From: "Eregon (Benoit Daloze) via ruby-core" <ruby-core@...>
Date: 2025-12-15T20:52:53+00:00
Subject: [ruby-core:124219] [Ruby Bug#21784] Proc#source_location start column seems strange for -> {}

Issue #21784 has been updated by Eregon (Benoit Daloze).


I made a PR to fix this: https://github.com/ruby/ruby/pull/15568
Looking at https://github.com/ruby/ruby/pull/9872/files it's clear in Prism it was just done to be compatible with parse.y.

And in parse.y it's probably not intentional to use the beginning of the args as the start location for the scope, the whole `-> {}` defines a new scope.
In fact the lambda itself already had the right location with `RubyVM::AbstractSyntaxTree`, just the scope within it had the wrong location:
```
$ RUBYOPT=--parser=parse.y irb                       
irb(main):001> l = -> { a }
=> #<Proc:0x00007fc276e9d8c0 (irb):1 (lambda)>
irb(main):002> a=RubyVM::AbstractSyntaxTree.of(l)
=> 
(LAMBDA@1:4-1:12
...
irb(main):003> a.locations
=> 
[#<RubyVM::AbstractSyntaxTree::Location:@1:4-1:12>,
 #<RubyVM::AbstractSyntaxTree::Location:@1:4-1:6>,
 #<RubyVM::AbstractSyntaxTree::Location:@1:7-1:8>,
 #<RubyVM::AbstractSyntaxTree::Location:@1:11-1:12>]
irb(main):004> a
=> 
(LAMBDA@1:4-1:12
   (SCOPE@1:6-1:12
    tbl: []
    args:
      (ARGS@1:6-1:6
       pre_num: 0
       pre_init: nil
       opt: nil
       first_post: nil
       post_num: 0
       post_init: nil
       rest: nil
       kw: nil
       kwrest: nil
       block: nil)
    body: (VCALL@1:9-1:10 :a)))
```

----------------------------------------
Bug #21784: Proc#source_location start column seems strange for -> {}
https://bugs.ruby-lang.org/issues/21784#change-115702

* Author: Eregon (Benoit Daloze)
* Status: Open
* ruby -v: ruby 4.0.0dev (2025-12-14T07:11:02Z master 711d14992e) +PRISM [x86_64-linux]
* Backport: 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN
----------------------------------------
```
$ ruby -e 'p -> { a }.source_location' 
["-e", 1, 4, 1, 10]
```
So it considers the stabby lambda to be at:
```ruby
p -> { a }.source_location
    ^^^^^^
```
Note it starts at a whitespace after the `->`.
I think it should just include the `->`, i.e. return `["-e", 1, 2, 1, 10]`.
Or possibly start at the `{`, i.e. return `["-e", 1, 3, 1, 10]`.
But starting on a whitespace like here seems really strange, it looks like a bug.

It's the same result with `--parser=parse.y`, so I don't show it.

---

For context:
For Procs/block it looks like this:
```
$ ruby -e 'p proc { a }.source_location'
["-e", 1, 7, 1, 12]
```
```ruby
p proc { a }.source_location
       ^^^^^
```
This looks fine.
The block could of course be given to any other method so it won't always be `proc` in front.
Maybe it could include the method too (so it would return start column 2 here), I think either is fine.

For `for` blocks it looks like this:
```
$ ruby -e '                                                             
def self.each(&b); yield b; end;
for b in self
  42
end
p b.source_location'
["-e", 3, 0, 5, 3]
```
That is, it covers the entire `for` expression from `for` until `end`.
I think that's good and fine as-is.

For `def` methods it covers everything from `def` to `end` (or end of line for `def m = 42`), as expected.



-- 
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