1 files changed, 28 insertions, 0 deletions

diff --git a/macros/src/explain.rs b/macros/src/explain.rs
new file mode 100644
index 0000000..41dc5d4
--- /dev/null
+++ b/macros/src/explain.rs
@@ -0,0 +1,28 @@
+use proc_macro2::TokenStream as TokenStream2;
+use quote::quote;
+use syn::{ItemStruct, Lit, Meta, MetaNameValue};
+
+pub fn generate_explain_impl(struct_item: &ItemStruct) -> TokenStream2 {
+    let struct_name = &struct_item.ident;
+    let explain = struct_item
+        .attrs
+        .iter()
+        .filter_map(|attr| match attr.parse_meta().ok() {
+            Some(Meta::NameValue(MetaNameValue {
+                path,
+                lit: Lit::Str(str_lit),
+                ..
+            })) if path.is_ident("doc") => Some(str_lit.value()),
+            _ => None,
+        })
+        .map(|s| s.strip_prefix(' ').unwrap_or(&s).to_owned())
+        .collect::<Vec<_>>()
+        .join("\n");
+    quote! {
+        impl crate::Explain for #struct_name {
+            fn explanation(&self) -> &'static str {
+                #explain
+            }
+        }
+    }
+}