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feat: add docstrings to generated rust code #665

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c6d9c72
feat: add docstrings to generated rust code
ksil Jun 8, 2026
bf4ceb6
added other comments
ksil Jun 8, 2026
f0b0f91
fix file-level comments
ksil Jun 8, 2026
22399f9
removed struct comments for Owned, Reader, Builder, and Pipeline
ksil Jun 16, 2026
a396442
removed unnecessary Branch statements
ksil Jun 16, 2026
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2 changes: 2 additions & 0 deletions .gitignore
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Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -11,3 +11,5 @@
Cargo.lock
/target/

# IDEs
.idea
206 changes: 173 additions & 33 deletions capnpc/src/codegen.rs
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Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -199,6 +199,8 @@ pub struct GeneratorContext<'a> {
pub request: schema_capnp::code_generator_request::Reader<'a>,
pub node_map: collections::hash_map::HashMap<u64, schema_capnp::node::Reader<'a>>,
pub scope_map: collections::hash_map::HashMap<u64, Vec<String>>,
pub source_info_map:
collections::hash_map::HashMap<u64, schema_capnp::node::source_info::Reader<'a>>,

/// Map from node ID to the node ID of its parent scope. This is equal to node.scope_id
/// for all nodes except for autogenerated interface Param and Result structs;
Expand Down Expand Up @@ -228,6 +230,10 @@ impl<'a> GeneratorContext<'a> {
request: message.get_root()?,
node_map: collections::hash_map::HashMap::<u64, schema_capnp::node::Reader<'a>>::new(),
scope_map: collections::hash_map::HashMap::<u64, Vec<String>>::new(),
source_info_map: collections::hash_map::HashMap::<
u64,
schema_capnp::node::source_info::Reader<'a>,
>::new(),
node_parents: collections::hash_map::HashMap::new(),
capnp_root: code_generation_command.capnp_root.clone(),
};
Expand All @@ -239,6 +245,13 @@ impl<'a> GeneratorContext<'a> {
ctx.node_parents.insert(node.get_id(), node.get_scope_id());
}

if ctx.request.has_source_info() {
for source_info in ctx.request.get_source_info()? {
ctx.source_info_map
.insert(source_info.get_id(), source_info);
}
}

// Fix up "anonymous" method params and results scopes.
for node in ctx.request.get_nodes()? {
if let Ok(schema_capnp::node::Interface(interface_reader)) = node.which() {
Expand Down Expand Up @@ -492,6 +505,57 @@ pub fn line(inner: impl ToString) -> FormattedText {
Line(inner.to_string())
}

fn get_node_doc_comment(ctx: &GeneratorContext, node_id: u64) -> Option<String> {
if let Some(source_info) = ctx.source_info_map.get(&node_id) {
if !source_info.has_doc_comment() {
return None;
}
if let Ok(comment) = source_info.get_doc_comment() {
if let Ok(comment_str) = comment.to_string() {
return Some(comment_str);
}
}
}
None
}

fn get_member_doc_comment(
ctx: &GeneratorContext,
node_id: u64,
member_index: u32,
) -> Option<String> {
if let Some(source_info) = ctx.source_info_map.get(&node_id) {
if !source_info.has_members() {
return None;
}
if let Ok(members) = source_info.get_members() {
if member_index >= members.len() {
return None;
}
let member = members.get(member_index);
if !member.has_doc_comment() {
return None;
}
if let Ok(comment) = member.get_doc_comment() {
if let Ok(comment_str) = comment.to_string() {
return Some(comment_str);
}
}
}
}
None
}

fn generate_doc_comment(comment: Option<String>) -> Vec<FormattedText> {
let mut result = Vec::new();
if let Some(comment_str) = comment {
for line_str in comment_str.lines() {
result.push(Line(format!("/// {}", line_str)));
}
}
result
}

fn to_lines(ft: &FormattedText, indent: usize) -> Vec<String> {
match ft {
Indent(ft) => to_lines(ft, indent + 1),
Expand Down Expand Up @@ -2015,12 +2079,23 @@ fn generate_node(

match node_reader.which()? {
node::File(()) => {
let file_doc_lines = get_node_doc_comment(ctx, node_id);
if let Some(comment_str) = file_doc_lines {
for line_str in comment_str.lines() {
output.push(Line(format!("// {}", line_str)));
}
}
output.push(Branch(nested_output));
}
node::Struct(struct_reader) => {
let params = node_reader.parameters_texts(ctx);
output.push(BlankLine);

let struct_doc_lines = generate_doc_comment(get_node_doc_comment(ctx, node_id));
if !struct_doc_lines.is_empty() {
output.push(Branch(struct_doc_lines.clone()));
}

let is_generic = node_reader.get_is_generic();
if is_generic {
output.push(Line(format!(
Expand Down Expand Up @@ -2079,7 +2154,10 @@ fn generate_node(

let mut has_pointer_field = false;
let fields = struct_reader.get_fields()?;
for field in fields {
for (field_index, field) in fields.iter().enumerate() {
let field_doc_lines =
generate_doc_comment(get_member_doc_comment(ctx, node_id, field_index as u32));

let name = get_field_name(field)?;
let styled_name = camel_to_snake_case(name);

Expand All @@ -2100,12 +2178,20 @@ fn generate_node(
}

if !is_union_field {
pipeline_impl_interior.push(generate_pipeline_getter(ctx, field)?);
let mut p_getter = generate_pipeline_getter(ctx, field)?;
if let Branch(ref mut p_vec) = p_getter {
if !p_vec.is_empty() {
p_vec.insert(0, Branch(field_doc_lines.clone()));
}
}
pipeline_impl_interior.push(p_getter);

let (ty, get, default_decl) = getter_text(ctx, &field, true, true)?;
if let Some(default) = default_decl {
private_mod_interior.push(default.clone());
}
reader_members.push(Branch(vec![
Branch(field_doc_lines.clone()),
line("#[inline]"),
Line(format!("pub fn get_{styled_name}(self) {ty} {{")),
indent(get),
Expand All @@ -2114,6 +2200,7 @@ fn generate_node(

let (ty_b, get_b, _) = getter_text(ctx, &field, false, true)?;
builder_members.push(Branch(vec![
Branch(field_doc_lines.clone()),
line("#[inline]"),
Line(format!("pub fn get_{styled_name}(self) {ty_b} {{")),
indent(get_b),
Expand All @@ -2123,25 +2210,29 @@ fn generate_node(
union_fields.push(field);
}

builder_members.push(generate_setter(
ctx,
discriminant_offset,
&styled_name,
&field,
)?);

reader_members.push(generate_haser(
discriminant_offset,
&styled_name,
&field,
true,
)?);
builder_members.push(generate_haser(
discriminant_offset,
&styled_name,
&field,
false,
)?);
let mut setter = generate_setter(ctx, discriminant_offset, &styled_name, &field)?;
if let Branch(ref mut s_vec) = setter {
if !s_vec.is_empty() {
s_vec.insert(0, Branch(field_doc_lines.clone()));
}
}
builder_members.push(setter);

let mut r_haser = generate_haser(discriminant_offset, &styled_name, &field, true)?;
if let Branch(ref mut h_vec) = r_haser {
if !h_vec.is_empty() {
h_vec.insert(0, Branch(field_doc_lines.clone()));
}
}
reader_members.push(r_haser);

let mut b_haser = generate_haser(discriminant_offset, &styled_name, &field, false)?;
if let Branch(ref mut h_vec) = b_haser {
if !h_vec.is_empty() {
h_vec.insert(0, Branch(field_doc_lines.clone()));
}
}
builder_members.push(b_haser);

if let Ok(field::Group(group)) = field.which() {
let id = group.get_type_id();
Expand Down Expand Up @@ -2451,10 +2542,18 @@ fn generate_node(
let name_as_mod = module_name(last_name);
output.push(BlankLine);

let enum_doc_lines = generate_doc_comment(get_node_doc_comment(ctx, node_id));

let mut members = Vec::new();
let mut match_branches = Vec::new();
let enumerants = enum_reader.get_enumerants()?;
for (ii, enumerant) in enumerants.into_iter().enumerate() {
let enumerant_doc_lines =
generate_doc_comment(get_member_doc_comment(ctx, node_id, ii as u32));
if !enumerant_doc_lines.is_empty() {
members.push(Branch(enumerant_doc_lines));
}

let enumerant = capitalize_first_letter(get_enumerant_name(enumerant)?);
members.push(Line(format!("{enumerant} = {ii},")));
match_branches.push(Line(format!(
Expand All @@ -2466,13 +2565,17 @@ fn generate_node(
"n => ::core::result::Result::Err({capnp}::NotInSchema(n)),"
)));

output.push(Branch(vec![
line("#[repr(u16)]"),
line("#[derive(Clone, Copy, Debug, PartialEq, Eq)]"),
Line(format!("pub enum {last_name} {{")),
indent(members),
line("}"),
]));
let mut enum_declaration = vec![];
if !enum_doc_lines.is_empty() {
enum_declaration.push(Branch(enum_doc_lines));
}
enum_declaration.push(line("#[repr(u16)]"));
enum_declaration.push(line("#[derive(Clone, Copy, Debug, PartialEq, Eq)]"));
enum_declaration.push(Line(format!("pub enum {last_name} {{")));
enum_declaration.push(indent(members));
enum_declaration.push(line("}"));

output.push(Branch(enum_declaration));

output.push(BlankLine);
output.push(Branch(vec![
Expand Down Expand Up @@ -2549,6 +2652,8 @@ fn generate_node(
let params = node_reader.parameters_texts(ctx);
output.push(BlankLine);

let interface_doc_lines = generate_doc_comment(get_node_doc_comment(ctx, node_id));

let is_generic = node_reader.get_is_generic();

let names = &ctx.scope_map[&node_id];
Expand Down Expand Up @@ -2605,6 +2710,9 @@ fn generate_node(
param_type
)));

let method_doc_lines =
generate_doc_comment(get_member_doc_comment(ctx, node_id, ordinal as u32));

let result_id = method.get_result_struct_type();
if result_id != STREAM_RESULT_ID {
dispatch_arms.push(
Expand Down Expand Up @@ -2639,6 +2747,10 @@ fn generate_node(
results_ty_params,
result_type
)));

if !method_doc_lines.is_empty() {
server_interior.push(Branch(method_doc_lines.clone()));
}
server_interior.push(
Line(fmt!(ctx,
"fn {}(self: {capnp}::capability::Rc<Self>, _: {}Params<{}>, _: {}Results<{}>) -> impl ::core::future::Future<Output = Result<(), {capnp}::Error>> + 'static {{ ::core::future::ready(Err({capnp}::Error::unimplemented(\"method {}::Server::{} not implemented\".to_string()))) }}",
Expand All @@ -2648,6 +2760,9 @@ fn generate_node(
node_name, module_name(name)
)));

if !method_doc_lines.is_empty() {
client_impl_interior.push(Branch(method_doc_lines.clone()));
}
client_impl_interior.push(Line(fmt!(
ctx,
"pub fn {}_request(&self) -> {capnp}::capability::Request<{},{}> {{",
Expand All @@ -2668,13 +2783,20 @@ fn generate_node(

module_name(name))));

if !method_doc_lines.is_empty() {
server_interior.push(Branch(method_doc_lines.clone()));
}
server_interior.push(
Line(fmt!(ctx,
"fn {}(self: {capnp}::capability::Rc<Self>, _: {}Params<{}>) -> impl ::core::future::Future<Output = Result<(), {capnp}::Error>> + 'static {{ ::core::future::ready(Err({capnp}::Error::unimplemented(\"method {}::Server::{} not implemented\".to_string()))) }}",
module_name(name),
capitalize_first_letter(name), params_ty_params,
node_name, module_name(name)
)));

if !method_doc_lines.is_empty() {
client_impl_interior.push(Branch(method_doc_lines.clone()));
}
client_impl_interior.push(Line(fmt!(
ctx,
"pub fn {}_request(&self) -> {capnp}::capability::StreamingRequest<{}> {{",
Expand Down Expand Up @@ -2739,6 +2861,9 @@ fn generate_node(
};

mod_interior.push(BlankLine);
if !interface_doc_lines.is_empty() {
mod_interior.push(Branch(interface_doc_lines.clone()));
}
mod_interior.push(Line(format!("pub struct Client{bracketed_params} {{")));
mod_interior.push(indent(Line(fmt!(
ctx,
Expand Down Expand Up @@ -2852,6 +2977,9 @@ fn generate_node(
line("}"),
]));

if !interface_doc_lines.is_empty() {
mod_interior.push(Branch(interface_doc_lines.clone()));
}
mod_interior.push(Branch(vec![
Line(format!(
"pub trait Server<{}> {} {} {{",
Expand Down Expand Up @@ -2972,6 +3100,8 @@ fn generate_node(
node::Const(c) => {
let styled_name = snake_to_upper_case(ctx.get_last_name(node_id)?);

let const_doc_lines = generate_doc_comment(get_node_doc_comment(ctx, node_id));

let typ = c.get_type()?;
let formatted_text = match (typ.which()?, c.get_value()?.which()?) {
(type_::Void(()), value::Void(())) => {
Expand Down Expand Up @@ -3096,10 +3226,15 @@ fn generate_node(
}
};

if !const_doc_lines.is_empty() {
output.push(Branch(const_doc_lines));
}
output.push(formatted_text);
}

node::Annotation(annotation_reader) => {
let annotation_doc_lines = generate_doc_comment(get_node_doc_comment(ctx, node_id));

let is_generic = node_reader.get_is_generic();
let params = node_reader.parameters_texts(ctx);
let last_name = ctx.get_last_name(node_id)?;
Expand All @@ -3113,11 +3248,16 @@ fn generate_node(
} else {
interior.push(Line(fmt!(ctx,"pub fn get_type<{0}>() -> {capnp}::introspect::Type {1} {{ <{2} as {capnp}::introspect::Introspect>::introspect() }}", params.params, params.where_clause, ty.type_string(ctx, Leaf::Owned)?)));
}
output.push(Branch(vec![
Line(format!("pub mod {last_name} {{")),
indent(interior),
Line("}".into()),
]));

let mut annotation_module = vec![];
if !annotation_doc_lines.is_empty() {
annotation_module.push(Branch(annotation_doc_lines));
}
annotation_module.push(Line(format!("pub mod {last_name} {{")));
annotation_module.push(indent(interior));
annotation_module.push(Line("}".into()));

output.push(Branch(annotation_module));
}
}

Expand Down
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