From 2007f30b1137eec20678e3e9cd96788dc6c1b222 Mon Sep 17 00:00:00 2001
From: Laurenz <laurmaedje@gmail.com>
Date: Tue, 28 Nov 2023 18:54:51 +0100
Subject: [PATCH] Better error message for named instead of positional argument

---
 crates/typst/src/foundations/args.rs | 20 ++++++++++++++++++--
 tests/typ/compiler/call.typ          |  5 +++++
 2 files changed, 23 insertions(+), 2 deletions(-)

diff --git a/crates/typst/src/foundations/args.rs b/crates/typst/src/foundations/args.rs
index 8732c7b50..74e8e2be2 100644
--- a/crates/typst/src/foundations/args.rs
+++ b/crates/typst/src/foundations/args.rs
@@ -2,7 +2,7 @@ use std::fmt::{self, Debug, Formatter};
 
 use ecow::{eco_format, eco_vec, EcoString, EcoVec};
 
-use crate::diag::{bail, At, SourceDiagnostic, SourceResult};
+use crate::diag::{bail, error, At, SourceDiagnostic, SourceResult};
 use crate::foundations::{
     func, repr, scope, ty, Array, Dict, FromValue, IntoValue, Repr, Str, Value,
 };
@@ -121,10 +121,26 @@ impl Args {
     {
         match self.eat()? {
             Some(v) => Ok(v),
-            None => bail!(self.span, "missing argument: {what}"),
+            None => bail!(self.missing_argument(what)),
         }
     }
 
+    /// The error message for missing arguments.
+    fn missing_argument(&self, what: &str) -> SourceDiagnostic {
+        for item in &self.items {
+            let Some(name) = item.name.as_deref() else { continue };
+            if name == what {
+                return error!(
+                    item.span,
+                    "the argument `{what}` is positional";
+                    hint: "try removing `{}:`", name,
+                );
+            }
+        }
+
+        error!(self.span, "missing argument: {what}")
+    }
+
     /// Find and consume the first castable positional argument.
     pub fn find<T>(&mut self) -> SourceResult<Option<T>>
     where
diff --git a/tests/typ/compiler/call.typ b/tests/typ/compiler/call.typ
index 5297ec159..e48eabfd7 100644
--- a/tests/typ/compiler/call.typ
+++ b/tests/typ/compiler/call.typ
@@ -47,6 +47,11 @@
 // Error: 26-30 duplicate argument: font
 #set text(font: "Arial", font: "Helvetica")
 
+---
+// Error: 4-15 the argument `amount` is positional
+// Hint: 4-15 try removing `amount:`
+#h(amount: 0.5)
+
 ---
 // Error: 2-6 expected function, found boolean
 #true()