Add --path to pip freeze to support --target installations (#6450)

* Add support for --path in pip freeze

5 files changed, 94 insertions, 8 deletions

diff --git a/news/6404.feature b/news/6404.feature
new file mode 100644
index 000000000..f3f6bae55
--- /dev/null
+++ b/news/6404.feature
@@ -0,0 +1,2 @@
+Add a ``--path`` argument to ``pip freeze`` to support ``--target``
+installations.
diff --git a/src/pip/_internal/commands/freeze.py b/src/pip/_internal/commands/freeze.py
index dc9c53a6b..47bd443a4 100644
--- a/src/pip/_internal/commands/freeze.py
+++ b/src/pip/_internal/commands/freeze.py
@@ -4,6 +4,7 @@ import sys
 
 from pip._internal.cache import WheelCache
 from pip._internal.cli.base_command import Command
+from pip._internal.exceptions import CommandError
 from pip._internal.models.format_control import FormatControl
 from pip._internal.operations.freeze import freeze
 from pip._internal.utils.compat import stdlib_pkgs
@@ -57,6 +58,12 @@ class FreezeCommand(Command):
             default=False,
             help='Only output packages installed in user-site.')
         self.cmd_opts.add_option(
+            '--path',
+            dest='path',
+            action='append',
+            help='Restrict to the specified installation path for listing '
+                 'packages (can be used multiple times).')
+        self.cmd_opts.add_option(
             '--all',
             dest='freeze_all',
             action='store_true',
@@ -77,11 +84,17 @@ class FreezeCommand(Command):
         if not options.freeze_all:
             skip.update(DEV_PKGS)
 
+        if options.path and (options.user or options.local):
+            raise CommandError(
+                "Cannot combine '--path' with '--user' or '--local'"
+            )
+
         freeze_kwargs = dict(
             requirement=options.requirements,
             find_links=options.find_links,
             local_only=options.local,
             user_only=options.user,
+            paths=options.path,
             skip_regex=options.skip_requirements_regex,
             isolated=options.isolated_mode,
             wheel_cache=wheel_cache,
diff --git a/src/pip/_internal/operations/freeze.py b/src/pip/_internal/operations/freeze.py
index 03e8696bb..6f5a3dd97 100644
--- a/src/pip/_internal/operations/freeze.py
+++ b/src/pip/_internal/operations/freeze.py
@@ -39,6 +39,7 @@ def freeze(
     find_links=None,  # type: Optional[List[str]]
     local_only=None,  # type: Optional[bool]
     user_only=None,  # type: Optional[bool]
+    paths=None,  # type: Optional[List[str]]
     skip_regex=None,  # type: Optional[str]
     isolated=False,  # type: bool
     wheel_cache=None,  # type: Optional[WheelCache]
@@ -57,7 +58,8 @@ def freeze(
     installations = {}  # type: Dict[str, FrozenRequirement]
     for dist in get_installed_distributions(local_only=local_only,
                                             skip=(),
-                                            user_only=user_only):
+                                            user_only=user_only,
+                                            paths=paths):
         try:
             req = FrozenRequirement.from_dist(dist)
         except RequirementParseError as exc:
diff --git a/src/pip/_internal/utils/misc.py b/src/pip/_internal/utils/misc.py
index 024f4e750..67ab33cef 100644
--- a/src/pip/_internal/utils/misc.py
+++ b/src/pip/_internal/utils/misc.py
@@ -390,12 +390,15 @@ def dist_is_editable(dist):
     return False
 
 
-def get_installed_distributions(local_only=True,
-                                skip=stdlib_pkgs,
-                                include_editables=True,
-                                editables_only=False,
-                                user_only=False):
-    # type: (bool, Container[str], bool, bool, bool) -> List[Distribution]
+def get_installed_distributions(
+        local_only=True,  # type: bool
+        skip=stdlib_pkgs,  # type: Container[str]
+        include_editables=True,  # type: bool
+        editables_only=False,  # type: bool
+        user_only=False,  # type: bool
+        paths=None  # type: Optional[List[str]]
+):
+    # type: (...) -> List[Distribution]
     """
     Return a list of installed Distribution objects.
 
@@ -412,7 +415,14 @@ def get_installed_distributions(local_only=True,
     If ``user_only`` is True , only report installations in the user
     site directory.
 
+    If ``paths`` is set, only report the distributions present at the
+    specified list of locations.
     """
+    if paths:
+        working_set = pkg_resources.WorkingSet(paths)
+    else:
+        working_set = pkg_resources.working_set
+
     if local_only:
         local_test = dist_is_local
     else:
@@ -440,7 +450,7 @@ def get_installed_distributions(local_only=True,
             return True
 
     # because of pkg_resources vendoring, mypy cannot find stub in typeshed
-    return [d for d in pkg_resources.working_set  # type: ignore
+    return [d for d in working_set  # type: ignore
             if local_test(d) and
             d.key not in skip and
             editable_test(d) and
diff --git a/tests/functional/test_freeze.py b/tests/functional/test_freeze.py
index 68625ff43..38fad0a66 100644
--- a/tests/functional/test_freeze.py
+++ b/tests/functional/test_freeze.py
@@ -659,3 +659,62 @@ def test_freeze_user(script, virtualenv, data):
         <BLANKLINE>""")
     _check_output(result.stdout, expected)
     assert 'simple2' not in result.stdout
+
+
+def test_freeze_path(tmpdir, script, data):
+    """
+    Test freeze with --path.
+    """
+    script.pip('install', '--find-links', data.find_links,
+               '--target', tmpdir, 'simple==2.0')
+    result = script.pip('freeze', '--path', tmpdir)
+    expected = textwrap.dedent("""\
+        simple==2.0
+        <BLANKLINE>""")
+    _check_output(result.stdout, expected)
+
+
+def test_freeze_path_exclude_user(tmpdir, script, data):
+    """
+    Test freeze with --path and make sure packages from --user are not picked
+    up.
+    """
+    script.pip_install_local('--find-links', data.find_links,
+                             '--user', 'simple2')
+    script.pip('install', '--find-links', data.find_links,
+               '--target', tmpdir, 'simple==1.0')
+    result = script.pip('freeze', '--user')
+    expected = textwrap.dedent("""\
+        simple2==3.0
+        <BLANKLINE>""")
+    _check_output(result.stdout, expected)
+    result = script.pip('freeze', '--path', tmpdir)
+    expected = textwrap.dedent("""\
+        simple==1.0
+        <BLANKLINE>""")
+    _check_output(result.stdout, expected)
+
+
+def test_freeze_path_multiple(tmpdir, script, data):
+    """
+    Test freeze with multiple --path arguments.
+    """
+    path1 = tmpdir / "path1"
+    os.mkdir(path1)
+    path2 = tmpdir / "path2"
+    os.mkdir(path2)
+    script.pip('install', '--find-links', data.find_links,
+               '--target', path1, 'simple==2.0')
+    script.pip('install', '--find-links', data.find_links,
+               '--target', path2, 'simple2==3.0')
+    result = script.pip('freeze', '--path', path1)
+    expected = textwrap.dedent("""\
+        simple==2.0
+        <BLANKLINE>""")
+    _check_output(result.stdout, expected)
+    result = script.pip('freeze', '--path', path1, '--path', path2)
+    expected = textwrap.dedent("""\
+        simple==2.0
+        simple2==3.0
+        <BLANKLINE>""")
+    _check_output(result.stdout, expected)