Fix #2399: Avoid negative scores by default (#5595)

8 files changed, 31 insertions, 13 deletions

diff --git a/ChangeLog b/ChangeLog
index 77e77dfe5..87cf8b765 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -96,6 +96,10 @@ Release date: TBA
 
 * ``fatal`` was added to the variables permitted in score evaluation expressions.
 
+* The default score evaluation now uses a floor of 0.
+
+  Closes #2399
+
 * Fix false positive - Allow unpacking of ``self`` in a subclass of ``typing.NamedTuple``.
 
   Closes #5312
diff --git a/doc/faq.rst b/doc/faq.rst
index a2c0f2252..47dc9b501 100644
--- a/doc/faq.rst
+++ b/doc/faq.rst
@@ -249,15 +249,16 @@ default value by changing the mixin-class-rgx option.
 6.1 Pylint gave my code a negative rating out of ten. That can't be right!
 --------------------------------------------------------------------------
 
-Even though the final rating Pylint renders is nominally out of ten, there's no
-lower bound on it. By default, the formula to calculate score is ::
+Prior to Pylint 2.13.0, the score formula used by default had no lower
+bound. The new default score formula is ::
 
-    0 if fatal else 10.0 - ((float(5 * error + warning + refactor + convention) / statement) * 10)
-
-However, this option can be changed in the Pylint rc file. If having negative
-values really bugs you, you can set the formula to be the maximum of 0 and the
-above expression.
+    max(0, 0 if fatal else 10.0 - ((float(5 * error + warning + refactor + convention) / statement) * 10))
 
+If your project contains a configuration file created by an earlier version of
+Pylint, you can set ``evaluation`` to the above expression to get the new
+behavior. Likewise, since negative values are still technically supported,
+``evaluation`` can be set to a version of the above expression that does not
+enforce a floor of zero.
 
 6.2 I think I found a bug in Pylint. What should I do?
 -------------------------------------------------------
diff --git a/doc/whatsnew/2.13.rst b/doc/whatsnew/2.13.rst
index 219aec512..bf38d767e 100644
--- a/doc/whatsnew/2.13.rst
+++ b/doc/whatsnew/2.13.rst
@@ -104,6 +104,10 @@ Other Changes
 
 * ``fatal`` was added to the variables permitted in score evaluation expressions.
 
+* The default score evaluation now uses a floor of 0.
+
+  Closes #2399
+
 * Fix ``comparison-with-callable`` false positive for callables that raise, such
   as typing constants.
 
diff --git a/examples/pylintrc b/examples/pylintrc
index eb48b4a1f..8fb3c179a 100644
--- a/examples/pylintrc
+++ b/examples/pylintrc
@@ -94,7 +94,7 @@ enable=c-extension-no-member
 # which contain the number of messages in each category, as well as 'statement'
 # which is the total number of statements analyzed. This score is used by the
 # global evaluation report (RP0004).
-evaluation=0 if fatal else 10.0 - ((float(5 * error + warning + refactor + convention) / statement) * 10)
+evaluation=max(0, 0 if fatal else 10.0 - ((float(5 * error + warning + refactor + convention) / statement) * 10))
 
 # Template used to display messages. This is a python new-style format string
 # used to format the message information. See doc for all details.
diff --git a/pylint/lint/pylinter.py b/pylint/lint/pylinter.py
index e46577615..db316caed 100644
--- a/pylint/lint/pylinter.py
+++ b/pylint/lint/pylinter.py
@@ -310,8 +310,8 @@ class PyLinter(
                     "metavar": "<python_expression>",
                     "group": "Reports",
                     "level": 1,
-                    "default": "0 if fatal else 10.0 - ((float(5 * error + warning + refactor + "
-                    "convention) / statement) * 10)",
+                    "default": "max(0, 0 if fatal else 10.0 - ((float(5 * error + warning + refactor + "
+                    "convention) / statement) * 10))",
                     "help": "Python expression which should return a score less "
                     "than or equal to 10. You have access to the variables 'fatal', "
                     "'error', 'warning', 'refactor', 'convention', and 'info' which "
diff --git a/pylintrc b/pylintrc
index 8dec45074..4e093a87c 100644
--- a/pylintrc
+++ b/pylintrc
@@ -120,7 +120,7 @@ reports=no
 # and 'info', which contain the number of messages in each category, as
 # well as 'statement', which is the total number of statements analyzed. This
 # score is used by the global evaluation report (RP0004).
-evaluation=0 if fatal else 10.0 - ((float(5 * error + warning + refactor + convention) / statement) * 10)
+evaluation=max(0, 0 if fatal else 10.0 - ((float(5 * error + warning + refactor + convention) / statement) * 10))
 
 # Template used to display messages. This is a python new-style format string
 # used to format the message information. See doc for all details
diff --git a/tests/test_self.py b/tests/test_self.py
index 27bf17cf6..9f33d745c 100644
--- a/tests/test_self.py
+++ b/tests/test_self.py
@@ -718,11 +718,15 @@ class TestRunTC:
             ],
             code=0,
         )
+        # Need the old evaluation formula to test a negative score
+        # failing below a negative --fail-under threshold
         self._runtest(
             [
                 "--fail-under",
                 "-9",
                 "--enable=all",
+                "--evaluation",
+                "0 if fatal else 10.0 - ((float(5 * error + warning + refactor + convention) / statement) * 10)",
                 join(HERE, "regrtest_data", "fail_under_minus10.py"),
             ],
             code=22,
@@ -732,6 +736,8 @@ class TestRunTC:
                 "--fail-under",
                 "-5",
                 "--enable=all",
+                "--evaluation",
+                "0 if fatal else 10.0 - ((float(5 * error + warning + refactor + convention) / statement) * 10)",
                 join(HERE, "regrtest_data", "fail_under_minus10.py"),
             ],
             code=22,
@@ -777,6 +783,9 @@ class TestRunTC:
                 f"--fail-on={fo_msgs}",
                 "--enable=all",
                 join(HERE, "regrtest_data", fname),
+                # Use the old form of the evaluation that can go negative
+                "--evaluation",
+                "0 if fatal else 10.0 - ((float(5 * error + warning + refactor + convention) / statement) * 10)",
             ],
             code=out,
         )
diff --git a/tests/unittest_reporting.py b/tests/unittest_reporting.py
index dbf2eb1fd..29aac8640 100644
--- a/tests/unittest_reporting.py
+++ b/tests/unittest_reporting.py
@@ -332,8 +332,8 @@ def test_multi_format_output(tmp_path):
         "\n"
         "\n"
         "\n"
-        "-------------------------------------\n"
-        "Your code has been rated at -10.00/10\n"
+        "-----------------------------------\n"
+        "Your code has been rated at 0.00/10\n"
         "\n"
         "direct output\n"
     )