Use serde's default annotation for Document

cove-macro/src/util.rs

@@ -1,6 +1,22 @@
-use syn::{Expr, ExprLit, Field, Lit, LitStr};
+use proc_macro2::Span;
+use syn::parse::Parse;
+use syn::punctuated::Punctuated;
+use syn::{Expr, ExprLit, Field, Lit, LitStr, Path, Token};
 
-pub fn strlit(expr: &Expr) -> Option<&LitStr> {
+pub fn bail<T>(span: Span, message: &str) -> syn::Result<T> {
+    Err(syn::Error::new(span, message))
+}
+
+pub fn litstr(expr: &Expr) -> Option<&LitStr> {
+    match expr {
+        Expr::Lit(ExprLit {
+            lit: Lit::Str(lit), ..
+        }) => Some(lit),
+        _ => None,
+    }
+}
+
+pub fn into_litstr(expr: Expr) -> Option<LitStr> {
     match expr {
         Expr::Lit(ExprLit {
             lit: Lit::Str(lit), ..
@@ -19,7 +35,7 @@ pub fn docstring(field: &Field) -> syn::Result<String> {
         .iter()
         .filter(|attr| attr.path().is_ident("doc"))
     {
-        if let Some(lit) = strlit(&attr.meta.require_name_value()?.value) {
+        if let Some(lit) = litstr(&attr.meta.require_name_value()?.value) {
             let value = lit.value();
             let value = value
                 .strip_prefix(' ')
@@ -31,3 +47,36 @@ pub fn docstring(field: &Field) -> syn::Result<String> {
 
     Ok(lines.join("\n"))
 }
+
+pub struct AttributeArgument {
+    pub path: Path,
+    pub value: Option<Expr>,
+}
+
+impl Parse for AttributeArgument {
+    fn parse(input: syn::parse::ParseStream<'_>) -> syn::Result<Self> {
+        let path = Path::parse(input)?;
+        let value = if input.peek(Token![=]) {
+            input.parse::<Token![=]>()?;
+            Some(Expr::parse(input)?)
+        } else {
+            None
+        };
+        Ok(Self { path, value })
+    }
+}
+
+/// Given a struct field, this finds all arguments of the form `#[path(key)]`
+/// and `#[path(key = value)]`. Multiple arguments may be specified in a single
+/// annotation, e.g. `#[foo(bar, baz = true)]`.
+pub fn attribute_arguments(field: &Field, path: &str) -> syn::Result<Vec<AttributeArgument>> {
+    let mut attrs = vec![];
+
+    for attr in field.attrs.iter().filter(|attr| attr.path().is_ident(path)) {
+        let args =
+            attr.parse_args_with(Punctuated::<AttributeArgument, Token![,]>::parse_terminated)?;
+        attrs.extend(args);
+    }
+
+    Ok(attrs)
+}