modules: append trailing delimiter to MANPATH when set (#36678)

Update modulefile templates to append a trailing delimiter to MANPATH
environment variable, if the modulefile sets it.

With a trailing delimiter at ends of MANPATH's value, man will search
the system man pages after searching the specific paths set.

Using append-path/append_path to add this element, the module tool
ensures it is appended only once. When modulefile is unloaded, the
number of append attempt is decreased, thus the trailing delimiter is
removed only if this number equals 0.

Disclaimer: no path element should be appended to MANPATH by generated
modulefiles. It should always be prepended to ensure this variable's
value ends with the trailing delimiter.

Fixes #11355.

share/spack/templates/modules/modulefile.lua

@@ -84,6 +84,10 @@ setenv("{{ cmd.name }}", "{{ cmd.value }}")
 unsetenv("{{ cmd.name }}")
 {% endif %}
 {% endfor %}
+{# Make sure system man pages are enabled by appending trailing delimiter to MANPATH #}
+{% if has_manpath_modifications %}
+append_path("MANPATH", "", ":")
+{% endif %}
 {% endblock %}
 
 {% block footer %}

share/spack/templates/modules/modulefile.tcl

@@ -58,6 +58,10 @@ unsetenv {{ cmd.name }}
 {% endif %}
 {#  #}
 {% endfor %}
+{# Make sure system man pages are enabled by appending trailing delimiter to MANPATH #}
+{% if has_manpath_modifications %}
+append-path --delim ":" MANPATH ""
+{% endif %}
 {% endblock %}
 
 {% block footer %}