initial example-config generator

Signed-off-by: Jason Volk <jason@zemos.net>

src/macros/config.rs

@@ -0,0 +1,98 @@
+use std::fmt::Write;
+
+use proc_macro::TokenStream;
+use quote::ToTokens;
+use syn::{Expr, ExprLit, Field, Fields, FieldsNamed, ItemStruct, Lit, Meta, MetaNameValue, Type, TypePath};
+
+use crate::{utils::is_cargo_build, Result};
+
+#[allow(clippy::needless_pass_by_value)]
+pub(super) fn example_generator(input: ItemStruct, args: &[Meta]) -> Result<TokenStream> {
+	if is_cargo_build() {
+		generate_example(&input, args)?;
+	}
+
+	Ok(input.to_token_stream().into())
+}
+
+#[allow(clippy::needless_pass_by_value)]
+#[allow(unused_variables)]
+fn generate_example(input: &ItemStruct, _args: &[Meta]) -> Result<()> {
+	if let Fields::Named(FieldsNamed {
+		named,
+		..
+	}) = &input.fields
+	{
+		for field in named {
+			let Some(ident) = &field.ident else {
+				continue;
+			};
+
+			let Some(doc) = get_doc_comment(field) else {
+				continue;
+			};
+
+			let Some(type_name) = get_type_name(field) else {
+				continue;
+			};
+
+			//println!("{:?} {type_name:?}\n{doc}", ident.to_string());
+		}
+	}
+
+	Ok(())
+}
+
+fn get_doc_comment(field: &Field) -> Option<String> {
+	let mut out = String::new();
+	for attr in &field.attrs {
+		let Meta::NameValue(MetaNameValue {
+			path,
+			value,
+			..
+		}) = &attr.meta
+		else {
+			continue;
+		};
+
+		if !path
+			.segments
+			.iter()
+			.next()
+			.is_some_and(|s| s.ident == "doc")
+		{
+			continue;
+		}
+
+		let Expr::Lit(ExprLit {
+			lit,
+			..
+		}) = &value
+		else {
+			continue;
+		};
+
+		let Lit::Str(token) = &lit else {
+			continue;
+		};
+
+		writeln!(&mut out, "# {}", token.value()).expect("wrote to output string buffer");
+	}
+
+	(!out.is_empty()).then_some(out)
+}
+
+fn get_type_name(field: &Field) -> Option<String> {
+	let Type::Path(TypePath {
+		path,
+		..
+	}) = &field.ty
+	else {
+		return None;
+	};
+
+	path.segments
+		.iter()
+		.next()
+		.map(|segment| segment.ident.to_string())
+}