[Man-db-devel] erroneous error message with .pso/.so?

[Alexis Huxley]

Sorry for posting to the devel list, but I didn't find a more appropriate
forum.

In order to allow some paths mentioned in a man page I've written to be
dynamically defined (depending on user's environment), I've added '-U' 
to the arguments of groff and nroff in manpath.config:

chifferi$ grep roff /etc/manpath.config 
DEFINE  troff   groff -U -mandoc
DEFINE  nroff   nroff -U -mandoc
chifferi$

and this works fine. 

Here's a simplified example of what I'm doing:

chifferi$ cat simple-test.1 
.pso sh -c 'echo .ds include_dir /home/alexis/experiment/include'
.so \*[include_dir]/simple-test-include.1
.TH SIMPLE\-TEST 1 "Wed Jul 29 18:23:40 CEST 2015"
.SH NAME
simple\-test \- perform a simple test
.br
.ne 5
.SH SYNOPSIS
.B simple\-test
.br
.ne 5
.SH DESCRIPTION
If the next line is '/home/alexis/experiment/include' then .pso directives are
being executed:
.IP
\*[include_dir]
.PP
If the next line says is 'simple test' then .so directives are being executed:
.IP
\*[simple_test_macro]
chifferi$

and:

chifferi$ cat include/simple-test-include.1 
.eo
.de simple_test_macro
.nop simple test
..
.ec
chifferi$

and man'ing it works as expected:

SIMPLE-TEST(1)                                          SIMPLE-TEST(1)



NAME
       simple-test - perform a simple test

SYNOPSIS
       simple-test

DESCRIPTION
       If the next line is '/home/alexis/experiment/include' then .pso
       directives are being executed:

              /home/alexis/experiment/include

       If the next line says is 'simple test' then .so directives  are
       being executed:

              simple test




                     Wed Jul 29 18:23:40 CEST 2015      SIMPLE-TEST(1)
chifferi$ 

But now here's the same command with stdout discarded instead of stderr:

chifferi$ man ./simple-test.1 >/dev/null 
man: can't open \*[include_dir]/simple-test-include.1: No such file or directory
man: -:2: warning: failed .so request
chifferi$ 

But, as the first output from man indicates, the man command clearly
*is* opening simple-test-include.1. So is the man command erroneously 
reporting an error? :-)

On the assumption that man must be calling *roff *twice*, with '-U'
one time and without it the other, I straced it to look for the *roff
calls:

chifferi$ strace -qfe trace=execve man ./simple-test.1 2>&1 | grep roff
[pid 24501] execve("/home/alexis/bin/chifferi/nroff", ["nroff", "-U", 
"-mandoc", "-rLL=70n", "-rLT=70n", "-Tascii"], [/* 46 vars */] <unfinished ...>
[pid 24501] execve("/usr/local/bin/nroff", ["nroff", "-U", "-mandoc", 
"-rLL=70n", "-rLT=70n", "-Tascii"], [/* 46 vars */] <unfinished ...>
[pid 24501] execve("/usr/bin/nroff", ["nroff", "-U", "-mandoc", "-rLL=70n", 
"-rLT=70n", "-Tascii"], [/* 46 vars */]) = 0
[pid 24504] execve("/usr/bin/groff", ["groff", "-mtty-char", "-Tascii", "-U", 
"-mandoc", "-rLL=70n", "-rLT=70n"], [/* 47 vars */]) = 0
[pid 24505] execve("/usr/bin/troff", ["troff", "-U", "-mtty-char", "-mandoc", 
"-rLL=70n", "-rLT=70n", "-Tascii"], [/* 48 vars */] <unfinished ...>
chifferi$ 

Running these commands directly (not the first two, which is man 
looking in the wrong dirs in $PATH) no error message is displayed.

So what's going on? Any advice appreciated. Thanks.

Alexis