fix: support use of constant in other constant and for struct field d…

…efault value before declaration (#1478)

* fix: support use of constant in other constant and for struct field default value before declaration

Fixes #1477
Fixes #879

* added CHANGELOG.md entry

* fixed review issues and added more positive tests

* use `??=`

* fix

* merge

* fixed review issues

* fixed review issue

* fixed review issue

* fixed review issue

dev-docs/CHANGELOG.md

@@ -66,6 +66,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Incorrect arithmetic bit shift operations optimizations: PR [#1501](https://github.com/tact-lang/tact/pull/1501)
 - Throwing from functions with non-trivial branching in the `try` statement: PR [#1501](https://github.com/tact-lang/tact/pull/1501)
 - Forbid read and write to self in contract init function: PR [#1482](https://github.com/tact-lang/tact/pull/1482)
+- Support for using a constant within another constant and for the default value of a struct field before constant declaration: PR [#1478](https://github.com/tact-lang/tact/pull/1478)
 
 ### Docs
 

src/optimizer/interpreter.ts

@@ -5,9 +5,9 @@ import * as A from "../ast/ast";
 import { evalConstantExpression } from "./constEval";
 import { CompilerContext } from "../context/context";
 import {
+    idTextErr,
     TactCompilationError,
     TactConstEvalError,
-    idTextErr,
     throwConstEvalError,
     throwInternalCompilerError,
 } from "../error/errors";
@@ -20,7 +20,7 @@ import {
     hasStaticFunction,
 } from "../types/resolveDescriptors";
 import { getExpType } from "../types/resolveExpression";
-import { TypeRef, showValue } from "../types/types";
+import { showValue, TypeRef } from "../types/types";
 import { sha256_sync } from "@ton/crypto";
 import { defaultParser, getParser, Parser } from "../grammar/grammar";
 import { dummySrcInfo, SrcInfo } from "../grammar";
@@ -69,6 +69,7 @@ function throwErrorConstEval(msg: string, source: SrcInfo): never {
         source,
     );
 }
+
 type EvalResult =
     | { kind: "ok"; value: A.AstLiteral }
     | { kind: "error"; message: string };
@@ -719,6 +720,18 @@ that binds a variable name to its corresponding value.
 export class Interpreter {
     private envStack: EnvironmentStack;
     private context: CompilerContext;
+
+    /**
+     * Stores all visited constants during the current computation.
+     */
+    private visitedConstants: Set<string> = new Set();
+
+    /**
+     * Stores all constants that were calculated during the computation of some constant,
+     * and the functions that were called for this process.
+     * Used only in case of circular dependencies to return a clear error.
+     */
+    private constantComputationPath: string[] = [];
     private config: InterpreterConfig;
     private util: AstUtil;
 
@@ -870,18 +883,41 @@ export class Interpreter {
     }
 
     public interpretName(ast: A.AstId): A.AstLiteral {
-        if (hasStaticConstant(this.context, idText(ast))) {
-            const constant = getStaticConstant(this.context, idText(ast));
+        const name = idText(ast);
+
+        if (hasStaticConstant(this.context, name)) {
+            const constant = getStaticConstant(this.context, name);
             if (constant.value !== undefined) {
                 return constant.value;
-            } else {
+            }
+
+            // Since we call `interpretExpression` on a constant value below, we don't want
+            // infinite recursion due to circular dependencies. To prevent this, let's collect
+            // all the constants we process in this iteration. That way, any circular dependencies
+            // will result in a second occurrence here and thus an early (before stack overflow)
+            // exception being thrown here.
+            if (this.visitedConstants.has(name)) {
                 throwErrorConstEval(
-                    `cannot evaluate declared constant ${idTextErr(ast)} as it does not have a body`,
+                    `cannot evaluate ${name} as it has circular dependencies: [${this.formatComputationPath(name)}]`,
                     ast.loc,
                 );
             }
+            this.visitedConstants.add(name);
+
+            const astNode = constant.ast;
+            if (astNode.kind === "constant_def") {
+                constant.value = this.inComputationPath(name, () =>
+                    this.interpretExpression(astNode.initializer),
+                );
+                return constant.value;
+            }
+
+            throwErrorConstEval(
+                `cannot evaluate declared constant ${idTextErr(ast)} as it does not have a body`,
+                ast.loc,
+            );
         }
-        const variableBinding = this.envStack.getBinding(idText(ast));
+        const variableBinding = this.envStack.getBinding(name);
         if (variableBinding !== undefined) {
             return variableBinding;
         }
@@ -1401,21 +1437,26 @@ export class Interpreter {
                         this.context,
                         idText(ast.function),
                     );
-                    switch (functionDescription.ast.kind) {
-                        case "function_def":
+                    const functionNode = functionDescription.ast;
+                    switch (functionNode.kind) {
+                        case "function_def": {
                             // Currently, no attribute is supported
-                            if (functionDescription.ast.attributes.length > 0) {
+                            if (functionNode.attributes.length > 0) {
                                 throwNonFatalErrorConstEval(
                                     "calls to functions with attributes are currently not supported",
                                     ast.loc,
                                 );
                             }
-                            return this.evalStaticFunction(
-                                functionDescription.ast,
-                                ast.args,
-                                functionDescription.returns,
+                            return this.inComputationPath(
+                                `${functionDescription.name}()`,
+                                () =>
+                                    this.evalStaticFunction(
+                                        functionNode,
+                                        ast.args,
+                                        functionDescription.returns,
+                                    ),
                             );
-
+                        }
                         case "asm_function_def":
                             throwNonFatalErrorConstEval(
                                 `${idTextErr(ast.function)} cannot be interpreted because it's an asm-function`,
@@ -1771,4 +1812,26 @@ export class Interpreter {
             ast.statements.forEach(this.interpretStatement, this);
         });
     }
+
+    private inComputationPath<T>(path: string, cb: () => T) {
+        this.constantComputationPath.push(path);
+        const res = cb();
+        this.constantComputationPath.pop();
+        return res;
+    }
+
+    private formatComputationPath(name: string): string {
+        const start = this.constantComputationPath.indexOf(name);
+        const path =
+            start !== -1
+                ? this.constantComputationPath.slice(start)
+                : this.constantComputationPath;
+
+        const shortPath =
+            path.length > 10
+                ? [...path.slice(0, 5), "...", ...path.slice(path.length - 4)]
+                : path;
+
+        return `${shortPath.join(" -> ")} -> ${name}`;
+    }
 }

src/test/compilation-failed/const-eval-failed.spec.ts

@@ -193,4 +193,41 @@ describe("fail-const-eval", () => {
         errorMessage:
             "Cannot evaluate expression to a constant: ascii string cannot be empty",
     });
+    itShouldNotCompile({
+        testName: "const-eval-constant-circular-dependency",
+        errorMessage:
+            "Cannot evaluate expression to a constant: cannot evaluate C as it has circular dependencies: [C -> A -> C]",
+    });
+    itShouldNotCompile({
+        testName: "const-eval-constant-deep-circular-dependency",
+        errorMessage:
+            "Cannot evaluate expression to a constant: cannot evaluate E as it has circular dependencies: [E -> D -> C -> B -> A -> E]",
+    });
+    itShouldNotCompile({
+        testName: "const-eval-constant-circular-dependency-with-function",
+        errorMessage:
+            "Cannot evaluate expression to a constant: cannot evaluate C as it has circular dependencies: [C -> A -> foo() -> C]",
+    });
+    itShouldNotCompile({
+        testName: "const-eval-constant-circular-dependency-with-functions",
+        errorMessage:
+            "Cannot evaluate expression to a constant: cannot evaluate C as it has circular dependencies: [C -> A -> foo() -> bar() -> baz() -> C]",
+    });
+    itShouldNotCompile({
+        testName:
+            "const-eval-constant-circular-dependency-with-recursive-function",
+        errorMessage:
+            "Cannot evaluate expression to a constant: cannot evaluate C as it has circular dependencies: [C -> A -> foo() -> foo() -> foo() -> C]",
+    });
+    itShouldNotCompile({
+        testName:
+            "const-eval-constant-circular-dependency-with-deep-recursive-function",
+        errorMessage:
+            "Cannot evaluate expression to a constant: cannot evaluate C as it has circular dependencies: [C -> A -> foo() -> foo() -> foo() -> ... -> foo() -> foo() -> foo() -> foo() -> C]",
+    });
+    itShouldNotCompile({
+        testName: "const-eval-constant-circular-dependency-self-assignment",
+        errorMessage:
+            "Cannot evaluate expression to a constant: cannot evaluate A as it has circular dependencies: [A -> A]",
+    });
 });

src/test/compilation-failed/contracts/const-eval-constant-circular-dependency-self-assignment.tact

@@ -0,0 +1,7 @@
+const A: Int = A;
+
+contract Test {
+    get fun getConstant(): Int {
+        return A;
+    }
+}

src/test/compilation-failed/contracts/const-eval-constant-circular-dependency-with-deep-recursive-function.tact

@@ -0,0 +1,15 @@
+const A: Int = foo(20);
+const C: Int = A;
+
+fun foo(value: Int): Int {
+    if (value > 1) {
+        return foo(value - 1)
+    }
+    return C;
+}
+
+contract Test {
+    get fun getConstant(): Int {
+        return C;
+    }
+}

src/test/compilation-failed/contracts/const-eval-constant-circular-dependency-with-function.tact

@@ -0,0 +1,12 @@
+const A: Int = foo();
+const C: Int = A;
+
+fun foo(): Int {
+    return C;
+}
+
+contract Test {
+    get fun getConstant(): Int {
+        return C;
+    }
+}

src/test/compilation-failed/contracts/const-eval-constant-circular-dependency-with-functions.tact

@@ -0,0 +1,20 @@
+const A: Int = foo();
+const C: Int = A;
+
+fun foo(): Int {
+    return bar()
+}
+
+fun bar(): Int {
+    return baz()
+}
+
+fun baz(): Int {
+    return C
+}
+
+contract Test {
+    get fun getConstant(): Int {
+        return C;
+    }
+}

src/test/compilation-failed/contracts/const-eval-constant-circular-dependency-with-recursive-function.tact

@@ -0,0 +1,15 @@
+const A: Int = foo(3);
+const C: Int = A;
+
+fun foo(value: Int): Int {
+    if (value > 1) {
+        return foo(value - 1)
+    }
+    return C;
+}
+
+contract Test {
+    get fun getConstant(): Int {
+        return C;
+    }
+}

src/test/compilation-failed/contracts/const-eval-constant-circular-dependency.tact

@@ -0,0 +1,8 @@
+const A: Int = C;
+const C: Int = A;
+
+contract Test {
+    get fun getConstant(): Int {
+        return C;
+    }
+}

src/test/compilation-failed/contracts/const-eval-constant-deep-circular-dependency.tact

@@ -0,0 +1,11 @@
+const A: Int = E;
+const B: Int = A;
+const C: Int = B;
+const D: Int = C;
+const E: Int = D;
+
+contract Test {
+    get fun getConstant(): Int {
+        return E;
+    }
+}

src/test/e2e-emulated/constants.spec.ts

@@ -129,5 +129,10 @@ describe("constants", () => {
         expect(await contract.getGlobalConst11()).toEqual(24n);
         expect(await contract.getGlobalConst12()).toEqual(8n);
         expect(await contract.getGlobalConst13()).toEqual(8n);
+
+        expect(await contract.getBeforeDefinedA()).toEqual(10n);
+        expect(await contract.getBeforeDefinedC()).toEqual(20n);
+        expect(await contract.getDefaultFieldB()).toEqual(20n);
+        expect(await contract.getNoCircularA()).toEqual(200n);
     });
 });

src/test/e2e-emulated/contracts/constants.tact

@@ -14,6 +14,14 @@ const globalConst11: Int = factorial_iterative(globalConst3);  // 4! = 24
 const globalConst12: Int = fibonacci_recursive(globalConst3 + 2);  // fibonacci(6) = 8
 const globalConst13: Int = fibonacci_iterative(globalConst3 + 2);  // fibonacci(6) = 8
 
+const beforeDefinedC: Int = beforeDefinedA + beforeDefinedB;
+const beforeDefinedA: Int = beforeDefinedB;
+const beforeDefinedB: Int = 10;
+
+struct A {
+    b: Int = beforeDefinedC;
+}
+
 struct S {
     a: Bool;
     b: Int;
@@ -24,6 +32,17 @@ struct T {
     s: S;
 }
 
+const NoCircularA: Int = NoCircularB;
+const NoCircularB: Int = useAConditionally(1);
+
+fun useAConditionally(v: Int): Int {
+    if (v == 1) {
+        return 100;
+    } else {
+        return NoCircularA; // The else never executes, so no circular dependence at compile-time
+    }
+}
+
 // Global functions
 
 // Test assignments
@@ -327,6 +346,13 @@ contract ConstantTester {
     get fun globalConst12(): Int { return globalConst12; }
     get fun globalConst13(): Int { return globalConst13; }
 
+    get fun beforeDefinedA(): Int { return beforeDefinedA; }
+    get fun beforeDefinedC(): Int { return beforeDefinedC; }
+
+    get fun defaultFieldB(): Int { return A {}.b; }
+
+    get fun noCircularA(): Int { return NoCircularA + NoCircularB; }
+
     get fun minInt1(): Int {
         return -115792089237316195423570985008687907853269984665640564039457584007913129639936;
     }
@@ -342,4 +368,4 @@ contract ConstantTester {
     get fun globalConst(): Int {
         return someGlobalConst;
     }
-}
+}

src/types/__snapshots__/resolveStatements.spec.ts.snap

@@ -1789,6 +1789,32 @@ exports[`resolveStatements should resolve statements for assign-self-mutating-me
 ]
 `;
 
+exports[`resolveStatements should resolve statements for constant-as-default-value-of-struct-field 1`] = `
+[
+  [
+    "100",
+    "Int",
+  ],
+  [
+    "C",
+    "Int",
+  ],
+]
+`;
+
+exports[`resolveStatements should resolve statements for constant-as-default-value-of-struct-field-2 1`] = `
+[
+  [
+    "100",
+    "Int",
+  ],
+  [
+    "C",
+    "Int",
+  ],
+]
+`;
+
 exports[`resolveStatements should resolve statements for contract-getter-with-method-id-1 1`] = `
 [
   [