Fixes PY-253: foo[1]=2 now has foo as reference, not target

python/src/com/jetbrains/python/parsing/ExpressionParsing.java

@@ -257,6 +257,11 @@ public class ExpressionParsing extends Parsing {
             else {
               checkMatches(PyTokenTypes.RBRACKET, message("PARSE.expected.rbracket"));
               expr.done(PyElementTypes.SUBSCRIPTION_EXPRESSION);
+              if (first_identifier_is_target) {
+                recast_first_identifier = true; // subscription is always a reference
+                expr.rollbackTo();
+                break;
+              }
             }
           }
           expr = expr.precede();
@@ -265,6 +270,7 @@ public class ExpressionParsing extends Parsing {
           expr.drop();
           break;
         }
+        recast_first_identifier = false; // it is true only after a break; normal flow always unsets it.
       }
     }
     while (recast_first_identifier);

python/testData/psi/SubscribedAssignmentLHS.py

@@ -0,0 +1 @@
+a[1] = 2

python/testData/psi/SubscribedAssignmentLHS.txt

@@ -0,0 +1,14 @@
+PyFile:SubscribedAssignmentLHS.py(0,8)
+  PyAssignmentStatement(0,8)
+    PySubscriptionExpression(0,4)
+      PyReferenceExpression: a(0,1)
+        PsiElement(Py:IDENTIFIER)('a')(0,1)
+      PsiElement(Py:LBRACKET)('[')(1,2)
+      PyNumericLiteralExpression(2,3)
+        PsiElement(Py:INTEGER_LITERAL)('1')(2,3)
+      PsiElement(Py:RBRACKET)(']')(3,4)
+    PsiWhiteSpace(' ')(4,5)
+    PsiElement(Py:EQ)('=')(5,6)
+    PsiWhiteSpace(' ')(6,7)
+    PyNumericLiteralExpression(7,8)
+      PsiElement(Py:INTEGER_LITERAL)('2')(7,8)

python/testSrc/com/jetbrains/python/PythonParsingTest.java

@@ -26,6 +26,10 @@ public class PythonParsingTest extends ParsingTestCase {
     doTest(true);
   }
 
+  public void testSubscribedAssignmentLHS() throws Exception {
+    doTest(true);
+  }
+
   public void testConditionalParenLambda() throws Exception {
     doTest(true);
   }