Trac #31013: Remove unused class from sage_setup.optional extension

The code in `optional_extension` was mostly unused and is removed in
this ticket (and similarly `extension.skip_build` was nowhere else set).
The only still used method was `is_package_installed_and_updated` which
is moved to `sage.misc.package`.

Related: #28815

URL: https://trac.sagemath.org/31013
Reported by: gh-tobiasdiez
Ticket author(s): Tobias Diez
Reviewer(s): François Bissey

build/pkgs/sagelib/spkg-install

@@ -14,8 +14,7 @@ fi
 ## Building takes places in the build/ subdirectory.
 ##
 ## As a special exception, we feed SAGE_PKGS and SAGE_SPKG_INST.
-## They are needed by src/sage_setup/optional_extension.py
-## via src/sage/misc/package.py.  See meta-ticket #28815 for planned changes to this.
+## They are needed by src/sage/misc/package.py.  See meta-ticket #28815 for planned changes to this.
 
 export SAGE_PKGS="$SAGE_ROOT"/build/pkgs
 export SAGE_ROOT=/doesnotexist

pkgs/sagemath-standard/setup.py

@@ -78,7 +78,7 @@
     # TODO: This should be quiet by default
     print("Discovering Python/Cython source code....")
     t = time.time()
-    from sage_setup.optional_extension import is_package_installed_and_updated
+    from sage.misc.package import is_package_installed_and_updated
     distributions = ['']
     optional_packages_with_extensions = ['mcqd', 'bliss', 'tdlib',
                                          'coxeter3', 'fes', 'sirocco', 'meataxe']

src/sage/misc/package.py

@@ -55,6 +55,7 @@
 
 DEFAULT_PYPI = 'https://pypi.org/pypi'
 
+
 def pkgname_split(name):
     r"""
     Split a pkgname into a list of strings, 'name, version'.
@@ -69,6 +70,7 @@ def pkgname_split(name):
     """
     return (name.split('-',1) + [''])[:2]
 
+
 def pip_remote_version(pkg, pypi_url=DEFAULT_PYPI, ignore_URLError=False):
     r"""
     Return the version of this pip package available on PyPI.
@@ -123,6 +125,7 @@ def pip_remote_version(pkg, pypi_url=DEFAULT_PYPI, ignore_URLError=False):
     stable_releases = [v for v in info['releases'] if 'a' not in v and 'b' not in v]
     return max(stable_releases)
 
+
 def pip_installed_packages(normalization=None):
     r"""
     Return a dictionary `name->version` of installed pip packages.
@@ -446,6 +449,29 @@ def is_package_installed(package, exclude_pip=True):
     return any(p == package for p in installed_packages(exclude_pip))
 
 
+def is_package_installed_and_updated(package: str) -> bool:
+    r"""
+    Return whether the given package is installed and up-to-date.
+
+    INPUT:
+
+    - ``package`` -- the name of the package.
+
+    EXAMPLES::
+
+        sage: from sage.misc.package import is_package_installed_and_updated
+        sage: is_package_installed_and_updated("alabaster")    # optional - build, random
+        False
+    """
+    try:
+        all_packages = list_packages(local=True)
+        pkginfo = all_packages[package]
+        return pkginfo.installed_version == pkginfo.remote_version
+    except KeyError:
+        # Might be an installed old-style package
+        return is_package_installed(package)
+
+
 def package_versions(package_type, local=False):
     r"""
     Return version information for each Sage package.

src/sage_setup/command/sage_build_cython.py

@@ -234,9 +234,6 @@ def run(self):
             cache=False,
             )
 
-        # Filter out extensions with skip_build=True
-        extensions = [ext for ext in extensions if not getattr(ext, "skip_build", False)]
-
         # We use [:] to change the list in-place because the same list
         # object is pointed to from different places.
         self.extensions[:] = extensions

src/setup.py

@@ -21,7 +21,7 @@
 
 import sage.misc.lazy_import_cache
 
-from sage_setup.optional_extension import is_package_installed_and_updated
+from sage.misc.package import is_package_installed_and_updated
 from sage_setup.command.sage_build_ext_minimal import sage_build_ext_minimal
 from sage_setup.command.sage_install import sage_install
 from sage_setup.find import filter_cython_sources