feat(derive): improved derive support, including partial help format string support!

miette-derive/src/help.rs

@@ -21,11 +21,37 @@ impl Parse for Help {
             if la.peek(syn::token::Paren) {
                 let content;
                 parenthesized!(content in input);
-                let str = content.parse::<syn::LitStr>()?;
+                let mut fmt = None;
-                Ok(Help {
+                let mut args = Vec::new();
-                    fmt: str.value(),
+                let punc = syn::punctuated::Punctuated::<syn::Expr, Token![,]>::parse_terminated(
-                    args: Vec::new(),
+                    &content,
-                })
+                )?;
+                for (i, arg) in punc.into_iter().enumerate() {
+                    if i == 0 {
+                        if let syn::Expr::Lit(syn::ExprLit {
+                            lit: syn::Lit::Str(str),
+                            ..
+                        }) = arg
+                        {
+                            fmt = Some(str.value());
+                        }
+                    } else {
+                        args.push(arg);
+                    }
+                }
+                if let Some(fmt) = fmt {
+                    Ok(Help { fmt, args })
+                } else if !args.is_empty() {
+                    Err(syn::Error::new(
+                        ident.span(),
+                        "The first arg to help() must be a literal format string.",
+                    ))
+                } else {
+                    Err(syn::Error::new(
+                        ident.span(),
+                        "help() format string is required",
+                    ))
+                }
             } else {
                 input.parse::<Token![=]>()?;
                 Ok(Help {
@@ -53,9 +79,9 @@ impl Help {
                      ref fields,
                      ..
                  }| {
-                     let help = &help.as_ref().unwrap();
+                    let help = &help.as_ref().unwrap();
-                     let fmt = &help.fmt;
+                    let fmt = &help.fmt;
-                     let args = help.args.iter().map(|arg| quote! { #arg, });
+                    let args = &help.args;
                     match fields {
                         syn::Fields::Named(_) => {
                             quote! { Self::#ident{..} => std::option::Option::Some(std::boxed::Box::new(format!(#fmt, #(#args),*))), }

tests/derive.rs

@@ -132,7 +132,6 @@ fn list_help() {
     );
 }
 
-/*
 #[test]
 fn fmt_help() {
     #[derive(Debug, Diagnostic, Error)]
@@ -144,8 +143,8 @@ fn fmt_help() {
     struct FooStruct(String);
 
     assert_eq!(
-        "1 bar".to_string(),
+        "1 hello".to_string(),
-        FooStruct.help().unwrap().to_string()
+        FooStruct("hello".into()).help().unwrap().to_string()
     );
 
     #[derive(Debug, Diagnostic, Error)]
@@ -163,4 +162,3 @@ fn fmt_help() {
         FooEnum::X.help().unwrap().to_string()
     );
 }
-*/