang.org/issues/20043#change-108721

* Author: tenderlovemaking (Aaron Patterson)
* Status: Open
* ruby -v: ruby 3.3.0dev (2023-12-05T21:25:34Z master 56eccb350b) [arm64-darwin23]
* Backport: 3.0: UNKNOWN, 3.1: UNKNOWN, 3.2: UNKNOWN
----------------------------------------
When an expression is passed to `defined?`, it will _sometimes_ check if a method in a sub-expression is defined and sometimes it won't.

For example:

```
$ ./miniruby -e'p defined?(a)'
nil
$ ./miniruby -e'p defined?([a])'
nil
```

In the above case, Ruby will check whether or not the method `a` is defined, and it returns `nil`.  However, if you use a splat, it will not check:

```
$ ./miniruby -e'p defined?([*a])'
"expression"
```

The same thing seems to happen with method parameters:

```
$ ./miniruby -e'p defined?(itself)'
"method"
$ ./miniruby -e'p defined?(itself(a))'
nil
$ ./miniruby -e'p defined?(itself(*a))'
"method"
```

Oddly, `defined?` will check contents of arrays, but _won't_ check contents of hashes:

```
$ ./miniruby -e'p defined?([[[[a]]]])'
nil
$ ./miniruby -e'p defined?({ a => a })'
"expression"
```

I think all of the cases that refer to `a` should check whether or not `a` is defined regardless of splats or hashes.

---Files--------------------------------
clipboard-202312191405-owvpy.png (27.3 KB)
general - ruby-lang - 4 new items - Slack 2023-12-19 16-10-39.png (100 KB)


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