add doctest

src/lib.rs

@@ -1,8 +1,11 @@
+//! This crate creates `miniconf::Tree` implementations fields in a struct. These carry some extra
+//! extra information about the field.
+
 use std::iter::once;
 
 use convert_case::{Case, Casing};
 use proc_macro::TokenStream;
-use proc_macro2::{Span as Span2, TokenStream as TokenStream2};
+use proc_macro2::{Span as Span2, TokenStream as TokenStream2, TokenTree as TokenTree2};
 use quote::{format_ident, quote, ToTokens};
 use syn::{
     parse_macro_input, parse_quote, Attribute, DataStruct, DeriveInput, Expr, ExprLit, Field,
@@ -12,6 +15,20 @@ use syn::{
 /// Creates structs for the values to extend them with extra metadata.
 ///
 /// supported metadata is `min`, `max` and `default`. Doc comments are parsed as `description`
+///
+/// # Example
+/// ```
+/// use macroconf::config;
+///
+/// #[config]
+/// struct Config {
+///     /// This will be parsed as description
+///     #[min] // This will use i32::MIN for the minimum
+///     #[max = 50] // The value 50 is used for the maximum
+///     #[default = 42] // A `Default` implementation will be generated returning 42
+///     field1: i32,
+/// }
+/// ```
 #[proc_macro_attribute]
 pub fn config(_attr: TokenStream, item: TokenStream) -> TokenStream {
     let mut input = parse_macro_input!(item as DeriveInput);
@@ -37,6 +54,32 @@ pub fn config(_attr: TokenStream, item: TokenStream) -> TokenStream {
         }
     }
 
+    if let Some(attr) = input
+        .attrs
+        .iter_mut()
+        .find(|attr| attr.path().is_ident("derive"))
+    {
+        if let Ok(meta) = attr.meta.require_list() {
+            let derives_tree = meta
+                .tokens
+                .clone()
+                .into_iter()
+                .filter_map(|token| match token {
+                    TokenTree2::Ident(ident) if ident == Ident::new("Tree", ident.span()) => {
+                        Some(ident)
+                    }
+                    _ => None,
+                })
+                .count()
+                == 1;
+            if !derives_tree {
+                input.attrs.push(parse_quote!(#[derive(::miniconf::Tree)]));
+            }
+        }
+    } else {
+        input.attrs.push(parse_quote!(#[derive(::miniconf::Tree)]));
+    }
+
     quote! {
         #input
         #(#new_types)*
@@ -339,7 +382,7 @@ fn generate_serde(ident: &Ident, ty: &Type, checked_new: bool) -> TokenStream2 {
     let conversion = if checked_new {
         quote! {
             Self::new(value).ok_or_else(|| {
-                D::Error::custom("checking value bounds")
+                <D::Error as ::serde::de::Error>::custom("checking value bounds")
             })
         }
     } else {