Add output for poetry lock --check

src/poetry/console/commands/export.py

@@ -59,10 +59,9 @@ def handle(self) -> None:
         if not locker.is_fresh():
             self.line_error(
                 "<warning>"
-                "Warning: The lock file is not up to date with "
-                "the latest changes in pyproject.toml. "
-                "You may be getting outdated dependencies. "
-                "Run update to update them."
+                "Warning: poetry.lock is not consistent with pyproject.toml. "
+                "You may be getting improper dependencies. "
+                "Run `poetry lock [--no-update]` to fix it."
                 "</warning>"
             )
 

src/poetry/console/commands/lock.py

@@ -37,11 +37,16 @@ def handle(self) -> int:
         )
 
         if self.option("check"):
-            return (
-                0
-                if self.poetry.locker.is_locked() and self.poetry.locker.is_fresh()
-                else 1
+            if self.poetry.locker.is_locked() and self.poetry.locker.is_fresh():
+                self.line("poetry.lock is consistent with pyproject.toml.")
+                return 0
+            self.line(
+                "<error>"
+                "Error: poetry.lock is not consistent with pyproject.toml. "
+                "Run `poetry lock [--no-update]` to fix it."
+                "</error>"
             )
+            return 1
 
         self._installer.lock(update=not self.option("no-update"))
 

src/poetry/installation/installer.py

@@ -258,10 +258,9 @@ def _do_install(self, local_repo: Repository) -> int:
             if not self._locker.is_fresh():
                 self._io.write_line(
                     "<warning>"
-                    "Warning: The lock file is not up to date with "
-                    "the latest changes in pyproject.toml. "
-                    "You may be getting outdated dependencies. "
-                    "Run update to update them."
+                    "Warning: poetry.lock is not consistent with pyproject.toml. "
+                    "You may be getting improper dependencies. "
+                    "Run `poetry lock [--no-update]` to fix it."
                     "</warning>"
                 )
 

tests/console/commands/test_lock.py

@@ -81,6 +81,12 @@ def test_lock_check_outdated(
 
     tester = command_tester_factory("lock", poetry=poetry_with_outdated_lockfile)
     status_code = tester.execute("--check")
+    expected = (
+        "Error: poetry.lock is not consistent with pyproject.toml. "
+        "Run `poetry lock [--no-update]` to fix it.\n"
+    )
+
+    assert tester.io.fetch_output() == expected
 
     # exit with an error
     assert status_code == 1
@@ -101,6 +107,8 @@ def test_lock_check_up_to_date(
 
     tester = command_tester_factory("lock", poetry=poetry_with_up_to_date_lockfile)
     status_code = tester.execute("--check")
+    expected = "poetry.lock is consistent with pyproject.toml.\n"
+    assert tester.io.fetch_output() == expected
 
     # exit with an error
     assert status_code == 0