implement --dry-run

Author: cosmicexplorer

src/pip/_internal/cli/req_command.py

@@ -313,6 +313,7 @@ def make_resolver(
         use_user_site: bool = False,
         ignore_installed: bool = True,
         ignore_requires_python: bool = False,
+        dry_run: bool = False,
         force_reinstall: bool = False,
         upgrade_strategy: str = "to-satisfy-only",
         use_pep517: Optional[bool] = None,
@@ -344,6 +345,7 @@ def make_resolver(
                 ignore_dependencies=options.ignore_dependencies,
                 ignore_installed=ignore_installed,
                 ignore_requires_python=ignore_requires_python,
+                dry_run=dry_run,
                 force_reinstall=force_reinstall,
                 upgrade_strategy=upgrade_strategy,
                 py_version_info=py_version_info,

src/pip/_internal/commands/download.py

@@ -62,6 +62,13 @@ def add_options(self) -> None:
             help="Download packages into <dir>.",
         )
 
+        self.cmd_opts.add_option(
+            "--dry-run",
+            dest="dry_run",
+            action="store_true",
+            help="Avoid actually downloading wheels.",
+        )
+
         cmdoptions.add_target_python_options(self.cmd_opts)
 
         index_opts = cmdoptions.make_option_group(
@@ -122,19 +129,21 @@ def run(self, options: Values, args: List[str]) -> int:
             options=options,
             ignore_requires_python=options.ignore_requires_python,
             py_version_info=options.python_version,
+            dry_run=options.dry_run,
         )
 
         self.trace_basic_info(finder)
 
         requirement_set = resolver.resolve(reqs, check_supported_wheels=True)
 
-        downloaded: List[str] = []
-        for req in requirement_set.requirements.values():
-            if req.satisfied_by is None:
-                assert req.name is not None
-                preparer.save_linked_requirement(req)
-                downloaded.append(req.name)
-        if downloaded:
-            write_output("Successfully downloaded %s", " ".join(downloaded))
+        if not options.dry_run:
+            downloaded: List[str] = []
+            for req in requirement_set.requirements.values():
+                if req.satisfied_by is None:
+                    assert req.name is not None
+                    preparer.save_linked_requirement(req)
+                    downloaded.append(req.name)
+            if downloaded:
+                write_output("Successfully downloaded %s", " ".join(downloaded))
 
         return SUCCESS

src/pip/_internal/resolution/resolvelib/resolver.py

@@ -45,6 +45,7 @@ def __init__(
         ignore_dependencies: bool,
         ignore_installed: bool,
         ignore_requires_python: bool,
+        dry_run: bool,
         force_reinstall: bool,
         upgrade_strategy: str,
         suppress_build_failures: bool,
@@ -66,6 +67,7 @@ def __init__(
             py_version_info=py_version_info,
         )
         self.ignore_dependencies = ignore_dependencies
+        self.dry_run = dry_run
         self.upgrade_strategy = upgrade_strategy
         self._result: Optional[Result] = None
 
@@ -159,8 +161,10 @@ def resolve(
 
             req_set.add_named_requirement(ireq)
 
-        reqs = req_set.all_requirements
-        self.factory.preparer.prepare_linked_requirements_more(reqs)
+        if not self.dry_run:
+            reqs = req_set.all_requirements
+            self.factory.preparer.prepare_linked_requirements_more(reqs)
+
         return req_set
 
     def get_installation_order(

tests/functional/test_download.py

@@ -90,6 +90,17 @@ def test_basic_download_should_download_dependencies(
     result.did_not_create(script.site_packages / "openid")
 
 
+@pytest.mark.network
+def test_dry_run_should_not_download_dependencies(
+    script: PipTestEnvironment,
+) -> None:
+    """
+    It should not download dependencies into the scratch path.
+    """
+    result = script.pip("download", "--dry-run", "Paste[openid]==1.7.5.1", "-d", ".")
+    result.did_not_create(Path("scratch") / "Paste-1.7.5.1.tar.gz")
+
+
 def test_download_wheel_archive(script: PipTestEnvironment, data: TestData) -> None:
     """
     It should download a wheel archive path

tests/unit/resolution_resolvelib/test_resolver.py

@@ -28,6 +28,7 @@ def resolver(preparer: RequirementPreparer, finder: PackageFinder) -> Resolver:
         ignore_installed=False,
         ignore_requires_python=False,
         force_reinstall=False,
+        dry_run=True,
         upgrade_strategy="to-satisfy-only",
         suppress_build_failures=False,
     )