SONARPY-931 Fix parse error: assignment expression within subscription (#997)

Author: guillaume-dequenne

python-frontend/src/main/java/org/sonar/python/api/PythonGrammar.java

@@ -286,7 +286,7 @@ public static void grammar(LexerfulGrammarBuilder b) {
     b.rule(SUBSCRIPTLIST).is(SUBSCRIPT, b.zeroOrMore(",", SUBSCRIPT), b.optional(","));
     b.rule(SUBSCRIPT).is(b.firstOf(
         b.sequence(b.optional(TEST), ":", b.optional(TEST), b.optional(SLICEOP)),
-        TEST));
+        NAMED_EXPR_TEST));
     b.rule(SLICEOP).is(":", b.optional(TEST));
     b.rule(EXPRLIST).is(b.firstOf(EXPR, STAR_EXPR), b.zeroOrMore(",", b.firstOf(EXPR, STAR_EXPR)), b.optional(","));
     b.rule(TESTLIST).is(TEST, b.zeroOrMore(",", TEST), b.optional(","));

python-frontend/src/main/java/org/sonar/python/tree/PythonTreeMaker.java

@@ -1336,7 +1336,7 @@ private Expression subscriptionOrSlicing(Expression expr, Token leftBracket, Ast
     for (AstNode subscript : subscriptList.getChildren(PythonGrammar.SUBSCRIPT)) {
       AstNode colon = subscript.getFirstChild(PythonPunctuator.COLON);
       if (colon == null) {
-        slices.add(expression(subscript.getFirstChild(PythonGrammar.TEST)));
+        slices.add(expression(subscript.getFirstChild(PythonGrammar.NAMED_EXPR_TEST)));
       } else {
         slices.add(sliceItem(subscript));
       }

python-frontend/src/test/java/org/sonar/python/tree/PythonTreeMakerTest.java

@@ -1752,6 +1752,12 @@ public void subscription_expressions() {
     assertThat(subscripts.children().get(1)).isSameAs(subscripts.commas().get(0));
     assertThat(subscripts.expressions()).extracting(Tree::getKind)
       .containsExactly(Tree.Kind.NAME, Tree.Kind.NUMERIC_LITERAL);
+
+    SubscriptionExpression subscriptionExpression = (SubscriptionExpression) parse("a[b:=1]", treeMaker::expression);
+    assertThat(subscriptionExpression.subscripts().expressions()).hasSize(1);
+    AssignmentExpression assignmentExpression = ((AssignmentExpression) subscriptionExpression.subscripts().expressions().get(0));
+    assertThat(assignmentExpression.lhsName().name()).isEqualTo("b");
+    assertThat(((NumericLiteral) assignmentExpression.expression()).valueAsLong()).isEqualTo(1);
   }
 
   @Test