bug#33195: 27.0.50; user-login-name has no group-login-name

bug#33195: 27.0.50; user-login-name has no group-login-name

[Jules Tamagnan]

I've found it difficult to go from an integer group id to the name of
that group. I've looked at the source for `user-login-name` and
`system-groups` and could not find a way to do what I needed.

As such I think it would be great to add a function to do that. This is
my first change to emacs C code, so I'm unsure how to make an argument
not be optional. I have signed the FSF CLA for emacs.

diff --git a/src/editfns.c b/src/editfns.c
index 84cfbb2..c25164a 100644
--- a/src/editfns.c
+++ b/src/editfns.c
@@ -1352,6 +1352,24 @@ of the user with that uid, or nil if there is no such user.  */)
   return (pw ? build_string (pw->pw_name) : Qnil);
 }

+DEFUN ("group-name", Fgroup_name, Sgroup_name, 0, 1, 0,
+       doc: /* If argument GID is an integer or a float, return the login name
+of the group with that GID, or nil if there is no such GID.  */)
+  (Lisp_Object gid)
+{
+  struct group *gr;
+  gid_t id;
+
+  if (NILP (gid))
+    return Qnil;
+
+  CONS_TO_INTEGER (gid, gid_t, id);
+  block_input ();
+  gr = getgrgid (id);
+  unblock_input ();
+  return (gr ? build_string (gr->gr_name) : Qnil);
+}
+
 DEFUN ("user-real-login-name", Fuser_real_login_name, Suser_real_login_name,
        0, 0, 0,
        doc: /* Return the name of the user's real uid, as a string.
@@ -5517,6 +5535,7 @@ functions if all the text being accessed has this property.  */);
   defsubr (&Sinsert_byte);

   defsubr (&Suser_login_name);
+  defsubr (&Sgroup_name);
   defsubr (&Suser_real_login_name);
   defsubr (&Suser_uid);
   defsubr (&Suser_real_uid);


In GNU Emacs 27.0.50 (build 6, x86_64-pc-linux-gnu, GTK+ Version 3.18.9)
 of 2018-10-29 built on jat-delphix-lap
Repository revision: 5b5f441ff8986800aa5f175bb5db2dd90e642a3a
Windowing system distributor 'The X.Org Foundation', version 11.0.11804000
System Description:	Ubuntu 16.04.5 LTS

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bug#33195: 27.0.50; user-login-name has no group-login-name

[Eli Zaretskii]

> From: Jules Tamagnan <jtamagnan@gmail.com>
> Date: Mon, 29 Oct 2018 11:52:17 -0700
> 
> I've found it difficult to go from an integer group id to the name of
> that group. I've looked at the source for `user-login-name` and
> `system-groups` and could not find a way to do what I needed.
> 
> As such I think it would be great to add a function to do that.

Thanks.  Please allow me a few comments:

Please always provide a ChangeLog-style commit log message describing
your changes.  The file CONTRIBUTE has more about that.

> I'm unsure how to make an argument not be optional.

You want the argument NOT to be optional?  If so, make this:

> +DEFUN ("group-name", Fgroup_name, Sgroup_name, 0, 1, 0,

say this instead:

> +DEFUN ("group-name", Fgroup_name, Sgroup_name, 1, 1, 0,

See the node "Writing Emacs Primitives" in the ELisp manual, which
describes how to use the DEFUN macro.

> +DEFUN ("group-name", Fgroup_name, Sgroup_name, 0, 1, 0,
> +       doc: /* If argument GID is an integer or a float, return the login name
> +of the group with that GID, or nil if there is no such GID.  */)
> +  (Lisp_Object gid)
> +{
> +  struct group *gr;
> +  gid_t id;
> +
> +  if (NILP (gid))
> +    return Qnil;

Wouldn't it be more useful to return user's group name when the
argument is nil or omitted?

Also, would you please write a couple of simple tests for this new
function?

Finally, this function should be announced in NEWS and documented in
the ELisp manual.

bug#33195: 27.0.50; user-login-name has no group-login-name

[Jules Tamagnan]

[-- Attachment #1: Type: text/plain, Size: 2376 bytes --]


First off I want to say thank you for your review and your time

Eli Zaretskii <eliz@gnu.org> writes:

>> From: Jules Tamagnan <jtamagnan@gmail.com>
>> Date: Mon, 29 Oct 2018 11:52:17 -0700
>>
>> I've found it difficult to go from an integer group id to the name of
>> that group. I've looked at the source for `user-login-name` and
>> `system-groups` and could not find a way to do what I needed.
>>
>> As such I think it would be great to add a function to do that.
>
> Thanks.  Please allow me a few comments:
>
> Please always provide a ChangeLog-style commit log message describing
> your changes.  The file CONTRIBUTE has more about that.
>
>> I'm unsure how to make an argument not be optional.
>
> You want the argument NOT to be optional?  If so, make this:
>
>> +DEFUN ("group-name", Fgroup_name, Sgroup_name, 0, 1, 0,
>
> say this instead:
>
>> +DEFUN ("group-name", Fgroup_name, Sgroup_name, 1, 1, 0,
>
> See the node "Writing Emacs Primitives" in the ELisp manual, which
> describes how to use the DEFUN macro.

Turns out there is a word for not optional... required :)

>> +DEFUN ("group-name", Fgroup_name, Sgroup_name, 0, 1, 0,
>> +       doc: /* If argument GID is an integer or a float, return the login name
>> +of the group with that GID, or nil if there is no such GID.  */)
>> +  (Lisp_Object gid)
>> +{
>> +  struct group *gr;
>> +  gid_t id;
>> +
>> +  if (NILP (gid))
>> +    return Qnil;
>
> Wouldn't it be more useful to return user's group name when the
> argument is nil or omitted?

I always thought that user could have many groups, for example if I run

    $ groups $(id -un)

I get a long list of groups. I'm not sure if I misunderstood your
statement or the desired behavior but for the moment I think a separate
function would be best for this. Or maybe the `system-groups` function
could be modified to take in a UID and then list groups for that UID,
then if no argument is passed in, it would return the full list of
system-groups as it does now.

> Also, would you please write a couple of simple tests for this new
> function?

I've tried my hand at writing a test for this but am dubious it will
pass on all machines, I believe it should work on gnu/linux

> Finally, this function should be announced in NEWS and documented in
> the ELisp manual.

I've added a short entry in NEWS under "Lisp Changes in Emacs 27.1" and
in os.texi


[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
[-- Attachment #2: Patch --]
[-- Type: text/x-diff, Size: 2932 bytes --]

From 671c8b55d80743a13d6fda99f5181558cd56eea6 Mon Sep 17 00:00:00 2001
From: Jules Tamagnan <jtamagnan@gmail.com>
Date: Tue, 30 Oct 2018 10:22:03 -0700
Subject: [PATCH] src/editfns.c (group-name): New function.

---
 doc/lispref/os.texi       |  5 +++++
 etc/NEWS                  |  3 +++
 src/editfns.c             | 16 ++++++++++++++++
 test/src/editfns-tests.el |  7 +++++++
 4 files changed, 31 insertions(+)

diff --git a/doc/lispref/os.texi b/doc/lispref/os.texi
index cb33757..dc32958 100644
--- a/doc/lispref/os.texi
+++ b/doc/lispref/os.texi
@@ -1230,6 +1230,11 @@ User Identification
 return value is @code{nil}.
 @end defun
 
+@defun user-login-name &optional gid
+This runction returns the group name that corresponds to @var{gid},
+or @code{nil} if there is no such group.
+@end defun
+
 
 @node Time of Day
 @section Time of Day
diff --git a/etc/NEWS b/etc/NEWS
index 226ae1e..a0bcbb5 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -1228,6 +1228,9 @@ where there's no better alternative.  We believe that the incorrect
 uses of this function all but disappeared by now, so we are
 un-obsoleting it.
 
++++
+** New function 'group-name' returns a group name based on a group-GID
+
 \f
 * Changes in Emacs 27.1 on Non-Free Operating Systems
 
diff --git a/src/editfns.c b/src/editfns.c
index e995b38..15a0fa7 100644
--- a/src/editfns.c
+++ b/src/editfns.c
@@ -1143,6 +1143,21 @@ of the user with that uid, or nil if there is no such user.  */)
   return (pw ? build_string (pw->pw_name) : Qnil);
 }
 
+DEFUN ("group-name", Fgroup_name, Sgroup_name, 1, 1, 0,
+       doc: /* If argument GID is an integer or a float, return the login name
+of the group with that gid, or nil if there is no such GID.  */)
+  (Lisp_Object gid)
+{
+  struct group *gr;
+  gid_t id;
+
+  CONS_TO_INTEGER (gid, gid_t, id);
+  block_input ();
+  gr = getgrgid (id);
+  unblock_input ();
+  return (gr ? build_string (gr->gr_name) : Qnil);
+}
+
 DEFUN ("user-real-login-name", Fuser_real_login_name, Suser_real_login_name,
        0, 0, 0,
        doc: /* Return the name of the user's real uid, as a string.
@@ -4487,6 +4502,7 @@ it to be non-nil.  */);
   defsubr (&Sinsert_byte);
 
   defsubr (&Suser_login_name);
+  defsubr (&Sgroup_name);
   defsubr (&Suser_real_login_name);
   defsubr (&Suser_uid);
   defsubr (&Suser_real_uid);
diff --git a/test/src/editfns-tests.el b/test/src/editfns-tests.el
index 17b2c51..6ee0ab0 100644
--- a/test/src/editfns-tests.el
+++ b/test/src/editfns-tests.el
@@ -351,4 +351,11 @@ transpose-test-get-byte-positions
     (should (equal (format "%-#50.40x" v3)
                    "-0x000000003ffffffffffffffe000000000000000        "))))
 
+(ert-deftest group-name ()
+  (let ((list `((0 . "root")
+                (1000 . ,(user-login-name 1000))
+                (1212345 . nil))))
+    (dolist (test list)
+      (should (equal (group-name (car test)) (cdr test))))))
+
 ;;; editfns-tests.el ends here
-- 
2.7.4

bug#33195: 27.0.50; user-login-name has no group-login-name

[Jules Tamagnan]

[-- Attachment #1: Type: text/plain, Size: 94 bytes --]

I noticed that I had marked GID as optional in the manual, below is a
patch with that fixed.


[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
[-- Attachment #2: Patch-2 --]
[-- Type: text/x-diff, Size: 2922 bytes --]

From 5c67d0177ba14428e6e3f5acdaf34c2be7ee93be Mon Sep 17 00:00:00 2001
From: Jules Tamagnan <jtamagnan@gmail.com>
Date: Tue, 30 Oct 2018 10:22:03 -0700
Subject: [PATCH] src/editfns.c (group-name): New function.

---
 doc/lispref/os.texi       |  5 +++++
 etc/NEWS                  |  3 +++
 src/editfns.c             | 16 ++++++++++++++++
 test/src/editfns-tests.el |  7 +++++++
 4 files changed, 31 insertions(+)

diff --git a/doc/lispref/os.texi b/doc/lispref/os.texi
index cb33757..6d1b3f3 100644
--- a/doc/lispref/os.texi
+++ b/doc/lispref/os.texi
@@ -1230,6 +1230,11 @@ User Identification
 return value is @code{nil}.
 @end defun
 
+@defun user-login-name gid
+This runction returns the group name that corresponds to @var{gid},
+or @code{nil} if there is no such group.
+@end defun
+
 
 @node Time of Day
 @section Time of Day
diff --git a/etc/NEWS b/etc/NEWS
index 226ae1e..a0bcbb5 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -1228,6 +1228,9 @@ where there's no better alternative.  We believe that the incorrect
 uses of this function all but disappeared by now, so we are
 un-obsoleting it.
 
++++
+** New function 'group-name' returns a group name based on a group-GID
+
 \f
 * Changes in Emacs 27.1 on Non-Free Operating Systems
 
diff --git a/src/editfns.c b/src/editfns.c
index e995b38..15a0fa7 100644
--- a/src/editfns.c
+++ b/src/editfns.c
@@ -1143,6 +1143,21 @@ of the user with that uid, or nil if there is no such user.  */)
   return (pw ? build_string (pw->pw_name) : Qnil);
 }
 
+DEFUN ("group-name", Fgroup_name, Sgroup_name, 1, 1, 0,
+       doc: /* If argument GID is an integer or a float, return the login name
+of the group with that gid, or nil if there is no such GID.  */)
+  (Lisp_Object gid)
+{
+  struct group *gr;
+  gid_t id;
+
+  CONS_TO_INTEGER (gid, gid_t, id);
+  block_input ();
+  gr = getgrgid (id);
+  unblock_input ();
+  return (gr ? build_string (gr->gr_name) : Qnil);
+}
+
 DEFUN ("user-real-login-name", Fuser_real_login_name, Suser_real_login_name,
        0, 0, 0,
        doc: /* Return the name of the user's real uid, as a string.
@@ -4487,6 +4502,7 @@ it to be non-nil.  */);
   defsubr (&Sinsert_byte);
 
   defsubr (&Suser_login_name);
+  defsubr (&Sgroup_name);
   defsubr (&Suser_real_login_name);
   defsubr (&Suser_uid);
   defsubr (&Suser_real_uid);
diff --git a/test/src/editfns-tests.el b/test/src/editfns-tests.el
index 17b2c51..6ee0ab0 100644
--- a/test/src/editfns-tests.el
+++ b/test/src/editfns-tests.el
@@ -351,4 +351,11 @@ transpose-test-get-byte-positions
     (should (equal (format "%-#50.40x" v3)
                    "-0x000000003ffffffffffffffe000000000000000        "))))
 
+(ert-deftest group-name ()
+  (let ((list `((0 . "root")
+                (1000 . ,(user-login-name 1000))
+                (1212345 . nil))))
+    (dolist (test list)
+      (should (equal (group-name (car test)) (cdr test))))))
+
 ;;; editfns-tests.el ends here
-- 
2.7.4

bug#33195: 27.0.50; user-login-name has no group-login-name

[Eli Zaretskii]

> From: Jules Tamagnan <jtamagnan@gmail.com>
> Cc: 33195@debbugs.gnu.org
> Date: Tue, 30 Oct 2018 11:28:16 -0700
> 
> I noticed that I had marked GID as optional in the manual, below is a
> patch with that fixed.

Thanks, I pushed this to the master branch, and I'm closing the bug
report.

Please note the following nits for the future:

 . Please include a ChangeLog-style commit log message, which names
   all the new/modified functions and nodes in the manuals.
 . Arguments to functions should be tested for validity, to avoid
   crashes if called with invalid arguments.
 . The first line a of a doc string should be a complete sentence
   shorter than 80 characters, so it fits on a single screen line, and
   it should mention all the mandatory arguments of the function.

bug#33195: 27.0.50; user-login-name has no group-login-name

[Glenn Morris]

Jules Tamagnan wrote:

> I've tried my hand at writing a test for this but am dubious it will
> pass on all machines, I believe it should work on gnu/linux
[...]
> +(ert-deftest group-name ()
> +  (let ((list `((0 . "root")
> +                (1000 . ,(user-login-name 1000))
> +                (1212345 . nil))))
> +    (dolist (test list)
> +      (should (equal (group-name (car test)) (cdr test))))))

This assumes that user 1000's primary group is the same as their login name.
This is not at all guaranteed, so I will remove it.
Eg it fails for me on rhel 7.5, and also on hydra.nixos.org, ref
https://hydra.nixos.org/eval/1488740

I guess that UID 0 is always the root group, but I wouldn't swear to it.
The 1212345 thing relies on UID 1212345 not existing.
It seems to me that this is fragile too.
So all in all, I'm not sure this test is very useful.

bug#33195: 27.0.50; user-login-name has no group-login-name

[Glenn Morris]

Glenn Morris wrote:

> This assumes that user 1000's primary group is the same as their login name.

Correction, it assumes gid 1000 exists and has the same name as uid 1000
has user name. Anyway, neither of these need be true.

bug#33195: 27.0.50; user-login-name has no group-login-name

[Jules Tamagnan]

Glenn Morris <rgm@gnu.org> writes:

> Glenn Morris wrote:
>
>> This assumes that user 1000's primary group is the same as their login name.
>
> Correction, it assumes gid 1000 exists and has the same name as uid 1000
> has user name. Anyway, neither of these need be true.

Hi Glenn, I totally agree with removing that test. I was very unsure
about how to test this change but it was my best effort. I would have
been surprised if it had worked on all machines. Thank you for dealing
with the fallout of my change and I'm sorry for any inconvenience.

Best,
Jules

bug#33195: 27.0.50; user-login-name has no group-login-name

[Glenn Morris]

No worries!

I think a better test might be something like checking for equality of:

Emacs: (group-name (group-gid))
shell: getent group GID | cut -d: -f1
 if and only if the latter returns non-zero

bug#33195: 27.0.50; user-login-name has no group-login-name

[Eli Zaretskii]

> From: Glenn Morris <rgm@gnu.org>
> Cc: Eli Zaretskii <eliz@gnu.org>,  33195@debbugs.gnu.org
> Date: Sat, 10 Nov 2018 13:36:47 -0500
> 
> Jules Tamagnan wrote:
> 
> > I've tried my hand at writing a test for this but am dubious it will
> > pass on all machines, I believe it should work on gnu/linux
> [...]
> > +(ert-deftest group-name ()
> > +  (let ((list `((0 . "root")
> > +                (1000 . ,(user-login-name 1000))
> > +                (1212345 . nil))))
> > +    (dolist (test list)
> > +      (should (equal (group-name (car test)) (cdr test))))))
> 
> This assumes that user 1000's primary group is the same as their login name.
> This is not at all guaranteed, so I will remove it.
> Eg it fails for me on rhel 7.5, and also on hydra.nixos.org, ref
> https://hydra.nixos.org/eval/1488740
> 
> I guess that UID 0 is always the root group, but I wouldn't swear to it.
> The 1212345 thing relies on UID 1212345 not existing.
> It seems to me that this is fragile too.
> So all in all, I'm not sure this test is very useful.

Maybe all platforms should use the same code as MS-Windows for this
test, then.

bug#33195: 27.0.50; user-login-name has no group-login-name

[Andreas Schwab]

On Nov 10 2018, Glenn Morris <rgm@gnu.org> wrote:

> I guess that UID 0 is always the root group, but I wouldn't swear to it.

GID 0 is typically called wheel on BSD.

Andreas.

-- 
Andreas Schwab, schwab@linux-m68k.org
GPG Key fingerprint = 7578 EB47 D4E5 4D69 2510  2552 DF73 E780 A9DA AEC1
"And now for something completely different."

bug#33195: 27.0.50; user-login-name has no group-login-name

[Glenn Morris]

Andreas Schwab wrote:

> On Nov 10 2018, Glenn Morris <rgm@gnu.org> wrote:
>
>> I guess that UID 0 is always the root group, but I wouldn't swear to it.
>
> GID 0 is typically called wheel on BSD.

Thanks for the info. I hope I've made this test more portable in c30f24d03d.