Add wielding of try/catch statements

teavm-core/src/main/java/org/teavm/javascript/OptimizingVisitor.java

@@ -321,9 +321,45 @@ class OptimizingVisitor implements StatementVisitor, ExprVisitor {
                 return false;
             }
         }
+        wieldTryCatch(statements);
         return true;
     }
 
+    private void wieldTryCatch(List<Statement> statements) {
+        for (int i = 0; i < statements.size() - 1; ++i) {
+            if (statements.get(i) instanceof TryCatchStatement && statements.get(i + 1) instanceof TryCatchStatement) {
+                TryCatchStatement first = (TryCatchStatement)statements.get(i);
+                TryCatchStatement second = (TryCatchStatement)statements.get(i + 1);
+                if (Objects.equals(first.getExceptionType(), second.getExceptionType()) &&
+                        Objects.equals(first.getExceptionVariable(), second.getExceptionVariable()) &&
+                        briefStatementComparison(first.getHandler(), second.getHandler())) {
+                    first.getProtectedBody().addAll(second.getProtectedBody());
+                    statements.remove(i + 1);
+                    wieldTryCatch(first.getProtectedBody());
+                    --i;
+                    continue;
+                }
+            }
+        }
+    }
+
+    private boolean briefStatementComparison(List<Statement> firstSeq, List<Statement> secondSeq) {
+        if (firstSeq.isEmpty() && secondSeq.isEmpty()) {
+            return true;
+        }
+        if (firstSeq.size() != 1 || secondSeq.size() != 1) {
+            return false;
+        }
+        Statement first = firstSeq.get(0);
+        Statement second = secondSeq.get(0);
+        if (first instanceof BreakStatement && second instanceof BreakStatement) {
+            BreakStatement firstBreak = (BreakStatement)first;
+            BreakStatement secondBreak = (BreakStatement)second;
+            return firstBreak.getTarget() == secondBreak.getTarget();
+        }
+        return false;
+    }
+
     private void eliminateRedundantBreaks(List<Statement> statements, IdentifiedStatement exit) {
         if (statements.isEmpty()) {
             return;

teavm-core/src/main/java/org/teavm/javascript/Renderer.java

@@ -641,7 +641,6 @@ public class Renderer implements ExprVisitor, StatementVisitor, RenderingContext
                     writer.append(")").ws().append("{").indent().softNewLine();
                     AsyncMethodPart part = methodNode.getBody().get(i);
                     part.getStatement().acceptVisitor(Renderer.this);
-                    writer.append("return $return($rt_asyncError($guard));").softNewLine();
                     writer.outdent().append("},").ws().append("$return);").softNewLine();
                 }
                 writer.append("return $part_0();").softNewLine();

teavm-samples/teavm-samples-async/src/main/java/org/teavm/samples/async/AsyncProgram.java

@@ -55,5 +55,18 @@ public final class AsyncProgram {
             }
         }
         System.out.println("Complete async");
+
+        System.out.println("Throwing exception");
+        try {
+            throwException();
+        } catch (IllegalStateException e) {
+            System.out.println("Exception caught");
+        }
+    }
+
+    private static void throwException() {
+        Thread.yield();
+        System.out.println("Thread.yield called");
+        throw new IllegalStateException();
     }
 }