Fix ref without mut parameter check on methods and associated functions

sway-core/src/language/ty/declaration/declaration.rs

@@ -385,6 +385,7 @@ impl DisplayWithEngines for TyDecl {
                     match mutability {
                         VariableMutability::Mutable => builder.push_str("mut"),
                         VariableMutability::RefMutable => builder.push_str("ref mut"),
+                        VariableMutability::RefImmutable => builder.push_str("ref"),
                         VariableMutability::Immutable => {}
                     }
                     builder.push_str(name.as_str());
@@ -441,6 +442,7 @@ impl DebugWithEngines for TyDecl {
                     match mutability {
                         VariableMutability::Mutable => builder.push_str("mut"),
                         VariableMutability::RefMutable => builder.push_str("ref mut"),
+                        VariableMutability::RefImmutable => builder.push_str("ref"),
                         VariableMutability::Immutable => {}
                     }
                     builder.push_str(name.as_str());

sway-core/src/language/ty/variable_mutability.rs

@@ -7,15 +7,19 @@ pub enum VariableMutability {
     Mutable,
     // referenceable + mutable
     RefMutable,
+    // referenceable + immutable
+    RefImmutable,
     // immutable
     #[default]
     Immutable,
 }
 
 impl VariableMutability {
     pub fn new_from_ref_mut(is_reference: bool, is_mutable: bool) -> VariableMutability {
-        if is_reference {
+        if is_reference && is_mutable {
             VariableMutability::RefMutable
+        } else if is_reference {
+            VariableMutability::RefImmutable
         } else if is_mutable {
             VariableMutability::Mutable
         } else {

sway-core/src/semantic_analysis/ast_node/expression/typed_expression/function_application.rs

@@ -216,9 +216,11 @@ fn unify_arguments_and_parameters(
             }
 
             // check for matching mutability
-            let param_mutability =
-                ty::VariableMutability::new_from_ref_mut(param.is_reference, param.is_mutable);
-            if arg.gather_mutability().is_immutable() && param_mutability.is_mutable() {
+            // Only ref mut params require mutable args.
+            if arg.gather_mutability().is_immutable()
+                && param.is_reference
+                && param.is_mutable
+            {
                 handler.emit_err(CompileError::ImmutableArgumentToMutableParameter {
                     span: arg.span.clone(),
                 });

test/src/e2e_vm_tests/test_programs/should_fail/ref_without_mut_not_assignable/Forc.lock

@@ -0,0 +1,3 @@
+[[package]]
+name = "ref_without_mut_not_assignable"
+source = "member"

test/src/e2e_vm_tests/test_programs/should_fail/ref_without_mut_not_assignable/Forc.toml

@@ -0,0 +1,6 @@
+[project]
+name = "ref_without_mut_not_assignable"
+authors = ["Fuel Labs <contact@fuel.sh>"]
+entry = "main.sw"
+license = "Apache-2.0"
+implicit-std = false

test/src/e2e_vm_tests/test_programs/should_fail/ref_without_mut_not_assignable/src/main.sw

@@ -0,0 +1,17 @@
+script;
+
+fn ref_immutable(ref x: u64) {
+    x = 10;
+}
+
+fn ref_mut_immutable_arg(ref mut _x: u64) { }
+
+fn main() -> u64 {
+    let y = 42;
+
+    ref_immutable(y);
+
+    ref_mut_immutable_arg(y);
+
+    y
+}

test/src/e2e_vm_tests/test_programs/should_fail/ref_without_mut_not_assignable/test.toml

@@ -0,0 +1,9 @@
+category = "fail"
+
+# ref without mut: parameter should be immutable inside the function body
+# check: $()x = 10;
+# nextln: $()cannot be assigned to, because it is an immutable variable
+
+# ref mut with immutable argument: should still require mutable arg
+# check: $()ref_mut_immutable_arg(y);
+# nextln: $()Cannot pass immutable argument to mutable parameter

test/src/e2e_vm_tests/test_programs/should_pass/language/ref_without_mut/Forc.lock

@@ -0,0 +1,8 @@
+[[package]]
+name = "ref_without_mut"
+source = "member"
+dependencies = ["std"]
+
+[[package]]
+name = "std"
+source = "path+from-root-9C22439F46EC1A75"

test/src/e2e_vm_tests/test_programs/should_pass/language/ref_without_mut/Forc.toml

@@ -0,0 +1,9 @@
+[project]
+authors = ["Fuel Labs <contact@fuel.sh>"]
+license = "Apache-2.0"
+name = "ref_without_mut"
+entry = "main.sw"
+implicit-std = false
+
+[dependencies]
+std = { path = "../../../../reduced_std_libs/sway-lib-std-core" }

test/src/e2e_vm_tests/test_programs/should_pass/language/ref_without_mut/src/main.sw

@@ -0,0 +1,33 @@
+script;
+
+struct S {
+    value: u64,
+}
+
+impl S {
+    fn method(self, ref _x: u64) -> u64 {
+        _x
+    }
+
+    fn associated_fn(ref _x: u64) -> u64 {
+        _x
+    }
+}
+
+fn ref_pass(ref _x: u64) -> u64 {
+    _x
+}
+
+fn main() -> u64 {
+    let x = 42;
+
+    let a = ref_pass(x);
+    let b = S { value: 1 }.method(x);
+    let c = S::associated_fn(x);
+
+    if a == 42 && b == 42 && c == 42 {
+        42
+    } else {
+        0
+    }
+}

test/src/e2e_vm_tests/test_programs/should_pass/language/ref_without_mut/test.toml

@@ -0,0 +1,3 @@
+category = "run"
+expected_result = { action = "return", value = 42 }
+expected_result_new_encoding = { action = "return_data", value = "000000000000002A" }