Remove redundant code paths (1/2)

We are now constrained on `pip >= 21.2.4` (bcfd93c). This commit
elliminates code paths that were there previously in order to cater to
the older versions of Pip:

- `PipSession` is now only found in `pip._internal._network.session`.
- `install_req_from_line` is always used.

Author: MrMino

pip_check_reqs/common.py

@@ -13,11 +13,8 @@
 
 from . import __version__
 
-# Between different versions of pip the location of PipSession has changed.
-try:
-    from pip._internal.network.session import PipSession
-except ImportError:  # pragma: no cover
-    from pip._internal.download import PipSession
+from pip._internal.network.session import PipSession
+from pip._internal.req.constructors import install_req_from_line
 from pip._internal.req.req_file import parse_requirements
 
 
@@ -137,16 +134,9 @@ def find_required_modules(options, requirements_filename: str):
     explicit = set()
     for requirement in parse_requirements(requirements_filename,
                                           session=PipSession()):
-        try:
-            requirement_name = requirement.name
-        # The type of "requirement" changed between pip versions.
-        # We exclude the "except" from coverage so that on any pip version we
-        # can report 100% coverage.
-        except AttributeError:  # pragma: no cover
-            from pip._internal.req.constructors import install_req_from_line
-            requirement_name = install_req_from_line(
-                requirement.requirement,
-            ).name
+        requirement_name = install_req_from_line(
+            requirement.requirement,
+        ).name
 
         if options.ignore_reqs(requirement):
             log.debug('ignoring requirement: %s', requirement_name)
@@ -193,13 +183,10 @@ def ignorer(ignore_cfg):
     def f(candidate, ignore_cfg=ignore_cfg):
         for ignore in ignore_cfg:
             try:
-                from pip._internal.req.constructors import (
-                    install_req_from_line,
-                )
-                candidate_path = install_req_from_line(  # pragma: no cover
+                candidate_path = install_req_from_line(
                     candidate.requirement,
                 ).name
-            except (ImportError, AttributeError):
+            except AttributeError:
                 try:
                     candidate_path = candidate.name
                 except AttributeError:

pip_check_reqs/find_missing_reqs.py

@@ -8,11 +8,8 @@
 
 from packaging.utils import canonicalize_name
 from pip._internal.commands.show import search_packages_info
-# Between different versions of pip the location of PipSession has changed.
-try:
-    from pip._internal.network.session import PipSession
-except ImportError:  # pragma: no cover
-    from pip._internal.download import PipSession
+from pip._internal.network.session import PipSession
+from pip._internal.req.constructors import install_req_from_line
 from pip._internal.req.req_file import parse_requirements
 
 from pip_check_reqs import common
@@ -89,16 +86,9 @@ def find_missing_reqs(options, requirements_filename):
         requirements_filename,
         session=PipSession(),
     ):
-        try:
-            requirement_name = requirement.name
-        # The type of "requirement" changed between pip versions.
-        # We exclude the "except" from coverage so that on any pip version we
-        # can report 100% coverage.
-        except AttributeError:  # pragma: no cover
-            from pip._internal.req.constructors import install_req_from_line
-            requirement_name = install_req_from_line(
-                requirement.requirement,
-            ).name
+        requirement_name = install_req_from_line(
+            requirement.requirement,
+        ).name
 
         log.debug('found requirement: %s', requirement_name)
         explicit.add(canonicalize_name(requirement_name))

tests/package_info_mock.py

@@ -0,0 +1,9 @@
+from typing import List, Optional, NamedTuple
+
+
+# A stand-in for pip._internal.commands.show._PackageInfo, as returned by
+# search_packages_info from the same module
+class _PackageInfo(NamedTuple):
+    name: str
+    location: str
+    files: Optional[List[str]]