core: improve function call errors

nac3core/src/typecheck/type_error.rs

@@ -4,15 +4,22 @@ use std::fmt::Display;
 use crate::typecheck::typedef::TypeEnum;
 
 use super::typedef::{RecordKey, Type, Unifier};
+use itertools::Itertools;
 use nac3parser::ast::{Location, StrRef};
 
 #[derive(Debug, Clone)]
 pub enum TypeErrorKind {
-    TooManyArguments {
-        expected: usize,
-        got: usize,
+    GotMultipleValues {
+        name: StrRef,
+    },
+    TooManyArguments {
+        expected_min_count: usize,
+        expected_max_count: usize,
+        got_count: usize,
+    },
+    MissingArgs {
+        missing_arg_names: Vec<StrRef>,
     },
-    MissingArgs(String),
     UnknownArgName(StrRef),
     IncorrectArgType {
         name: StrRef,
@@ -77,10 +84,20 @@ impl<'a> Display for DisplayTypeError<'a> {
         use TypeErrorKind::*;
         let mut notes = Some(HashMap::new());
         match &self.err.kind {
-            TooManyArguments { expected, got } => {
-                write!(f, "Too many arguments. Expected {expected} but got {got}")
+            GotMultipleValues { name } => {
+                write!(f, "For multiple values for parameter {name}")
             }
-            MissingArgs(args) => {
+            TooManyArguments { expected_min_count, expected_max_count, got_count } => {
+                debug_assert!(expected_min_count <= expected_max_count);
+                if expected_min_count == expected_max_count {
+                    let expected_count = expected_min_count; // or expected_max_count
+                    write!(f, "Too many arguments. Expected {expected_count} but got {got_count}")
+                } else {
+                    write!(f, "Too many arguments. Expected {expected_min_count} to {expected_max_count} arguments but got {got_count}")
+                }
+            }
+            MissingArgs { missing_arg_names } => {
+                let args = missing_arg_names.iter().join(", ");
                 write!(f, "Missing arguments: {args}")
             }
             UnknownArgName(name) => {
@@ -89,7 +106,7 @@ impl<'a> Display for DisplayTypeError<'a> {
             IncorrectArgType { name, expected, got } => {
                 let expected = self.unifier.stringify_with_notes(*expected, &mut notes);
                 let got = self.unifier.stringify_with_notes(*got, &mut notes);
-                write!(f, "Incorrect argument type for {name}. Expected {expected}, but got {got}")
+                write!(f, "Incorrect argument type for parameter {name}. Expected {expected}, but got {got}")
             }
             FieldUnificationError { field, types, loc } => {
                 let lhs = self.unifier.stringify_with_notes(types.0, &mut notes);

nac3core/src/typecheck/type_inferencer/mod.rs

@@ -641,14 +641,7 @@ impl<'a> Inferencer<'a> {
                                     })
                                     .unwrap();
                             }
-                            let required: Vec<_> = sign
-                                .args
-                                .iter()
-                                .filter(|v| v.default_value.is_none())
-                                .map(|v| v.name)
-                                .rev()
-                                .collect();
-                            self.unifier.unify_call(&call, ty, sign, &required).map_err(|e| {
+                            self.unifier.unify_call(&call, ty, sign).map_err(|e| {
                                 HashSet::from([e
                                     .at(Some(location))
                                     .to_display(self.unifier)
@@ -1346,16 +1339,9 @@ impl<'a> Inferencer<'a> {
                     ret: sign.ret,
                     loc: Some(location),
                 };
-                let required: Vec<_> = sign
-                    .args
-                    .iter()
-                    .filter(|v| v.default_value.is_none())
-                    .map(|v| v.name)
-                    .rev()
-                    .collect();
-                self.unifier.unify_call(&call, func.custom.unwrap(), sign, &required).map_err(
-                    |e| HashSet::from([e.at(Some(location)).to_display(self.unifier).to_string()]),
-                )?;
+                self.unifier.unify_call(&call, func.custom.unwrap(), sign).map_err(|e| {
+                    HashSet::from([e.at(Some(location)).to_display(self.unifier).to_string()])
+                })?;
                 return Ok(Located {
                     location,
                     custom: Some(sign.ret),

nac3core/src/typecheck/typedef/mod.rs

@@ -89,6 +89,13 @@ pub struct FuncArg {
     pub default_value: Option<SymbolValue>,
 }
 
+impl FuncArg {
+    #[must_use]
+    pub fn is_required(&self) -> bool {
+        self.default_value.is_none()
+    }
+}
+
 #[derive(Debug, Clone)]
 pub struct FunSignature {
     pub args: Vec<FuncArg>,
@@ -562,61 +569,153 @@ impl Unifier {
         call: &Call,
         b: Type,
         signature: &FunSignature,
-        required: &[StrRef],
     ) -> Result<(), TypeError> {
+        /*
+            NOTE: scenarios to consider:
+
+            ```python
+            def func1(x: int32, y: int32, z: int32 = 5): pass
+
+            # Normal scenarios
+            func1(23, 45) # OK, z has default
+            func1(23, 45, 67) # OK, z's default is overwritten
+            func1(x = 23, y = 45) # OK, user is using kwargs to set positional args
+            func1(y = 45, x = 23) # OK, kwargs order doesn't matter
+
+            # Error scenarios
+            func1() # ERROR: Missing arguments: x, y
+            func1(23) # ERROR: Missing arguments: y
+            func1(z = 23) # ERROR: Missing arguments: x, y
+            func1(x = 23) # ERROR: Missing arguments: y
+            func1(23, 45, x = 5) # ERROR: Got multiple values for x
+            func1(23, 45, x = 5, y = 6) # ERROR: Got multiple values for x (y too but Python does not report it)
+            func1(23, 45, 67, z = 89) # ERROR: Got multiple values for z
+            func1(23, 45, 67, 89) # ERROR: Function only takes from 2 to 3 positional arguments but 4 were given.
+            func1(23, 45, 67, w = 3) # ERROR: Got an unexpected keyword argument 'w'
+
+            # Error scenarios that do not need to be handled here.
+            func1(23, 45, z = 67, z = 89) # ERROR: Keyword argument repeated: z, the parser panics on this.
+            ```
+        */
+
+        struct ParamInfo<'a> {
+            /// Has this parameter been supplied with an argument already?
+            has_been_supplied: bool,
+            /// The corresponding [`FuncArg`] instance of this parameter (for fast table lookups)
+            param: &'a FuncArg,
+        }
+
         let snapshot = self.unification_table.get_snapshot();
         if self.snapshot.is_none() {
             self.snapshot = Some(snapshot);
         }
 
+        // Get details about the function signature/parameters.
+        let num_params = signature.args.len();
+
+        // Force the type vars in `b` and `signature' to be up-to-date.
+        let b = self.instantiate_fun(b, signature);
+        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 instantiated = self.instantiate_fun(b, signature);
-        let r = self.get_ty(instantiated);
-        let r = r.as_ref();
-        let TypeEnum::TFunc(signature) = r else { unreachable!() };
-        // we check to make sure that all required arguments (those without default
-        // arguments) are provided, and do not provide the same argument twice.
-        let mut required = required.to_vec();
-        let mut all_names: Vec<_> = signature.args.iter().map(|v| (v.name, v.ty)).rev().collect();
-        for (i, t) in posargs.iter().enumerate() {
-            if signature.args.len() <= i {
+        let num_args = posargs.len() + kwargs.len();
+
+        // Now we check the arguments against the parameters
+
+        // Helper lambdas
+        let mut type_check_arg = |param_name, expected_arg_ty, arg_ty| {
+            let ok = self.unify_impl(expected_arg_ty, arg_ty, false).is_ok();
+            if ok {
+                Ok(())
+            } else {
+                // Typecheck failed, throw an error.
                 self.restore_snapshot();
-                return Err(TypeError::new(
-                    TypeErrorKind::TooManyArguments {
-                        expected: signature.args.len(),
-                        got: posargs.len() + kwargs.len(),
+                Err(TypeError::new(
+                    TypeErrorKind::IncorrectArgType {
+                        name: param_name,
+                        expected: expected_arg_ty,
+                        got: arg_ty,
                     },
                     *loc,
-                ));
+                ))
             }
-            required.pop();
-            let (name, expected) = all_names.pop().unwrap();
-            self.unify_impl(expected, *t, false).map_err(|_| {
-                self.restore_snapshot();
-                TypeError::new(TypeErrorKind::IncorrectArgType { name, expected, got: *t }, *loc)
-            })?;
-        }
-        for (k, t) in kwargs {
-            if let Some(i) = required.iter().position(|v| v == k) {
-                required.remove(i);
-            }
-            let i = all_names.iter().position(|v| &v.0 == k).ok_or_else(|| {
-                self.restore_snapshot();
-                TypeError::new(TypeErrorKind::UnknownArgName(*k), *loc)
-            })?;
-            let (name, expected) = all_names.remove(i);
-            self.unify_impl(expected, *t, false).map_err(|_| {
-                self.restore_snapshot();
-                TypeError::new(TypeErrorKind::IncorrectArgType { name, expected, got: *t }, *loc)
-            })?;
-        }
-        if !required.is_empty() {
+        };
+
+        // Check for "too many arguments"
+        if num_params < posargs.len() {
+            let expected_min_count =
+                signature.args.iter().filter(|param| param.is_required()).count();
+            let expected_max_count = num_params;
+
             self.restore_snapshot();
             return Err(TypeError::new(
-                TypeErrorKind::MissingArgs(required.iter().join(", ")),
+                TypeErrorKind::TooManyArguments {
+                    expected_min_count,
+                    expected_max_count,
+                    got_count: num_args,
+                },
                 *loc,
             ));
         }
+
+        // NOTE: order of `param_info_by_name` is leveraged, so use an IndexMap
+        let mut param_info_by_name: IndexMap<StrRef, ParamInfo> = signature
+            .args
+            .iter()
+            .map(|arg| (arg.name, ParamInfo { has_been_supplied: false, param: arg }))
+            .collect();
+
+        // Now consume all positional arguments and typecheck them.
+        for (&arg_ty, param) in zip(posargs, signature.args.iter()) {
+            // We will also use this opportunity to mark the corresponding `param_info` as having been supplied.
+            let param_info = param_info_by_name.get_mut(&param.name).unwrap();
+            param_info.has_been_supplied = true;
+
+            // Typecheck
+            type_check_arg(param.name, param.ty, arg_ty)?;
+        }
+
+        // Now consume all keyword arguments and typecheck them.
+        for (&param_name, &arg_ty) in kwargs {
+            // We will also use this opportunity to check if this keyword argument is "legal".
+
+            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));
+            };
+
+            if param_info.has_been_supplied {
+                // NOTE: Duplicate keyword argument (i.e., `hello(1, 2, 3, arg = 4, arg = 5)`)
+                // is IMPOSSIBLE as the parser would have already failed.
+                // We only have to care about "got multiple values for XYZ"
+
+                self.restore_snapshot();
+                return Err(TypeError::new(
+                    TypeErrorKind::GotMultipleValues { name: param_name },
+                    *loc,
+                ));
+            }
+
+            param_info.has_been_supplied = true;
+
+            // Typecheck
+            type_check_arg(param_name, param_info.param.ty, arg_ty)?;
+        }
+
+        // After checking posargs and kwargs, check if there are any
+        // unsupported 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)
+            .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));
+        }
+
+        // Finally, check the Call's return type
         self.unify_impl(*ret, signature.ret, false).map_err(|mut err| {
             self.restore_snapshot();
             if err.loc.is_none() {
@@ -624,7 +723,8 @@ impl Unifier {
             }
             err
         })?;
-        *fun.borrow_mut() = Some(instantiated);
+
+        *fun.borrow_mut() = Some(b);
 
         self.discard_snapshot(snapshot);
         Ok(())
@@ -990,17 +1090,10 @@ impl Unifier {
                 self.unification_table.set_value(b, Rc::new(TCall(calls)));
             }
             (TCall(calls), TFunc(signature)) => {
-                let required: Vec<StrRef> = signature
-                    .args
-                    .iter()
-                    .filter(|v| v.default_value.is_none())
-                    .map(|v| v.name)
-                    .rev()
-                    .collect();
                 // we unify every calls to the function signature.
                 for c in calls {
                     let call = self.calls[c.0].clone();
-                    self.unify_call(&call, b, signature, &required)?;
+                    self.unify_call(&call, b, signature)?;
                 }
                 self.set_a_to_b(a, b);
             }