function input mutable by default

asg/tests/fail/mutability/function_input.leo

@@ -1,4 +1,4 @@
-// Function input are immutable by default.
-function main(a: bool) {
+// Const function input are immutable.
+function main(const a: bool) {
     a = false;
 }

asg/tests/pass/function/value_unchanged.leo

@@ -7,7 +7,7 @@
 //   line 11: variable `x` is set to value `0`.
 //   line 18: program returns the value of `a`.
 
-function bad_mutate(mut x: u32) {
+function bad_mutate(x: u32) {
     x = 0; // <- does not change `a`
 }
 

asg/tests/pass/mutability/function_input_mut.leo

@@ -1,5 +1,5 @@
-// Adding the `mut` keyword makes a function variable mutable.
-function main(mut a: bool) {
+// Function input are mutable by default.
+function main(a: bool) {
     a = true;
 
     console.assert(a == true);

asg/tests/pass/mutability/swap.leo

@@ -1,5 +1,5 @@
 // Swap two elements of an array.
-function swap(mut a: [u32; 2], const i: u32, const j: u32) -> [u32; 2] {
+function swap(a: [u32; 2], const i: u32, const j: u32) -> [u32; 2] {
     const t = a[i];
     a[i] = a[j];
     a[j] = t;

compiler/tests/function/value_unchanged.leo

@@ -7,7 +7,7 @@
 //   line 11: variable `x` is set to value `0`.
 //   line 18: program returns the value of `a`.
 
-function bad_mutate(mut x: u32) {
+function bad_mutate(x: u32) {
     x = 0; // <- does not change `a`
 }
 

compiler/tests/mutability/function_input.leo

@@ -1,4 +1,4 @@
-// Function input are immutable by default.
-function main(a: bool) {
+// Const function input are immutable.
+function main(const a: bool) {
     a = false;
 }

compiler/tests/mutability/function_input_mut.leo

@@ -1,5 +1,5 @@
-// Adding the `mut` keyword makes a function variable mutable.
-function main(mut a: bool) {
+// Function input are mutable by default.
+function main(a: bool) {
     a = true;
 
     console.assert(a == true);

compiler/tests/mutability/swap.leo

@@ -1,5 +1,5 @@
 // Swap two elements of an array.
-function swap(mut a: [u32; 2], const i: u32, const j: u32) -> [u32; 2] {
+function swap(a: [u32; 2], const i: u32, const j: u32) -> [u32; 2] {
     const t = a[i];
     a[i] = a[j];
     a[j] = t;

parser/src/errors/deprecated.rs

@@ -43,9 +43,19 @@ impl LeoError for DeprecatedError {
 }
 
 impl DeprecatedError {
-    pub fn let_mut_statement(span: &Span) -> Self {
+    pub fn mut_function_input(mut span: Span) -> Self {
+        let message =
+            "function func(mut a: u32) { ... } is deprecated. Passed variables are mutable by default.".to_string();
+        span.col_start -= 1;
+        span.col_stop -= 1;
+        Self::new_from_span(message, &span)
+    }
+
+    pub fn let_mut_statement(mut span: Span) -> Self {
         let message = "let mut = ... is deprecated. `let` keyword implies mutabality by default.".to_string();
-        Self::new_from_span(message, span)
+        span.col_start -= 1;
+        span.col_stop -= 1;
+        Self::new_from_span(message, &span)
     }
 
     pub fn test_function(span: &Span) -> Self {

parser/src/parser/file.rs

@@ -332,11 +332,18 @@ impl ParserContext {
             }
             return Ok(FunctionInput::SelfKeyword(SelfKeyword { span: name.span }));
         }
+
+        if let Some(mutable) = &mutable {
+            return Err(SyntaxError::DeprecatedError(DeprecatedError::mut_function_input(
+                &mutable.span + &name.span,
+            )));
+        }
+
         self.expect(Token::Colon)?;
         let type_ = self.parse_type()?.0;
         Ok(FunctionInput::Variable(FunctionInputVariable {
             const_: const_.is_some(),
-            mutable: mutable.is_some(),
+            mutable: const_.is_none(),
             type_,
             span: name.span.clone(),
             identifier: name,

parser/src/parser/statement.rs

@@ -287,9 +287,10 @@ impl ParserContext {
     /// valid keywords.
     ///
     pub fn parse_variable_name(&mut self, span: &SpannedToken) -> SyntaxResult<VariableName> {
-        if self.eat(Token::Mut).is_some() {
+        let mutable = self.eat(Token::Mut);
+        if let Some(mutable) = &mutable {
             return Err(SyntaxError::DeprecatedError(DeprecatedError::let_mut_statement(
-                &span.span,
+                &mutable.span + &span.span,
             )));
         }
 

tests/pass/parse/function/value_unchanged.leo

@@ -7,7 +7,7 @@
 //   line 11: variable `x` is set to value `0`.
 //   line 18: program returns the value of `a`.
 
-function bad_mutate(mut x: u32) {
+function bad_mutate(x: u32) {
     x = 0; // <- does not change `a`
 }
 

tests/pass/parse/mutability/function_input_mut.leo

@@ -1,5 +1,5 @@
-// Adding the `mut` keyword makes a function variable mutable.
-function main(mut a: bool) {
+// Function input are mutable by default.
+function main(a: bool) {
     a = true;
 
     console.assert(a == true);

tests/pass/parse/mutability/swap.leo

@@ -1,5 +1,5 @@
 // Swap two elements of an array.
-function swap(mut a: [u32; 2], const i: u32, const j: u32) -> [u32; 2] {
+function swap(a: [u32; 2], const i: u32, const j: u32) -> [u32; 2] {
     const t = a[i];
     a[i] = a[j];
     a[j] = t;