Require single config root object

Otherwise global attributes and attributes for the root object have the
same syntax (`#![...]`). This way, it is way clearer.

examples/simple.rs

@@ -5,16 +5,18 @@ mod config {
     confique::config! {
         #![derive_for_all(Debug, Clone)]
 
-        log: {
-            /// Determines how many messages are logged. Log messages below
-            /// this level are not emitted. Possible values: "trace", "debug",
-            /// "info", "warn", "error" and "off".
-            level: log::LevelFilter = "debug",
+        config: {
+            log: {
+                /// Determines how many messages are logged. Log messages below
+                /// this level are not emitted. Possible values: "trace", "debug",
+                /// "info", "warn", "error" and "off".
+                level: log::LevelFilter = "debug",
 
-            /// If this is set, log messages are also written to this file.
-            #[example = "/var/log/test.log"]
-            file: Option<PathBuf>,
-        },
+                /// If this is set, log messages are also written to this file.
+                #[example = "/var/log/test.log"]
+                file: Option<PathBuf>,
+            },
+        }
     }
 }
 

macro/src/parse.rs

@@ -1,4 +1,4 @@
-use proc_macro2::{Span, TokenStream};
+use proc_macro2::TokenStream;
 use quote::ToTokens;
 use syn::{
     Error, Ident,
@@ -16,31 +16,28 @@ impl Parse for Input {
         let mut outer_attrs = input.call(syn::Attribute::parse_inner)?;
         let visibility = extract_visibility(&mut outer_attrs)?;
         let derive_for_all = extract_single_list_attr("derive_for_all", &mut outer_attrs)?;
-
-        let doc = extract_doc(&mut outer_attrs)?;
-        let typename = extract_typename(&mut outer_attrs)?;
-
-        // Extract attributes that we will just forward/emit verbatim. Well, not
-        // completely verbatim: we have to change the type to outer attribute.
-        let mut forwarded_attrs = extract_attrs(&["derive"], &mut outer_attrs);
-        for a in &mut forwarded_attrs {
-            a.style = syn::AttrStyle::Outer;
-        }
-
         assert_no_extra_attrs(&outer_attrs)?;
 
-        // Parse children
-        let children = input.call(<Punctuated<_, syn::Token![,]>>::parse_terminated)?;
+        // Parse top level object.
+        let root: Node = input.parse()?;
+        if root.name != "config" {
+            return Err(syn::Error::new(
+                root.name.span(),
+                "top level object must have the name 'config'",
+            ));
+        }
 
-        let root = Node {
-            doc,
-            attrs: forwarded_attrs,
-            name: Ident::new("config", Span::call_site()),
-            kind: NodeKind::Obj(Obj {
-                typename,
-                children: children.into_iter().collect(),
-            }),
-        };
+        // Make sure we have at most one trailing comma
+        if input.peek(syn::Token![,]) {
+            let _: syn::Token![,] = input.parse().unwrap();
+        }
+
+        if !input.is_empty() {
+            return Err(syn::Error::new(
+                input.span(),
+                "unexpected additional tokens (only one root element allowed)",
+            ));
+        }
 
         Ok(Self { root, visibility, derive_for_all })
     }

src/example.rs

@@ -12,31 +12,32 @@ use std::{net::IpAddr, path::PathBuf};
 use crate as confique;
 
 crate::config! {
-    //! An example configuration.
+    // This is used here to make all items show up in the documentation.
     #![visibility = "pub"]
-    #![derive(Clone)]
 
-    #[derive(Clone, Copy)]
-    dns: {
-        /// The DNS server IP address.
-        #[example = "1.1.1.1"]
-        server: IpAddr,
+    /// An example configuration.
+    config: {
+        dns: {
+            /// The DNS server IP address.
+            #[example = "1.1.1.1"]
+            server: IpAddr,
 
-        /// Whether to use a local DNS resolution cache.
-        use_cache: bool = true,
+            /// Whether to use a local DNS resolution cache.
+            use_cache: bool = true,
 
-        /// How often to reattempt reaching the DNS server.
-        retry_attempts: u32 = 27,
-    },
+            /// How often to reattempt reaching the DNS server.
+            retry_attempts: u32 = 27,
+        },
 
-    #[typename = "Logger"]
-    log: {
-        /// Sets the log level. Possible values: "trace", "debug", "info",
-        /// "warn", "error" and "off".
-        level: log::LevelFilter = "info",
+        #[typename = "Logger"]
+        log: {
+            /// Sets the log level. Possible values: "trace", "debug", "info",
+            /// "warn", "error" and "off".
+            level: log::LevelFilter = "info",
 
-        /// If this is set, log messages are also written to this file.
-        #[example = "/var/log/test.log"]
-        file: Option<PathBuf>,
-    },
+            /// If this is set, log messages are also written to this file.
+            #[example = "/var/log/test.log"]
+            file: Option<PathBuf>,
+        },
+    }
 }