[literal-comparison] Make the message explicit with the solution

Also update the confidence

Closes #5237

7 files changed, 43 insertions, 26 deletions

diff --git a/doc/data/messages/l/literal-comparison/bad.py b/doc/data/messages/l/literal-comparison/bad.py
index d85667b7e..154d7d6c7 100644
--- a/doc/data/messages/l/literal-comparison/bad.py
+++ b/doc/data/messages/l/literal-comparison/bad.py
@@ -1,2 +1,2 @@
 def is_an_orange(fruit):
-    return fruit is "orange" # [literal-comparison]
+    return fruit is "orange"  # [literal-comparison]
diff --git a/doc/user_guide/checkers/features.rst b/doc/user_guide/checkers/features.rst
index ad6285f07..a23c57c3e 100644
--- a/doc/user_guide/checkers/features.rst
+++ b/doc/user_guide/checkers/features.rst
@@ -168,7 +168,7 @@ Basic checker Messages
   When two literals are compared with each other the result is a constant.
   Using the constant directly is both easier to read and more performant.
   Initializing 'True' and 'False' this way is not required since Python 2.3.
-:literal-comparison (R0123): *Comparison to literal*
+:literal-comparison (R0123): *In '%s', use '%s' when comparing constant literals not '%s' ('%s')*
   Used when comparing an object to a literal, which is usually what you do not
   want to do, since you can compare to a different literal than what was
   expected altogether.
diff --git a/doc/whatsnew/fragments/5237.other b/doc/whatsnew/fragments/5237.other
new file mode 100644
index 000000000..2b3fadfc1
--- /dev/null
+++ b/doc/whatsnew/fragments/5237.other
@@ -0,0 +1,4 @@
+The message for ``literal-comparison`` is now more explicit about the problem and the
+solution.
+
+Closes #5237
diff --git a/pylint/checkers/base/comparison_checker.py b/pylint/checkers/base/comparison_checker.py
index 35e85b82c..98b0ec258 100644
--- a/pylint/checkers/base/comparison_checker.py
+++ b/pylint/checkers/base/comparison_checker.py
@@ -48,7 +48,7 @@ class ComparisonChecker(_BasicChecker):
             {"old_names": [("W0154", "old-unidiomatic-typecheck")]},
         ),
         "R0123": (
-            "Comparison to literal",
+            "In '%s', use '%s' when comparing constant literals not '%s' ('%s')",
             "literal-comparison",
             "Used when comparing an object to a literal, which is usually "
             "what you do not want to do, since you can compare to a different "
@@ -201,7 +201,20 @@ class ComparisonChecker(_BasicChecker):
             is_const = isinstance(literal.value, (bytes, str, int, float))
 
         if is_const or is_other_literal:
-            self.add_message("literal-comparison", node=node)
+            bad = node.as_string()
+            if "is not" in bad:
+                equal_or_not_equal = "!="
+                is_or_is_not = "is not"
+            else:
+                equal_or_not_equal = "=="
+                is_or_is_not = "is"
+            good = bad.replace(is_or_is_not, equal_or_not_equal)
+            self.add_message(
+                "literal-comparison",
+                args=(bad, equal_or_not_equal, is_or_is_not, good),
+                node=node,
+                confidence=HIGH,
+            )
 
     def _check_logical_tautology(self, node: nodes.Compare) -> None:
         """Check if identifier is compared against itself.
diff --git a/tests/functional/c/comparison_of_constants.txt b/tests/functional/c/comparison_of_constants.txt
index 1a0984024..60b421009 100644
--- a/tests/functional/c/comparison_of_constants.txt
+++ b/tests/functional/c/comparison_of_constants.txt
@@ -1,9 +1,9 @@
 comparison-of-constants:4:3:4:9::"Comparison between constants: '2 is 2' has a constant value":HIGH
-literal-comparison:4:3:4:9::Comparison to literal:UNDEFINED
+literal-comparison:4:3:4:9::In '2 is 2', use '==' when comparing constant literals not 'is' ('2 == 2'):HIGH
 comparison-of-constants:7:6:7:12::"Comparison between constants: '2 == 2' has a constant value":HIGH
 comparison-of-constants:10:6:10:11::"Comparison between constants: '2 > 2' has a constant value":HIGH
 comparison-of-constants:20:3:20:15::"Comparison between constants: 'True == True' has a constant value":HIGH
 singleton-comparison:20:3:20:15::Comparison 'True == True' should be 'True is True' if checking for the singleton value True, or 'True' if testing for truthiness:UNDEFINED
-literal-comparison:25:3:25:13::Comparison to literal:UNDEFINED
-literal-comparison:28:3:28:13::Comparison to literal:UNDEFINED
-literal-comparison:31:3:31:14::Comparison to literal:UNDEFINED
+literal-comparison:25:3:25:13::In 'CONST is 0', use '==' when comparing constant literals not 'is' ('CONST == 0'):HIGH
+literal-comparison:28:3:28:13::In 'CONST is 1', use '==' when comparing constant literals not 'is' ('CONST == 1'):HIGH
+literal-comparison:31:3:31:14::In 'CONST is 42', use '==' when comparing constant literals not 'is' ('CONST == 42'):HIGH
diff --git a/tests/functional/l/literal_comparison.py b/tests/functional/l/literal_comparison.py
index b5e31a0e7..603c0da7a 100644
--- a/tests/functional/l/literal_comparison.py
+++ b/tests/functional/l/literal_comparison.py
@@ -1,25 +1,25 @@
 # pylint: disable=missing-docstring, comparison-with-itself
 
 
-if 2 is 2: # [literal-comparison, comparison-of-constants]
+if 2 is 2:  # [literal-comparison, comparison-of-constants]
     pass
 
-if "a" is b"a": # [literal-comparison, comparison-of-constants]
+if "a" is b"a":  # [literal-comparison, comparison-of-constants]
     pass
 
-if 2.0 is 3.0: # [literal-comparison, comparison-of-constants]
+if 2.0 is 3.0:  # [literal-comparison, comparison-of-constants]
     pass
 
 if () is (1, 2, 3):
     pass
 
-if () is {1:2, 2:3}: # [literal-comparison]
+if () is {1:2, 2:3}:  # [literal-comparison]
     pass
 
-if [] is [4, 5, 6]: # [literal-comparison]
+if [] is [4, 5, 6]:  # [literal-comparison]
     pass
 
-if () is {1, 2, 3}: # [literal-comparison]
+if () is {1, 2, 3}:  # [literal-comparison]
     pass
 
 if () is not {1:2, 2:3}: # [literal-comparison]
diff --git a/tests/functional/l/literal_comparison.txt b/tests/functional/l/literal_comparison.txt
index c1a679c76..f14c73219 100644
--- a/tests/functional/l/literal_comparison.txt
+++ b/tests/functional/l/literal_comparison.txt
@@ -1,15 +1,15 @@
 comparison-of-constants:4:3:4:9::"Comparison between constants: '2 is 2' has a constant value":HIGH
-literal-comparison:4:3:4:9::Comparison to literal:UNDEFINED
+literal-comparison:4:3:4:9::In '2 is 2', use '==' when comparing constant literals not 'is' ('2 == 2'):HIGH
 comparison-of-constants:7:3:7:14::"Comparison between constants: 'a is b'a'' has a constant value":HIGH
-literal-comparison:7:3:7:14::Comparison to literal:UNDEFINED
+literal-comparison:7:3:7:14::In ''a' is b'a'', use '==' when comparing constant literals not 'is' (''a' == b'a''):HIGH
 comparison-of-constants:10:3:10:13::"Comparison between constants: '2.0 is 3.0' has a constant value":HIGH
-literal-comparison:10:3:10:13::Comparison to literal:UNDEFINED
-literal-comparison:16:3:16:19::Comparison to literal:UNDEFINED
-literal-comparison:19:3:19:18::Comparison to literal:UNDEFINED
-literal-comparison:22:3:22:18::Comparison to literal:UNDEFINED
-literal-comparison:25:3:25:23::Comparison to literal:UNDEFINED
-literal-comparison:28:3:28:22::Comparison to literal:UNDEFINED
-literal-comparison:31:3:31:22::Comparison to literal:UNDEFINED
-literal-comparison:38:3:38:13::Comparison to literal:UNDEFINED
-literal-comparison:41:3:41:13::Comparison to literal:UNDEFINED
-literal-comparison:44:3:44:14::Comparison to literal:UNDEFINED
+literal-comparison:10:3:10:13::In '2.0 is 3.0', use '==' when comparing constant literals not 'is' ('2.0 == 3.0'):HIGH
+literal-comparison:16:3:16:19::"In '() is {1: 2, 2: 3}', use '==' when comparing constant literals not 'is' ('() == {1: 2, 2: 3}')":HIGH
+literal-comparison:19:3:19:18::In '[] is [4, 5, 6]', use '==' when comparing constant literals not 'is' ('[] == [4, 5, 6]'):HIGH
+literal-comparison:22:3:22:18::In '() is {1, 2, 3}', use '==' when comparing constant literals not 'is' ('() == {1, 2, 3}'):HIGH
+literal-comparison:25:3:25:23::"In '() is not {1: 2, 2: 3}', use '!=' when comparing constant literals not 'is not' ('() != {1: 2, 2: 3}')":HIGH
+literal-comparison:28:3:28:22::In '[] is not [4, 5, 6]', use '!=' when comparing constant literals not 'is not' ('[] != [4, 5, 6]'):HIGH
+literal-comparison:31:3:31:22::In '() is not {1, 2, 3}', use '!=' when comparing constant literals not 'is not' ('() != {1, 2, 3}'):HIGH
+literal-comparison:38:3:38:13::In 'CONST is 0', use '==' when comparing constant literals not 'is' ('CONST == 0'):HIGH
+literal-comparison:41:3:41:13::In 'CONST is 1', use '==' when comparing constant literals not 'is' ('CONST == 1'):HIGH
+literal-comparison:44:3:44:14::In 'CONST is 42', use '==' when comparing constant literals not 'is' ('CONST == 42'):HIGH