core: improve binop and cmpop error messages

nac3core/src/codegen/expr.rs

@@ -1202,11 +1202,11 @@ pub fn gen_binop_expr_with_values<'ctx, G: CodeGenerator>(
     {
         let llvm_usize = generator.get_size_type(ctx.ctx);
 
-        if is_aug_assign {
+        if op.variant == BinopVariant::AugAssign {
             todo!("Augmented assignment operators not implemented for lists")
         }
 
-        match op {
+        match op.base {
             Operator::Add => {
                 debug_assert_eq!(ty1.obj_id(&ctx.unifier), Some(PrimDef::List.id()));
                 debug_assert_eq!(ty2.obj_id(&ctx.unifier), Some(PrimDef::List.id()));

nac3core/src/typecheck/magic_methods.rs

@@ -486,18 +486,20 @@ pub fn typeof_binop(
     lhs: Type,
     rhs: Type,
 ) -> Result<Option<Type>, String> {
+    let op = Binop { base: op, variant: BinopVariant::Normal };
+
     let is_left_list = lhs.obj_id(unifier).is_some_and(|id| id == PrimDef::List.id());
     let is_right_list = rhs.obj_id(unifier).is_some_and(|id| id == PrimDef::List.id());
     let is_left_ndarray = lhs.obj_id(unifier).is_some_and(|id| id == PrimDef::NDArray.id());
     let is_right_ndarray = rhs.obj_id(unifier).is_some_and(|id| id == PrimDef::NDArray.id());
 
-    Ok(Some(match op {
+    Ok(Some(match op.base {
         Operator::Add | Operator::Sub | Operator::Mult | Operator::Mod | Operator::FloorDiv => {
             if is_left_list || is_right_list {
-                if ![Operator::Add, Operator::Mult].contains(&op) {
+                if ![Operator::Add, Operator::Mult].contains(&op.base) {
                     return Err(format!(
                         "Binary operator {} not supported for list",
-                        binop_name(op)
+                        op.op_info().symbol
                     ));
                 }
 

nac3core/src/typecheck/type_error.rs

@@ -1,11 +1,14 @@
 use std::collections::HashMap;
 use std::fmt::Display;
 
-use crate::typecheck::typedef::TypeEnum;
+use crate::typecheck::{magic_methods::HasOpInfo, typedef::TypeEnum};
 
-use super::typedef::{RecordKey, Type, Unifier};
+use super::{
+    magic_methods::Binop,
+    typedef::{RecordKey, Type, Unifier},
+};
 use itertools::Itertools;
-use nac3parser::ast::{Location, StrRef};
+use nac3parser::ast::{Cmpop, Location, StrRef};
 
 #[derive(Debug, Clone)]
 pub enum TypeErrorKind {
@@ -26,6 +29,18 @@ pub enum TypeErrorKind {
         expected: Type,
         got: Type,
     },
+    UnsupportedBinaryOpTypes {
+        operator: Binop,
+        lhs_type: Type,
+        rhs_type: Type,
+        expected_rhs_type: Type,
+    },
+    UnsupportedComparsionOpTypes {
+        operator: Cmpop,
+        lhs_type: Type,
+        rhs_type: Type,
+        expected_rhs_type: Type,
+    },
     FieldUnificationError {
         field: RecordKey,
         types: (Type, Type),
@@ -101,6 +116,26 @@ impl<'a> Display for DisplayTypeError<'a> {
                 let args = missing_arg_names.iter().join(", ");
                 write!(f, "Missing arguments: {args}")
             }
+            UnsupportedBinaryOpTypes { operator, lhs_type, rhs_type, expected_rhs_type } => {
+                let op_symbol = operator.op_info().symbol;
+
+                let lhs_type_str = self.unifier.stringify_with_notes(*lhs_type, &mut notes);
+                let rhs_type_str = self.unifier.stringify_with_notes(*rhs_type, &mut notes);
+                let expected_rhs_type_str =
+                    self.unifier.stringify_with_notes(*expected_rhs_type, &mut notes);
+
+                write!(f, "Unsupported operand type(s) for {op_symbol}: '{lhs_type_str}' and '{rhs_type_str}' (right operand should have type {expected_rhs_type_str})")
+            }
+            UnsupportedComparsionOpTypes { operator, lhs_type, rhs_type, expected_rhs_type } => {
+                let op_symbol = operator.op_info().symbol;
+
+                let lhs_type_str = self.unifier.stringify_with_notes(*lhs_type, &mut notes);
+                let rhs_type_str = self.unifier.stringify_with_notes(*rhs_type, &mut notes);
+                let expected_rhs_type_str =
+                    self.unifier.stringify_with_notes(*expected_rhs_type, &mut notes);
+
+                write!(f, "'{op_symbol}' not supported between instances of '{lhs_type_str}' and '{rhs_type_str}' (right operand should have type {expected_rhs_type_str})")
+            }
             UnknownArgName(name) => {
                 write!(f, "Unknown argument name: {name}")
             }

nac3core/src/typecheck/type_inferencer/mod.rs

@@ -4,6 +4,7 @@ use std::iter::once;
 use std::ops::Not;
 use std::{cell::RefCell, sync::Arc};
 
+use super::typedef::OperatorInfo;
 use super::{
     magic_methods::*,
     type_error::TypeError,
@@ -641,6 +642,7 @@ impl<'a> Inferencer<'a> {
         obj: Type,
         params: Vec<Type>,
         ret: Option<Type>,
+        operator_info: Option<OperatorInfo>,
     ) -> InferenceResult {
         if let TypeEnum::TObj { params: class_params, fields, .. } = &*self.unifier.get_ty(obj) {
             if class_params.is_empty() {
@@ -654,6 +656,7 @@ impl<'a> Inferencer<'a> {
                                 ret: sign.ret,
                                 fun: RefCell::new(None),
                                 loc: Some(location),
+                                operator_info,
                             };
                             if let Some(ret) = ret {
                                 self.unifier
@@ -688,6 +691,7 @@ impl<'a> Inferencer<'a> {
             ret,
             fun: RefCell::new(None),
             loc: Some(location),
+            operator_info,
         });
         self.calls.insert(location.into(), call);
         let call = self.unifier.add_ty(TypeEnum::TCall(vec![call]));
@@ -1523,6 +1527,7 @@ impl<'a> Inferencer<'a> {
                     fun: RefCell::new(None),
                     ret: sign.ret,
                     loc: Some(location),
+                    operator_info: None,
                 };
                 self.unifier.unify_call(&call, func.custom.unwrap(), sign).map_err(|e| {
                     HashSet::from([e.at(Some(location)).to_display(self.unifier).to_string()])
@@ -1545,6 +1550,7 @@ impl<'a> Inferencer<'a> {
             fun: RefCell::new(None),
             ret,
             loc: Some(location),
+            operator_info: None,
         });
         self.calls.insert(location.into(), call);
         let call = self.unifier.add_ty(TypeEnum::TCall(vec![call]));
@@ -1765,7 +1771,14 @@ impl<'a> Inferencer<'a> {
             }
         };
 
-        self.build_method_call(location, method.into(), left_ty, vec![right_ty], ret)
+        self.build_method_call(
+            location,
+            method.into(),
+            left_ty,
+            vec![right_ty],
+            ret,
+            Some(OperatorInfo::IsBinaryOp { self_type: left.custom.unwrap(), operator: op }),
+        )
     }
 
     fn infer_unary_ops(
@@ -1779,7 +1792,14 @@ impl<'a> Inferencer<'a> {
         let ret = typeof_unaryop(self.unifier, self.primitives, op, operand.custom.unwrap())
             .map_err(|e| HashSet::from([format!("{e} (at {location})")]))?;
 
-        self.build_method_call(location, method, operand.custom.unwrap(), vec![], ret)
+        self.build_method_call(
+            location,
+            method,
+            operand.custom.unwrap(),
+            vec![],
+            ret,
+            Some(OperatorInfo::IsUnaryOp { self_type: operand.custom.unwrap(), operator: op }),
+        )
     }
 
     fn infer_compare(
@@ -1825,6 +1845,10 @@ impl<'a> Inferencer<'a> {
                 a.custom.unwrap(),
                 vec![b.custom.unwrap()],
                 ret,
+                Some(OperatorInfo::IsComparisonOp {
+                    self_type: left.custom.unwrap(),
+                    operator: *c,
+                }),
             )?);
         }
 

nac3core/src/typecheck/typedef/mod.rs

@@ -8,12 +8,15 @@ use std::rc::Rc;
 use std::sync::{Arc, Mutex};
 use std::{borrow::Cow, collections::HashSet};
 
-use nac3parser::ast::{Location, StrRef};
+use nac3parser::ast::{Cmpop, Location, StrRef, Unaryop};
 
+use super::magic_methods::Binop;
 use super::type_error::{TypeError, TypeErrorKind};
 use super::unification_table::{UnificationKey, UnificationTable};
 use crate::symbol_resolver::SymbolValue;
-use crate::toplevel::{helper::PrimDef, DefinitionId, TopLevelContext, TopLevelDef};
+use crate::toplevel::helper::PrimDef;
+use crate::toplevel::{DefinitionId, TopLevelContext, TopLevelDef};
+use crate::typecheck::magic_methods::OpInfo;
 use crate::typecheck::type_inferencer::PrimitiveStore;
 
 #[cfg(test)]
@@ -73,6 +76,28 @@ pub fn iter_type_vars(var_map: &VarMap) -> impl Iterator<Item = TypeVar> + '_ {
     var_map.iter().map(|(&id, &ty)| TypeVar { id, ty })
 }
 
+#[derive(Debug, Clone)]
+pub enum OperatorInfo {
+    /// The call was written as an unary operation, e.g., `~a` or `not a`.
+    IsUnaryOp {
+        /// The [`Type`] of the `self` object
+        self_type: Type,
+        operator: Unaryop,
+    },
+    /// The call was written as a binary operation, e.g., `a + b` or `a += b`.
+    IsBinaryOp {
+        /// The [`Type`] of the `self` object
+        self_type: Type,
+        operator: Binop,
+    },
+    /// The call was written as a binary comparison operation, e.g., `a < b`.
+    IsComparisonOp {
+        /// The [`Type`] of the `self` object
+        self_type: Type,
+        operator: Cmpop,
+    },
+}
+
 #[derive(Clone)]
 pub struct Call {
     pub posargs: Vec<Type>,
@@ -80,6 +105,9 @@ pub struct Call {
     pub ret: Type,
     pub fun: RefCell<Option<Type>>,
     pub loc: Option<Location>,
+
+    /// Details about the associated Python user operator expression of this call, if any.
+    pub operator_info: Option<OperatorInfo>,
 }
 
 #[derive(Debug, Clone)]
@@ -627,10 +655,67 @@ impl Unifier {
         let TypeEnum::TFunc(signature) = &*self.get_ty(b) else { unreachable!() };
 
         // Get details about the input arguments
-        let Call { posargs, kwargs, ret, fun, loc } = call;
+        let Call { posargs, kwargs, ret, fun, loc, operator_info } = call;
         let num_args = posargs.len() + kwargs.len();
 
-        // Now we check the arguments against the parameters
+        // Now we check the arguments against the parameters,
+        // and depending on what `call_info` is, we might change how the behavior `unify_call()`
+        // in hopes to improve user error messages when type checking fails.
+        match operator_info {
+            Some(OperatorInfo::IsBinaryOp { self_type, operator }) => {
+                // The call is written in the form of (say) `a + b`.
+                // Technically, it is `a.__add__(b)`, and they have the following constraints:
+                assert_eq!(posargs.len(), 1);
+                assert_eq!(kwargs.len(), 0);
+                assert_eq!(num_params, 1);
+
+                let other_type = posargs[0]; // the second operand
+                let expected_other_type = signature.args[0].ty;
+
+                let ok = self.unify_impl(expected_other_type, other_type, false).is_ok();
+                if !ok {
+                    self.restore_snapshot();
+                    return Err(TypeError::new(
+                        TypeErrorKind::UnsupportedBinaryOpTypes {
+                            operator: *operator,
+                            lhs_type: *self_type,
+                            rhs_type: other_type,
+                            expected_rhs_type: expected_other_type,
+                        },
+                        *loc,
+                    ));
+                }
+            }
+            Some(OperatorInfo::IsComparisonOp { self_type, operator })
+                if OpInfo::supports_cmpop(*operator) // Otherwise that comparison operator is not supported.
+                =>
+            {
+                // The call is written in the form of (say) `a <= b`.
+                // Technically, it is `a.__le__(b)`, and they have the following constraints:
+                assert_eq!(posargs.len(), 1);
+                assert_eq!(kwargs.len(), 0);
+                assert_eq!(num_params, 1);
+
+                let other_type = posargs[0]; // the second operand
+                let expected_other_type = signature.args[0].ty;
+
+                let ok = self.unify_impl(expected_other_type, other_type, false).is_ok();
+                if !ok {
+                    self.restore_snapshot();
+                    return Err(TypeError::new(
+                        TypeErrorKind::UnsupportedComparsionOpTypes {
+                            operator: *operator,
+                            lhs_type: *self_type,
+                            rhs_type: other_type,
+                            expected_rhs_type: expected_other_type,
+                        },
+                        *loc,
+                    ));
+                }
+            }
+            _ => {
+                // Handle [`CallInfo::IsNormalFunctionCall`] and other uninteresting variants
+                // of [`CallInfo`] (e.g, `CallInfo::IsUnaryOp` and unsupported comparison operators)
 
                 // Helper lambdas
                 let mut type_check_arg = |param_name, expected_arg_ty, arg_ty| {
@@ -691,7 +776,10 @@ impl Unifier {
 
                     let Some(param_info) = param_info_by_name.get_mut(&param_name) else {
                         self.restore_snapshot();
-                return Err(TypeError::new(TypeErrorKind::UnknownArgName(param_name), *loc));
+                        return Err(TypeError::new(
+                            TypeErrorKind::UnknownArgName(param_name),
+                            *loc,
+                        ));
                     };
 
                     if param_info.has_been_supplied {
@@ -716,12 +804,17 @@ impl Unifier {
                 // unsupplied required parameters, and throw an error if they exist.
                 let missing_arg_names = param_info_by_name
                     .values()
-            .filter(|param_info| param_info.param.is_required() && !param_info.has_been_supplied)
+                    .filter(|param_info| {
+                        param_info.param.is_required() && !param_info.has_been_supplied
+                    })
                     .map(|param_info| param_info.param.name)
                     .collect_vec();
                 if !missing_arg_names.is_empty() {
                     self.restore_snapshot();
-            return Err(TypeError::new(TypeErrorKind::MissingArgs { missing_arg_names }, *loc));
+                    return Err(TypeError::new(
+                        TypeErrorKind::MissingArgs { missing_arg_names },
+                        *loc,
+                    ));
                 }
 
                 // Finally, check the Call's return type
@@ -732,6 +825,8 @@ impl Unifier {
                     }
                     err
                 })?;
+            }
+        }
 
         *fun.borrow_mut() = Some(b);