Re: Ruby 1.8.6 binding value after "if" expression evaluation

A slightly shorter patch by sinking common code:

Index: eval.c
===================================================================
--- eval.c    (revision 15769)
+++ eval.c    (working copy)
@@ -3038,15 +3038,15 @@
     RETURN(Qfalse);

       case NODE_IF:
-    EXEC_EVENT_HOOK(RUBY_EVENT_LINE, node, self,
-            ruby_frame->last_func,
-            ruby_frame->last_class);
     if (RTEST(rb_eval(self, node->nd_cond))) {
         node = node->nd_body;
     }
     else {
         node = node->nd_else;
     }
+    EXEC_EVENT_HOOK(RUBY_EVENT_LINE, node, self,
+            ruby_frame->last_func,
+            ruby_frame->last_class);
     goto again;

       case NODE_WHEN:


On Thu, Mar 13, 2008 at 10:13 PM, Rocky Bernstein <[e-mail]>
wrote:

> I think I've found why this is happening. The trace hook for NODE_IF is
> getting called a before the expression evaluation occurs when it should be
> called afterwards. Attached is a patch. I will also update  #18722<http://rubyforge.org/tracker/index.php?func=detail&aid=18722&group_id=426&atid=22040>with this information.
>
> Thanks.
>
> On Thu, Mar 13, 2008 at 2:32 PM, Rocky Bernstein <
> [e-mail]> wrote:
>
> > Thanks. The output you report matches what I get in 1.8.6 and suggests
> > where to start looking for a bug. I'm not sure this is strictly related to
> > blocks. In particular try this:
> >
> > x = 6.2*1 if
> >   x=6.1
> >
> > The line break after the "if" is intentional since it more clearly shows
> > which part gets run when. In this code,
> > first there are two stops on the x=6.1 presumably before and after the
> > assignment. But by the time of the c-call to multiply 6.2*1, the value
> > of x is 6.1. It is like some sort of register flushing that is going
> > before the c-call, but again that's pure guess.
> >
> > On Thu, Mar 13, 2008 at 12:59 PM, Yemi I. D. Bedu <[e-mail]>
> > wrote:
> >
> > >  Hello,
> > >
> > >  I tried this and it has to do with implicit / explicit block. Also I
> > > expanded example:
> > >
> > >
> > >
> > > p RUBY_VERSION
> > >
> > >
> > >
> > > def trace_func(event, file, line, id, binding, klass, *)
> > >
> > >   printf("%s:%d (%s) x=%s\n", file, line, event, eval("x", binding))
> > >
> > > end
> > >
> > >
> > >
> > > set_trace_func method(:trace_func).to_proc
> > >
> > >
> > >
> > > x=2
> > >
> > > (x=3.2) if x=3.1
> > >
> > > begin x=4.2 end if x=4.1
> > >
> > > x=5.2 if x=5.1
> > >
> > > x=6.2*1 if x=6.1*1
> > >
> > > if x=7.1 then x=7.2 end
> > >
> > > x=8
> > >
> > > x=9
> > >
> > >
> > >
> > > My Results were:
> > >
> > >
> > >
> > > "1.8.2"
> > >
> > >
> > >
> > > tt.rb:9 (line) x=
> > >
> > >
> > >
> > > tt.rb:10 (line) x=2
> > >
> > > tt.rb:10 (line) x=2
> > >
> > > tt.rb:10 (line) x=3.1
> > >
> > >
> > >
> > > tt.rb:11 (line) x=3.2
> > >
> > > tt.rb:11 (line) x=3.2
> > >
> > > tt.rb:11 (line) x=4.1
> > >
> > >
> > >
> > > tt.rb:12 (line) x=4.2
> > >
> > > tt.rb:12 (line) x=4.2
> > >
> > >
> > >
> > > tt.rb:13 (line) x=5.2
> > >
> > > tt.rb:13 (line) x=5.2
> > >
> > > tt.rb:13 (c-call) x=5.2
> > >
> > > tt.rb:13 (c-return) x=5.2
> > >
> > > tt.rb:13 (c-call) x=6.1
> > >
> > > tt.rb:13 (c-return) x=6.1
> > >
> > >
> > >
> > > tt.rb:14 (line) x=6.2
> > >
> > > tt.rb:14 (line) x=6.2
> > >
> > > tt.rb:14 (line) x=7.1
> > >
> > >
> > >
> > > tt.rb:15 (line) x=7.2
> > >
> > >
> > >
> > > tt.rb:16 (line) x=8
> > >
> > >
> > >
> > > You would need to either have parens, explicit block or use the other
> > > if form to get that last firing from the trace. It seems to token out each
> > > expression unit on a line and then call eval to get the previous lines
> > > value. I don't know if you can confirm this on your 1.8.6 install. The
> > > lines with the multiply do func calls so they eval before going into the new
> > > env and when the come back. You might want to have a more complex expression
> > > execute like a list comprehension or a map. Good day.
> > >
> > > Yemi Bedu
> > >
> > > P&R Fasteners, Inc.
> > > P&R Castings, LLC.
> > > 325 Pierce St
> > > Somerset, NJ 08873
> > > (T) 732-302-3600
> > > (F) 732-302-3636
> > >   ------------------------------
> > >
> > > *From:* Rocky Bernstein [mailto:[e-mail]]
> > > *Sent:* Wednesday, March 12, 2008 11:21 PM
> > > *To:* [e-mail]
> > > *Subject:* Ruby 1.8.6 binding value after "if" expression evaluation
> > >
> > >
> > >
> > > Here's another trace hook weirdness that I've encountered.
> > >
> > > Consider this program and its output:
> > >
> > > def trace_func(event, file, line, id, binding, klass, *)
> > >   printf("%s:%d (%s) x=%s\n", file, line, event, eval("x", binding))
> > > end
> > > set_trace_func method(:trace_func).to_proc
> > > x=5
> > > x=6.2 if x=6.1
> > > x=7
> > >
> > >
> > > $ ruby bug2.rb
> > > bug2.rb:6: warning: found = in conditional, should be ==
> > > bug2.rb:5 (line) x=
> > > bug2.rb:6 (line) x=5
> > > bug2.rb:6 (line) x=5
> > > bug2.rb:7 (line) x=6.2
> > >
> > > Why does x appear to have value 5 the second time on line 7 rather
> > > than 6.1?
> > >
> > > Looking at eval.c what's supposed to happen (I think) is that the
> > > trace hook is called before the expression (x=6.1) is evaluated and
> > > then called before the assignment "x=6.2" in which case it should have
> > > value 6.1, not 5.
> > >
> > > Can anyone explain why this happens?
> > >
> > > Again this is ruby 1.8.6
> > >
> >
> >
>