34185: take care of joined features

src/sage/doctest/control.py

@@ -1351,7 +1351,7 @@ def run(self):
             sage: with open(filename, 'w') as f:
             ....:     f.write(test_hide)
             ....:     f.close()
-            402
+            729
             sage: DF = DocTestDefaults(hide='buckygen,all')
             sage: DC = DocTestController(DF, [filename])
             sage: DC.run()
@@ -1360,7 +1360,7 @@ def run(self):
             Features to be detected: ...
             Doctesting 1 file.
             sage -t ....py
-                [2 tests, ... s]
+                [4 tests, ... s]
             ----------------------------------------------------------------------
             All tests passed!
             ----------------------------------------------------------------------
@@ -1378,7 +1378,7 @@ def run(self):
             Features to be detected: ...
             Doctesting 1 file.
             sage -t ....py
-                [2 tests, ... s]
+                [4 tests, ... s]
             ----------------------------------------------------------------------
             All tests passed!
             ----------------------------------------------------------------------
@@ -1438,6 +1438,9 @@ def run(self):
                     if f.is_present():
                         f.hide()
                         self.options.hidden_features.add(f)
+                        for g in f.joined_features():
+                            if g.name in self.options.optional:
+                                self.options.optional.discard(g.name)
 
             for o in self.options.disabled_optional:
                 try:
@@ -1561,5 +1564,12 @@ def stringify(x):
 ...
 sage: len(list(graphs.fusenes(2)))  # optional benzene
 1
+sage: from sage.matrix.matrix_space import get_matrix_class
+sage: get_matrix_class(GF(25,'x'), 4, 4, False, 'meataxe')
+Failed lazy import:
+sage.matrix.matrix_gfpn_dense is not available.
+...
+sage: get_matrix_class(GF(25,'x'), 4, 4, False, 'meataxe') # optional meataxe
+<class 'sage.matrix.matrix_gfpn_dense.Matrix_gfpn_dense'>
 {}
 """.format('r"""', '"""')

src/sage/features/__init__.py

@@ -275,6 +275,28 @@ def resolution(self):
         self._cache_resolution = "\n".join(lines)
         return self._cache_resolution
 
+    def joined_features(self):
+        r"""
+        Return a list of features joined with ``self``.
+
+        OUTPUT:
+
+        A (possibly empty) list of instances of :class:`Feature`.
+
+        EXAMPLES::
+
+            sage: from sage.features.graphviz import Graphviz
+            sage: Graphviz().joined_features()
+            [Feature('dot'), Feature('neato'), Feature('twopi')]
+            sage: from sage.features.interfaces import Mathematica
+            sage: Mathematica().joined_features()
+            []
+        """
+        from sage.features.join_feature import JoinFeature
+        if isinstance(self, JoinFeature):
+            return self._features
+        return []
+
     def is_standard(self):
         r"""
         Return whether this feature corresponds to a standard SPKG.

src/sage/features/join_feature.py

@@ -94,3 +94,50 @@ def is_functional(self):
             if not test:
                 return test
         return FeatureTestResult(self, True)
+
+    def hide(self):
+        r"""
+        Hide this feature and all its joined features.
+
+        EXAMPLES:
+
+            sage: from sage.features.sagemath import sage__groups
+            sage: f = sage__groups()
+            sage: f.hide()
+            sage: f._features[0].is_present()
+            FeatureTestResult('sage.groups.perm_gps.permgroup', False)
+
+            sage: f.require()
+            Traceback (most recent call last):
+            ...
+            FeatureNotPresentError: sage.groups is not available.
+            Feature `sage.groups` is hidden.
+            Use method `unhide` to make it available again.
+        """
+        for f in self._features:
+            f.hide()
+        super(JoinFeature, self).hide()
+
+    def unhide(self):
+        r"""
+        Hide this feature and all its joined features.
+
+        EXAMPLES:
+
+            sage: from sage.features.sagemath import sage__groups
+            sage: f = sage__groups()
+            sage: f.hide()
+            sage: f.is_present()
+            FeatureTestResult('sage.groups', False)
+            sage: f._features[0].is_present()
+            FeatureTestResult('sage.groups.perm_gps.permgroup', False)
+
+            sage: f.unhide()
+            sage: f.is_present()    # optional sage.groups
+            FeatureTestResult('sage.groups', True)
+            sage: f._features[0].is_present() # optional sage.groups
+            FeatureTestResult('sage.groups.perm_gps.permgroup', True)
+        """
+        for f in self._features:
+            f.unhide()
+        super(JoinFeature, self).unhide()

src/sage/misc/lazy_import.pyx

@@ -248,13 +248,18 @@ cdef class LazyImport():
             if finish_startup_called:
                 warn(f"Option ``at_startup=True`` for lazy import {self._name} not needed anymore")
 
+        feature = self._feature
         try:
             self._object = getattr(__import__(self._module, {}, {}, [self._name]), self._name)
         except ImportError as e:
-            if self._feature:
+            if feature:
                 raise FeatureNotPresentError(self._feature, reason=f'Importing {self._name} failed: {e}')
             raise
 
+        if feature:
+            # for the case that the feature is hidden
+            feature.require()
+
         name = self._as_name
         if self._deprecation is not None:
             from sage.misc.superseded import deprecation_cython as deprecation