Add support for reassigning variables inside tuple assignments

packages/cashc/src/Errors.ts

@@ -20,6 +20,7 @@ import {
   ContractNode,
   SliceNode,
   IntLiteralNode,
+  TupleAssignmentNode,
 } from './ast/AST.js';
 import { Symbol, SymbolType } from './ast/SymbolTable.js';
 import { Location } from './ast/Location.js';
@@ -283,6 +284,15 @@ export class DivisionByZeroError extends CashScriptError {
   }
 }
 
+export class DuplicateTupleTargetError extends CashScriptError {
+  constructor(
+    node: TupleAssignmentNode,
+    name: string,
+  ) {
+    super(node, `Duplicate target '${name}' in tuple destructuring`);
+  }
+}
+
 export class ConstantModificationError extends CashScriptError {
   constructor(node: VariableDefinitionNode | ConstantDefinitionNode);
   constructor(node: Node, name: string);

packages/cashc/src/ast/AST.ts

@@ -155,13 +155,13 @@ export class VariableDefinitionNode extends NonControlStatementNode implements N
 }
 
 export interface TupleAssignmentTarget {
-  name: string;
-  type: Type;
+  identifier: IdentifierNode;
+  type?: Type;
+  isReassignment?: boolean;
 }
 
 export class TupleAssignmentNode extends NonControlStatementNode {
   constructor(
-    // TODO: Use IdentifierNodes instead of a custom type
     public targets: TupleAssignmentTarget[],
     public tuple: ExpressionNode,
   ) {

packages/cashc/src/ast/AstBuilder.ts

@@ -249,11 +249,16 @@ export default class AstBuilder
 
   visitTupleAssignment(ctx: TupleAssignmentContext): TupleAssignmentNode {
     const expression = this.visit(ctx.expression());
-    const types = ctx.typeName_list();
-    const targets = ctx.Identifier_list().map((name, i) => ({
-      name: name.getText(),
-      type: parseType(types[i].getText()),
-    }));
+    const targets = ctx.tupleTarget_list().map((target) => {
+      const typeName = target.typeName();
+      const identifier = new IdentifierNode(target.Identifier().getText());
+      identifier.location = Location.fromToken(target.Identifier().symbol);
+      return {
+        identifier,
+        type: typeName ? parseType(typeName.getText()) : undefined,
+        isReassignment: !typeName,
+      };
+    });
     const tupleAssignment = new TupleAssignmentNode(targets, expression);
     tupleAssignment.location = Location.fromCtx(ctx);
     return tupleAssignment;

packages/cashc/src/generation/GenerateTargetTraversal.ts

@@ -508,8 +508,34 @@ export default class GenerateTargetTraversal extends AstTraversal {
 
   visitTupleAssignment(node: TupleAssignmentNode): Node {
     node.tuple = this.visit(node.tuple);
-    this.popFromStack(node.targets.length);
-    node.targets.forEach((target) => this.pushToStack(target.name));
+
+    // Outside of a loop/branch, a reassignment is just a rename (the old value stays on the stack)
+    const scopedReassign = this.scopeDepth > 0 && node.targets.some((target) => target.isReassignment);
+    if (!scopedReassign) {
+      this.popFromStack(node.targets.length);
+      node.targets.forEach((target) => this.pushToStack(target.identifier.name));
+      return node;
+    }
+
+    const locationData = { location: node.location, positionHint: PositionHint.END };
+    const parkedDeclarations: string[] = [];
+
+    const reversedTargets = [...node.targets].reverse();
+    reversedTargets.forEach((target) => {
+      if (target.isReassignment) {
+        this.emitReplace(this.getStackIndex(target.identifier.name), node);
+      } else {
+        this.emit(Op.OP_TOALTSTACK, locationData);
+        parkedDeclarations.push(target.identifier.name);
+      }
+      this.popFromStack();
+    });
+
+    parkedDeclarations.reverse().forEach((name) => {
+      this.emit(Op.OP_FROMALTSTACK, locationData);
+      this.pushToStack(name);
+    });
+
     return node;
   }
 
@@ -1017,4 +1043,3 @@ export default class GenerateTargetTraversal extends AstTraversal {
     return node;
   }
 }
-

packages/cashc/src/grammar/CashScript.g4

@@ -101,7 +101,13 @@ variableDefinition
     ;
 
 tupleAssignment
-    : typeName Identifier (',' typeName Identifier)+ '=' expression
+    : tupleTarget (',' tupleTarget)+ '=' expression
+    | '(' tupleTarget (',' tupleTarget)+ ')' '=' expression
+    ;
+
+tupleTarget
+    : typeName Identifier
+    | Identifier
     ;
 
 assignStatement
@@ -215,8 +221,8 @@ numberLiteral
     ;
 
 typeName
-    : PrimitiveType 
-    | BoundedBytes 
+    : PrimitiveType
+    | BoundedBytes
     | UnboundedBytes
     ;