From: "Eregon (Benoit Daloze) via ruby-core" <ruby-core@...>
Date: 2023-12-06T12:55:39+00:00
Subject: [ruby-core:115605] [Ruby master Bug#20043] `defined?` checks for method existence but only sometimes

Issue #20043 has been updated by Eregon (Benoit Daloze).


I wonder if `defined?` should only be defined for constant paths and method call without arguments, e.g. `defined?(RubyVM.keep_script_lines)`.
Is there any use case for `defined?` besides those?

IOW, I think the simpler `defined?` is the better (less complexity in Ruby implementations, I think little value in practice).
That could mean don't recurse into nested nodes or so, except for constant paths.

----------------------------------------
Bug #20043: `defined?` checks for method existence but only sometimes
https://bugs.ruby-lang.org/issues/20043#change-105536

* Author: tenderlovemaking (Aaron Patterson)
* Status: Open
* Priority: Normal
* 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.



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