fix: do not allow assignments to constants

CHANGELOG.md

@@ -23,6 +23,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Typechecking for optional types when the argument type is not an equality type: PR [#650](https://github.com/tact-lang/tact/pull/650)
 - Getters now return flattened types for structs as before: PR [#679](https://github.com/tact-lang/tact/pull/679)
 - New bindings cannot shadow global constants: PR [#680](https://github.com/tact-lang/tact/pull/680)
+- Disallow using assignment operators on constants: PR [#682](https://github.com/tact-lang/tact/pull/682)
 
 ## [1.4.1] - 2024-07-26
 

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

@@ -1,5 +1,85 @@
 // Jest Snapshot v1, https://goo.gl/fbAQLP
 
+exports[`resolveStatements should fail statements for assign-augmented-const-contract 1`] = `
+"<unknown>:8:9: Modifications of constant expressions are not allowed
+Line 8, col 9:
+  7 |     fun bar() {
+> 8 |         self.foo += 1 // <-- trying to assign to a constant
+              ^~~~~~~~
+  9 |     }
+"
+`;
+
+exports[`resolveStatements should fail statements for assign-augmented-const-global 1`] = `
+"<unknown>:6:5: Modifications of constant expressions are not allowed
+Line 6, col 5:
+  5 | fun bar() {
+> 6 |     foo += 1 // <-- trying to assign to a constant
+          ^~~
+  7 | }
+"
+`;
+
+exports[`resolveStatements should fail statements for assign-augmented-const-struct-contract 1`] = `
+"<unknown>:12:9: Modifications of constant expressions are not allowed
+Line 12, col 9:
+  11 |         self.baz.x += 1; // ok
+> 12 |         self.foo.y -= 1 // <-- trying to assign to a constant
+               ^~~~~~~~~~
+  13 |     }
+"
+`;
+
+exports[`resolveStatements should fail statements for assign-augmented-const-struct-global 1`] = `
+"<unknown>:10:5: Modifications of constant expressions are not allowed
+Line 10, col 5:
+   9 |     baz.x += 1; // ok
+> 10 |     foo.y -= 1 // <-- trying to assign to a constant
+           ^~~~~
+  11 | }
+"
+`;
+
+exports[`resolveStatements should fail statements for assign-const-contract 1`] = `
+"<unknown>:8:9: Modifications of constant expressions are not allowed
+Line 8, col 9:
+  7 |     fun bar() {
+> 8 |         self.foo = 43 // <-- trying to assign to a constant
+              ^~~~~~~~
+  9 |     }
+"
+`;
+
+exports[`resolveStatements should fail statements for assign-const-global 1`] = `
+"<unknown>:6:5: Modifications of constant expressions are not allowed
+Line 6, col 5:
+  5 | fun bar() {
+> 6 |     foo = 43 // <-- trying to assign to a constant
+          ^~~
+  7 | }
+"
+`;
+
+exports[`resolveStatements should fail statements for assign-const-struct-contract 1`] = `
+"<unknown>:12:9: Modifications of constant expressions are not allowed
+Line 12, col 9:
+  11 |         self.baz.x = 1; // ok
+> 12 |         self.foo.y = 42 // <-- trying to assign to a constant
+               ^~~~~~~~~~
+  13 |     }
+"
+`;
+
+exports[`resolveStatements should fail statements for assign-const-struct-global 1`] = `
+"<unknown>:10:5: Modifications of constant expressions are not allowed
+Line 10, col 5:
+   9 |     baz.x = 1; // ok
+> 10 |     foo.y = 42 // <-- trying to assign to a constant
+           ^~~~~
+  11 | }
+"
+`;
+
 exports[`resolveStatements should fail statements for bounced-type-is-smaller 1`] = `
 "<unknown>:23:22: Type bounced<"A"> does not have a field named "c"
 Line 23, col 22:
@@ -1085,6 +1165,31 @@ Line 9, col 12:
 "
 `;
 
+exports[`resolveStatements should resolve statements for assign-self-mutating-method 1`] = `
+[
+  [
+    "self",
+    "IntWrapper",
+  ],
+  [
+    "self.x",
+    "Int",
+  ],
+  [
+    "42",
+    "Int",
+  ],
+  [
+    "self",
+    "Int",
+  ],
+  [
+    "42",
+    "Int",
+  ],
+]
+`;
+
 exports[`resolveStatements should resolve statements for contract-receiver-bounced 1`] = `
 [
   [

src/types/resolveStatements.ts

@@ -8,6 +8,8 @@ import {
     idText,
     isWildcard,
     selfId,
+    isSelfId,
+    eqNames,
 } from "../grammar/ast";
 import { isAssignable } from "./subtyping";
 import {
@@ -18,6 +20,7 @@ import {
 import {
     getAllStaticFunctions,
     getAllTypes,
+    getType,
     hasStaticConstant,
     resolveTypeRef,
 } from "./resolveDescriptors";
@@ -183,6 +186,29 @@ function processCondition(
     };
 }
 
+// Precondition: `self` here means a contract or a trait,
+// and not a `self` parameter of a mutating method
+function isLvalue(path: AstId[], ctx: CompilerContext): boolean {
+    const headId = path[0]!;
+    if (isSelfId(headId) && path.length > 1) {
+        // we can be dealing with a contract/trait constant `self.constFoo`
+        const selfTypeRef = getExpType(ctx, headId);
+        if (selfTypeRef.kind == "ref") {
+            const contractTypeDescription = getType(ctx, selfTypeRef.name);
+            return (
+                contractTypeDescription.constants.findIndex((constDescr) =>
+                    eqNames(path[1]!, constDescr.name),
+                ) === -1
+            );
+        } else {
+            return true;
+        }
+    } else {
+        // if the head path symbol is a global constant, then the whole path expression is a constant
+        return !hasStaticConstant(ctx, idText(headId));
+    }
+}
+
 function processStatements(
     statements: AstStatement[],
     sctx: StatementContext,
@@ -251,6 +277,12 @@ function processStatements(
                             s.path.loc,
                         );
                     }
+                    if (!isLvalue(path, ctx)) {
+                        throwCompilationError(
+                            "Modifications of constant expressions are not allowed",
+                            s.path.loc,
+                        );
+                    }
 
                     // Process expression
                     ctx = resolveExpression(s.expression, sctx, ctx);
@@ -289,6 +321,12 @@ function processStatements(
                             s.path.loc,
                         );
                     }
+                    if (!isLvalue(path, ctx)) {
+                        throwCompilationError(
+                            "Modifications of constant expressions are not allowed",
+                            s.path.loc,
+                        );
+                    }
 
                     // Process expression
                     ctx = resolveExpression(s.expression, sctx, ctx);

src/types/stmts-failed/assign-augmented-const-contract.tact

@@ -0,0 +1,10 @@
+primitive Int;
+trait BaseTrait { }
+
+contract Test {
+    const foo: Int = 42;
+
+    fun bar() {
+        self.foo += 1 // <-- trying to assign to a constant
+    }
+}

src/types/stmts-failed/assign-augmented-const-global.tact

@@ -0,0 +1,7 @@
+primitive Int;
+
+const foo: Int = 42;
+
+fun bar() {
+    foo += 1 // <-- trying to assign to a constant
+}

src/types/stmts-failed/assign-augmented-const-struct-contract.tact

@@ -0,0 +1,14 @@
+primitive Int;
+trait BaseTrait { }
+
+struct Foo {x: Int; y: Int}
+
+contract Test {
+    const foo: Foo = Foo {x: 42, y: 43};
+    baz: Foo = Foo {x: 42, y: 43};
+
+    fun bar() {
+        self.baz.x += 1; // ok
+        self.foo.y -= 1 // <-- trying to assign to a constant
+    }
+}

src/types/stmts-failed/assign-augmented-const-struct-global.tact

@@ -0,0 +1,11 @@
+primitive Int;
+
+struct Foo {x: Int; y: Int}
+
+const foo: Foo = Foo {x: 42, y: 43};
+
+fun bar() {
+    let baz: Foo = Foo {x: 42, y: 43};
+    baz.x += 1; // ok
+    foo.y -= 1 // <-- trying to assign to a constant
+}

src/types/stmts-failed/assign-const-contract.tact

@@ -0,0 +1,10 @@
+primitive Int;
+trait BaseTrait { }
+
+contract Test {
+    const foo: Int = 42;
+
+    fun bar() {
+        self.foo = 43 // <-- trying to assign to a constant
+    }
+}

src/types/stmts-failed/assign-const-global.tact

@@ -0,0 +1,7 @@
+primitive Int;
+
+const foo: Int = 42;
+
+fun bar() {
+    foo = 43 // <-- trying to assign to a constant
+}

src/types/stmts-failed/assign-const-struct-contract.tact

@@ -0,0 +1,14 @@
+primitive Int;
+trait BaseTrait { }
+
+struct Foo {x: Int; y: Int}
+
+contract Test {
+    const foo: Foo = Foo {x: 42, y: 43};
+    baz: Foo = Foo {x: 42, y: 43};
+
+    fun bar() {
+        self.baz.x = 1; // ok
+        self.foo.y = 42 // <-- trying to assign to a constant
+    }
+}

src/types/stmts-failed/assign-const-struct-global.tact

@@ -0,0 +1,11 @@
+primitive Int;
+
+struct Foo {x: Int; y: Int}
+
+const foo: Foo = Foo {x: 42, y: 43};
+
+fun bar() {
+    let baz: Foo = Foo {x: 42, y: 43};
+    baz.x = 1; // ok
+    foo.y = 42 // <-- trying to assign to a constant
+}

src/types/stmts/assign-self-mutating-method.tact

@@ -0,0 +1,11 @@
+primitive Int;
+
+struct IntWrapper { x: Int }
+
+extends mutates fun foo(self: IntWrapper) {
+    self.x = 42
+}
+
+extends mutates fun bar(self: Int) {
+    self = 42
+}