re-add syntax in, then add deprecation warning for it

asg/src/statement/definition.rs

@@ -29,6 +29,8 @@ use crate::{
     Variable,
 };
 
+use leo_ast::{AstError, DeprecatedError};
+
 use std::{
     cell::RefCell,
     sync::{Arc, Weak},
@@ -92,6 +94,12 @@ impl FromAst<leo_ast::DefinitionStatement> for Arc<Statement> {
         }
 
         for (variable, type_) in statement.variable_names.iter().zip(output_types.into_iter()) {
+            if statement.declaration_type == leo_ast::Declare::Const {
+                return Err(AsgConvertError::AstError(AstError::DeprecatedError(
+                    DeprecatedError::const_statement(&statement.span),
+                )));
+            }
+
             variables.push(Arc::new(RefCell::new(InnerVariable {
                 id: uuid::Uuid::new_v4(),
                 name: variable.identifier.clone(),

ast/src/errors/deprecated.rs

@@ -61,3 +61,10 @@ impl<'ast> TryFrom<AnnotationName<'ast>> for DeprecatedError {
         }
     }
 }
+
+impl DeprecatedError {
+    pub fn const_statement(span: &Span) -> Self {
+        let message = "const _ = ... is deprecated. Did you mean let?".to_string();
+        Self::new_from_span(message, span.clone())
+    }
+}

ast/src/statements/definition/declare.rs

@@ -21,12 +21,14 @@ use std::fmt;
 
 #[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
 pub enum Declare {
+    Const,
     Let,
 }
 
 impl<'ast> From<GrammarDeclare> for Declare {
     fn from(declare: GrammarDeclare) -> Self {
         match declare {
+            GrammarDeclare::Const(_) => Declare::Const,
             GrammarDeclare::Let(_) => Declare::Let,
         }
     }
@@ -35,6 +37,7 @@ impl<'ast> From<GrammarDeclare> for Declare {
 impl fmt::Display for Declare {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         match self {
+            Declare::Const => write!(f, "const"),
             Declare::Let => write!(f, "let"),
         }
     }

grammar/src/common/declare.rs

@@ -22,6 +22,7 @@ use serde::Serialize;
 #[derive(Clone, Debug, FromPest, PartialEq, Serialize)]
 #[pest_ast(rule(Rule::declare))]
 pub enum Declare {
+    Const(Const),
     Let(Let),
 }
 

grammar/src/leo.pest

@@ -99,7 +99,7 @@ variable_name_tuple = _{"(" ~ variable_name ~ ("," ~ variable_name)+ ~ ")"}
 variables = { ( variable_name_tuple | variable_name ) ~ (":" ~ type_ )? }
 
 // Declared in common/declare.rs
-declare = { let_ }
+declare = { let_ | const_ }
 const_ = { "const " }
 let_ = { "let " }