Do not perform final-verify check inside loops

Author: rkalis

packages/cashc/src/generation/GenerateTargetTraversal.ts

@@ -198,7 +198,7 @@ export default class GenerateTargetTraversalWithLocation extends AstTraversal {
 
   removeFinalVerifyFromFunction(functionBodyNode: Node): void {
     // After EnsureFinalRequireTraversal, we know that the final opcodes are either
-    // "OP_VERIFY", "OP_CHECK{LOCKTIME|SEQUENCE}VERIFY OP_DROP" or "OP_ENDIF"
+    // "OP_VERIFY", "OP_CHECK{LOCKTIME|SEQUENCE}VERIFY OP_DROP", "OP_ENDIF" or "OP_UNTIL"
 
     const finalOp = this.output.pop() as Op;
     const { location, positionHint } = this.locationData.pop()!;
@@ -220,7 +220,7 @@ export default class GenerateTargetTraversalWithLocation extends AstTraversal {
       this.emit(finalOp, { location, positionHint: PositionHint.END });
 
       // At this point there is no verification value left on the stack:
-      //  - scoped stack is cleared inside branch ended by OP_ENDIF
+      //  - scoped stack is cleared inside block ended by OP_ENDIF or OP_UNTIL
       //  - OP_CHECK{LOCKTIME|SEQUENCE}VERIFY OP_DROP does not leave a verification value
       //  - OP_VERIFY does not leave a verification value
       // so we add OP_1 to the script (indicating success)

packages/cashc/src/semantic/EnsureFinalRequireTraversal.ts

@@ -51,8 +51,9 @@ function ensureFinalStatementIsRequire(statements: StatementNode[] = []): void {
     return;
   }
 
+  // TODO: Revisit this later, for now we allow do-while loops to not have a require() at the end
   if (finalStatement instanceof DoWhileNode) {
-    ensureFinalStatementIsRequire(finalStatement.block.statements);
+    // ensureFinalStatementIsRequire(finalStatement.block.statements);
     return;
   }
 

packages/cashc/test/valid-contract-files/do_while_loop_no_tokens_in_inputs.cash

@@ -0,0 +1,13 @@
+pragma cashscript ^0.12.0;
+
+contract Loopy() {
+    function doLoop() {
+        int inputIndex = 0;
+
+        // Loop over all inputs (variable length), and make sure that none of them contain tokens
+        do {
+            require(tx.inputs[inputIndex].tokenCategory == 0x);
+            inputIndex = inputIndex + 1;
+        } while (inputIndex < tx.inputs.length);
+    }
+}