behaviour of "info" makes it hard to migrate to $prefix/share/info

[Bruno Haible]

Hi,

The way "info" interprets dir files makes it hard to migrate from
$prefix/info to $prefix/share/info. To reproduce:

- Install texinfo-4.8 with --prefix=/tmp/prefix
  This will create
    /tmp/prefix/info
    /tmp/prefix/info/dir
    /tmp/prefix/info/texinfo*

- Set
    $ export INFOPATH=/tmp/prefix/share/info:/tmp/prefix/info

- Try
    $ /tmp/prefix/bin/info texinfo
  Works: display the doc of texinfo-4.8.

- Install gcl-2.6.6 with --prefix=/tmp/prefix and changing the definition
  of INFO_DIR in gcl-2.6.6/makedefs to /tmp/prefix/share/info/.
  This will create
    /tmp/prefix/share/info
    /tmp/prefix/share/info/dir
    /tmp/prefix/share/info/gcl*
  (gcl-2.6.6 is one of the few programs that already install their doc
  in $prefix/share/info by default.)

- Try
    $ /tmp/prefix/bin/info texinfo
  Doesn't work: gives error "info: Cannot find node `Top'."

The /tmp/prefix/share/info/dir, created by GCL the old way (using
"echo ... >> dir" commands), looks like this:

========================= /tmp/prefix/share/info/dir =========================
* GCL Doc: (gcl-si.info).       GNU Common Lisp specific Documentation.
* GCL TK Doc: (gcl-tk.info).    TK window GCL interface.
* GCL Ansi Doc: (gcl.info).  Ansi Common Lisp Specification.
==============================================================================

Even if this file is malformed, there is no reason why info should not
try the other directories from $INFOPATH after /tmp/prefix/share/info.

If this file is malformed, the error message should mention it, through
something like
   "info: invalid contents of /tmp/prefix/share/info/dir: Cannot find node 
`Top'."
rather than
   "info: Cannot find node `Top'."
I mean, without a filename in the error message, the problem is hard to debug:
in the example above "info texinfo" broke although nothing in the directory
containing the texinfo info file had changed.

Bruno