git.bitcoin.ninja Git - rust-lightning/blob - c-bindings-gen/src/blocks.rs

   1 //! Printing logic for basic blocks of Rust-mapped code - parts of functions and declarations but
   2 //! not the full mapping logic.
   3
   4 use std::fs::File;
   5 use std::io::Write;
   6 use proc_macro2::{TokenTree, Span};
   7
   8 use crate::types::*;
   9
  10 /// Writes out a C++ wrapper class for the given type, which contains various utilities to access
  11 /// the underlying C-mapped type safely avoiding some common memory management issues by handling
  12 /// resource-freeing and prevending accidental raw copies.
  13 pub fn write_cpp_wrapper(cpp_header_file: &mut File, ty: &str, has_destructor: bool) {
  14         writeln!(cpp_header_file, "class {} {{", ty).unwrap();
  15         writeln!(cpp_header_file, "private:").unwrap();
  16         writeln!(cpp_header_file, "\tLDK{} self;", ty).unwrap();
  17         writeln!(cpp_header_file, "public:").unwrap();
  18         writeln!(cpp_header_file, "\t{}(const {}&) = delete;", ty, ty).unwrap();
  19         writeln!(cpp_header_file, "\t{}({}&& o) : self(o.self) {{ memset(&o, 0, sizeof({})); }}", ty, ty, ty).unwrap();
  20         writeln!(cpp_header_file, "\t{}(LDK{}&& m_self) : self(m_self) {{ memset(&m_self, 0, sizeof(LDK{})); }}", ty, ty, ty).unwrap();
  21         writeln!(cpp_header_file, "\toperator LDK{}() && {{ LDK{} res = self; memset(&self, 0, sizeof(LDK{})); return res; }}", ty, ty, ty).unwrap();
  22         if has_destructor {
  23                 writeln!(cpp_header_file, "\t~{}() {{ {}_free(self); }}", ty, ty).unwrap();
  24                 writeln!(cpp_header_file, "\t{}& operator=({}&& o) {{ {}_free(self); self = o.self; memset(&o, 0, sizeof({})); return *this; }}", ty, ty, ty, ty).unwrap();
  25         } else {
  26                 writeln!(cpp_header_file, "\t{}& operator=({}&& o) {{ self = o.self; memset(&o, 0, sizeof({})); return *this; }}", ty, ty, ty).unwrap();
  27         }
  28         writeln!(cpp_header_file, "\tLDK{}* operator &() {{ return &self; }}", ty).unwrap();
  29         writeln!(cpp_header_file, "\tLDK{}* operator ->() {{ return &self; }}", ty).unwrap();
  30         writeln!(cpp_header_file, "\tconst LDK{}* operator &() const {{ return &self; }}", ty).unwrap();
  31         writeln!(cpp_header_file, "\tconst LDK{}* operator ->() const {{ return &self; }}", ty).unwrap();
  32         writeln!(cpp_header_file, "}};").unwrap();
  33 }
  34
  35 /// Writes out a C-callable concrete Result<A, B> struct and utility methods
  36 pub fn write_result_block<W: std::io::Write>(w: &mut W, mangled_container: &str, ok_type: &str, err_type: &str) {
  37         writeln!(w, "#[repr(C)]").unwrap();
  38         writeln!(w, "pub union {}Ptr {{", mangled_container).unwrap();
  39         if ok_type != "()" {
  40                 writeln!(w, "\tpub result: *mut {},", ok_type).unwrap();
  41         } else {
  42                 writeln!(w, "\t/// Note that this value is always NULL, as there are no contents in the OK variant").unwrap();
  43                 writeln!(w, "\tpub result: *mut std::ffi::c_void,").unwrap();
  44         }
  45         if err_type != "()" {
  46                 writeln!(w, "\tpub err: *mut {},", err_type).unwrap();
  47         } else {
  48                 writeln!(w, "\t/// Note that this value is always NULL, as there are no contents in the Err variant").unwrap();
  49                 writeln!(w, "\tpub err: *mut std::ffi::c_void,").unwrap();
  50         }
  51         writeln!(w, "}}").unwrap();
  52         writeln!(w, "#[repr(C)]").unwrap();
  53         writeln!(w, "pub struct {} {{", mangled_container).unwrap();
  54         writeln!(w, "\tpub contents: {}Ptr,", mangled_container).unwrap();
  55         writeln!(w, "\tpub result_ok: bool,").unwrap();
  56         writeln!(w, "}}").unwrap();
  57
  58         writeln!(w, "#[no_mangle]").unwrap();
  59         if ok_type != "()" {
  60                 writeln!(w, "pub extern \"C\" fn {}_ok(o: {}) -> {} {{", mangled_container, ok_type, mangled_container).unwrap();
  61         } else {
  62                 writeln!(w, "pub extern \"C\" fn {}_ok() -> {} {{", mangled_container, mangled_container).unwrap();
  63         }
  64         writeln!(w, "\t{} {{", mangled_container).unwrap();
  65         writeln!(w, "\t\tcontents: {}Ptr {{", mangled_container).unwrap();
  66         if ok_type != "()" {
  67                 writeln!(w, "\t\t\tresult: Box::into_raw(Box::new(o)),").unwrap();
  68         } else {
  69                 writeln!(w, "\t\t\tresult: std::ptr::null_mut(),").unwrap();
  70         }
  71         writeln!(w, "\t\t}},").unwrap();
  72         writeln!(w, "\t\tresult_ok: true,").unwrap();
  73         writeln!(w, "\t}}").unwrap();
  74         writeln!(w, "}}").unwrap();
  75
  76         writeln!(w, "#[no_mangle]").unwrap();
  77         if err_type != "()" {
  78                 writeln!(w, "pub extern \"C\" fn {}_err(e: {}) -> {} {{", mangled_container, err_type, mangled_container).unwrap();
  79         } else {
  80                 writeln!(w, "pub extern \"C\" fn {}_err() -> {} {{", mangled_container, mangled_container).unwrap();
  81         }
  82         writeln!(w, "\t{} {{", mangled_container).unwrap();
  83         writeln!(w, "\t\tcontents: {}Ptr {{", mangled_container).unwrap();
  84         if err_type != "()" {
  85                 writeln!(w, "\t\t\terr: Box::into_raw(Box::new(e)),").unwrap();
  86         } else {
  87                 writeln!(w, "\t\t\terr: std::ptr::null_mut(),").unwrap();
  88         }
  89         writeln!(w, "\t\t}},").unwrap();
  90         writeln!(w, "\t\tresult_ok: false,").unwrap();
  91         writeln!(w, "\t}}").unwrap();
  92         writeln!(w, "}}").unwrap();
  93
  94         writeln!(w, "#[no_mangle]").unwrap();
  95         writeln!(w, "pub extern \"C\" fn {}_free(_res: {}) {{ }}", mangled_container, mangled_container).unwrap();
  96         writeln!(w, "impl Drop for {} {{", mangled_container).unwrap();
  97         writeln!(w, "\tfn drop(&mut self) {{").unwrap();
  98         writeln!(w, "\t\tif self.result_ok {{").unwrap();
  99         if ok_type != "()" {
 100                 writeln!(w, "\t\t\tif unsafe {{ !(self.contents.result as *mut ()).is_null() }} {{").unwrap();
 101                 writeln!(w, "\t\t\t\tlet _ = unsafe {{ Box::from_raw(self.contents.result) }};").unwrap();
 102                 writeln!(w, "\t\t\t}}").unwrap();
 103         }
 104         writeln!(w, "\t\t}} else {{").unwrap();
 105         if err_type != "()" {
 106                 writeln!(w, "\t\t\tif unsafe {{ !(self.contents.err as *mut ()).is_null() }} {{").unwrap();
 107                 writeln!(w, "\t\t\t\tlet _ = unsafe {{ Box::from_raw(self.contents.err) }};").unwrap();
 108                 writeln!(w, "\t\t\t}}").unwrap();
 109         }
 110         writeln!(w, "\t\t}}").unwrap();
 111         writeln!(w, "\t}}").unwrap();
 112         writeln!(w, "}}").unwrap();
 113
 114         // TODO: Templates should use () now that they can, too
 115         let templ_ok_type = if ok_type != "()" { ok_type } else { "u8" };
 116         let templ_err_type = if err_type != "()" { err_type } else { "u8" };
 117
 118         writeln!(w, "impl From<crate::c_types::CResultTempl<{}, {}>> for {} {{", templ_ok_type, templ_err_type, mangled_container).unwrap();
 119         writeln!(w, "\tfn from(mut o: crate::c_types::CResultTempl<{}, {}>) -> Self {{", templ_ok_type, templ_err_type).unwrap();
 120         writeln!(w, "\t\tlet contents = if o.result_ok {{").unwrap();
 121         if ok_type != "()" {
 122                 writeln!(w, "\t\t\tlet result = unsafe {{ o.contents.result }};").unwrap();
 123                 writeln!(w, "\t\t\tunsafe {{ o.contents.result = std::ptr::null_mut() }};").unwrap();
 124                 writeln!(w, "\t\t\t{}Ptr {{ result }}", mangled_container).unwrap();
 125         } else {
 126                 writeln!(w, "\t\t\tlet _ = unsafe {{ Box::from_raw(o.contents.result) }};").unwrap();
 127                 writeln!(w, "\t\t\to.contents.result = std::ptr::null_mut();").unwrap();
 128                 writeln!(w, "\t\t\t{}Ptr {{ result: std::ptr::null_mut() }}", mangled_container).unwrap();
 129         }
 130         writeln!(w, "\t\t}} else {{").unwrap();
 131         if err_type != "()" {
 132                 writeln!(w, "\t\t\tlet err = unsafe {{ o.contents.err }};").unwrap();
 133                 writeln!(w, "\t\t\tunsafe {{ o.contents.err = std::ptr::null_mut(); }}").unwrap();
 134                 writeln!(w, "\t\t\t{}Ptr {{ err }}", mangled_container).unwrap();
 135         } else {
 136                 writeln!(w, "\t\t\tlet _ = unsafe {{ Box::from_raw(o.contents.err) }};").unwrap();
 137                 writeln!(w, "\t\t\to.contents.err = std::ptr::null_mut();").unwrap();
 138                 writeln!(w, "\t\t\t{}Ptr {{ err: std::ptr::null_mut() }}", mangled_container).unwrap();
 139         }
 140         writeln!(w, "\t\t}};").unwrap();
 141         writeln!(w, "\t\tSelf {{").unwrap();
 142         writeln!(w, "\t\t\tcontents,").unwrap();
 143         writeln!(w, "\t\t\tresult_ok: o.result_ok,").unwrap();
 144         writeln!(w, "\t\t}}").unwrap();
 145         writeln!(w, "\t}}").unwrap();
 146         writeln!(w, "}}").unwrap();
 147 }
 148
 149 /// Prints the docs from a given attribute list unless its tagged no export
 150 pub fn writeln_docs<W: std::io::Write>(w: &mut W, attrs: &[syn::Attribute], prefix: &str) {
 151         for attr in attrs.iter() {
 152                 let tokens_clone = attr.tokens.clone();
 153                 let mut token_iter = tokens_clone.into_iter();
 154                 if let Some(token) = token_iter.next() {
 155                         match token {
 156                                 TokenTree::Punct(c) if c.as_char() == '=' => {
 157                                         // syn gets '=' from '///' or '//!' as it is syntax for #[doc = ""]
 158                                 },
 159                                 TokenTree::Group(_) => continue, // eg #[derive()]
 160                                 _ => unimplemented!(),
 161                         }
 162                 } else { continue; }
 163                 match attr.style {
 164                         syn::AttrStyle::Inner(_) => {
 165                                 match token_iter.next().unwrap() {
 166                                         TokenTree::Literal(lit) => {
 167                                                 // Drop the first and last chars from lit as they are always "
 168                                                 let doc = format!("{}", lit);
 169                                                 writeln!(w, "{}//!{}", prefix, &doc[1..doc.len() - 1]).unwrap();
 170                                         },
 171                                         _ => unimplemented!(),
 172                                 }
 173                         },
 174                         syn::AttrStyle::Outer => {
 175                                 match token_iter.next().unwrap() {
 176                                         TokenTree::Literal(lit) => {
 177                                                 // Drop the first and last chars from lit as they are always "
 178                                                 let doc = format!("{}", lit);
 179                                                 writeln!(w, "{}///{}", prefix, &doc[1..doc.len() - 1]).unwrap();
 180                                         },
 181                                         _ => unimplemented!(),
 182                                 }
 183                         },
 184                 }
 185         }
 186 }
 187
 188 /// Print the parameters in a method declaration, starting after the open parenthesis, through and
 189 /// including the closing parenthesis and return value, but not including the open bracket or any
 190 /// trailing semicolons.
 191 ///
 192 /// Usable both for a function definition and declaration.
 193 ///
 194 /// this_param is used when returning Self or accepting a self parameter, and should be the
 195 /// concrete, mapped type.
 196 pub fn write_method_params<W: std::io::Write>(w: &mut W, sig: &syn::Signature, this_param: &str, types: &mut TypeResolver, generics: Option<&GenericTypes>, self_ptr: bool, fn_decl: bool) {
 197         if sig.constness.is_some() || sig.asyncness.is_some() || sig.unsafety.is_some() ||
 198                         sig.abi.is_some() || sig.variadic.is_some() {
 199                 unimplemented!();
 200         }
 201         if sig.generics.lt_token.is_some() {
 202                 for generic in sig.generics.params.iter() {
 203                         match generic {
 204                                 syn::GenericParam::Type(_)|syn::GenericParam::Lifetime(_) => {
 205                                         // We ignore these, if they're not on skipped args, we'll blow up
 206                                         // later, and lifetimes we just hope the C client enforces.
 207                                 },
 208                                 _ => unimplemented!(),
 209                         }
 210                 }
 211         }
 212
 213         let mut first_arg = true;
 214         let mut num_unused = 0;
 215         for inp in sig.inputs.iter() {
 216                 match inp {
 217                         syn::FnArg::Receiver(recv) => {
 218                                 if !recv.attrs.is_empty() || recv.reference.is_none() { unimplemented!(); }
 219                                 write!(w, "this_arg: {}{}",
 220                                         match (self_ptr, recv.mutability.is_some()) {
 221                                                 (true, true) => "*mut ",
 222                                                 (true, false) => "*const ",
 223                                                 (false, true) => "&mut ",
 224                                                 (false, false) => "&",
 225                                         }, this_param).unwrap();
 226                                 assert!(first_arg);
 227                                 first_arg = false;
 228                         },
 229                         syn::FnArg::Typed(arg) => {
 230                                 if types.skip_arg(&*arg.ty, generics) { continue; }
 231                                 if !arg.attrs.is_empty() { unimplemented!(); }
 232                                 // First get the c type so that we can check if it ends up being a reference:
 233                                 let mut c_type = Vec::new();
 234                                 types.write_c_type(&mut c_type, &*arg.ty, generics, false);
 235                                 match &*arg.pat {
 236                                         syn::Pat::Ident(ident) => {
 237                                                 if !ident.attrs.is_empty() || ident.subpat.is_some() {
 238                                                         unimplemented!();
 239                                                 }
 240                                                 write!(w, "{}{}{}: ", if first_arg { "" } else { ", " }, if !fn_decl || c_type[0] == '&' as u8 || c_type[0] == '*' as u8 { "" } else { "mut " }, ident.ident).unwrap();
 241                                                 first_arg = false;
 242                                         },
 243                                         syn::Pat::Wild(wild) => {
 244                                                 if !wild.attrs.is_empty() { unimplemented!(); }
 245                                                 write!(w, "{}unused_{}: ", if first_arg { "" } else { ", " }, num_unused).unwrap();
 246                                                 num_unused += 1;
 247                                         },
 248                                         _ => unimplemented!(),
 249                                 }
 250                                 w.write(&c_type).unwrap();
 251                         }
 252                 }
 253         }
 254         write!(w, ")").unwrap();
 255         match &sig.output {
 256                 syn::ReturnType::Type(_, rtype) => {
 257                         write!(w, " -> ").unwrap();
 258                         if let Some(mut remaining_path) = first_seg_self(&*rtype) {
 259                                 if remaining_path.next().is_none() {
 260                                         write!(w, "{}", this_param).unwrap();
 261                                         return;
 262                                 }
 263                         }
 264                         if let syn::Type::Reference(r) = &**rtype {
 265                                 // We can't return a reference, cause we allocate things on the stack.
 266                                 types.write_c_type(w, &*r.elem, generics, true);
 267                         } else {
 268                                 types.write_c_type(w, &*rtype, generics, true);
 269                         }
 270                 },
 271                 _ => {},
 272         }
 273 }
 274
 275 /// Print the main part of a method declaration body, starting with a newline after the function
 276 /// open bracket and converting each function parameter to or from C-mapped types. Ends with "let
 277 /// mut ret = " assuming the next print will be the unmapped Rust function to call followed by the
 278 /// parameters we mapped to/from C here.
 279 pub fn write_method_var_decl_body<W: std::io::Write>(w: &mut W, sig: &syn::Signature, extra_indent: &str, types: &TypeResolver, generics: Option<&GenericTypes>, to_c: bool) {
 280         let mut num_unused = 0;
 281         for inp in sig.inputs.iter() {
 282                 match inp {
 283                         syn::FnArg::Receiver(_) => {},
 284                         syn::FnArg::Typed(arg) => {
 285                                 if types.skip_arg(&*arg.ty, generics) { continue; }
 286                                 if !arg.attrs.is_empty() { unimplemented!(); }
 287                                 macro_rules! write_new_var {
 288                                         ($ident: expr, $ty: expr) => {
 289                                                 if to_c {
 290                                                         if types.write_to_c_conversion_new_var(w, &$ident, &$ty, generics, false) {
 291                                                                 write!(w, "\n\t{}", extra_indent).unwrap();
 292                                                         }
 293                                                 } else {
 294                                                         if types.write_from_c_conversion_new_var(w, &$ident, &$ty, generics) {
 295                                                                 write!(w, "\n\t{}", extra_indent).unwrap();
 296                                                         }
 297                                                 }
 298                                         }
 299                                 }
 300                                 match &*arg.pat {
 301                                         syn::Pat::Ident(ident) => {
 302                                                 if !ident.attrs.is_empty() || ident.subpat.is_some() {
 303                                                         unimplemented!();
 304                                                 }
 305                                                 write_new_var!(ident.ident, *arg.ty);
 306                                         },
 307                                         syn::Pat::Wild(w) => {
 308                                                 if !w.attrs.is_empty() { unimplemented!(); }
 309                                                 write_new_var!(syn::Ident::new(&format!("unused_{}", num_unused), Span::call_site()), *arg.ty);
 310                                                 num_unused += 1;
 311                                         },
 312                                         _ => unimplemented!(),
 313                                 }
 314                         }
 315                 }
 316         }
 317         match &sig.output {
 318                 syn::ReturnType::Type(_, _) => {
 319                         write!(w, "let mut ret = ").unwrap();
 320                 },
 321                 _ => {},
 322         }
 323 }
 324
 325 /// Prints the parameters in a method call, starting after the open parenthesis and ending with a
 326 /// final return statement returning the method's result. Should be followed by a single closing
 327 /// bracket.
 328 ///
 329 /// The return value is expected to be bound to a variable named `ret` which is available after a
 330 /// method-call-ending semicolon.
 331 pub fn write_method_call_params<W: std::io::Write>(w: &mut W, sig: &syn::Signature, extra_indent: &str, types: &TypeResolver, generics: Option<&GenericTypes>, this_type: &str, to_c: bool) {
 332         let mut first_arg = true;
 333         let mut num_unused = 0;
 334         for inp in sig.inputs.iter() {
 335                 match inp {
 336                         syn::FnArg::Receiver(recv) => {
 337                                 if !recv.attrs.is_empty() || recv.reference.is_none() { unimplemented!(); }
 338                                 if to_c {
 339                                         write!(w, "self.this_arg").unwrap();
 340                                         first_arg = false;
 341                                 }
 342                         },
 343                         syn::FnArg::Typed(arg) => {
 344                                 if types.skip_arg(&*arg.ty, generics) {
 345                                         if !to_c {
 346                                                 if !first_arg {
 347                                                         write!(w, ", ").unwrap();
 348                                                 }
 349                                                 first_arg = false;
 350                                                 types.no_arg_to_rust(w, &*arg.ty, generics);
 351                                         }
 352                                         continue;
 353                                 }
 354                                 if !arg.attrs.is_empty() { unimplemented!(); }
 355                                 macro_rules! write_ident {
 356                                         ($ident: expr) => {
 357                                                 if !first_arg {
 358                                                         write!(w, ", ").unwrap();
 359                                                 }
 360                                                 first_arg = false;
 361                                                 if to_c {
 362                                                         types.write_to_c_conversion_inline_prefix(w, &*arg.ty, generics, false);
 363                                                         write!(w, "{}", $ident).unwrap();
 364                                                         types.write_to_c_conversion_inline_suffix(w, &*arg.ty, generics, false);
 365                                                 } else {
 366                                                         types.write_from_c_conversion_prefix(w, &*arg.ty, generics);
 367                                                         write!(w, "{}", $ident).unwrap();
 368                                                         types.write_from_c_conversion_suffix(w, &*arg.ty, generics);
 369                                                 }
 370                                         }
 371                                 }
 372                                 match &*arg.pat {
 373                                         syn::Pat::Ident(ident) => {
 374                                                 if !ident.attrs.is_empty() || ident.subpat.is_some() {
 375                                                         unimplemented!();
 376                                                 }
 377                                                 write_ident!(ident.ident);
 378                                         },
 379                                         syn::Pat::Wild(w) => {
 380                                                 if !w.attrs.is_empty() { unimplemented!(); }
 381                                                 write_ident!(format!("unused_{}", num_unused));
 382                                                 num_unused += 1;
 383                                         },
 384                                         _ => unimplemented!(),
 385                                 }
 386                         }
 387                 }
 388         }
 389         write!(w, ")").unwrap();
 390         match &sig.output {
 391                 syn::ReturnType::Type(_, rtype) => {
 392                         write!(w, ";\n\t{}", extra_indent).unwrap();
 393
 394                         let self_segs_iter = first_seg_self(&*rtype);
 395                         if to_c && first_seg_self(&*rtype).is_some() {
 396                                 // Assume rather blindly that we're returning an associated trait from a C fn call to a Rust trait object.
 397                                 write!(w, "ret").unwrap();
 398                         } else if !to_c && self_segs_iter.is_some() && self_segs_iter.unwrap().next().is_none() {
 399                                 // If we're returning "Self" (and not "Self::X"), just do it manually
 400                                 write!(w, "{} {{ inner: Box::into_raw(Box::new(ret)), is_owned: true }}", this_type).unwrap();
 401                         } else if to_c {
 402                                 let new_var = types.write_from_c_conversion_new_var(w, &syn::Ident::new("ret", Span::call_site()), rtype, generics);
 403                                 if new_var {
 404                                         write!(w, "\n\t{}", extra_indent).unwrap();
 405                                 }
 406                                 types.write_from_c_conversion_prefix(w, &*rtype, generics);
 407                                 write!(w, "ret").unwrap();
 408                                 types.write_from_c_conversion_suffix(w, &*rtype, generics);
 409                         } else {
 410                                 let ret_returned = if let syn::Type::Reference(_) = &**rtype { true } else { false };
 411                                 let new_var = types.write_to_c_conversion_new_var(w, &syn::Ident::new("ret", Span::call_site()), &rtype, generics, true);
 412                                 if new_var {
 413                                         write!(w, "\n\t{}", extra_indent).unwrap();
 414                                 }
 415                                 types.write_to_c_conversion_inline_prefix(w, &rtype, generics, true);
 416                                 write!(w, "{}ret", if ret_returned && !new_var { "*" } else { "" }).unwrap();
 417                                 types.write_to_c_conversion_inline_suffix(w, &rtype, generics, true);
 418                         }
 419                 }
 420                 _ => {},
 421         }
 422 }
 423
 424 /// Prints concrete generic parameters for a struct/trait/function, including the less-than and
 425 /// greater-than symbols, if any generic parameters are defined.
 426 pub fn maybe_write_generics<W: std::io::Write>(w: &mut W, generics: &syn::Generics, types: &TypeResolver, concrete_lifetimes: bool) {
 427         let mut gen_types = GenericTypes::new();
 428         assert!(gen_types.learn_generics(generics, types));
 429         if !generics.params.is_empty() {
 430                 write!(w, "<").unwrap();
 431                 for (idx, generic) in generics.params.iter().enumerate() {
 432                         match generic {
 433                                 syn::GenericParam::Type(type_param) => {
 434                                         let mut printed_param = false;
 435                                         for bound in type_param.bounds.iter() {
 436                                                 if let syn::TypeParamBound::Trait(trait_bound) = bound {
 437                                                         assert_simple_bound(&trait_bound);
 438                                                         write!(w, "{}{}", if idx != 0 { ", " } else { "" }, gen_types.maybe_resolve_ident(&type_param.ident).unwrap()).unwrap();
 439                                                         if printed_param {
 440                                                                 unimplemented!("Can't print generic params that have multiple non-lifetime bounds");
 441                                                         }
 442                                                         printed_param = true;
 443                                                 }
 444                                         }
 445                                 },
 446                                 syn::GenericParam::Lifetime(lt) => {
 447                                         if concrete_lifetimes {
 448                                                 write!(w, "'static").unwrap();
 449                                         } else {
 450                                                 write!(w, "{}'{}", if idx != 0 { ", " } else { "" }, lt.lifetime.ident).unwrap();
 451                                         }
 452                                 },
 453                                 _ => unimplemented!(),
 454                         }
 455                 }
 456                 write!(w, ">").unwrap();
 457         }
 458 }
 459
 460