feat: improve macro error messages

1 files changed, 116 insertions, 0 deletions

diff --git a/macros/src/util/error.rs b/macros/src/util/error.rs
new file mode 100644
index 0000000..d068661
--- /dev/null
+++ b/macros/src/util/error.rs
@@ -0,0 +1,116 @@
+/// Used to create a error enum that converts into a [`Diagnostic`].
+///
+/// [`Diagnostic`]: proc_macro_error::Diagnostic
+macro_rules! diagnostic_error_enum {
+    ($(#[$meta: meta])* $visibility: vis enum $name: ident {
+        $(
+            #[error($($error: tt)*), span = $error_span: expr]
+            $(#[note($($note: tt)*)$(, span = $note_span: expr)?])*
+            $(#[help($($help: tt)*)$(, span = $help_span: expr)?])*
+            $(#[err($($err: tt)*)$(, span = $err_span: expr)?])*
+            $(#[source($source: ident)])?
+            $variant: ident {
+                $($variant_field: ident: $variant_field_type: ty),*
+            },
+        )*
+    }) => {
+        $(#[$meta])*
+        #[derive(Debug, Clone)]
+        $visibility enum $name
+        {
+            $(
+                $variant {
+                    $($variant_field: $variant_field_type),*
+                },
+            )*
+        }
+
+        impl From<$name> for ::proc_macro_error::Diagnostic
+        {
+            #[must_use]
+            fn from(err: $name) -> Self
+            {
+                let (error, span, notes, helps, errs, source): (
+                    String,
+                    ::proc_macro2::Span,
+                    Vec<(String, ::proc_macro2::Span)>,
+                    Vec<(String, ::proc_macro2::Span)>,
+                    Vec<(String, ::proc_macro2::Span)>,
+                    Option<::proc_macro_error::Diagnostic>
+                ) = match err {
+                    $(
+                        $name::$variant {
+                            $($variant_field),*
+                        } => {
+                            (
+                                format!($($error)*),
+                                $error_span,
+                                vec![$(
+                                    (
+                                        format!($($note)*),
+                                        $crate::util::or!(
+                                            ($($note_span)?)
+                                            else (::proc_macro2::Span::call_site())
+                                        )
+                                    )
+                                ),*],
+                                vec![$(
+                                    (
+                                        format!($($help)*),
+                                        $crate::util::or!(
+                                            ($($help_span)?)
+                                            else (::proc_macro2::Span::call_site())
+                                        )
+                                    )
+                                ),*],
+                                vec![$(
+                                    (
+                                        format!($($err)*),
+                                        $crate::util::or!(
+                                            ($($err_span)?)
+                                            else (::proc_macro2::Span::call_site())
+                                        )
+                                    )
+                                ),*],
+                                $crate::util::to_option!($($source.into())?)
+                            )
+                        }
+                    ),*
+                };
+
+                if let Some(source_diagnostic) = source {
+                    source_diagnostic.emit();
+                }
+
+                let mut diagnostic = ::proc_macro_error::Diagnostic::spanned(
+                    span,
+                    ::proc_macro_error::Level::Error,
+                    error
+                );
+
+                if !notes.is_empty() {
+                    for (note, note_span) in notes {
+                        diagnostic = diagnostic.span_note(note_span, note);
+                    }
+                }
+
+                if !helps.is_empty() {
+                    for (help, help_span) in helps {
+                        diagnostic = diagnostic.span_help(help_span, help);
+                    }
+                }
+
+                if !errs.is_empty() {
+                    for (err, err_span) in errs {
+                        diagnostic = diagnostic.span_error(err_span, err);
+                    }
+                }
+
+                diagnostic
+            }
+        }
+
+    };
+}
+
+pub(crate) use diagnostic_error_enum;