fix: contract method calls in return statements (#829)

CHANGELOG.md

@@ -39,6 +39,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Return-statements in `init()` function do not cause FunC compilation error anymore: PR [#794](https://github.com/tact-lang/tact/pull/794)
 - `emptyMap()` in equality comparison expressions does not cause code generation failures: PR [#814](https://github.com/tact-lang/tact/pull/814)
 - Maps with `coins` as value type are now correctly handled in structs: PR [#821](https://github.com/tact-lang/tact/pull/821)
+- Contract method calls in return statements: PR [#829](https://github.com/tact-lang/tact/pull/829)
 
 ## [1.4.4] - 2024-08-18
 

src/generator/writers/writeFunction.ts

@@ -88,7 +88,14 @@ export function writeStatement(
 
                 // Return
                 if (self) {
-                    ctx.append(`return (${self}, ${result});`);
+                    // we introduce an intermediate return variable here
+                    // to treat the case of a contract method call which
+                    // can modify "self", otherwise the "self" below would
+                    // contain the old state of contract, not the one
+                    // updated in the "result" expression
+                    const retVar = freshIdentifier("ret");
+                    ctx.append(`var ${retVar} = ${result};`);
+                    ctx.append(`return (${self}, ${retVar});`);
                 } else {
                     ctx.append(`return ${result};`);
                 }

src/test/e2e-emulated/contract-methods.spec.ts

@@ -0,0 +1,32 @@
+import { toNano } from "@ton/core";
+import { Blockchain, SandboxContract, TreasuryContract } from "@ton/sandbox";
+import { Test } from "./contracts/output/contract-methods_Test";
+import "@ton/test-utils";
+
+describe("contract-methods", () => {
+    let blockchain: Blockchain;
+    let treasure: SandboxContract<TreasuryContract>;
+    let contract: SandboxContract<Test>;
+
+    beforeEach(async () => {
+        blockchain = await Blockchain.create();
+        blockchain.verbosity.print = false;
+        treasure = await blockchain.treasury("treasure");
+
+        contract = blockchain.openContract(await Test.fromInit());
+
+        const deployResult = await contract.send(
+            treasure.getSender(),
+            { value: toNano("10") },
+            null,
+        );
+        expect(deployResult.transactions).toHaveTransaction({
+            from: treasure.address,
+            to: contract.address,
+            success: true,
+            deploy: true,
+        });
+    });
+
+    it("should implement contract methods correctly", async () => {});
+});

src/test/e2e-emulated/contracts/contract-methods.tact

@@ -0,0 +1,24 @@
+contract Test {
+    flags: Int as uint256 = 0;
+    oneMoreVar: Int = 239;
+    receive() {
+        self.checkImmediateReturn();
+        require(self.flags == 42, "checkImmediateReturn() is mis-compiled");
+        self.flags = 0;
+        self.checkReturnViaLocalVar();
+        require(self.flags == 42, "checkReturnViaLocalVar() is mis-compiled");
+    }
+
+    fun checkImmediateReturn(): Bool {
+        return self.check();
+    }
+    fun checkReturnViaLocalVar(): Bool {
+        let foo = self.check();
+        return foo;
+    }
+    fun check(): Bool {
+        self.flags = 42;
+        return true;
+    }
+}
+

tact.config.json

@@ -410,6 +410,11 @@
       "name": "semantics",
       "path": "./src/test/e2e-emulated/contracts/semantics.tact",
       "output": "./src/test/e2e-emulated/contracts/output"
+    },
+    {
+      "name": "contract-methods",
+      "path": "./src/test/e2e-emulated/contracts/contract-methods.tact",
+      "output": "./src/test/e2e-emulated/contracts/output"
     }
   ]
 }