Add 'pip cache dir' command to show cache directory

news/7350.feature

@@ -0,0 +1 @@
+Add ``pip cache dir`` to show the cache directory.

src/pip/_internal/commands/cache.py

@@ -24,6 +24,7 @@ class CacheCommand(Command):
 
     Subcommands:
 
+        dir: Show the cache directory.
         info: Show information about the cache.
         list: List filenames of packages stored in the cache.
         remove: Remove one or more package from the cache.
@@ -33,6 +34,7 @@ class CacheCommand(Command):
     """
 
     usage = """
+        %prog dir
         %prog info
         %prog list [<pattern>]
         %prog remove <pattern>
@@ -42,6 +44,7 @@ class CacheCommand(Command):
     def run(self, options, args):
         # type: (Values, List[Any]) -> int
         handlers = {
+            "dir": self.get_cache_dir,
             "info": self.get_cache_info,
             "list": self.list_cache_items,
             "remove": self.remove_cache_items,
@@ -66,6 +69,13 @@ def run(self, options, args):
 
         return SUCCESS
 
+    def get_cache_dir(self, options, args):
+        # type: (Values, List[Any]) -> None
+        if args:
+            raise CommandError('Too many arguments')
+
+        logger.info(options.cache_dir)
+
     def get_cache_info(self, options, args):
         # type: (Values, List[Any]) -> None
         if args:

tests/functional/test_cache.py

@@ -95,6 +95,22 @@ def _remove_matches_wheel(wheel_name, result):
     return _remove_matches_wheel
 
 
+def test_cache_dir(script, cache_dir):
+    result = script.pip('cache', 'dir')
+
+    assert os.path.normcase(cache_dir) == result.stdout.strip()
+
+
+def test_cache_dir_too_many_args(script, cache_dir):
+    result = script.pip('cache', 'dir', 'aaa', expect_error=True)
+
+    assert result.stdout == ''
+
+    # This would be `result.stderr == ...`, but pip prints deprecation
+    # warnings on Python 2.7, so we check if the _line_ is in stderr.
+    assert 'ERROR: Too many arguments' in result.stderr.splitlines()
+
+
 @pytest.mark.usefixtures("populate_wheel_cache")
 def test_cache_info(script, wheel_cache_dir, wheel_cache_files):
     result = script.pip('cache', 'info')
@@ -209,7 +225,7 @@ def test_cache_purge_too_many_args(script, wheel_cache_files):
                         expect_error=True)
     assert result.stdout == ''
 
-    # This would be `result.stderr == ...`, but Pip prints deprecation
+    # This would be `result.stderr == ...`, but pip prints deprecation
     # warnings on Python 2.7, so we check if the _line_ is in stderr.
     assert 'ERROR: Too many arguments' in result.stderr.splitlines()