Make 'UnexpectedLabelArg' errors more helpful

## Before

  ```
   × Checking
   ╰─▶ Unexpected labeled argument

       t

     ╭─[/Users/mati/Devel/OpenSource/time_lock_aiken/validators/time_lock.ak:13:1]
  13 │   let now = when context.transaction.validity_range.lower_bound.bound_type is {
  14 │     Finite { t } -> t
     ·              ─
  15 │     NegativeInfinity -> 0
     ╰────
  ```

  ## After

  ```
    × Type-checking
    ╰─▶ Unexpected labeled argument 't'

      ╭─[../stdlib/validators/tmp.ak:10:1]
   10 │   let now = when context.transaction.validity_range.lower_bound.bound_type is {
   11 │     interval.Finite { t } -> t
      ·                       ─
   12 │     interval.NegativeInfinity -> 0
      ╰────
    help: The constructor 'Finite' does not have any labeled field. Its fields
          must therefore be matched only by position.

          Perhaps, try the following:

          ╰─▶  interval.Finite(t)
  ```

crates/aiken-lang/src/format.rs

@@ -796,7 +796,7 @@ impl<'comments> Formatter<'comments> {
         }
     }
 
-    fn pattern_constructor<'a>(
+    pub fn pattern_constructor<'a>(
         &mut self,
         name: &'a str,
         args: &'a [CallArg<UntypedPattern>],
@@ -1478,7 +1478,7 @@ impl<'comments> Formatter<'comments> {
         list(elements_document, elements.len(), tail)
     }
 
-    fn pattern<'a>(&mut self, pattern: &'a UntypedPattern) -> Document<'a> {
+    pub fn pattern<'a>(&mut self, pattern: &'a UntypedPattern) -> Document<'a> {
         let comments = self.pop_comments(pattern.location().start);
         let doc = match pattern {
             Pattern::Int { value, .. } => value.to_doc(),

crates/aiken-lang/src/tipo/environment.rs

@@ -10,9 +10,10 @@ use crate::{
     ast::{
         Annotation, CallArg, DataType, Definition, Function, ModuleConstant, Pattern,
         RecordConstructor, RecordConstructorArg, Span, TypeAlias, TypedDefinition,
-        UnqualifiedImport, UntypedDefinition, Use, PIPE_VARIABLE,
+        UnqualifiedImport, UntypedDefinition, UntypedPattern, Use, PIPE_VARIABLE,
     },
     builtins::{self, function, generic_var, tuple, unbound_var},
+    format::Formatter,
     tipo::fields::FieldMap,
     IdGenerator,
 };
@@ -1603,12 +1604,53 @@ fn assert_unique_const_name<'a>(
     }
 }
 
+pub(super) fn assert_no_labeled_arguments_in_pattern<'a>(
+    name: &str,
+    args: &[CallArg<UntypedPattern>],
+    module: &'a Option<String>,
+    with_spread: bool,
+) -> Result<(), Error> {
+    for arg in args {
+        if let Some(label) = &arg.label {
+            let fixed_args = args
+                .iter()
+                .map(|arg| CallArg {
+                    label: None,
+                    location: arg.location,
+                    value: arg.value.clone(),
+                })
+                .collect::<Vec<_>>();
+
+            let suggestion = Formatter::new()
+                .pattern_constructor(name, &fixed_args, module, with_spread, false)
+                .to_pretty_string(70);
+
+            let hint = format!(
+                r#"The constructor '{name}' does not have any labeled field. Its fields
+must therefore be matched only by position.
+
+Perhaps, try the following:
+
+╰─▶  {suggestion}"#
+            );
+
+            return Err(Error::UnexpectedLabeledArg {
+                location: arg.location,
+                label: label.to_string(),
+                hint: Some(hint),
+            });
+        }
+    }
+    Ok(())
+}
+
 pub(super) fn assert_no_labeled_arguments<A>(args: &[CallArg<A>]) -> Result<(), Error> {
     for arg in args {
         if let Some(label) = &arg.label {
             return Err(Error::UnexpectedLabeledArg {
                 location: arg.location,
                 label: label.to_string(),
+                hint: None,
             });
         }
     }

crates/aiken-lang/src/tipo/error.rs

@@ -144,11 +144,14 @@ pub enum Error {
     #[error("{name} is a reserved module name\n")]
     ReservedModuleName { name: String },
 
-    #[error("Unexpected labeled argument\n\n{label}\n")]
+    #[error("Unexpected labeled argument '{label}'\n")]
+    #[diagnostic()]
     UnexpectedLabeledArg {
         #[label]
         location: Span,
         label: String,
+        #[help]
+        hint: Option<String>,
     },
 
     #[error("Unexpected type hole\n")]
@@ -229,8 +232,8 @@ pub enum Error {
     #[diagnostic(help(
         r#"Did you forget to import it?
 
-Data-type constructors are not automatically imported, even if their type is
+Data-type constructors are not automatically imported, even if their type
-imported. So, if a module `aiken/pet` defines the following type:
+is imported. So, if a module `aiken/pet` defines the following type:
 
  ┍━ aiken/pet.ak ━━━━━━━━
  │ pub type Pet {{

crates/aiken-lang/src/tipo/pattern.rs

@@ -9,7 +9,9 @@ use std::{
 use itertools::Itertools;
 
 use super::{
-    environment::{assert_no_labeled_arguments, collapse_links, EntityKind, Environment},
+    environment::{
+        assert_no_labeled_arguments_in_pattern, collapse_links, EntityKind, Environment,
+    },
     error::Error,
     hydrator::Hydrator,
     PatternConstructor, Type, ValueConstructor, ValueConstructorVariant,
@@ -483,7 +485,12 @@ impl<'a, 'b> PatternTyper<'a, 'b> {
                     }
 
                     // The fun has no field map and so we error if arguments have been labelled
-                    None => assert_no_labeled_arguments(&pattern_args)?,
+                    None => assert_no_labeled_arguments_in_pattern(
+                        &name,
+                        &pattern_args,
+                        &module,
+                        with_spread,
+                    )?,
                 }
 
                 let constructor_typ = cons.tipo.clone();