feat(noir): added assert keyword

crates/nargo_cli/tests/test_data/assert/Nargo.toml

@@ -0,0 +1,5 @@
+[package]
+authors = [""]
+compiler_version = "0.1"
+
+[dependencies]

crates/nargo_cli/tests/test_data/assert/Prover.toml

@@ -0,0 +1 @@
+x = "1"

crates/nargo_cli/tests/test_data/assert/src/main.nr

@@ -0,0 +1,3 @@
+fn main(x: Field) {
+    assert(x == 1);
+}

crates/noirc_frontend/src/lexer/lexer.rs

@@ -560,6 +560,7 @@ fn test_basic_language_syntax() {
             x * y;
         };
         constrain mul(five, ten) == 50;
+        assert(ten + five == 15);
     ";
 
     let expected = vec![
@@ -601,6 +602,15 @@ fn test_basic_language_syntax() {
         Token::Equal,
         Token::Int(50_i128.into()),
         Token::Semicolon,
+        Token::Keyword(Keyword::Assert),
+        Token::LeftParen,
+        Token::Ident("ten".to_string()),
+        Token::Plus,
+        Token::Ident("five".to_string()),
+        Token::Equal,
+        Token::Int(15_i128.into()),
+        Token::RightParen,
+        Token::Semicolon,
         Token::EOF,
     ];
     let mut lexer = Lexer::new(input);

crates/noirc_frontend/src/lexer/token.rs

@@ -414,6 +414,7 @@ impl AsRef<str> for Attribute {
 #[cfg_attr(test, derive(strum_macros::EnumIter))]
 pub enum Keyword {
     As,
+    Assert,
     Bool,
     Char,
     CompTime,
@@ -447,6 +448,7 @@ impl fmt::Display for Keyword {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         match *self {
             Keyword::As => write!(f, "as"),
+            Keyword::Assert => write!(f, "assert"),
             Keyword::Bool => write!(f, "bool"),
             Keyword::Char => write!(f, "char"),
             Keyword::CompTime => write!(f, "comptime"),
@@ -483,6 +485,7 @@ impl Keyword {
     pub(crate) fn lookup_keyword(word: &str) -> Option<Token> {
         let keyword = match word {
             "as" => Keyword::As,
+            "assert" => Keyword::Assert,
             "bool" => Keyword::Bool,
             "char" => Keyword::Char,
             "comptime" => Keyword::CompTime,

crates/noirc_frontend/src/parser/parser.rs

@@ -428,6 +428,7 @@ where
 {
     choice((
         constrain(expr_parser.clone()),
+        assertion(expr_parser.clone()),
         declaration(expr_parser.clone()),
         assignment(expr_parser.clone()),
         expr_parser.map(Statement::Expression),
@@ -442,6 +443,15 @@ where
         .map(|expr| Statement::Constrain(ConstrainStatement(expr)))
 }
 
+fn assertion<'a, P>(expr_parser: P) -> impl NoirParser<Statement> + 'a
+where
+    P: ExprParser + 'a,
+{
+    ignore_then_commit(keyword(Keyword::Assert), parenthesized(expr_parser))
+        .labelled("statement")
+        .map(|expr| Statement::Constrain(ConstrainStatement(expr)))
+}
+
 fn declaration<'a, P>(expr_parser: P) -> impl NoirParser<Statement> + 'a
 where
     P: ExprParser + 'a,
@@ -1214,6 +1224,47 @@ mod test {
         );
     }
 
+      #[test]
+      fn parse_assert() {
+          parse_with(assertion(expression()), "assert(x == y)").unwrap();
+
+          // Currently we disallow constrain statements where the outer infix operator
+          // produces a value. This would require an implicit `==` which
+          // may not be intuitive to the user.
+          //
+          // If this is deemed useful, one would either apply a transformation
+          // or interpret it with an `==` in the evaluator
+          let disallowed_operators = vec![
+              BinaryOpKind::And,
+              BinaryOpKind::Subtract,
+              BinaryOpKind::Divide,
+              BinaryOpKind::Multiply,
+              BinaryOpKind::Or,
+          ];
+
+          for operator in disallowed_operators {
+              let src = format!("assert(x {} y);", operator.as_string());
+              parse_with(assertion(expression()), &src).unwrap_err();
+          }
+
+          // These are general cases which should always work.
+          //
+          // The first case is the most noteworthy. It contains two `==`
+          // The first (inner) `==` is a predicate which returns 0/1
+          // The outer layer is an infix `==` which is
+          // associated with the Constrain statement
+          parse_all(
+              assertion(expression()),
+              vec![
+                  "assert(((x + y) == k) + z == y)",
+                  "assert((x + !y) == y)",
+                  "assert((x ^ y) == y)",
+                  "assert((x ^ y) == (y + m))",
+                  "assert(x + x ^ x == y | m)",
+              ],
+          );
+      }
+
     #[test]
     fn parse_let() {
         // Why is it valid to specify a let declaration as having type u8?
@@ -1468,7 +1519,9 @@ mod test {
             ("let", 3, "let $error: unspecified = Error"),
             ("foo = one two three", 1, "foo = plain::one"),
             ("constrain", 1, "constrain Error"),
+            ("assert", 1, "constrain Error"),
             ("constrain x ==", 1, "constrain (plain::x == Error)"),
+            ("assert(x ==)", 1, "constrain (plain::x == Error)"),
         ];
 
         let show_errors = |v| vecmap(v, ToString::to_string).join("\n");