gprolog DESTDIR and optional install directories

[Keri Harris]

Hi

I ran into the following issue when installing gprolog-1.5.0 when DESTDIR is set:

In src/Makefile.in the target install directories are defined such that DESTDIR is respected:

INSTALL_DIR    = $(DESTDIR)@INSTALL_DIR@

LINKS_DIR      = $(DESTDIR)@LINKS_DIR@

DOC_DIR        = $(DESTDIR)@DOC_DIR@

HTML_DIR       = $(DESTDIR)@HTML_DIR@

EXAMPLES_DIR   = $(DESTDIR)@EXAMPLES_DIR@

So far so good. However, there are special checks in the Makefile to see if these destination directories are disabled by way of them being set to "none", e.g:

    if test $(LINKS_DIR) != none; then ...

    if test $(DOC_DIR) != none; then ...

    if test $(HTML_DIR) != none; then ...

    if test $(EXAMPLES_DIR) != none; then ...

If DESTDIR is set, then the above comparisons will always succeed even if the the configure script has set the directories to none. In this case we are comparing "$(DESTDIR)none" vs "none".

There are two ways of addressing this:

1. compare against $(DESTDIR)none. e.g:

    if test $(LINKS_DIR) != $(DESTDIR)none; then ...

2. compare the directories without DESTDIR against none. e.g:

    if test @LINKS_DIR@ != none; then ...

I've attached a patch I'm using on Gentoo Linux. (The patch applies cleanly on top of the gprolog-1.5.0-links.patch [1]).

Thanks

Keri

[1] https://mail.gnu.org/archive/html/bug-prolog/2021-07/msg00001.html

gprolog-1.5.0-destdir.patch
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