[ruby-core:116151] [Ruby master Bug#20175] Broken File.dirname(__FILE__) in eval blocks

Issue #20175 has been updated by kiskoza (Zsolt Kozaroczy).


I see why `__FILE__` was an intended change, I'm going to change all my codes inside eval that depends on its value, thanks for pointing it out.

However, as `__dir__` returns nil instead of a string, it requires some changes to replace `File.dirname(__FILE__)` with `__dir__`.
Is it a viable option to return the already known directory inside evals? The change should be something like this:

```diff
diff --git a/vm_eval.c b/vm_eval.c
--- a/vm_eval.c
+++ b/vm_eval.c
@@ -2545,7 +2545,8 @@ rb_current_realfilepath(void)
             const char *const ptr = RSTRING_PTR(path);
             if (ptr[len - 1] == ')' &&
                 memcmp(ptr, "("EVAL_LOCATION_MARK, EVAL_LOCATION_MARK_LEN+1) == 0) {
-                return Qnil;
+                VALUE implicit_path = rb_str_substr(path, 1 + EVAL_LOCATION_MARK_LEN, len - 1);
+                return implicit_path;
             }
         }
```

and then the output would be this:

```ruby
# eval.rb
eval('puts file: __FILE__, dir: __dir__')
```

```bash
ruby /Codes/eval.rb
# {:file=>"(eval at /Codes/eval.rb:1)", :dir=>"/Codes"}
```

----------------------------------------
Bug #20175: Broken File.dirname(__FILE__) in eval blocks
https://bugs.ruby-lang.org/issues/20175#change-106156

* Author: kiskoza (Zsolt Kozaroczy)
* Status: Open
* Priority: Normal
* ruby -v: ruby 3.3.0 (2023-12-25 revision 5124f9ac75) [x86_64-linux]
* Backport: 3.0: UNKNOWN, 3.1: UNKNOWN, 3.2: UNKNOWN, 3.3: UNKNOWN
----------------------------------------
Since #19755 eval use caller location by default, however, it broke `File.dirname(__FILE__)` in some cases.

```ruby
# eval.rb
eval('puts file: __FILE__, dirname: File.dirname(__FILE__)')
```

Up to Ruby 3.2.2 it gave back the same results, even if it wasn't technically correct in some cases

```bash
## Ruby 3.2.2

ruby eval.rb
# {:file=>"(eval)", :dirname=>"."}

ruby ./eval.rb
# {:file=>"(eval)", :dirname=>"."}

cd folder && ruby ../eval.rb
# {:file=>"(eval)", :dirname=>"."}
# This one is not pointing to the right directory, but still returns a valid path

ruby /Codes/eval.rb
# {:file=>"(eval)", :dirname=>"."}
# This one is not pointing to the right directory, but still returns a valid path
```

In Ruby 3.3.0 (introduced in commit:43a5c19135), it gives back different paths, trying to point to the right directory, but it has the `(eval at ` prefix which makes it broken for codes expecting a valid path.

```bash
## Ruby 3.3.0

ruby eval.rb
# {:file=>"(eval at eval.rb:1)", :dirname=>"."}

ruby ./eval.rb
# {:file=>"(eval at ./eval.rb:1)", :dirname=>"(eval at ."}
# Broken path

cd folder && ruby ../eval.rb
# {:file=>"(eval at ../eval.rb:1)", :dirname=>"(eval at .."}
# This one is trying to point to the right directory, but it has a broken syntax

ruby /Codes/eval.rb
# {:file=>"(eval at /Codes/eval.rb:1)", :dirname=>"(eval at /Codes"}
# This one is trying to point to the right directory, but it has a broken syntax
```

I was able to reproduce it on current master as well.



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