Provide installation instructions in RequirementCache error message

src/lightning_utilities/core/imports.py

@@ -95,7 +95,7 @@ def _check_requirement(self) -> None:
                 self.message = f"Requirement {self.requirement!r} met"
             except Exception as ex:
                 self.available = False
-                self.message = f"Requirement {self.requirement!r} not met, {ex.__class__.__name__}: {ex}"
+                self.message = f"{ex.__class__.__name__}: {ex}. HINT: Try running `pip install {self.requirement!r}`"
 
     def __bool__(self) -> bool:
         self._check_requirement()

tests/unittests/core/test_imports.py

@@ -37,4 +37,4 @@ def test_requirement_cache():
 
     assert RequirementCache(f"pytest>={pytest.__version__}")
     assert not RequirementCache(f"pytest<{pytest.__version__}")
-    assert "Requirement '-' not met" in str(RequirementCache("-"))
+    assert "pip install '-'" in str(RequirementCache("-"))