Test and implementation for KT-6819. Now when entry condition data flow information is used for subsequent conditions. #KT-6819 Fixed

compiler/frontend/src/org/jetbrains/kotlin/types/expressions/PatternMatchingTypingVisitor.java

@@ -143,15 +143,17 @@ public class PatternMatchingTypingVisitor extends ExpressionTypingVisitor {
         }
 
         DataFlowInfos infos = null;
+        ExpressionTypingContext contextForCondition = context;
         for (JetWhenCondition condition : whenEntry.getConditions()) {
             DataFlowInfos conditionInfos = checkWhenCondition(subjectExpression, subjectType, condition,
-                                                              context, subjectDataFlowValue);
+                                                              contextForCondition, subjectDataFlowValue);
             if (infos != null) {
                 infos = new DataFlowInfos(infos.thenInfo.or(conditionInfos.thenInfo), infos.elseInfo.and(conditionInfos.elseInfo));
             }
             else {
                 infos = conditionInfos;
             }
+            contextForCondition = contextForCondition.replaceDataFlowInfo(conditionInfos.elseInfo);
         }
         return infos != null ? infos : new DataFlowInfos(context.dataFlowInfo);
     }

compiler/testData/diagnostics/tests/smartCasts/varnotnull/kt6819.kt

@@ -0,0 +1,7 @@
+public fun test(o: String?): Boolean {
+    return when {
+        // Data flow info should propagate from o == null to o.length()
+        o == null, <!DEBUG_INFO_SMARTCAST!>o<!>.length() == 0 -> false 
+        else -> true
+    }
+}

compiler/testData/diagnostics/tests/smartCasts/varnotnull/kt6819.txt

@@ -0,0 +1,3 @@
+package
+
+public fun test(/*0*/ o: kotlin.String?): kotlin.Boolean

compiler/tests/org/jetbrains/kotlin/checkers/JetDiagnosticsTestGenerated.java

@@ -11412,6 +11412,12 @@ public class JetDiagnosticsTestGenerated extends AbstractJetDiagnosticsTest {
                     String fileName = JetTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/smartCasts/varnotnull/kt5907var.kt");
                     doTest(fileName);
                 }
+
+                @TestMetadata("kt6819.kt")
+                public void testKt6819() throws Exception {
+                    String fileName = JetTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/smartCasts/varnotnull/kt6819.kt");
+                    doTest(fileName);
+                }
             }
         }