More info on infinite recursion

From: scottlburson (Gyro_at_[hidden])
Date: 2005-05-06 18:58:38

Hi group,

I am running into an infinite recursion in bjam when trying to build
Boost (1.32.0, on a SuSE 9.0 system). It appears that others have
also encountered this problem (see e.g. message 9256).

I have spent a few hours poking at it, and have some interesting
information, though not a solution.

`tools/build/v1/allyourbase.jam' contains these lines:

local top = [ root-paths $($(gTOP)) : [ PWD ] ] ;
if ! $(gINCLUDED($(JAMRULES:R=$(top))))
{
# Gated entry.

gINCLUDED($(JAMRULES:R=$(top))) = TRUE ; # <--

# Include it.

project-root ;
include $(JAMRULES:R=$(top)) ;
}

Being new to Boost and Jam, I have not taken the time to understand
how the code in this file works. I have discovered, however, that the
variable `gTOP' is never acquiring a nonnull value, nor is `top'. 
Evidently, because `top' never has a value, the assignment marked
"<--" fails. Anyway, despite the attempt at a "gated entry", as the
comment puts it, an infinite recursion results.

So my question for someone who understands this code is, what is
supposed to happen? And why would `gTOP' fail to acquire a value? 
Where is its value supposed to come from?

Any clues appreciated.

-- Scott