Emit using-constant-test when testing truth value of a call returning a generator

doc/whatsnew/2/2.15/index.rst

@@ -36,6 +36,10 @@ False negatives fixed
 
   Closes #6648
 
+* Emit ``using-constant-test`` when testing the truth value of a call that only returns generators.
+
+  Closes #6909
+
 
 Other bug fixes
 ===============

pylint/checkers/base/basic_checker.py

@@ -17,7 +17,7 @@
 
 from pylint import utils as lint_utils
 from pylint.checkers import BaseChecker, utils
-from pylint.interfaces import HIGH
+from pylint.interfaces import HIGH, INFERENCE
 from pylint.reporters.ureports import nodes as reporter_nodes
 from pylint.utils import LinterStats
 
@@ -317,6 +317,22 @@ def _check_using_constant_test(
         emit = isinstance(test, (nodes.Const,) + structs + const_nodes)
         if not isinstance(test, except_nodes):
             inferred = utils.safe_infer(test)
+        # Emit if calling a function that only returns GeneratorExp (always tests True)
+        elif isinstance(test, nodes.Call):
+            inferred_call = utils.safe_infer(test.func)
+            if isinstance(inferred_call, nodes.FunctionDef):
+                # Can't use all(x) or not any(not x) for this condition, because it
+                # will return True for empty generators, which is not what we want.
+                all_returns_were_generator = None
+                for return_node in inferred_call._get_return_nodes_skip_functions():
+                    if not isinstance(return_node.value, nodes.GeneratorExp):
+                        all_returns_were_generator = False
+                        break
+                    all_returns_were_generator = True
+                if all_returns_were_generator:
+                    self.add_message(
+                        "using-constant-test", node=node, confidence=INFERENCE
+                    )
 
         if emit:
             self.add_message("using-constant-test", node=test)
@@ -336,12 +352,14 @@ def _check_using_constant_test(
                     for inf_call in call_inferred:
                         if inf_call != astroid.Uninferable:
                             self.add_message(
-                                "missing-parentheses-for-call-in-test", node=test
+                                "missing-parentheses-for-call-in-test",
+                                node=test,
+                                confidence=INFERENCE,
                             )
                             break
                 except astroid.InferenceError:
                     pass
-            self.add_message("using-constant-test", node=test)
+            self.add_message("using-constant-test", node=test, confidence=INFERENCE)
 
     def visit_module(self, _: nodes.Module) -> None:
         """Check module name, docstring and required arguments."""

tests/functional/m/missing/missing_parentheses_for_call_in_test.txt

@@ -1,15 +1,15 @@
-missing-parentheses-for-call-in-test:29:3:29:16::Using a conditional statement with potentially wrong function or method call due to missing parentheses:UNDEFINED
-missing-parentheses-for-call-in-test:35:3:35:19::Using a conditional statement with potentially wrong function or method call due to missing parentheses:UNDEFINED
-missing-parentheses-for-call-in-test:43:3:43:23::Using a conditional statement with potentially wrong function or method call due to missing parentheses:UNDEFINED
-missing-parentheses-for-call-in-test:51:5:51:25::Using a conditional statement with potentially wrong function or method call due to missing parentheses:UNDEFINED
-missing-parentheses-for-call-in-test:56:3:56:14::Using a conditional statement with potentially wrong function or method call due to missing parentheses:UNDEFINED
-missing-parentheses-for-call-in-test:64:3:64:17::Using a conditional statement with potentially wrong function or method call due to missing parentheses:UNDEFINED
-missing-parentheses-for-call-in-test:70:17:70:30::Using a conditional statement with potentially wrong function or method call due to missing parentheses:UNDEFINED
-missing-parentheses-for-call-in-test:72:23:72:34::Using a conditional statement with potentially wrong function or method call due to missing parentheses:UNDEFINED
-missing-parentheses-for-call-in-test:73:24:73:38::Using a conditional statement with potentially wrong function or method call due to missing parentheses:UNDEFINED
-missing-parentheses-for-call-in-test:75:26:75:39::Using a conditional statement with potentially wrong function or method call due to missing parentheses:UNDEFINED
-missing-parentheses-for-call-in-test:76:26:76:37::Using a conditional statement with potentially wrong function or method call due to missing parentheses:UNDEFINED
-missing-parentheses-for-call-in-test:79:26:79:40::Using a conditional statement with potentially wrong function or method call due to missing parentheses:UNDEFINED
-missing-parentheses-for-call-in-test:80:26:80:42::Using a conditional statement with potentially wrong function or method call due to missing parentheses:UNDEFINED
-missing-parentheses-for-call-in-test:85:3:85:26::Using a conditional statement with potentially wrong function or method call due to missing parentheses:UNDEFINED
-missing-parentheses-for-call-in-test:91:3:91:20::Using a conditional statement with potentially wrong function or method call due to missing parentheses:UNDEFINED
+missing-parentheses-for-call-in-test:29:3:29:16::Using a conditional statement with potentially wrong function or method call due to missing parentheses:INFERENCE
+missing-parentheses-for-call-in-test:35:3:35:19::Using a conditional statement with potentially wrong function or method call due to missing parentheses:INFERENCE
+missing-parentheses-for-call-in-test:43:3:43:23::Using a conditional statement with potentially wrong function or method call due to missing parentheses:INFERENCE
+missing-parentheses-for-call-in-test:51:5:51:25::Using a conditional statement with potentially wrong function or method call due to missing parentheses:INFERENCE
+missing-parentheses-for-call-in-test:56:3:56:14::Using a conditional statement with potentially wrong function or method call due to missing parentheses:INFERENCE
+missing-parentheses-for-call-in-test:64:3:64:17::Using a conditional statement with potentially wrong function or method call due to missing parentheses:INFERENCE
+missing-parentheses-for-call-in-test:70:17:70:30::Using a conditional statement with potentially wrong function or method call due to missing parentheses:INFERENCE
+missing-parentheses-for-call-in-test:72:23:72:34::Using a conditional statement with potentially wrong function or method call due to missing parentheses:INFERENCE
+missing-parentheses-for-call-in-test:73:24:73:38::Using a conditional statement with potentially wrong function or method call due to missing parentheses:INFERENCE
+missing-parentheses-for-call-in-test:75:26:75:39::Using a conditional statement with potentially wrong function or method call due to missing parentheses:INFERENCE
+missing-parentheses-for-call-in-test:76:26:76:37::Using a conditional statement with potentially wrong function or method call due to missing parentheses:INFERENCE
+missing-parentheses-for-call-in-test:79:26:79:40::Using a conditional statement with potentially wrong function or method call due to missing parentheses:INFERENCE
+missing-parentheses-for-call-in-test:80:26:80:42::Using a conditional statement with potentially wrong function or method call due to missing parentheses:INFERENCE
+missing-parentheses-for-call-in-test:85:3:85:26::Using a conditional statement with potentially wrong function or method call due to missing parentheses:INFERENCE
+missing-parentheses-for-call-in-test:91:3:91:20::Using a conditional statement with potentially wrong function or method call due to missing parentheses:INFERENCE

tests/functional/u/using_constant_test.py

@@ -147,3 +147,19 @@ def test_good_comprehension_checks():
     {data for data in range(100) if abs(data)}
     {data: 1 for data in range(100) if data}
     {data: 1 for data in range(100)}
+
+
+# Calls to functions returning generator expressions are always truthy
+def get_generator():
+    return (x for x in range(0))
+
+if get_generator():  # [using-constant-test]
+    pass
+
+def maybe_get_generator(arg):
+    if arg:
+        return (x for x in range(0))
+    return None
+
+if maybe_get_generator(None):
+    pass

tests/functional/u/using_constant_test.txt

@@ -1,8 +1,8 @@
-using-constant-test:22:3:22:14::Using a conditional statement with a constant value:UNDEFINED
+using-constant-test:22:3:22:14::Using a conditional statement with a constant value:INFERENCE
 using-constant-test:26:3:26:31::Using a conditional statement with a constant value:UNDEFINED
 using-constant-test:29:3:29:15:<lambda>:Using a conditional statement with a constant value:UNDEFINED
-using-constant-test:32:3:32:11::Using a conditional statement with a constant value:UNDEFINED
-using-constant-test:35:3:35:8::Using a conditional statement with a constant value:UNDEFINED
+using-constant-test:32:3:32:11::Using a conditional statement with a constant value:INFERENCE
+using-constant-test:35:3:35:8::Using a conditional statement with a constant value:INFERENCE
 using-constant-test:38:3:38:4::Using a conditional statement with a constant value:UNDEFINED
 using-constant-test:41:3:41:7::Using a conditional statement with a constant value:UNDEFINED
 using-constant-test:44:3:44:5::Using a conditional statement with a constant value:UNDEFINED
@@ -14,14 +14,15 @@ using-constant-test:59:3:59:12::Using a conditional statement with a constant va
 using-constant-test:62:3:62:5::Using a conditional statement with a constant value:UNDEFINED
 using-constant-test:65:3:65:12::Using a conditional statement with a constant value:UNDEFINED
 using-constant-test:68:3:68:5::Using a conditional statement with a constant value:UNDEFINED
-using-constant-test:73:3:73:12::Using a conditional statement with a constant value:UNDEFINED
+using-constant-test:73:3:73:12::Using a conditional statement with a constant value:INFERENCE
 using-constant-test:76:8:76:9::Using a conditional statement with a constant value:UNDEFINED
-using-constant-test:80:36:80:39:test_comprehensions:Using a conditional statement with a constant value:UNDEFINED
+using-constant-test:80:36:80:39:test_comprehensions:Using a conditional statement with a constant value:INFERENCE
 using-constant-test:81:36:81:37:test_comprehensions:Using a conditional statement with a constant value:UNDEFINED
-using-constant-test:82:36:82:39:test_comprehensions:Using a conditional statement with a constant value:UNDEFINED
+using-constant-test:82:36:82:39:test_comprehensions:Using a conditional statement with a constant value:INFERENCE
 using-constant-test:83:36:83:37:test_comprehensions:Using a conditional statement with a constant value:UNDEFINED
-using-constant-test:84:36:84:39:test_comprehensions:Using a conditional statement with a constant value:UNDEFINED
-using-constant-test:85:39:85:42:test_comprehensions:Using a conditional statement with a constant value:UNDEFINED
-using-constant-test:89:3:89:15::Using a conditional statement with a constant value:UNDEFINED
-using-constant-test:93:3:93:18::Using a conditional statement with a constant value:UNDEFINED
+using-constant-test:84:36:84:39:test_comprehensions:Using a conditional statement with a constant value:INFERENCE
+using-constant-test:85:39:85:42:test_comprehensions:Using a conditional statement with a constant value:INFERENCE
+using-constant-test:89:3:89:15::Using a conditional statement with a constant value:INFERENCE
+using-constant-test:93:3:93:18::Using a conditional statement with a constant value:INFERENCE
 comparison-of-constants:117:3:117:8::"Comparison between constants: '2 < 3' has a constant value":HIGH
+using-constant-test:156:0:157:8::Using a conditional statement with a constant value:INFERENCE