Pass DataFlowInfo through when-conditions

compiler/frontend/src/org/jetbrains/jet/lang/types/expressions/PatternMatchingTypingVisitor.java

@@ -116,9 +116,6 @@ public class PatternMatchingTypingVisitor extends ExpressionTypingVisitor {
                 if (newDataFlowInfo == null) {
                     newDataFlowInfo = context.dataFlowInfo;
                 }
-                else {
-                    newDataFlowInfo = newDataFlowInfo.and(context.dataFlowInfo);
-                }
             }
             JetExpression bodyExpression = whenEntry.getExpression();
             if (bodyExpression != null) {
@@ -259,14 +256,21 @@ public class PatternMatchingTypingVisitor extends ExpressionTypingVisitor {
                 JetExpression expression = pattern.getExpression();
                 if (expression == null) return;
                 JetType type = facade.getTypeInfo(expression, context.replaceScope(scopeToExtend)).getType();
+                if (type == null) return;
                 if (conditionExpected) {
                     JetType booleanType = JetStandardLibrary.getInstance().getBooleanType();
-                    if (type != null && !JetTypeChecker.INSTANCE.equalTypes(booleanType, type)) {
+                    if (!JetTypeChecker.INSTANCE.equalTypes(booleanType, type)) {
                         context.trace.report(TYPE_MISMATCH_IN_CONDITION.on(pattern, type));
                     }
                     return;
                 }
                 checkTypeCompatibility(type, subjectType, pattern);
+                DataFlowInfo dataFlowInfo = context.dataFlowInfo;
+                DataFlowValue expressionDataFlowValue = DataFlowValueFactory.INSTANCE.createDataFlowValue(expression, type, context.trace.getBindingContext());
+                for (DataFlowValue subjectVariable : subjectVariables) {
+                    dataFlowInfo = dataFlowInfo.equate(subjectVariable, expressionDataFlowValue);
+                }
+                result.set(dataFlowInfo);
             }
 
             @Override

compiler/testData/diagnostics/tests/dataFlowInfoTraversal/When.jet

@@ -11,7 +11,7 @@ fun foo() {
     }
 
     when (x) {
-        0 -> { if (x == null) return }
+        0 -> { if (<!SENSELESS_COMPARISON!>x == null<!>) return }
         else -> { if (x == null) return }
     }
     bar(x)

compiler/testData/diagnostics/tests/regressions/Jet169.jet

@@ -1,7 +1,7 @@
 fun set(<!UNUSED_PARAMETER!>key<!> : String, <!UNUSED_PARAMETER!>value<!> : String) {
   val a : String? = ""
   when (a) {
-    "" -> a<!UNSAFE_CALL!>.<!>get(0)
+    "" -> a.get(0)
     is String, is Any -> a.compareTo("")
     else -> a.toString()
   }

idea/testData/checker/regression/Jet169.jet

@@ -1,7 +1,7 @@
 fun set(<warning>key</warning> : String, <warning>value</warning> : String) {
   val a : String? = ""
   when (a) {
-    "" -> a<error>.</error>get(0)
+    "" -> a.get(0)
     is String, is Any -> a.compareTo("")
     else -> a.toString()
   }