fail on inconsistent lock file

src/poetry_plugin_export/command.py

@@ -104,12 +104,12 @@ def handle(self) -> int:
 
         if not locker.is_fresh():
             self.line_error(
-                "<warning>"
-                "Warning: poetry.lock is not consistent with pyproject.toml. "
-                "You may be getting improper dependencies. "
-                "Run `poetry lock [--no-update]` to fix it."
-                "</warning>"
+                "<error>"
+                "pyproject.toml changed significantly since poetry.lock was last"
+                " generated. Run `poetry lock` to fix the lock file."
+                "</error>"
             )
+            return 1
 
         if self.option("extras") and self.option("all-extras"):
             self.line_error(

tests/command/test_command_export.py

@@ -21,6 +21,7 @@
     from cleo.testers.command_tester import CommandTester
     from poetry.poetry import Poetry
     from poetry.repositories import Repository
+    from pytest_mock import MockerFixture
 
     from tests.types import CommandTesterFactory
     from tests.types import ProjectFactory
@@ -134,6 +135,18 @@ def test_export_fails_on_invalid_format(tester: CommandTester, do_lock: None) ->
         tester.execute("--format invalid")
 
 
+def test_export_fails_if_lockfile_is_not_fresh(
+    tester: CommandTester,
+    poetry: Poetry,
+    tmp_path: Path,
+    do_lock: None,
+    mocker: MockerFixture,
+) -> None:
+    mocker.patch.object(poetry.locker, "is_fresh", return_value=False)
+    assert tester.execute() == 1
+    assert "pyproject.toml changed significantly" in tester.io.fetch_error()
+
+
 def test_export_prints_to_stdout_by_default(
     tester: CommandTester, do_lock: None
 ) -> None: