If an empty group is the default group, then treat it as empty on purpose

docs/use-cases/default-groups.md

@@ -13,6 +13,20 @@ To ignore the `default_group` and install all dependencies, use the `all` keywor
 $ gitman install all
 ```
 
+## Empty Default Groups
+
+To prevent any dependencies from being cloned by default, define a group with no members and set it as the `default_group`:
+
+```yaml
+groups:
+  - name: empty
+    members: null
+
+default_group: empty
+```
+
+When `gitman install` is run, no dependencies will be installed unless a specific group or dependency is requested, or the default group is overridden with `all` or `--no-defaults`.
+
 ## Nested Projects
 
 When nested Gitman projects are used default groups are installed if they

gitman/models/config.py

@@ -420,8 +420,9 @@ def _get_sources_filter(
             [source.name for source in sources if source.name in names_list]
         )
 
-        # Fall back to all sources if allowed
-        if not sources_filter:
+        # Fall back to all sources if allowed, unless a group matched (an
+        # empty group is intentionally empty, not a request for everything)
+        if not sources_filter and not groups_filter:
             if names and names_list != ["all"]:
                 log.warn(f"No dependencies match: {' '.join(names)}")
             else:

gitman/tests/test_models_config.py

@@ -5,7 +5,7 @@
 import pytest
 from expecter import expect
 
-from gitman.models import Config, load_config
+from gitman.models import Config, Group, Source, load_config
 
 from .conftest import FILES
 
@@ -135,6 +135,62 @@ def it_can_get_dependency_path(config):
                 "m/root/m/location/foobar"
             )
 
+    def describe_get_sources_filter():
+        def it_returns_empty_when_default_group_has_no_members(config):
+            config.sources = [Source(repo="http://example.com/repo1", name="repo1")]
+            config.groups = [Group(name="empty", members=[])]
+            config.default_group = "empty"
+
+            expect(
+                config._get_sources_filter(
+                    sources=config.sources, skip_default_group=False
+                )
+            ) == []
+
+        def it_returns_empty_when_empty_group_specified_by_name(config):
+            config.sources = [Source(repo="http://example.com/repo1", name="repo1")]
+            config.groups = [Group(name="empty", members=[])]
+            config.default_group = ""
+
+            expect(
+                config._get_sources_filter(
+                    "empty", sources=config.sources, skip_default_group=False
+                )
+            ) == []
+
+        def it_returns_all_when_skip_default_group_is_true(config):
+            config.sources = [Source(repo="http://example.com/repo1", name="repo1")]
+            config.groups = [Group(name="empty", members=[])]
+            config.default_group = "empty"
+
+            expect(
+                config._get_sources_filter(
+                    sources=config.sources, skip_default_group=True
+                )
+            ) == ["repo1"]
+
+        def it_returns_all_when_name_all_is_specified(config):
+            config.sources = [Source(repo="http://example.com/repo1", name="repo1")]
+            config.groups = [Group(name="empty", members=[])]
+            config.default_group = "empty"
+
+            expect(
+                config._get_sources_filter(
+                    "all", sources=config.sources, skip_default_group=False
+                )
+            ) == ["repo1"]
+
+        def it_returns_all_when_default_group_is_blank(config):
+            config.sources = [Source(repo="http://example.com/repo1", name="repo1")]
+            config.groups = [Group(name="empty", members=[])]
+            config.default_group = ""
+
+            expect(
+                config._get_sources_filter(
+                    sources=config.sources, skip_default_group=False
+                )
+            ) == ["repo1"]
+
 
 class TestLoad:
     def test_load_from_directory_with_config_file(self):

tests/test_api.py

@@ -2,7 +2,6 @@
 
 import inspect
 import os
-import shutil
 from contextlib import suppress
 
 import log
@@ -74,8 +73,11 @@
 def config():
     log.info("Temporary directory: %s", TMP)
 
-    with suppress(FileNotFoundError, PermissionError):
-        shutil.rmtree(TMP)
+    # Leave TMP first: Windows can't delete the current working directory,
+    # and other tests (e.g. `Config.install_dependencies`) may leave us inside it
+    os.chdir(ROOT)
+    # 'shell.rm' handles read-only files (e.g. `.git` objects) on Windows
+    shell.rm(TMP)
     with suppress(FileExistsError):
         os.makedirs(TMP)
     os.chdir(TMP)
@@ -623,6 +625,79 @@ def it_installs_all_sources_when_all_specified(config_with_default_group):
                 )
             ) == True
 
+        @pytest.fixture
+        def config_with_empty_default_group(config):
+            config.datafile.text = strip("""
+        location: deps
+        sources:
+          - repo: https://github.com/jacebrowning/gitman-demo
+            name: gitman_1
+            type: git
+            params:
+            sparse_paths:
+              -
+            rev: example-branch
+            links:
+              -
+            scripts:
+              -
+            patches:
+              -
+          - repo: https://github.com/jacebrowning/gitman-demo
+            name: gitman_2
+            type: git
+            params:
+            sparse_paths:
+              -
+            rev: example-tag
+            links:
+              -
+            scripts:
+              -
+            patches:
+              -
+        groups:
+          - name: empty
+            members: null
+          - name: secondary
+            members:
+              - gitman_2
+        default_group: 'empty'
+        """)
+            config.datafile.load()
+
+            return config
+
+        def it_installs_nothing_when_default_group_empty(
+            config_with_empty_default_group,
+        ):
+            gitman.install(depth=1, force=True)
+            expect(
+                os.path.exists(
+                    os.path.join(config_with_empty_default_group.location, "gitman_1")
+                )
+            ) == False
+            expect(
+                os.path.exists(
+                    os.path.join(config_with_empty_default_group.location, "gitman_2")
+                )
+            ) == False
+
+        def it_installs_all_sources_when_all_specified_and_empty_default_group(
+            config_with_empty_default_group,
+        ):
+            expect(gitman.install(depth=1, force=True, skip_default_group=True)) == True
+            expect(
+                os.path.exists(
+                    os.path.join(config_with_empty_default_group.location, "gitman_1")
+                )
+            ) == True
+            expect(
+                os.path.exists(
+                    os.path.join(config_with_empty_default_group.location, "gitman_2")
+                )
+            ) == True
+
 
 def describe_uninstall():
     def it_deletes_dependencies_when_they_exist(config):