PR# 14451 Compiler crashes if HOME environment variable not set

If the HOME environment variable is not set on Unix, compiler crashes.
It should instead report an error if it requires that this variable be set
and should perhaps check that it is an existing directory.

Here is the top few stack frames from the trace:

-------------------------------------------------------------------------------
Class / Object      Routine                Nature of exception           Effect
-------------------------------------------------------------------------------
ES_EIFFEL_LAYOUT    user_directory_name @6 Segmentation violation:
<0000000004F91EA8>  (From EIFFEL_ENV)      Operating system signal.      Exit
-------------------------------------------------------------------------------
ES_EIFFEL_LAYOUT    user_directory_name @6
<0000000004F91EA8>  (From EIFFEL_ENV)      Routine failure.              Exit
-------------------------------------------------------------------------------
ES_EIFFEL_LAYOUT    user_files_path @3
<0000000004F91EA8>  (From EIFFEL_ENV)      Routine failure.              Exit
-------------------------------------------------------------------------------
ES_EIFFEL_LAYOUT    check_environment_variable @43
<0000000004F91EA8>  (From EIFFEL_ENV)      Routine failure.              Exit
-------------------------------------------------------------------------------

Setup to use Eiffel on Unix, the do "unsetenv HOME"
Run "ec".  Compiler crashes.

One more comment on this: the current solution is worse than the old behavior
(a crash).  

Just in case you're not familiar with this, the operating system
does not know about "~".  If you check whether directory "~" exists in a
C program, you will get a "no" answer unless there is a directory whose actual
name is "~" in the current working directory.  When you give commands to the
shell, it translates "~" into the value of the "home" shell variable and then
passes the translated value to the OS.  The "home" shell variable
is set by the shell at some point from the value of the HOME environment
variable, which gets its value either inherited from a parent process or via
a call to getpwuid.

I assumed you already know this, but if you do then I don't understand why
you would return "~" for the value of the home directory in path_name.c if
the HOME environment variable is not set, since it can't possibly work as
intended.

I don't know how likely it is that HOME is undefined, but it seems to me that
Eiffel should do something reasonable if it isn't.  The only reasonable thing
to do on a Unix platform is to call `getpwuid' to find out what the home
directory is.  There is no other way to find out, as far as I know.  The
shell has to call getpwuid or getpwuid_r once at login to set the "home"
shell variable and the HOME environment variable values.

I don't think the C code to do this is very complicated.  There is a similar
example in file.c routine `file_owner'.

Another option would be to return "" (empty string) if HOME is undefined
but presumably this would violate the expectation of callers of 
{EXECUTION_ENVIRONMENT}.home_directory_name.  If you did this, then estudio
could refuse to run if HOME is not set, just as it does if ISE_EIFFEL is not
set.  I don't think this is a great solution.

A third option is to raise an exception if HOME environment variable is not
set, but then all programs would have to c
....
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I thought of using something along those lines, but the likelyhood that HOME is not defined is pretty low, isn't it? Moreover, in some of what I've read ~ will be $HOME is set, otherwise the value of your passwd file, but I must say it is not clear where to find reference documentation on that topic.

I don't think the solution (returning "~" if HOME environment variable is not
set) is going to fly.  "~" is translated by the shell to the user's home
directory, but the shell is not involved here.  I think the correct solution
is to call getpwuid (or its reentrant counterpart getpwuid_r, if available),
passing the value of either `getuid()' (real user id) or `geteuid()' (effective
user ID).  Then get the value of the pw_dir field from the returned 
struct passwd * pointer, call RTMS on it and return that value.

If I manually set the HOME environment variable to "~", the command line
compiler runs OK but estudio asks me for an activation code, presumably
because it can't find my license since it doesn't know where my home directory
is.

Reopening report.

David, this problem has been addressed in rev#78008