Trac #33167: Improve is_functional of lrs feature

From https://trac.sagemath.org/ticket/33101#comment:3 :

"''This was after a distclean. I had not explicitly installed lrslib, it
was on the system. If I understand the config.log correctly, the system
lrslib was not accepted by Sage. Yet, ptestlong runs the optional lrslib
tests.''"

{{{
## ------------------------------------------------------- ##
## Checking whether SageMath should install SPKG lrslib... ##
## ------------------------------------------------------- ##
configure:30190: checking whether any of gmp flint is installed as or
will be installed as SPKG
configure:30194: result: yes; install lrslib as well
configure:30296: no suitable system package found for SPKG lrslib
}}}

----

In this ticket, we add to the `is_functional` method a check
corresponding to the check made in `build/pkgs/lrslib/spkg-configure.m4`
so that if `lrslib` is not picked up by sagemath at configuration/build
time, then it is not picked up by sagemath at runtime or during
doctests.

URL: https://trac.sagemath.org/33167
Reported by: slabbe
Ticket author(s): Sébastien Labbé, Markus Wageringel
Reviewer(s): Matthias Koeppe

build/pkgs/lrslib/spkg-configure.m4

@@ -1,4 +1,7 @@
 SAGE_SPKG_CONFIGURE([lrslib], [
+    dnl Although lrs and lrsnash binaries are the only interfaces to lrslib that
+    dnl sagelib uses, the optional polymake package uses lrslib as a library, so
+    dnl the following DEPCHECK is needed.
     dnl System lrslib may already be 7.x, which may be compiled with FLINT
     SAGE_SPKG_DEPCHECK([gmp flint], [
         AC_CHECK_PROGS([LRSNASH], [lrsnash])

src/sage/features/lrs.py

@@ -3,11 +3,9 @@
 Feature for testing the presence of ``lrslib``
 """
 
-import os
 import subprocess
 
 from . import Executable, FeatureTestResult
-from sage.cpython.string import str_to_bytes, bytes_to_str
 
 
 class Lrs(Executable):
@@ -43,24 +41,49 @@ def is_functional(self):
             FeatureTestResult('lrslib', True)
         """
         from sage.misc.temporary_file import tmp_filename
+
+        # Check #1
         tf_name = tmp_filename()
-        with open(tf_name, 'wb') as tf:
-            tf.write(str_to_bytes("V-representation\nbegin\n 1 1 rational\n 1 \nend\nvolume"))
-        devnull = open(os.devnull, 'wb')
+        with open(tf_name, 'w') as tf:
+            tf.write("V-representation\nbegin\n 1 1 rational\n 1 \nend\nvolume")
         command = ['lrs', tf_name]
         try:
-            lines = bytes_to_str(subprocess.check_output(command, stderr=devnull))
-        except subprocess.CalledProcessError as e:
+            result = subprocess.run(command, capture_output=True, text=True)
+        except OSError as e:
+            return FeatureTestResult(self, False, reason='Running command "{}" '
+                        'raised an OSError "{}" '.format(' '.join(command), e))
+
+        if result.returncode:
             return FeatureTestResult(self, False,
-                reason="Call to `{command}` failed with exit code {e.returncode}.".format(command=" ".join(command), e=e))
+                reason="Call to `{command}` failed with exit code {result.returncode}.".format(command=" ".join(command), result=result))
 
         expected_list = ["Volume= 1", "Volume=1"]
-        if all(lines.find(expected) == -1 for expected in expected_list):
-            print(lines)
+        if all(result.stdout.find(expected) == -1 for expected in expected_list):
             return FeatureTestResult(self, False,
-                reason="Output of `{command}` did not contain the expected result {expected}.".format(
+                reason="Output of `{command}` did not contain the expected result {expected}; output: {result.stdout}".format(
                     command=" ".join(command),
-                    expected=" or ".join(expected_list)))
+                    expected=" or ".join(expected_list),
+                    result=result))
+
+        # Check #2
+        # Checking whether `lrsnash` can handle the new input format
+        # This test is currently done in build/pkgs/lrslib/spkg-configure.m4
+        tf_name = tmp_filename()
+        with open(tf_name, 'w') as tf:
+            tf.write("1 1\n \n 0\n \n 0\n")
+        command = ['lrsnash', tf_name]
+        try:
+            result = subprocess.run(command, capture_output=True, text=True)
+        except OSError as e:
+            return FeatureTestResult(self, False, reason='Running command "{}" '
+                        'raised an OSError "{}" '.format(' '.join(command), e))
+        if result.returncode:
+            return FeatureTestResult(self, False, reason='Running command "{}" '
+                        'returned non-zero exit status "{}" with stderr '
+                        '"{}" and stdout "{}".'.format(' '.join(result.args),
+                                                        result.returncode,
+                                                        result.stderr.strip(),
+                                                        result.stdout.strip()))
 
         return FeatureTestResult(self, True)