ruby-core

Issue #18780 has been updated by shyouhei (Shyouhei Urabe).


Updating the header document.

```patch
From b968f277386649b7531a8999be54eacf3c599cdb Mon Sep 17 00:00:00 2001
From: 卜部昌平 <[email protected]>
Date: Thu, 21 Jul 2022 18:00:04 +0900
Subject: [PATCH] [DOC] update rb_eval_string() document.

---
 include/ruby/internal/eval.h | 33 ++++++++++++++++++++++++++++++---
 template/Doxyfile.tmpl       |  1 +
 2 files changed, 31 insertions(+), 3 deletions(-)

diff --git a/include/ruby/internal/eval.h b/include/ruby/internal/eval.h
index 34a53849da..b7ab66515f 100644
--- a/include/ruby/internal/eval.h
+++ b/include/ruby/internal/eval.h
@@ -28,10 +28,12 @@ RBIMPL_SYMBOL_EXPORT_BEGIN()
 
 RBIMPL_ATTR_NONNULL(())
 /**
- * Evaluates the given string in an isolated binding.
+ * Evaluates the given string.
  *
- * Here  "isolated"  means  that  the   binding  does  not  inherit  any  other
- * bindings.  This behaves same as the binding for required libraries.
+ * In case  it is called  from within a  C-backended method, the  evaluation is
+ * done under  the current binding.  However  there can be no  method.  On such
+ * situation this  function evaluates  in an  isolated binding,  like `require`
+ * runs in a separate one.
  *
  * `__FILE__`  will  be  `"(eval)"`,  and  `__LINE__`  starts  from  1  in  the
  * evaluation.
@@ -39,6 +41,31 @@ RBIMPL_ATTR_NONNULL(())
  * @param[in]  str            Ruby code to evaluate.
  * @exception  rb_eException  Raises an exception on error.
  * @return     The evaluated result.
+ *
+ * @internal
+ *
+ * @shyouhei's old table about the birth and growth of this function:
+ *
+ * At  the beginning,  there  was no  rb_eval_string().   @shyouhei heard  that
+ * @shugo, author of  Apache httpd's mod_ruby module, requested  @matz for this
+ * API.  He wanted a way so that mod_ruby can evaluate ruby scripts one by one,
+ * separately, in each different contexts.  So  this function was made.  It was
+ * designed to be a global interpreter entry point like ruby_run_node().
+ *
+ * The  way it  is implemented  however  allows extension  libraries (not  just
+ * programs like  Apache httpd) to call  this function.  Because its  name says
+ * nothing  about the  initial design,  people  started to  think of  it as  an
+ * orthodox  way  to  call  ruby  level  `eval`  method  from  their  extension
+ * libraries.  Even our `extension.rdoc` has had a description of this function
+ * basically according to this understanding.
+ *
+ * The old  (mod_ruby like) usage still  works.  But over time,  usages of this
+ * function from extension libraries got  popular, while mod_ruby faded out; is
+ * no  longer maintained  now.  Devs  decided to  actively support  both.  This
+ * function  now auto-detects  how  it is  called, and  switches  how it  works
+ * depending on it.
+ *
+ * @see https://bugs.ruby-lang.org/issues/18780
  */
 VALUE rb_eval_string(const char *str);
 
diff --git a/template/Doxyfile.tmpl b/template/Doxyfile.tmpl
index 36c0b1c8d6..502e171384 100644
--- a/template/Doxyfile.tmpl
+++ b/template/Doxyfile.tmpl
@@ -274,6 +274,7 @@ ALIASES               += "old{1}=Old name of @ref \1.^^@deprecated Use @ref \1 i
 ALIASES               += "shyouhei=\@shyouhei"
 ALIASES               += "ko1=\@ko1"
 ALIASES               += "matz=\@matz"
+ALIASES               += "shugo=\@shugo"
 
 # Set the OPTIMIZE_OUTPUT_FOR_C tag to YES if your project consists of C sources
 # only. Doxygen will then generate output that is more tailored for C. For
-- 
2.17.1


```

----------------------------------------
Bug #18780: Incorrect binding receiver for C API rb_eval_string()
https://bugs.ruby-lang.org/issues/18780#change-98431

* Author: daveola (David Stellar)
* Status: Open
* Priority: Normal
* ruby -v: ruby 2.7.0p0 (2019-12-25 revision 647ee6f091) [x86_64-linux]
* Backport: 2.7: UNKNOWN, 3.0: UNKNOWN, 3.1: UNKNOWN
----------------------------------------

% ruby -v
ruby 2.7.0p0 (2019-12-25 revision 647ee6f091) [x86_64-linux]

(Though looking at the source code this problem still exists in ruby 3.0)


The rb_eval_string() is seemingly capable of everything that eval is capable of, with one slight deviation.  The binding is oddly setup to be correct except for the receiver/self.

This means that while these both act the same:

  ruby:    eval("puts someLocalVariable")
  C API:   rb_eval_string("puts someLocalVariable")

These do not:

  ruby:   eval("puts @someInstanceVar")
  C API:  rb_eval_string("puts @someInstanceVar")    # nil

And this is because these do not work:

  ruby:   eval("puts self")                          # self of calling context
  ruby:   eval("puts binding().receiver")            # self of calling context
  C API:  rb_eval_string("puts self")                # main
  C API:  rb_eval_string("puts binding().receiver")  # main

We can see the problem in the MRI source in ruby_eval_string_from_file() which has:

    return eval_string_with_cref(rb_vm_top_self(), rb_str_new2(str), NULL, file, 1);

We've passed in rb_vm_top_self instead of the correct 'self'

Although possibly the issue is in the API itself with the fact that there's no way to plumb through the receiver that you are given in the C extension method function call, i.e.:

        // My C extension that calls eval and knows what it's 'self' is.
        VALUE method_myCMethod(int argc, VALUE *argv, VALUE self) {
                rb_eval_string("...");  // <- no way to be given self?
        }

Having said that, rb_eval_string is able to determine the vast majority of the binding context, since it correctly builds the binding() object *except* that the receiver is set to main, so perhaps this is something that *can* be determined.  It is something that the builtin eval is able to do, after all.  So possibly this is just a failure with MRI.  I don't have other rubies to test.  (I'm on ruby 2.7.0 but the source relevant to this hasn't changed.)

I would argue this is a bug, because we are essentially given a corrupted result from binding() - one where we may have access to the local variables of an instance method, but one where the self itself is not properly set.  That's not an actual legit binding state in the ruby code.




-- 
https://bugs.ruby-lang.org/

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