feat: Implement println in the comptime interpreter (#5197)

# Description

## Problem\*

Resolves <!-- Link to GitHub Issue -->

## Summary\*



## Additional Context



## Documentation\*

Check one:
- [ ] No documentation needed.
- [ ] Documentation included in this PR.
- [x] **[For Experimental Features]** Documentation to be submitted in a
separate PR.

# PR Checklist\*

- [x] I have tested the changes locally.
- [x] I have formatted the changes with [Prettier](https://prettier.io/)
and/or `cargo fmt` on default settings.

compiler/noirc_frontend/src/ast/expression.rs

@@ -34,7 +34,7 @@ pub enum ExpressionKind {
     Lambda(Box<Lambda>),
     Parenthesized(Box<Expression>),
     Quote(BlockExpression),
-    Comptime(BlockExpression),
+    Comptime(BlockExpression, Span),
 
     // This variant is only emitted when inlining the result of comptime
     // code. It is used to translate function values back into the AST while
@@ -536,7 +536,7 @@ impl Display for ExpressionKind {
             Lambda(lambda) => lambda.fmt(f),
             Parenthesized(sub_expr) => write!(f, "({sub_expr})"),
             Quote(block) => write!(f, "quote {block}"),
-            Comptime(block) => write!(f, "comptime {block}"),
+            Comptime(block, _) => write!(f, "comptime {block}"),
             Error => write!(f, "Error"),
             Resolved(_) => write!(f, "?Resolved"),
         }

compiler/noirc_frontend/src/elaborator/expressions.rs

@@ -59,7 +59,7 @@ impl<'context> Elaborator<'context> {
             ExpressionKind::Lambda(lambda) => self.elaborate_lambda(*lambda),
             ExpressionKind::Parenthesized(expr) => return self.elaborate_expression(*expr),
             ExpressionKind::Quote(quote) => self.elaborate_quote(quote),
-            ExpressionKind::Comptime(comptime) => {
+            ExpressionKind::Comptime(comptime, _) => {
                 return self.elaborate_comptime_block(comptime, expr.span)
             }
             ExpressionKind::Resolved(id) => return (id, self.interner.id_type(id)),

compiler/noirc_frontend/src/hir/comptime/errors.rs

@@ -36,7 +36,7 @@ pub enum InterpreterError {
     CannotInlineMacro { value: Value, location: Location },
     UnquoteFoundDuringEvaluation { location: Location },
 
-    Unimplemented { item: &'static str, location: Location },
+    Unimplemented { item: String, location: Location },
 
     // Perhaps this should be unreachable! due to type checking also preventing this error?
     // Currently it and the Continue variant are the only interpreter errors without a Location field

compiler/noirc_frontend/src/hir/comptime/interpreter.rs

@@ -59,11 +59,6 @@ impl<'a> Interpreter<'a> {
         let previous_state = self.enter_function();
 
         let meta = self.interner.function_meta(&function);
-        if meta.kind != FunctionKind::Normal {
-            let item = "Evaluation for builtin functions";
-            return Err(InterpreterError::Unimplemented { item, location });
-        }
-
         if meta.parameters.len() != arguments.len() {
             return Err(InterpreterError::ArgumentCountMismatch {
                 expected: meta.parameters.len(),
@@ -72,6 +67,10 @@ impl<'a> Interpreter<'a> {
             });
         }
 
+        if meta.kind != FunctionKind::Normal {
+            return self.call_builtin(function, arguments, location);
+        }
+
         let parameters = meta.parameters.0.clone();
         for ((parameter, typ, _), (argument, arg_location)) in parameters.iter().zip(arguments) {
             self.define_pattern(parameter, typ, argument, arg_location)?;
@@ -84,6 +83,35 @@ impl<'a> Interpreter<'a> {
         Ok(result)
     }
 
+    fn call_builtin(
+        &mut self,
+        function: FuncId,
+        arguments: Vec<(Value, Location)>,
+        location: Location,
+    ) -> IResult<Value> {
+        let attributes = self.interner.function_attributes(&function);
+        let func_attrs = attributes.function.as_ref()
+            .expect("all builtin functions must contain a function  attribute which contains the opcode which it links to");
+
+        if let Some(builtin) = func_attrs.builtin() {
+            let item = format!("Evaluation for builtin functions like {builtin}");
+            Err(InterpreterError::Unimplemented { item, location })
+        } else if let Some(foreign) = func_attrs.foreign() {
+            let item = format!("Evaluation for foreign functions like {foreign}");
+            Err(InterpreterError::Unimplemented { item, location })
+        } else if let Some(oracle) = func_attrs.oracle() {
+            if oracle == "print" {
+                self.print_oracle(arguments)
+            } else {
+                let item = format!("Evaluation for oracle functions like {oracle}");
+                Err(InterpreterError::Unimplemented { item, location })
+            }
+        } else {
+            let name = self.interner.function_name(&function);
+            unreachable!("Non-builtin, lowlevel or oracle builtin fn '{name}'")
+        }
+    }
+
     fn call_closure(
         &mut self,
         closure: HirLambda,
@@ -219,7 +247,8 @@ impl<'a> Interpreter<'a> {
         argument: Value,
         location: Location,
     ) -> IResult<()> {
-        self.type_check(typ, &argument, location)?;
+        // Temporarily disabled since this fails on generic types
+        // self.type_check(typ, &argument, location)?;
         self.current_scope_mut().insert(id, argument);
         Ok(())
     }
@@ -360,7 +389,11 @@ impl<'a> Interpreter<'a> {
                 self.evaluate_integer(value, is_negative, id)
             }
             HirLiteral::Str(string) => Ok(Value::String(Rc::new(string))),
-            HirLiteral::FmtStr(_, _) => todo!("Evaluate format strings"),
+            HirLiteral::FmtStr(_, _) => {
+                let item = "format strings in a comptime context".into();
+                let location = self.interner.expr_location(&id);
+                Err(InterpreterError::Unimplemented { item, location })
+            }
             HirLiteral::Array(array) => self.evaluate_array(array, id),
             HirLiteral::Slice(array) => self.evaluate_slice(array, id),
         }
@@ -454,6 +487,14 @@ impl<'a> Interpreter<'a> {
                     Ok(Value::I64(value))
                 }
             }
+        } else if let Type::TypeVariable(variable, TypeVariableKind::IntegerOrField) = &typ {
+            Ok(Value::Field(value))
+        } else if let Type::TypeVariable(variable, TypeVariableKind::Integer) = &typ {
+            let value: u64 = value
+                .try_to_u64()
+                .ok_or(InterpreterError::IntegerOutOfRangeForType { value, typ, location })?;
+            let value = if is_negative { 0u64.wrapping_sub(value) } else { value };
+            Ok(Value::U64(value))
         } else {
             Err(InterpreterError::NonIntegerIntegerLiteral { typ, location })
         }
@@ -1269,4 +1310,17 @@ impl<'a> Interpreter<'a> {
     pub(super) fn evaluate_comptime(&mut self, statement: StmtId) -> IResult<Value> {
         self.evaluate_statement(statement)
     }
+
+    fn print_oracle(&self, arguments: Vec<(Value, Location)>) -> Result<Value, InterpreterError> {
+        assert_eq!(arguments.len(), 2);
+
+        let print_newline = arguments[0].0 == Value::Bool(true);
+        if print_newline {
+            println!("{}", arguments[1].0);
+        } else {
+            print!("{}", arguments[1].0);
+        }
+
+        Ok(Value::Unit)
+    }
 }

compiler/noirc_frontend/src/hir/comptime/value.rs

@@ -1,4 +1,4 @@
-use std::{borrow::Cow, rc::Rc};
+use std::{borrow::Cow, fmt::Display, rc::Rc};
 
 use acvm::{AcirField, FieldElement};
 use im::Vector;
@@ -135,7 +135,7 @@ impl Value {
             }
             Value::Closure(_lambda, _env, _typ) => {
                 // TODO: How should a closure's environment be inlined?
-                let item = "Returning closures from a comptime fn";
+                let item = "Returning closures from a comptime fn".into();
                 return Err(InterpreterError::Unimplemented { item, location });
             }
             Value::Tuple(fields) => {
@@ -235,7 +235,7 @@ impl Value {
             }
             Value::Closure(_lambda, _env, _typ) => {
                 // TODO: How should a closure's environment be inlined?
-                let item = "Returning closures from a comptime fn";
+                let item = "Returning closures from a comptime fn".into();
                 return Err(InterpreterError::Unimplemented { item, location });
             }
             Value::Tuple(fields) => {
@@ -306,3 +306,49 @@ impl Value {
 fn unwrap_rc<T: Clone>(rc: Rc<T>) -> T {
     Rc::try_unwrap(rc).unwrap_or_else(|rc| (*rc).clone())
 }
+
+impl Display for Value {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            Value::Unit => write!(f, "()"),
+            Value::Bool(value) => {
+                let msg = if *value { "true" } else { "false" };
+                write!(f, "{msg}")
+            }
+            Value::Field(value) => write!(f, "{value}"),
+            Value::I8(value) => write!(f, "{value}"),
+            Value::I16(value) => write!(f, "{value}"),
+            Value::I32(value) => write!(f, "{value}"),
+            Value::I64(value) => write!(f, "{value}"),
+            Value::U8(value) => write!(f, "{value}"),
+            Value::U16(value) => write!(f, "{value}"),
+            Value::U32(value) => write!(f, "{value}"),
+            Value::U64(value) => write!(f, "{value}"),
+            Value::String(value) => write!(f, "{value}"),
+            Value::Function(_, _) => write!(f, "(function)"),
+            Value::Closure(_, _, _) => write!(f, "(closure)"),
+            Value::Tuple(fields) => {
+                let fields = vecmap(fields, ToString::to_string);
+                write!(f, "({})", fields.join(", "))
+            }
+            Value::Struct(fields, typ) => {
+                let typename = match typ.follow_bindings() {
+                    Type::Struct(def, _) => def.borrow().name.to_string(),
+                    other => other.to_string(),
+                };
+                let fields = vecmap(fields, |(name, value)| format!("{}: {}", name, value));
+                write!(f, "{typename} {{ {} }}", fields.join(", "))
+            }
+            Value::Pointer(value) => write!(f, "&mut {}", value.borrow()),
+            Value::Array(values, _) => {
+                let values = vecmap(values, ToString::to_string);
+                write!(f, "[{}]", values.join(", "))
+            }
+            Value::Slice(values, _) => {
+                let values = vecmap(values, ToString::to_string);
+                write!(f, "&[{}]", values.join(", "))
+            }
+            Value::Code(_) => todo!(),
+        }
+    }
+}

compiler/noirc_frontend/src/hir/resolution/resolver.rs

@@ -1642,7 +1642,9 @@ impl<'a> Resolver<'a> {
 
             // The quoted expression isn't resolved since we don't want errors if variables aren't defined
             ExpressionKind::Quote(block) => HirExpression::Quote(block),
-            ExpressionKind::Comptime(block) => HirExpression::Comptime(self.resolve_block(block)),
+            ExpressionKind::Comptime(block, _) => {
+                HirExpression::Comptime(self.resolve_block(block))
+            }
             ExpressionKind::Resolved(_) => unreachable!(
                 "ExpressionKind::Resolved should only be emitted by the comptime interpreter"
             ),

compiler/noirc_frontend/src/lexer/token.rs

@@ -702,20 +702,27 @@ pub enum FunctionAttribute {
 }
 
 impl FunctionAttribute {
-    pub fn builtin(self) -> Option<String> {
+    pub fn builtin(&self) -> Option<&String> {
         match self {
             FunctionAttribute::Builtin(name) => Some(name),
             _ => None,
         }
     }
 
-    pub fn foreign(self) -> Option<String> {
+    pub fn foreign(&self) -> Option<&String> {
         match self {
             FunctionAttribute::Foreign(name) => Some(name),
             _ => None,
         }
     }
 
+    pub fn oracle(&self) -> Option<&String> {
+        match self {
+            FunctionAttribute::Oracle(name) => Some(name),
+            _ => None,
+        }
+    }
+
     pub fn is_foreign(&self) -> bool {
         matches!(self, FunctionAttribute::Foreign(_))
     }

compiler/noirc_frontend/src/monomorphization/mod.rs

@@ -18,7 +18,6 @@ use crate::{
         types,
     },
     node_interner::{self, DefinitionKind, NodeInterner, StmtId, TraitImplKind, TraitMethodId},
-    token::FunctionAttribute,
     Type, TypeBinding, TypeBindings, TypeVariable, TypeVariableKind,
 };
 use acvm::{acir::AcirField, FieldElement};
@@ -216,34 +215,30 @@ impl<'interner> Monomorphizer<'interner> {
                 let attributes = self.interner.function_attributes(&id);
                 match self.interner.function_meta(&id).kind {
                     FunctionKind::LowLevel => {
-                        let attribute = attributes.function.clone().expect("all low level functions must contain a function attribute which contains the opcode which it links to");
+                        let attribute = attributes.function.as_ref().expect("all low level functions must contain a function attribute which contains the opcode which it links to");
                         let opcode = attribute.foreign().expect(
                             "ice: function marked as foreign, but attribute kind does not match this",
                         );
-                        Definition::LowLevel(opcode)
+                        Definition::LowLevel(opcode.to_string())
                     }
                     FunctionKind::Builtin => {
-                        let attribute = attributes.function.clone().expect("all low level functions must contain a function  attribute which contains the opcode which it links to");
+                        let attribute = attributes.function.as_ref().expect("all builtin functions must contain a function attribute which contains the opcode which it links to");
                         let opcode = attribute.builtin().expect(
                             "ice: function marked as builtin, but attribute kind does not match this",
                         );
-                        Definition::Builtin(opcode)
+                        Definition::Builtin(opcode.to_string())
                     }
                     FunctionKind::Normal => {
                         let id =
                             self.queue_function(id, expr_id, typ, turbofish_generics, trait_method);
                         Definition::Function(id)
                     }
                     FunctionKind::Oracle => {
-                        let attr = attributes
-                            .function
-                            .clone()
-                            .expect("Oracle function must have an oracle attribute");
-
-                        match attr {
-                            FunctionAttribute::Oracle(name) => Definition::Oracle(name),
-                            _ => unreachable!("Oracle function must have an oracle attribute"),
-                        }
+                        let attribute = attributes.function.as_ref().expect("all oracle functions must contain a function attribute which contains the opcode which it links to");
+                        let opcode = attribute.oracle().expect(
+                            "ice: function marked as builtin, but attribute kind does not match this",
+                        );
+                        Definition::Oracle(opcode.to_string())
                     }
                     FunctionKind::Recursive => {
                         unreachable!("Only main can be specified as recursive, which should already be checked");

compiler/noirc_frontend/src/parser/parser.rs

@@ -545,7 +545,9 @@ fn comptime_expr<'a, S>(statement: S) -> impl NoirParser<ExpressionKind> + 'a
 where
     S: NoirParser<StatementKind> + 'a,
 {
-    keyword(Keyword::Comptime).ignore_then(block(statement)).map(ExpressionKind::Comptime)
+    keyword(Keyword::Comptime)
+        .ignore_then(spanned(block(statement)))
+        .map(|(block, span)| ExpressionKind::Comptime(block, span))
 }
 
 fn declaration<'a, P>(expr_parser: P) -> impl NoirParser<StatementKind> + 'a

test_programs/execution_success/comptime_println/Nargo.toml

@@ -0,0 +1,7 @@
+[package]
+name = "comptime_println"
+type = "bin"
+authors = [""]
+compiler_version = ">=0.27.0"
+
+[dependencies]

test_programs/execution_success/comptime_println/src/main.nr

@@ -0,0 +1,7 @@
+fn main() {
+    let x = comptime {
+        println("hello from compile-time!");
+        1 + 2
+    };
+    println(x);
+}

tooling/nargo_fmt/src/rewrite/expr.rs

@@ -167,8 +167,8 @@ pub(crate) fn rewrite(
         }
         ExpressionKind::Lambda(_) => visitor.slice(span).to_string(),
         ExpressionKind::Quote(block) => format!("quote {}", rewrite_block(visitor, block, span)),
-        ExpressionKind::Comptime(block) => {
-            format!("comptime {}", rewrite_block(visitor, block, span))
+        ExpressionKind::Comptime(block, block_span) => {
+            format!("comptime {}", rewrite_block(visitor, block, block_span))
         }
         ExpressionKind::Error => unreachable!(),
         ExpressionKind::Resolved(_) => {