Add help system with `#[help]` macro and `HelpRequest` trait

10 files changed, 309 insertions, 0 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index d2ba927..cd2ffc9 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -24,6 +24,15 @@ struct YourCommandEntry {
 
 2. **\[core\]** Added function `new_with_args` to `Program`
 3. **\[core\]** Added function `dispatch_args_dynamic` to `Program`
+4. **\[core\]** Impl `std::io::Write` trait for `RenderResult`
+5. **\[core\]** Added Help system, which allows binding an event for `--help` to an `Entry` via the `help!` macro
+
+```rust
+#[help]
+fn your_command_help(_prev: YourEntry) {
+    r_println!("Your help docs");
+}
+```
 
 #### **BREAKING CHANGES**:
 
diff --git a/mingling/src/lib.rs b/mingling/src/lib.rs
index d712ff0..5240682 100644
--- a/mingling/src/lib.rs
+++ b/mingling/src/lib.rs
@@ -84,6 +84,8 @@ pub mod macros {
     pub use mingling_macros::dispatcher_clap;
     /// Used to collect data and create a command-line context
     pub use mingling_macros::gen_program;
+    /// Used to generate a struct implementing the `HelpRequest` trait via a method
+    pub use mingling_macros::help;
     /// Used to create a `Node` struct via a literal
     pub use mingling_macros::node;
     /// Used to create a wrapper type for use with `Chain` and `Renderer`
@@ -103,6 +105,8 @@ pub mod macros {
     pub use mingling_macros::r_println;
     /// Used to register a chain
     pub use mingling_macros::register_chain;
+    /// Used to register a help
+    pub use mingling_macros::register_help;
     /// Used to register a renderer
     pub use mingling_macros::register_renderer;
     /// Used to register a type into the context
diff --git a/mingling_core/src/asset.rs b/mingling_core/src/asset.rs
index a4254ef..234fec1 100644
--- a/mingling_core/src/asset.rs
+++ b/mingling_core/src/asset.rs
@@ -16,3 +16,6 @@ pub mod node;
 
 #[doc(hidden)]
 pub mod renderer;
+
+#[doc(hidden)]
+pub mod help;
diff --git a/mingling_core/src/asset/help.rs b/mingling_core/src/asset/help.rs
new file mode 100644
index 0000000..ff2b3d4
--- /dev/null
+++ b/mingling_core/src/asset/help.rs
@@ -0,0 +1,10 @@
+use crate::RenderResult;
+
+/// Handles help rendering for command-line arguments
+pub trait HelpRequest {
+    /// The entry type
+    type Entry;
+
+    /// Process the previous value and write the result into the provided [`RenderResult`](./struct.RenderResult.html)
+    fn render_help(p: Self::Entry, r: &mut RenderResult);
+}
diff --git a/mingling_core/src/lib.rs b/mingling_core/src/lib.rs
index 87be806..aee0df6 100644
--- a/mingling_core/src/lib.rs
+++ b/mingling_core/src/lib.rs
@@ -25,6 +25,7 @@ pub use crate::asset::chain::*;
 pub use crate::asset::comp::*;
 pub use crate::asset::dispatcher::*;
 pub use crate::asset::enum_tag::*;
+pub use crate::asset::help::*;
 pub use crate::asset::node::*;
 pub use crate::asset::renderer::*;
 
diff --git a/mingling_core/src/program.rs b/mingling_core/src/program.rs
index c9cffbe..949dd45 100644
--- a/mingling_core/src/program.rs
+++ b/mingling_core/src/program.rs
@@ -289,6 +289,9 @@ pub trait ProgramCollect {
     /// Render the input [AnyOutput](./struct.AnyOutput.html)
     fn render(any: AnyOutput<Self::Enum>, r: &mut RenderResult);
 
+    /// Render help for Entry
+    fn render_help(any: AnyOutput<Self::Enum>, r: &mut RenderResult);
+
     /// Find a matching chain to continue execution based on the input [AnyOutput](./struct.AnyOutput.html), returning a new [AnyOutput](./struct.AnyOutput.html)
     #[cfg(feature = "async")]
     fn do_chain(
diff --git a/mingling_core/src/program/exec.rs b/mingling_core/src/program/exec.rs
index c1eada5..469f6d2 100644
--- a/mingling_core/src/program/exec.rs
+++ b/mingling_core/src/program/exec.rs
@@ -16,6 +16,11 @@ where
     let mut current = dispatch_args_dynamic(program, program.args.clone())?;
     let mut stop_next = false;
 
+    // If the program has Help enabled, skip actual logic and jump to Help
+    if program.user_context.help {
+        return Ok(render_help::<C>(program, current));
+    }
+
     loop {
         let final_exec = stop_next;
 
@@ -56,6 +61,11 @@ where
     let mut current = dispatch_args_dynamic(program, program.args.clone())?;
     let mut stop_next = false;
 
+    // If the program has Help enabled, skip actual logic and jump to Help
+    if program.user_context.help {
+        return Ok(render_help::<C>(program, current));
+    }
+
     loop {
         let final_exec = stop_next;
 
@@ -179,3 +189,28 @@ fn render<C: ProgramCollect<Enum = C>>(program: &Program<C>, any: AnyOutput<C>)
         }
     }
 }
+
+#[inline(always)]
+#[allow(unused_variables)]
+fn render_help<C: ProgramCollect<Enum = C>>(
+    program: &Program<C>,
+    entry: AnyOutput<C>,
+) -> RenderResult {
+    #[cfg(not(feature = "general_renderer"))]
+    {
+        let mut render_result = RenderResult::default();
+        C::render_help(entry, &mut render_result);
+        render_result
+    }
+    #[cfg(feature = "general_renderer")]
+    {
+        match program.general_renderer_name {
+            super::GeneralRendererSetting::Disable => {
+                let mut render_result = RenderResult::default();
+                C::render_help(entry, &mut render_result);
+                render_result
+            }
+            _ => RenderResult::default(),
+        }
+    }
+}
diff --git a/mingling_core/src/renderer/render_result.rs b/mingling_core/src/renderer/render_result.rs
index d9da7b7..3bde1ab 100644
--- a/mingling_core/src/renderer/render_result.rs
+++ b/mingling_core/src/renderer/render_result.rs
@@ -1,5 +1,6 @@
 use std::{
     fmt::{Display, Formatter},
+    io::Write,
     ops::Deref,
 };
 
@@ -9,6 +10,20 @@ pub struct RenderResult {
     render_text: String,
 }
 
+impl Write for RenderResult {
+    fn write(&mut self, buf: &[u8]) -> std::io::Result<usize> {
+        let s = std::str::from_utf8(buf).map_err(|_| {
+            std::io::Error::new(std::io::ErrorKind::InvalidInput, "not valid UTF-8")
+        })?;
+        self.render_text.push_str(s);
+        Ok(buf.len())
+    }
+
+    fn flush(&mut self) -> std::io::Result<()> {
+        Ok(())
+    }
+}
+
 impl Display for RenderResult {
     fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
         writeln!(f, "{}", self.render_text.trim())
diff --git a/mingling_macros/src/help.rs b/mingling_macros/src/help.rs
new file mode 100644
index 0000000..c0d8b99
--- /dev/null
+++ b/mingling_macros/src/help.rs
@@ -0,0 +1,202 @@
+//! Help Attribute Macro
+//!
+//! This module provides the `#[help]` attribute macro for automatically
+//! generating structs that implement the `HelpRequest` trait from functions.
+//!
+//! # Syntax
+//!
+//! ```rust,ignore
+//! #[help]
+//! fn help_my_entry(prev: MyEntry) {
+//!     // use r_println! here
+//!     r_println!("Help: ...");
+//! }
+//! ```
+//!
+//! This expands to:
+//! - A struct `HelpMyEntry` implementing `HelpRequest` with `Entry = MyEntry`
+//! - The original function with injected `RenderResult` dummy context
+
+use proc_macro::TokenStream;
+use quote::{ToTokens, quote};
+use syn::spanned::Spanned;
+use syn::{
+    FnArg, Ident, ItemFn, Pat, PatType, ReturnType, Signature, Type, TypePath, parse_macro_input,
+};
+
+/// Extracts the previous type and parameter name from function arguments
+fn extract_previous_info(sig: &Signature) -> syn::Result<(Pat, TypePath)> {
+    // The function should have exactly one parameter
+    if sig.inputs.len() != 1 {
+        return Err(syn::Error::new(
+            sig.inputs.span(),
+            "Help function must have exactly one parameter (the entry type)",
+        ));
+    }
+
+    // First and only parameter is the entry type
+    let arg = &sig.inputs[0];
+    match arg {
+        FnArg::Typed(PatType { pat, ty, .. }) => {
+            // Extract the pattern (parameter name)
+            let param_pat = (**pat).clone();
+
+            // Extract the type
+            match &**ty {
+                Type::Path(type_path) => Ok((param_pat, type_path.clone())),
+                _ => Err(syn::Error::new(
+                    ty.span(),
+                    "Parameter type must be a type path",
+                )),
+            }
+        }
+        FnArg::Receiver(_) => Err(syn::Error::new(
+            arg.span(),
+            "Help function cannot have self parameter",
+        )),
+    }
+}
+
+/// Validates the return type is () or empty
+fn validate_return_type(sig: &Signature) -> syn::Result<()> {
+    match &sig.output {
+        ReturnType::Type(_, ty) => match &**ty {
+            Type::Tuple(tuple) if tuple.elems.is_empty() => Ok(()),
+            _ => Err(syn::Error::new(
+                ty.span(),
+                "Help function must return () or have no return type",
+            )),
+        },
+        ReturnType::Default => Ok(()),
+    }
+}
+
+pub fn help_attr(item: TokenStream) -> TokenStream {
+    // Parse the function item
+    let input_fn = parse_macro_input!(item as ItemFn);
+
+    // Validate the function is not async
+    if input_fn.sig.asyncness.is_some() {
+        return syn::Error::new(input_fn.sig.span(), "Help function cannot be async")
+            .to_compile_error()
+            .into();
+    }
+
+    // Extract the entry type and parameter name from function arguments
+    let (prev_param, entry_type) = match extract_previous_info(&input_fn.sig) {
+        Ok(info) => info,
+        Err(e) => return e.to_compile_error().into(),
+    };
+
+    // Validate return type
+    if let Err(e) = validate_return_type(&input_fn.sig) {
+        return e.to_compile_error().into();
+    }
+
+    // Get the function body
+    let fn_body = &input_fn.block;
+
+    // Get function attributes (excluding the help attribute)
+    let mut fn_attrs = input_fn.attrs.clone();
+    fn_attrs.retain(|attr| !attr.path().is_ident("help"));
+
+    // Get function visibility
+    let vis = &input_fn.vis;
+
+    // Get function name
+    let fn_name = &input_fn.sig.ident;
+
+    // Generate struct name from function name using pascal_case
+    let pascal_case_name = just_fmt::pascal_case!(fn_name.to_string());
+    let struct_name = Ident::new(&pascal_case_name, fn_name.span());
+
+    // Register the help request mapping
+    let help_entry = build_help_entry(&struct_name, &entry_type);
+    let entry_str = help_entry.to_string();
+    crate::HELP_REQUESTS.lock().unwrap().insert(entry_str);
+
+    // Generate the struct and HelpRequest implementation
+    let expanded = quote! {
+        #(#fn_attrs)*
+        #[doc(hidden)]
+        #vis struct #struct_name;
+
+        impl ::mingling::HelpRequest for #struct_name {
+            type Entry = #entry_type;
+
+            fn render_help(#prev_param: Self::Entry, r: &mut ::mingling::RenderResult) {
+                // Create a local wrapper function that includes r parameter
+                // This allows r_println! to access r
+                #[allow(non_snake_case)]
+                fn help_wrapper(#prev_param: #entry_type, r: &mut ::mingling::RenderResult) {
+                    #fn_body
+                }
+
+                // Call the wrapper function
+                help_wrapper(#prev_param, r);
+            }
+        }
+
+        ::mingling::macros::register_help!(#entry_type, #struct_name);
+
+        // Keep the original function for internal use (without r parameter)
+        #(#fn_attrs)*
+        #vis fn #fn_name(#prev_param: #entry_type) {
+            let mut dummy_r = ::mingling::RenderResult::default();
+            let r = &mut dummy_r;
+            #fn_body
+        }
+    };
+
+    expanded.into()
+}
+
+/// Builds a help request entry for the global help requests list
+fn build_help_entry(struct_name: &Ident, entry_type: &TypePath) -> proc_macro2::TokenStream {
+    let enum_variant = &entry_type.path.segments.last().unwrap().ident;
+    quote! {
+        Self::#enum_variant => {
+            // SAFETY: The member_id check ensures that `any` contains a value of type `#entry_type`,
+            // so downcasting to `#entry_type` is safe.
+            let value = unsafe { any.downcast::<#entry_type>().unwrap_unchecked() };
+            <#struct_name as ::mingling::HelpRequest>::render_help(value, r);
+        }
+    }
+}
+
+pub fn register_help(input: TokenStream) -> TokenStream {
+    // Parse the input as a comma-separated list of arguments
+    let input_parsed = syn::parse_macro_input!(input with syn::punctuated::Punctuated<syn::Expr, syn::Token![,]>::parse_terminated);
+
+    // Check that we have exactly two elements
+    if input_parsed.len() != 2 {
+        return syn::Error::new(
+            input_parsed.span(),
+            "Expected exactly two comma-separated arguments: `EntryType, StructName`",
+        )
+        .to_compile_error()
+        .into();
+    }
+
+    // Extract the two elements
+    let entry_type_expr = &input_parsed[0];
+    let struct_name_expr = &input_parsed[1];
+
+    // Convert expressions to TypePath and Ident
+    let entry_type = match syn::parse2::<TypePath>(entry_type_expr.to_token_stream()) {
+        Ok(ty) => ty,
+        Err(e) => return e.to_compile_error().into(),
+    };
+
+    let struct_name = match syn::parse2::<syn::Ident>(struct_name_expr.to_token_stream()) {
+        Ok(ident) => ident,
+        Err(e) => return e.to_compile_error().into(),
+    };
+
+    // Register the help request mapping
+    let help_entry = build_help_entry(&struct_name, &entry_type);
+    let entry_str = help_entry.to_string();
+    crate::HELP_REQUESTS.lock().unwrap().insert(entry_str);
+
+    quote! {}.into()
+}
diff --git a/mingling_macros/src/lib.rs b/mingling_macros/src/lib.rs
index da3bf47..dbbc333 100644
--- a/mingling_macros/src/lib.rs
+++ b/mingling_macros/src/lib.rs
@@ -19,6 +19,7 @@ mod dispatcher;
 mod dispatcher_clap;
 mod enum_tag;
 mod groupped;
+mod help;
 mod node;
 mod pack;
 mod program_setup;
@@ -44,6 +45,8 @@ pub(crate) static CHAINS_EXIST: Lazy<Mutex<BTreeSet<String>>> =
     Lazy::new(|| Mutex::new(BTreeSet::new()));
 pub(crate) static RENDERERS_EXIST: Lazy<Mutex<BTreeSet<String>>> =
     Lazy::new(|| Mutex::new(BTreeSet::new()));
+pub(crate) static HELP_REQUESTS: Lazy<Mutex<BTreeSet<String>>> =
+    Lazy::new(|| Mutex::new(BTreeSet::new()));
 
 #[proc_macro]
 pub fn node(input: TokenStream) -> TokenStream {
@@ -97,6 +100,16 @@ pub fn dispatcher_clap(attr: TokenStream, item: TokenStream) -> TokenStream {
     dispatcher_clap::dispatcher_clap_attr(attr, item)
 }
 
+#[proc_macro]
+pub fn register_help(input: TokenStream) -> TokenStream {
+    help::register_help(input)
+}
+
+#[proc_macro_attribute]
+pub fn help(_attr: TokenStream, item: TokenStream) -> TokenStream {
+    help::help_attr(item)
+}
+
 #[proc_macro_derive(Groupped, attributes(group))]
 pub fn derive_groupped(input: TokenStream) -> TokenStream {
     groupped::derive_groupped(input)
@@ -308,6 +321,14 @@ pub fn program_final_gen(input: TokenStream) -> TokenStream {
     #[cfg(not(feature = "comp"))]
     let comp = quote! {};
 
+    let help_tokens: Vec<proc_macro2::TokenStream> = HELP_REQUESTS
+        .lock()
+        .unwrap()
+        .clone()
+        .iter()
+        .map(|s| syn::parse_str::<proc_macro2::TokenStream>(s).unwrap())
+        .collect();
+
     let expanded = quote! {
         #[derive(Debug, Default, PartialEq, Eq, Clone)]
         #[repr(u32)]
@@ -340,6 +361,12 @@ pub fn program_final_gen(input: TokenStream) -> TokenStream {
             ::mingling::__dispatch_program_chains!(
                 #(#chain_tokens)*
             );
+            fn render_help(any: ::mingling::AnyOutput<Self::Enum>, r: &mut ::mingling::RenderResult) {
+                match any.member_id {
+                    #(#help_tokens)*
+                    _ => (),
+                }
+            }
             fn has_renderer(any: &::mingling::AnyOutput<Self::Enum>) -> bool {
                 match any.member_id {
                     #(#renderer_exist_tokens)*