Issue 5004. Type inference with 'is!' and 'continue'.

compiler/java/com/google/dart/compiler/type/TypeAnalyzer.java

Index: compiler/java/com/google/dart/compiler/type/TypeAnalyzer.java
diff --git a/compiler/java/com/google/dart/compiler/type/TypeAnalyzer.java b/compiler/java/com/google/dart/compiler/type/TypeAnalyzer.java
index a3956a14f465c0649d8136032ee814314627dd02..dbb37a305817a62b395f549ba8bb5f02afe0d4ee 100644
--- a/compiler/java/com/google/dart/compiler/type/TypeAnalyzer.java
+++ b/compiler/java/com/google/dart/compiler/type/TypeAnalyzer.java
@@ -789,6 +789,22 @@ public class TypeAnalyzer implements DartCompilationPhase {
      *         the exit from the enclosing function.
      */
     private static boolean isExitFromFunction(DartStatement statement) {
+      return isExitFromFunction(statement, false);
+    }
+
+    /**
+     * @return <code>true</code> if we can prove that given {@link DartStatement} always leads to
+     *         the exit from the enclosing function, or stops execution of the enclosing loop.
+     */
+    private static boolean isExitFromFunctionOrLoop(DartStatement statement) {
+      return isExitFromFunction(statement, true);
+    }
+
+    /**
+     * @return <code>true</code> if we can prove that given {@link DartStatement} always leads to
+     *         the exit from the enclosing function, or stops enclosing loop execution.
+     */
+    private static boolean isExitFromFunction(DartStatement statement, boolean orLoop) {
       // "return" is always exit
       if (statement instanceof DartReturnStatement) {
         return true;
@@ -810,7 +826,16 @@ public class TypeAnalyzer implements DartCompilationPhase {
         DartBlock block = (DartBlock) statement;
         List<DartStatement> statements = block.getStatements();
         if (!statements.isEmpty()) {
-          return isExitFromFunction(statements.get(statements.size() - 1));
+          return isExitFromFunction(statements.get(statements.size() - 1), orLoop);
+        }
+      }
+      // check also if we stop execution of the loop body
+      if (orLoop) {
+        if (statement instanceof DartContinueStatement) {
+          return true;
+        }
+        if (statement instanceof DartBreakStatement) {
+          return true;
         }
       }
       // can not prove that given statement is always exit
@@ -1845,9 +1870,20 @@ public class TypeAnalyzer implements DartCompilationPhase {
           variableRestorer.restore();
           blockOldTypes.removeFirst();
         }
-        // if no "else", then inferred types applied to the end of the method
-        if (elseStatement == null && isExitFromFunction(thenStatement)) {
-          inferVariableTypesFromIsNotConditions(condition, variableRestorer);
+        // if no "else", then inferred types applied to the end of the method/loop
+        if (elseStatement == null) {
+          if (isExitFromFunction(thenStatement)) {
+            inferVariableTypesFromIsNotConditions(condition, variableRestorer);
+          } else if (isExitFromFunctionOrLoop(thenStatement)) {
+            DartBlock restoreBlock = getBlockForLoopTypesInference(node);
+            variableRestorer = restoreOnBlockExit.get(restoreBlock);
+            if (variableRestorer == null) {
+              variableRestorer = new VariableElementsRestorer();
+              restoreOnBlockExit.put(restoreBlock, variableRestorer);
+            }
+            restoreOnBlockExit.put(restoreBlock, variableRestorer);
+            inferVariableTypesFromIsNotConditions(condition, variableRestorer);
+          }
         }
       }
       Map<VariableElement, Type> elseVariableTypes = elseTypeContext.getNewTypesAndRestoreOld();
@@ -2585,6 +2621,21 @@ public class TypeAnalyzer implements DartCompilationPhase {
       return null;
     }
 
+    private static DartBlock getBlockForLoopTypesInference(DartNode node) {
+      while (node != null) {
+        if (node instanceof DartBlock) {
+          DartBlock block = (DartBlock) node;
+          DartNode p = block.getParent();
+          if (p instanceof DartForStatement || p instanceof DartForInStatement
+              || p instanceof DartWhileStatement) {
+            return block;
+          }
+        }
+        node = node.getParent();
+      }
+      return null;
+    }
+
     /**
      * Report warning if given {@link Element} is deprecated.
      */