From 6d6a326e922a98c10516dd76e15db47ab7974d2e Mon Sep 17 00:00:00 2001
From: Marc Mueller <30130371+cdce8p@users.noreply.github.com>
Date: Thu, 25 Mar 2021 22:26:01 +0100
Subject: [PATCH] Improve handling of assignment expressions

---
 ChangeLog                                    |  4 ++++
 pylint/checkers/variables.py                 | 23 +++++++++++++++++++-
 pylint/constants.py                          |  1 +
 tests/functional/a/assignment_expression.py  | 21 ++++++++++++++++++
 tests/functional/a/assignment_expression.txt |  7 +++---
 5 files changed, 52 insertions(+), 4 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index e9612696f9..c6914c618b 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -71,6 +71,10 @@ Release date: TBA
 
   Closes #4218
 
+* Improve handling of assignment expressions, better edge case handling
+
+  Closes #3763, #4238
+
 
 What's New in Pylint 2.7.2?
 ===========================
diff --git a/pylint/checkers/variables.py b/pylint/checkers/variables.py
index 3d7eadc20d..f9c1f0fe4c 100644
--- a/pylint/checkers/variables.py
+++ b/pylint/checkers/variables.py
@@ -59,6 +59,7 @@
 
 from pylint.checkers import BaseChecker, utils
 from pylint.checkers.utils import is_postponed_evaluation_enabled
+from pylint.constants import PY39_PLUS
 from pylint.interfaces import HIGH, INFERENCE, INFERENCE_FAILURE, IAstroidChecker
 from pylint.utils import get_global_option
 
@@ -1410,7 +1411,15 @@ def _is_variable_violation(
                     # same line as the function definition
                     maybee0601 = False
                 elif (
-                    isinstance(defstmt, astroid.Assign)
+                    isinstance(
+                        defstmt,
+                        (
+                            astroid.Assign,
+                            astroid.AnnAssign,
+                            astroid.AugAssign,
+                            astroid.Expr,
+                        ),
+                    )
                     and isinstance(defstmt.value, astroid.IfExp)
                     and frame is defframe
                     and defframe.parent_of(node)
@@ -1433,6 +1442,18 @@ def _is_variable_violation(
                             and defnode.col_offset < node.col_offset
                         )
                         or (defnode.lineno < node.lineno)
+                        or (
+                            # Issue in the `ast` module until py39
+                            # Nodes in a multiline string have the same lineno
+                            # Could be false-positive without check
+                            not PY39_PLUS
+                            and defnode.lineno == node.lineno
+                            and isinstance(
+                                defstmt,
+                                (astroid.Assign, astroid.AnnAssign, astroid.AugAssign),
+                            )
+                            and isinstance(defstmt.value, astroid.JoinedStr)
+                        )
                     )
                 ):
                     # Expressions, with assignment expressions
diff --git a/pylint/constants.py b/pylint/constants.py
index 929eed97ee..7181cb3550 100644
--- a/pylint/constants.py
+++ b/pylint/constants.py
@@ -8,6 +8,7 @@
 from pylint.__pkginfo__ import version as pylint_version
 
 PY38_PLUS = sys.version_info[:2] >= (3, 8)
+PY39_PLUS = sys.version_info[:2] >= (3, 9)
 PY310_PLUS = sys.version_info[:2] >= (3, 10)
 
 
diff --git a/tests/functional/a/assignment_expression.py b/tests/functional/a/assignment_expression.py
index ed8400163d..aa6a27874f 100644
--- a/tests/functional/a/assignment_expression.py
+++ b/tests/functional/a/assignment_expression.py
@@ -8,6 +8,9 @@
     x = False
 
 x = b if (b := True) else False
+x2: bool = b2 if (b2 := True) else False
+x3 = 0
+x3 += b3 if (b3 := 4) else 6
 
 a = ["a   ", "b   ", "c   "]
 c = [text for el in a if (text := el.strip()) == "b"]
@@ -49,6 +52,24 @@ def func():
 print(function())
 
 
+# https://github.com/PyCQA/pylint/issues/3763
+foo if (foo := 3 - 2) > 0 else 0  # [pointless-statement]
+
+
+# https://github.com/PyCQA/pylint/issues/4238
+l1 = f'The number {(count1 := 4)} ' \
+     f'is equal to {count1}'
+l2: str = (
+    f'The number {(count2 := 4)} '
+    f'is equal to {count2}'
+)
+l3 = "Hello "
+l3 += (
+    f'The number {(count3 := 4)} '
+    f'is equal to {count3}'
+)
+
+
 # check wrong usage
 assert err_a, (err_a := 2)  # [used-before-assignment]
 print(err_b and (err_b := 2))  # [used-before-assignment]
diff --git a/tests/functional/a/assignment_expression.txt b/tests/functional/a/assignment_expression.txt
index df472fdd20..1be4c1389d 100644
--- a/tests/functional/a/assignment_expression.txt
+++ b/tests/functional/a/assignment_expression.txt
@@ -1,3 +1,4 @@
-used-before-assignment:53:7::Using variable 'err_a' before assignment
-used-before-assignment:54:6::Using variable 'err_b' before assignment
-used-before-assignment:56:13::Using variable 'err_d' before assignment
+pointless-statement:56:0::Statement seems to have no effect
+used-before-assignment:74:7::Using variable 'err_a' before assignment
+used-before-assignment:75:6::Using variable 'err_b' before assignment
+used-before-assignment:77:13::Using variable 'err_d' before assignment