Re: [Tack-devel] ACK_HOME and em_path

[Carl E. C. <cec...@ya...>]

Greetings,
                Ok! Message well received... simply using ACK_HOME with no magic tricks then!!

Carl



-------- Original message --------
From: u-...@ae... 
Date: 2019/03/07  16:49  (GMT+08:00) 
To: Carl Eric Codere <cec...@ya...> 
Cc: tac...@li... 
Subject: Re: [Tack-devel] ACK_HOME and em_path 

Hello Carl Erik,

On Thu, Mar 07, 2019 at 01:10:06AM +0000, Carl Eric Codere via Tack-devel wrote:
> Greetings,
>               Is it ok if eventually em_path.h is completely removed and is replaced by something that is checked at runtime instead of compile time? I do feel that doing this at compile time gives a bit of a limit on moving the install directory.
> 
> For TMP_DIR, getenv() is used instead, this one is a no-brainer, and I already implemented it in the ANSI C porting.
> 
> Now for EM_DIR, I propose the following:
> * ACK_HOME environment variable would need to be set for it be used and should point to ACK install directory.

Consequently using a dedicated environment variable is good.

> Now the additional question, let us assume ACK_HOME is not set, do we simply fail, or do we try to check additional things, like the following:
> ** If argv[0] contains a path, from there find and set ACK_HOME by deducing the installation path?
> ** If argv[0] contains no path, search the PATH environment variable for the executable and from there deduce the installation path?

IMO (basically any) implicit heuristic search is harmful.

It makes un-/underconfigured installs deceptively look "right" and
leads to headaches when things assumed to "magically just work" subtly
work not exactly as one expected.

Neither argv[0] nor PATH are reliable pointers to the actually needed
resources, nor the path to the running executable, even when it could be
reliably found out on some platform.

Nor should they be assumed/constrained to be set up for such use,
because they also are under other unrelated constraints and carry or may
carry other important functions as well.

In other words, compiler development and system administration are
different domains, it is highly unreliable to make assumptions across
their borders.

As a matter of fact, I have to go out of my way to prevent possible harm
from gcc's resource guesses from its argv[0].

Please do not make ack act in such fashion.

Rune