Add new --check flag to lock command

docs/docs/cli.md

@@ -450,6 +450,10 @@ This command locks (without installing) the dependencies specified in `pyproject
 poetry lock
 ```
 
+### Options
+
+* `--check`: Verify that `poetry.lock` is consistent with `pyproject.toml`
+
 ## version
 
 This command shows the current version of the project or bumps the version of

docs/docs/pyproject.md

@@ -253,10 +253,10 @@ poetry install --extras "mysql pgsql"
 poetry install -E mysql -E pgsql
 ```
 
-When installing or specifying Poetry-built packages, the extras defined in this section can be activated 
+When installing or specifying Poetry-built packages, the extras defined in this section can be activated
 as described in [PEP 508](https://www.python.org/dev/peps/pep-0508/#extras).
 
-For example, when installing the package using `pip`, the dependencies required by 
+For example, when installing the package using `pip`, the dependencies required by
 the `databases` extra can be installed as shown below.
 
 ```bash

poetry/console/commands/lock.py

@@ -12,6 +12,12 @@ class LockCommand(InstallerCommand):
         option(
             "no-update", None, "Do not update locked versions, only refresh lock file."
         ),
+        option(
+            "check",
+            None,
+            "Check that the <comment>poetry.lock</> file corresponds to the current version "
+            "of <comment>pyproject.toml</>.",
+        ),
     ]
 
     help = """
@@ -29,6 +35,13 @@ def handle(self) -> int:
             self.poetry.config.get("experimental.new-installer", False)
         )
 
+        if self.option("check"):
+            return (
+                0
+                if self.poetry.locker.is_locked() and self.poetry.locker.is_fresh()
+                else 1
+            )
+
         self._installer.lock(update=not self.option("no-update"))
 
         return self._installer.run()

tests/console/commands/test_lock.py

@@ -16,9 +16,8 @@ def tester(command_tester_factory):
     return command_tester_factory("lock")
 
 
-@pytest.fixture
-def poetry_with_old_lockfile(project_factory, fixture_dir, source_dir):
-    source = fixture_dir("old_lock")
+def _project_factory(fixture_name, project_factory, fixture_dir):
+    source = fixture_dir(fixture_name)
     pyproject_content = (source / "pyproject.toml").read_text(encoding="utf-8")
     poetry_lock_content = (source / "poetry.lock").read_text(encoding="utf-8")
     return project_factory(
@@ -28,6 +27,57 @@ def poetry_with_old_lockfile(project_factory, fixture_dir, source_dir):
     )
 
 
+@pytest.fixture
+def poetry_with_outdated_lockfile(project_factory, fixture_dir):
+    return _project_factory("outdated_lock", project_factory, fixture_dir)
+
+
+@pytest.fixture
+def poetry_with_up_to_date_lockfile(project_factory, fixture_dir):
+    return _project_factory("up_to_date_lock", project_factory, fixture_dir)
+
+
+@pytest.fixture
+def poetry_with_old_lockfile(project_factory, fixture_dir):
+    return _project_factory("old_lock", project_factory, fixture_dir)
+
+
+def test_lock_check_outdated(
+    command_tester_factory, poetry_with_outdated_lockfile, http
+):
+    http.disable()
+
+    locker = Locker(
+        lock=poetry_with_outdated_lockfile.pyproject.file.path.parent / "poetry.lock",
+        local_config=poetry_with_outdated_lockfile.locker._local_config,
+    )
+    poetry_with_outdated_lockfile.set_locker(locker)
+
+    tester = command_tester_factory("lock", poetry=poetry_with_outdated_lockfile)
+    status_code = tester.execute("--check")
+
+    # exit with an error
+    assert status_code == 1
+
+
+def test_lock_check_up_to_date(
+    command_tester_factory, poetry_with_up_to_date_lockfile, http
+):
+    http.disable()
+
+    locker = Locker(
+        lock=poetry_with_up_to_date_lockfile.pyproject.file.path.parent / "poetry.lock",
+        local_config=poetry_with_up_to_date_lockfile.locker._local_config,
+    )
+    poetry_with_up_to_date_lockfile.set_locker(locker)
+
+    tester = command_tester_factory("lock", poetry=poetry_with_up_to_date_lockfile)
+    status_code = tester.execute("--check")
+
+    # exit with an error
+    assert status_code == 0
+
+
 def test_lock_no_update(command_tester_factory, poetry_with_old_lockfile, repo):
     repo.add_package(get_package("sampleproject", "1.3.1"))
     repo.add_package(get_package("sampleproject", "2.0.0"))

tests/fixtures/outdated_lock/pyproject.toml

@@ -0,0 +1,15 @@
+[tool.poetry]
+name = "foobar"
+version = "0.1.0"
+description = ""
+authors = ["Poetry Developer <developer@python-poetry.org>"]
+
+[tool.poetry.dependencies]
+python = "^3.8"
+docker = "4.3.1"
+
+[tool.poetry.dev-dependencies]
+
+[build-system]
+requires = ["poetry-core>=1.0.0"]
+build-backend = "poetry.core.masonry.api"