From 9ef0dd261fa537b280f32ea6f149785a69e33938 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Kat=20March=C3=A1n?= <kzm@zkat.tech>
Date: Sun, 15 Aug 2021 18:15:50 -0700
Subject: [PATCH] feat(derive): improved derive support, including partial help
 format string support!

---
 miette-derive/src/help.rs | 42 +++++++++++++++++++++++++++++++--------
 tests/derive.rs           |  6 ++----
 2 files changed, 36 insertions(+), 12 deletions(-)

diff --git a/miette-derive/src/help.rs b/miette-derive/src/help.rs
index a974d40..22e98b6 100644
--- a/miette-derive/src/help.rs
+++ b/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>()?;
-                Ok(Help {
-                    fmt: str.value(),
-                    args: Vec::new(),
-                })
+                let mut fmt = None;
+                let mut args = Vec::new();
+                let punc = syn::punctuated::Punctuated::<syn::Expr, Token![,]>::parse_terminated(
+                    &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 fmt = &help.fmt;
-                     let args = help.args.iter().map(|arg| quote! { #arg, });
+                    let help = &help.as_ref().unwrap();
+                    let fmt = &help.fmt;
+                    let args = &help.args;
                     match fields {
                         syn::Fields::Named(_) => {
                             quote! { Self::#ident{..} => std::option::Option::Some(std::boxed::Box::new(format!(#fmt, #(#args),*))), }
diff --git a/tests/derive.rs b/tests/derive.rs
index ef286e7..55c20c2 100644
--- a/tests/derive.rs
+++ b/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(),
-        FooStruct.help().unwrap().to_string()
+        "1 hello".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()
     );
 }
-*/