crates/ide_assists/src/utils/gen_trait_fn_body.rs

   1 //! This module contains functions to generate default trait impl function bodies where possible.
   2
   3 use syntax::{
   4     ast::{self, edit::AstNodeEdit, make, AstNode, BinaryOp, CmpOp, HasName, LogicOp},
   5     ted,
   6 };
   7
   8 /// Generate custom trait bodies where possible.
   9 ///
  10 /// Returns `Option` so that we can use `?` rather than `if let Some`. Returning
  11 /// `None` means that generating a custom trait body failed, and the body will remain
  12 /// as `todo!` instead.
  13 pub(crate) fn gen_trait_fn_body(
  14     func: &ast::Fn,
  15     trait_path: &ast::Path,
  16     adt: &ast::Adt,
  17 ) -> Option<()> {
  18     match trait_path.segment()?.name_ref()?.text().as_str() {
  19         "Clone" => gen_clone_impl(adt, func),
  20         "Debug" => gen_debug_impl(adt, func),
  21         "Default" => gen_default_impl(adt, func),
  22         "Hash" => gen_hash_impl(adt, func),
  23         "PartialEq" => gen_partial_eq(adt, func),
  24         "PartialOrd" => gen_partial_ord(adt, func),
  25         _ => None,
  26     }
  27 }
  28
  29 /// Generate a `Clone` impl based on the fields and members of the target type.
  30 fn gen_clone_impl(adt: &ast::Adt, func: &ast::Fn) -> Option<()> {
  31     fn gen_clone_call(target: ast::Expr) -> ast::Expr {
  32         let method = make::name_ref("clone");
  33         make::expr_method_call(target, method, make::arg_list(None))
  34     }
  35     let expr = match adt {
  36         // `Clone` cannot be derived for unions, so no default impl can be provided.
  37         ast::Adt::Union(_) => return None,
  38         ast::Adt::Enum(enum_) => {
  39             let list = enum_.variant_list()?;
  40             let mut arms = vec![];
  41             for variant in list.variants() {
  42                 let name = variant.name()?;
  43                 let variant_name = make::ext::path_from_idents(["Self", &format!("{}", name)])?;
  44
  45                 match variant.field_list() {
  46                     // => match self { Self::Name { x } => Self::Name { x: x.clone() } }
  47                     Some(ast::FieldList::RecordFieldList(list)) => {
  48                         let mut pats = vec![];
  49                         let mut fields = vec![];
  50                         for field in list.fields() {
  51                             let field_name = field.name()?;
  52                             let pat = make::ident_pat(false, false, field_name.clone());
  53                             pats.push(pat.into());
  54
  55                             let path = make::ext::ident_path(&field_name.to_string());
  56                             let method_call = gen_clone_call(make::expr_path(path));
  57                             let name_ref = make::name_ref(&field_name.to_string());
  58                             let field = make::record_expr_field(name_ref, Some(method_call));
  59                             fields.push(field);
  60                         }
  61                         let pat = make::record_pat(variant_name.clone(), pats.into_iter());
  62                         let fields = make::record_expr_field_list(fields);
  63                         let record_expr = make::record_expr(variant_name, fields).into();
  64                         arms.push(make::match_arm(Some(pat.into()), None, record_expr));
  65                     }
  66
  67                     // => match self { Self::Name(arg1) => Self::Name(arg1.clone()) }
  68                     Some(ast::FieldList::TupleFieldList(list)) => {
  69                         let mut pats = vec![];
  70                         let mut fields = vec![];
  71                         for (i, _) in list.fields().enumerate() {
  72                             let field_name = format!("arg{}", i);
  73                             let pat = make::ident_pat(false, false, make::name(&field_name));
  74                             pats.push(pat.into());
  75
  76                             let f_path = make::expr_path(make::ext::ident_path(&field_name));
  77                             fields.push(gen_clone_call(f_path));
  78                         }
  79                         let pat = make::tuple_struct_pat(variant_name.clone(), pats.into_iter());
  80                         let struct_name = make::expr_path(variant_name);
  81                         let tuple_expr = make::expr_call(struct_name, make::arg_list(fields));
  82                         arms.push(make::match_arm(Some(pat.into()), None, tuple_expr));
  83                     }
  84
  85                     // => match self { Self::Name => Self::Name }
  86                     None => {
  87                         let pattern = make::path_pat(variant_name.clone());
  88                         let variant_expr = make::expr_path(variant_name);
  89                         arms.push(make::match_arm(Some(pattern.into()), None, variant_expr));
  90                     }
  91                 }
  92             }
  93
  94             let match_target = make::expr_path(make::ext::ident_path("self"));
  95             let list = make::match_arm_list(arms).indent(ast::edit::IndentLevel(1));
  96             make::expr_match(match_target, list)
  97         }
  98         ast::Adt::Struct(strukt) => {
  99             match strukt.field_list() {
 100                 // => Self { name: self.name.clone() }
 101                 Some(ast::FieldList::RecordFieldList(field_list)) => {
 102                     let mut fields = vec![];
 103                     for field in field_list.fields() {
 104                         let base = make::expr_path(make::ext::ident_path("self"));
 105                         let target = make::expr_field(base, &field.name()?.to_string());
 106                         let method_call = gen_clone_call(target);
 107                         let name_ref = make::name_ref(&field.name()?.to_string());
 108                         let field = make::record_expr_field(name_ref, Some(method_call));
 109                         fields.push(field);
 110                     }
 111                     let struct_name = make::ext::ident_path("Self");
 112                     let fields = make::record_expr_field_list(fields);
 113                     make::record_expr(struct_name, fields).into()
 114                 }
 115                 // => Self(self.0.clone(), self.1.clone())
 116                 Some(ast::FieldList::TupleFieldList(field_list)) => {
 117                     let mut fields = vec![];
 118                     for (i, _) in field_list.fields().enumerate() {
 119                         let f_path = make::expr_path(make::ext::ident_path("self"));
 120                         let target = make::expr_field(f_path, &format!("{}", i)).into();
 121                         fields.push(gen_clone_call(target));
 122                     }
 123                     let struct_name = make::expr_path(make::ext::ident_path("Self"));
 124                     make::expr_call(struct_name, make::arg_list(fields))
 125                 }
 126                 // => Self { }
 127                 None => {
 128                     let struct_name = make::ext::ident_path("Self");
 129                     let fields = make::record_expr_field_list(None);
 130                     make::record_expr(struct_name, fields).into()
 131                 }
 132             }
 133         }
 134     };
 135     let body = make::block_expr(None, Some(expr)).indent(ast::edit::IndentLevel(1));
 136     ted::replace(func.body()?.syntax(), body.clone_for_update().syntax());
 137     Some(())
 138 }
 139
 140 /// Generate a `Debug` impl based on the fields and members of the target type.
 141 fn gen_debug_impl(adt: &ast::Adt, func: &ast::Fn) -> Option<()> {
 142     let annotated_name = adt.name()?;
 143     match adt {
 144         // `Debug` cannot be derived for unions, so no default impl can be provided.
 145         ast::Adt::Union(_) => None,
 146
 147         // => match self { Self::Variant => write!(f, "Variant") }
 148         ast::Adt::Enum(enum_) => {
 149             let list = enum_.variant_list()?;
 150             let mut arms = vec![];
 151             for variant in list.variants() {
 152                 let name = variant.name()?;
 153                 let variant_name = make::ext::path_from_idents(["Self", &format!("{}", name)])?;
 154                 let target = make::expr_path(make::ext::ident_path("f").into());
 155
 156                 match variant.field_list() {
 157                     Some(ast::FieldList::RecordFieldList(list)) => {
 158                         // => f.debug_struct(name)
 159                         let target = make::expr_path(make::ext::ident_path("f"));
 160                         let method = make::name_ref("debug_struct");
 161                         let struct_name = format!("\"{}\"", name);
 162                         let args = make::arg_list(Some(make::expr_literal(&struct_name).into()));
 163                         let mut expr = make::expr_method_call(target, method, args);
 164
 165                         let mut pats = vec![];
 166                         for field in list.fields() {
 167                             let field_name = field.name()?;
 168
 169                             // create a field pattern for use in `MyStruct { fields.. }`
 170                             let pat = make::ident_pat(false, false, field_name.clone());
 171                             pats.push(pat.into());
 172
 173                             // => <expr>.field("field_name", field)
 174                             let method_name = make::name_ref("field");
 175                             let name = make::expr_literal(&(format!("\"{}\"", field_name))).into();
 176                             let path = &format!("{}", field_name);
 177                             let path = make::expr_path(make::ext::ident_path(path));
 178                             let args = make::arg_list(vec![name, path]);
 179                             expr = make::expr_method_call(expr, method_name, args);
 180                         }
 181
 182                         // => <expr>.finish()
 183                         let method = make::name_ref("finish");
 184                         let expr = make::expr_method_call(expr, method, make::arg_list(None));
 185
 186                         // => MyStruct { fields.. } => f.debug_struct("MyStruct")...finish(),
 187                         let pat = make::record_pat(variant_name.clone(), pats.into_iter());
 188                         arms.push(make::match_arm(Some(pat.into()), None, expr));
 189                     }
 190                     Some(ast::FieldList::TupleFieldList(list)) => {
 191                         // => f.debug_tuple(name)
 192                         let target = make::expr_path(make::ext::ident_path("f"));
 193                         let method = make::name_ref("debug_tuple");
 194                         let struct_name = format!("\"{}\"", name);
 195                         let args = make::arg_list(Some(make::expr_literal(&struct_name).into()));
 196                         let mut expr = make::expr_method_call(target, method, args);
 197
 198                         let mut pats = vec![];
 199                         for (i, _) in list.fields().enumerate() {
 200                             let name = format!("arg{}", i);
 201
 202                             // create a field pattern for use in `MyStruct(fields..)`
 203                             let field_name = make::name(&name);
 204                             let pat = make::ident_pat(false, false, field_name.clone());
 205                             pats.push(pat.into());
 206
 207                             // => <expr>.field(field)
 208                             let method_name = make::name_ref("field");
 209                             let field_path = &format!("{}", name);
 210                             let field_path = make::expr_path(make::ext::ident_path(field_path));
 211                             let args = make::arg_list(vec![field_path]);
 212                             expr = make::expr_method_call(expr, method_name, args);
 213                         }
 214
 215                         // => <expr>.finish()
 216                         let method = make::name_ref("finish");
 217                         let expr = make::expr_method_call(expr, method, make::arg_list(None));
 218
 219                         // => MyStruct (fields..) => f.debug_tuple("MyStruct")...finish(),
 220                         let pat = make::tuple_struct_pat(variant_name.clone(), pats.into_iter());
 221                         arms.push(make::match_arm(Some(pat.into()), None, expr));
 222                     }
 223                     None => {
 224                         let fmt_string = make::expr_literal(&(format!("\"{}\"", name))).into();
 225                         let args = make::arg_list([target, fmt_string]);
 226                         let macro_name = make::expr_path(make::ext::ident_path("write"));
 227                         let macro_call = make::expr_macro_call(macro_name, args);
 228
 229                         let variant_name = make::path_pat(variant_name);
 230                         arms.push(make::match_arm(
 231                             Some(variant_name.into()),
 232                             None,
 233                             macro_call.into(),
 234                         ));
 235                     }
 236                 }
 237             }
 238
 239             let match_target = make::expr_path(make::ext::ident_path("self"));
 240             let list = make::match_arm_list(arms).indent(ast::edit::IndentLevel(1));
 241             let match_expr = make::expr_match(match_target, list);
 242
 243             let body = make::block_expr(None, Some(match_expr));
 244             let body = body.indent(ast::edit::IndentLevel(1));
 245             ted::replace(func.body()?.syntax(), body.clone_for_update().syntax());
 246             Some(())
 247         }
 248
 249         ast::Adt::Struct(strukt) => {
 250             let name = format!("\"{}\"", annotated_name);
 251             let args = make::arg_list(Some(make::expr_literal(&name).into()));
 252             let target = make::expr_path(make::ext::ident_path("f"));
 253
 254             let expr = match strukt.field_list() {
 255                 // => f.debug_struct("Name").finish()
 256                 None => make::expr_method_call(target, make::name_ref("debug_struct"), args),
 257
 258                 // => f.debug_struct("Name").field("foo", &self.foo).finish()
 259                 Some(ast::FieldList::RecordFieldList(field_list)) => {
 260                     let method = make::name_ref("debug_struct");
 261                     let mut expr = make::expr_method_call(target, method, args);
 262                     for field in field_list.fields() {
 263                         let name = field.name()?;
 264                         let f_name = make::expr_literal(&(format!("\"{}\"", name))).into();
 265                         let f_path = make::expr_path(make::ext::ident_path("self"));
 266                         let f_path = make::expr_ref(f_path, false);
 267                         let f_path = make::expr_field(f_path, &format!("{}", name)).into();
 268                         let args = make::arg_list([f_name, f_path]);
 269                         expr = make::expr_method_call(expr, make::name_ref("field"), args);
 270                     }
 271                     expr
 272                 }
 273
 274                 // => f.debug_tuple("Name").field(self.0).finish()
 275                 Some(ast::FieldList::TupleFieldList(field_list)) => {
 276                     let method = make::name_ref("debug_tuple");
 277                     let mut expr = make::expr_method_call(target, method, args);
 278                     for (i, _) in field_list.fields().enumerate() {
 279                         let f_path = make::expr_path(make::ext::ident_path("self"));
 280                         let f_path = make::expr_ref(f_path, false);
 281                         let f_path = make::expr_field(f_path, &format!("{}", i)).into();
 282                         let method = make::name_ref("field");
 283                         expr = make::expr_method_call(expr, method, make::arg_list(Some(f_path)));
 284                     }
 285                     expr
 286                 }
 287             };
 288
 289             let method = make::name_ref("finish");
 290             let expr = make::expr_method_call(expr, method, make::arg_list(None));
 291             let body = make::block_expr(None, Some(expr)).indent(ast::edit::IndentLevel(1));
 292             ted::replace(func.body()?.syntax(), body.clone_for_update().syntax());
 293             Some(())
 294         }
 295     }
 296 }
 297
 298 /// Generate a `Debug` impl based on the fields and members of the target type.
 299 fn gen_default_impl(adt: &ast::Adt, func: &ast::Fn) -> Option<()> {
 300     fn gen_default_call() -> Option<ast::Expr> {
 301         let fn_name = make::ext::path_from_idents(["Default", "default"])?;
 302         Some(make::expr_call(make::expr_path(fn_name), make::arg_list(None)))
 303     }
 304     match adt {
 305         // `Debug` cannot be derived for unions, so no default impl can be provided.
 306         ast::Adt::Union(_) => None,
 307         // Deriving `Debug` for enums is not stable yet.
 308         ast::Adt::Enum(_) => None,
 309         ast::Adt::Struct(strukt) => {
 310             let expr = match strukt.field_list() {
 311                 Some(ast::FieldList::RecordFieldList(field_list)) => {
 312                     let mut fields = vec![];
 313                     for field in field_list.fields() {
 314                         let method_call = gen_default_call()?;
 315                         let name_ref = make::name_ref(&field.name()?.to_string());
 316                         let field = make::record_expr_field(name_ref, Some(method_call));
 317                         fields.push(field);
 318                     }
 319                     let struct_name = make::ext::ident_path("Self");
 320                     let fields = make::record_expr_field_list(fields);
 321                     make::record_expr(struct_name, fields).into()
 322                 }
 323                 Some(ast::FieldList::TupleFieldList(field_list)) => {
 324                     let struct_name = make::expr_path(make::ext::ident_path("Self"));
 325                     let fields = field_list
 326                         .fields()
 327                         .map(|_| gen_default_call())
 328                         .collect::<Option<Vec<ast::Expr>>>()?;
 329                     make::expr_call(struct_name, make::arg_list(fields))
 330                 }
 331                 None => {
 332                     let struct_name = make::ext::ident_path("Self");
 333                     let fields = make::record_expr_field_list(None);
 334                     make::record_expr(struct_name, fields).into()
 335                 }
 336             };
 337             let body = make::block_expr(None, Some(expr)).indent(ast::edit::IndentLevel(1));
 338             ted::replace(func.body()?.syntax(), body.clone_for_update().syntax());
 339             Some(())
 340         }
 341     }
 342 }
 343
 344 /// Generate a `Hash` impl based on the fields and members of the target type.
 345 fn gen_hash_impl(adt: &ast::Adt, func: &ast::Fn) -> Option<()> {
 346     fn gen_hash_call(target: ast::Expr) -> ast::Stmt {
 347         let method = make::name_ref("hash");
 348         let arg = make::expr_path(make::ext::ident_path("state"));
 349         let expr = make::expr_method_call(target, method, make::arg_list(Some(arg)));
 350         make::expr_stmt(expr).into()
 351     }
 352
 353     let body = match adt {
 354         // `Hash` cannot be derived for unions, so no default impl can be provided.
 355         ast::Adt::Union(_) => return None,
 356
 357         // => std::mem::discriminant(self).hash(state);
 358         ast::Adt::Enum(_) => {
 359             let fn_name = make_discriminant()?;
 360
 361             let arg = make::expr_path(make::ext::ident_path("self"));
 362             let fn_call = make::expr_call(fn_name, make::arg_list(Some(arg)));
 363             let stmt = gen_hash_call(fn_call);
 364
 365             make::block_expr(Some(stmt), None).indent(ast::edit::IndentLevel(1))
 366         }
 367         ast::Adt::Struct(strukt) => match strukt.field_list() {
 368             // => self.<field>.hash(state);
 369             Some(ast::FieldList::RecordFieldList(field_list)) => {
 370                 let mut stmts = vec![];
 371                 for field in field_list.fields() {
 372                     let base = make::expr_path(make::ext::ident_path("self"));
 373                     let target = make::expr_field(base, &field.name()?.to_string());
 374                     stmts.push(gen_hash_call(target));
 375                 }
 376                 make::block_expr(stmts, None).indent(ast::edit::IndentLevel(1))
 377             }
 378
 379             // => self.<field_index>.hash(state);
 380             Some(ast::FieldList::TupleFieldList(field_list)) => {
 381                 let mut stmts = vec![];
 382                 for (i, _) in field_list.fields().enumerate() {
 383                     let base = make::expr_path(make::ext::ident_path("self"));
 384                     let target = make::expr_field(base, &format!("{}", i));
 385                     stmts.push(gen_hash_call(target));
 386                 }
 387                 make::block_expr(stmts, None).indent(ast::edit::IndentLevel(1))
 388             }
 389
 390             // No fields in the body means there's nothing to hash.
 391             None => return None,
 392         },
 393     };
 394
 395     ted::replace(func.body()?.syntax(), body.clone_for_update().syntax());
 396     Some(())
 397 }
 398
 399 /// Generate a `PartialEq` impl based on the fields and members of the target type.
 400 fn gen_partial_eq(adt: &ast::Adt, func: &ast::Fn) -> Option<()> {
 401     fn gen_eq_chain(expr: Option<ast::Expr>, cmp: ast::Expr) -> Option<ast::Expr> {
 402         match expr {
 403             Some(expr) => Some(make::expr_bin_op(expr, BinaryOp::LogicOp(LogicOp::And), cmp)),
 404             None => Some(cmp),
 405         }
 406     }
 407
 408     fn gen_record_pat_field(field_name: &str, pat_name: &str) -> ast::RecordPatField {
 409         let pat = make::ext::simple_ident_pat(make::name(&pat_name));
 410         let name_ref = make::name_ref(field_name);
 411         make::record_pat_field(name_ref, pat.into())
 412     }
 413
 414     fn gen_record_pat(record_name: ast::Path, fields: Vec<ast::RecordPatField>) -> ast::RecordPat {
 415         let list = make::record_pat_field_list(fields);
 416         make::record_pat_with_fields(record_name, list)
 417     }
 418
 419     fn gen_variant_path(variant: &ast::Variant) -> Option<ast::Path> {
 420         make::ext::path_from_idents(["Self", &variant.name()?.to_string()])
 421     }
 422
 423     fn gen_tuple_field(field_name: &String) -> ast::Pat {
 424         ast::Pat::IdentPat(make::ident_pat(false, false, make::name(field_name)))
 425     }
 426
 427     // FIXME: return `None` if the trait carries a generic type; we can only
 428     // generate this code `Self` for the time being.
 429
 430     let body = match adt {
 431         // `Hash` cannot be derived for unions, so no default impl can be provided.
 432         ast::Adt::Union(_) => return None,
 433
 434         ast::Adt::Enum(enum_) => {
 435             // => std::mem::discriminant(self) == std::mem::discriminant(other)
 436             let lhs_name = make::expr_path(make::ext::ident_path("self"));
 437             let lhs = make::expr_call(make_discriminant()?, make::arg_list(Some(lhs_name.clone())));
 438             let rhs_name = make::expr_path(make::ext::ident_path("other"));
 439             let rhs = make::expr_call(make_discriminant()?, make::arg_list(Some(rhs_name.clone())));
 440             let eq_check =
 441                 make::expr_bin_op(lhs, BinaryOp::CmpOp(CmpOp::Eq { negated: false }), rhs);
 442
 443             let mut n_cases = 0;
 444             let mut arms = vec![];
 445             for variant in enum_.variant_list()?.variants() {
 446                 n_cases += 1;
 447                 match variant.field_list() {
 448                     // => (Self::Bar { bin: l_bin }, Self::Bar { bin: r_bin }) => l_bin == r_bin,
 449                     Some(ast::FieldList::RecordFieldList(list)) => {
 450                         let mut expr = None;
 451                         let mut l_fields = vec![];
 452                         let mut r_fields = vec![];
 453
 454                         for field in list.fields() {
 455                             let field_name = field.name()?.to_string();
 456
 457                             let l_name = &format!("l_{}", field_name);
 458                             l_fields.push(gen_record_pat_field(&field_name, &l_name));
 459
 460                             let r_name = &format!("r_{}", field_name);
 461                             r_fields.push(gen_record_pat_field(&field_name, &r_name));
 462
 463                             let lhs = make::expr_path(make::ext::ident_path(l_name));
 464                             let rhs = make::expr_path(make::ext::ident_path(r_name));
 465                             let cmp = make::expr_bin_op(
 466                                 lhs,
 467                                 BinaryOp::CmpOp(CmpOp::Eq { negated: false }),
 468                                 rhs,
 469                             );
 470                             expr = gen_eq_chain(expr, cmp);
 471                         }
 472
 473                         let left = gen_record_pat(gen_variant_path(&variant)?, l_fields);
 474                         let right = gen_record_pat(gen_variant_path(&variant)?, r_fields);
 475                         let tuple = make::tuple_pat(vec![left.into(), right.into()]);
 476
 477                         if let Some(expr) = expr {
 478                             arms.push(make::match_arm(Some(tuple.into()), None, expr));
 479                         }
 480                     }
 481
 482                     Some(ast::FieldList::TupleFieldList(list)) => {
 483                         let mut expr = None;
 484                         let mut l_fields = vec![];
 485                         let mut r_fields = vec![];
 486
 487                         for (i, _) in list.fields().enumerate() {
 488                             let field_name = format!("{}", i);
 489
 490                             let l_name = format!("l{}", field_name);
 491                             l_fields.push(gen_tuple_field(&l_name));
 492
 493                             let r_name = format!("r{}", field_name);
 494                             r_fields.push(gen_tuple_field(&r_name));
 495
 496                             let lhs = make::expr_path(make::ext::ident_path(&l_name));
 497                             let rhs = make::expr_path(make::ext::ident_path(&r_name));
 498                             let cmp = make::expr_bin_op(
 499                                 lhs,
 500                                 BinaryOp::CmpOp(CmpOp::Eq { negated: false }),
 501                                 rhs,
 502                             );
 503                             expr = gen_eq_chain(expr, cmp);
 504                         }
 505
 506                         let left = make::tuple_struct_pat(gen_variant_path(&variant)?, l_fields);
 507                         let right = make::tuple_struct_pat(gen_variant_path(&variant)?, r_fields);
 508                         let tuple = make::tuple_pat(vec![left.into(), right.into()]);
 509
 510                         if let Some(expr) = expr {
 511                             arms.push(make::match_arm(Some(tuple.into()), None, expr));
 512                         }
 513                     }
 514                     None => continue,
 515                 }
 516             }
 517
 518             let expr = match arms.len() {
 519                 0 => eq_check,
 520                 _ => {
 521                     if n_cases > arms.len() {
 522                         let lhs = make::wildcard_pat().into();
 523                         arms.push(make::match_arm(Some(lhs), None, eq_check));
 524                     }
 525
 526                     let match_target = make::expr_tuple(vec![lhs_name, rhs_name]);
 527                     let list = make::match_arm_list(arms).indent(ast::edit::IndentLevel(1));
 528                     make::expr_match(match_target, list)
 529                 }
 530             };
 531
 532             make::block_expr(None, Some(expr)).indent(ast::edit::IndentLevel(1))
 533         }
 534         ast::Adt::Struct(strukt) => match strukt.field_list() {
 535             Some(ast::FieldList::RecordFieldList(field_list)) => {
 536                 let mut expr = None;
 537                 for field in field_list.fields() {
 538                     let lhs = make::expr_path(make::ext::ident_path("self"));
 539                     let lhs = make::expr_field(lhs, &field.name()?.to_string());
 540                     let rhs = make::expr_path(make::ext::ident_path("other"));
 541                     let rhs = make::expr_field(rhs, &field.name()?.to_string());
 542                     let cmp =
 543                         make::expr_bin_op(lhs, BinaryOp::CmpOp(CmpOp::Eq { negated: false }), rhs);
 544                     expr = gen_eq_chain(expr, cmp);
 545                 }
 546                 make::block_expr(None, expr).indent(ast::edit::IndentLevel(1))
 547             }
 548
 549             Some(ast::FieldList::TupleFieldList(field_list)) => {
 550                 let mut expr = None;
 551                 for (i, _) in field_list.fields().enumerate() {
 552                     let idx = format!("{}", i);
 553                     let lhs = make::expr_path(make::ext::ident_path("self"));
 554                     let lhs = make::expr_field(lhs, &idx);
 555                     let rhs = make::expr_path(make::ext::ident_path("other"));
 556                     let rhs = make::expr_field(rhs, &idx);
 557                     let cmp =
 558                         make::expr_bin_op(lhs, BinaryOp::CmpOp(CmpOp::Eq { negated: false }), rhs);
 559                     expr = gen_eq_chain(expr, cmp);
 560                 }
 561                 make::block_expr(None, expr).indent(ast::edit::IndentLevel(1))
 562             }
 563
 564             // No fields in the body means there's nothing to hash.
 565             None => {
 566                 let expr = make::expr_literal("true").into();
 567                 make::block_expr(None, Some(expr)).indent(ast::edit::IndentLevel(1))
 568             }
 569         },
 570     };
 571
 572     ted::replace(func.body()?.syntax(), body.clone_for_update().syntax());
 573     Some(())
 574 }
 575
 576 fn gen_partial_ord(adt: &ast::Adt, func: &ast::Fn) -> Option<()> {
 577     fn gen_eq_chain(expr: Option<ast::Expr>, cmp: ast::Expr) -> Option<ast::Expr> {
 578         match expr {
 579             Some(expr) => Some(make::expr_op(ast::BinOp::BooleanAnd, expr, cmp)),
 580             None => Some(cmp),
 581         }
 582     }
 583
 584     fn gen_partial_eq_match(match_target: ast::Expr) -> Option<ast::Stmt> {
 585         let mut arms = vec![];
 586
 587         let variant_name =
 588             make::path_pat(make::ext::path_from_idents(["core", "cmp", "Ordering", "Eq"])?);
 589         let lhs = make::tuple_struct_pat(make::ext::path_from_idents(["Some"])?, [variant_name]);
 590         arms.push(make::match_arm(Some(lhs.into()), None, make::expr_empty_block()));
 591
 592         arms.push(make::match_arm(
 593             [make::ident_pat(false, false, make::name("ord")).into()],
 594             None,
 595             make::expr_return(Some(make::expr_path(make::ext::ident_path("ord")))),
 596         ));
 597         let list = make::match_arm_list(arms).indent(ast::edit::IndentLevel(1));
 598         Some(make::expr_stmt(make::expr_match(match_target, list)).into())
 599     }
 600
 601     fn gen_partial_cmp_call(lhs: ast::Expr, rhs: ast::Expr) -> ast::Expr {
 602         let method = make::name_ref("partial_cmp");
 603         make::expr_method_call(lhs, method, make::arg_list(Some(rhs)))
 604     }
 605
 606     fn gen_record_pat_field(field_name: &str, pat_name: &str) -> ast::RecordPatField {
 607         let pat = make::ext::simple_ident_pat(make::name(&pat_name));
 608         let name_ref = make::name_ref(field_name);
 609         make::record_pat_field(name_ref, pat.into())
 610     }
 611
 612     fn gen_record_pat(record_name: ast::Path, fields: Vec<ast::RecordPatField>) -> ast::RecordPat {
 613         let list = make::record_pat_field_list(fields);
 614         make::record_pat_with_fields(record_name, list)
 615     }
 616
 617     fn gen_variant_path(variant: &ast::Variant) -> Option<ast::Path> {
 618         make::ext::path_from_idents(["Self", &variant.name()?.to_string()])
 619     }
 620
 621     fn gen_tuple_field(field_name: &String) -> ast::Pat {
 622         ast::Pat::IdentPat(make::ident_pat(false, false, make::name(field_name)))
 623     }
 624
 625     // FIXME: return `None` if the trait carries a generic type; we can only
 626     // generate this code `Self` for the time being.
 627
 628     let body = match adt {
 629         // `Hash` cannot be derived for unions, so no default impl can be provided.
 630         ast::Adt::Union(_) => return None,
 631
 632         ast::Adt::Enum(enum_) => {
 633             // => std::mem::discriminant(self) == std::mem::discriminant(other)
 634             let lhs_name = make::expr_path(make::ext::ident_path("self"));
 635             let lhs = make::expr_call(make_discriminant()?, make::arg_list(Some(lhs_name.clone())));
 636             let rhs_name = make::expr_path(make::ext::ident_path("other"));
 637             let rhs = make::expr_call(make_discriminant()?, make::arg_list(Some(rhs_name.clone())));
 638             let ord_check = gen_partial_cmp_call(lhs, rhs);
 639
 640             let mut case_count = 0;
 641             let mut arms = vec![];
 642             for variant in enum_.variant_list()?.variants() {
 643                 case_count += 1;
 644                 match variant.field_list() {
 645                     // => (Self::Bar { bin: l_bin }, Self::Bar { bin: r_bin }) => l_bin == r_bin,
 646                     Some(ast::FieldList::RecordFieldList(list)) => {
 647                         let mut exprs = vec![];
 648                         let mut l_fields = vec![];
 649                         let mut r_fields = vec![];
 650
 651                         for field in list.fields() {
 652                             let field_name = field.name()?.to_string();
 653
 654                             let l_name = &format!("l_{}", field_name);
 655                             l_fields.push(gen_record_pat_field(&field_name, &l_name));
 656
 657                             let r_name = &format!("r_{}", field_name);
 658                             r_fields.push(gen_record_pat_field(&field_name, &r_name));
 659
 660                             let lhs = make::expr_path(make::ext::ident_path(l_name));
 661                             let rhs = make::expr_path(make::ext::ident_path(r_name));
 662                             let ord = gen_partial_cmp_call(lhs, rhs);
 663                             exprs.push(ord);
 664                         }
 665
 666                         let left = gen_record_pat(gen_variant_path(&variant)?, l_fields);
 667                         let right = gen_record_pat(gen_variant_path(&variant)?, r_fields);
 668                         let tuple = make::tuple_pat(vec![left.into(), right.into()]);
 669
 670                         if let Some(tail) = exprs.pop() {
 671                             let stmts = exprs
 672                                 .into_iter()
 673                                 .map(gen_partial_eq_match)
 674                                 .collect::<Option<Vec<ast::Stmt>>>()?;
 675                             let expr = match stmts.len() {
 676                                 0 => tail,
 677                                 _ => make::block_expr(stmts.into_iter(), Some(tail))
 678                                     .indent(ast::edit::IndentLevel(1))
 679                                     .into(),
 680                             };
 681                             arms.push(make::match_arm(Some(tuple.into()), None, expr.into()));
 682                         }
 683                     }
 684
 685                     Some(ast::FieldList::TupleFieldList(list)) => {
 686                         let mut expr = None;
 687                         let mut l_fields = vec![];
 688                         let mut r_fields = vec![];
 689
 690                         for (i, _) in list.fields().enumerate() {
 691                             let field_name = format!("{}", i);
 692
 693                             let l_name = format!("l{}", field_name);
 694                             l_fields.push(gen_tuple_field(&l_name));
 695
 696                             let r_name = format!("r{}", field_name);
 697                             r_fields.push(gen_tuple_field(&r_name));
 698
 699                             let lhs = make::expr_path(make::ext::ident_path(&l_name));
 700                             let rhs = make::expr_path(make::ext::ident_path(&r_name));
 701                             let cmp = make::expr_op(ast::BinOp::EqualityTest, lhs, rhs);
 702                             expr = gen_eq_chain(expr, cmp);
 703                         }
 704
 705                         let left = make::tuple_struct_pat(gen_variant_path(&variant)?, l_fields);
 706                         let right = make::tuple_struct_pat(gen_variant_path(&variant)?, r_fields);
 707                         let tuple = make::tuple_pat(vec![left.into(), right.into()]);
 708
 709                         if let Some(expr) = expr {
 710                             arms.push(make::match_arm(Some(tuple.into()), None, expr));
 711                         }
 712                     }
 713                     None => continue,
 714                 }
 715             }
 716
 717             let expr = match arms.len() {
 718                 0 => ord_check,
 719                 _ => {
 720                     if case_count > arms.len() {
 721                         let lhs = make::wildcard_pat().into();
 722                         arms.push(make::match_arm(Some(lhs), None, ord_check));
 723                     }
 724
 725                     let match_target = make::expr_tuple(vec![lhs_name, rhs_name]);
 726                     let list = make::match_arm_list(arms).indent(ast::edit::IndentLevel(1));
 727                     make::expr_match(match_target, list)
 728                 }
 729             };
 730
 731             make::block_expr(None, Some(expr)).indent(ast::edit::IndentLevel(1))
 732         }
 733         ast::Adt::Struct(strukt) => match strukt.field_list() {
 734             Some(ast::FieldList::RecordFieldList(field_list)) => {
 735                 let mut exprs = vec![];
 736                 for field in field_list.fields() {
 737                     let lhs = make::expr_path(make::ext::ident_path("self"));
 738                     let lhs = make::expr_field(lhs, &field.name()?.to_string());
 739                     let rhs = make::expr_path(make::ext::ident_path("other"));
 740                     let rhs = make::expr_field(rhs, &field.name()?.to_string());
 741                     let ord = gen_partial_cmp_call(lhs, rhs);
 742                     exprs.push(ord);
 743                 }
 744
 745                 let tail = exprs.pop();
 746                 let stmts = exprs
 747                     .into_iter()
 748                     .map(gen_partial_eq_match)
 749                     .collect::<Option<Vec<ast::Stmt>>>()?;
 750                 make::block_expr(stmts.into_iter(), tail).indent(ast::edit::IndentLevel(1))
 751             }
 752
 753             Some(ast::FieldList::TupleFieldList(field_list)) => {
 754                 let mut exprs = vec![];
 755                 for (i, _) in field_list.fields().enumerate() {
 756                     let idx = format!("{}", i);
 757                     let lhs = make::expr_path(make::ext::ident_path("self"));
 758                     let lhs = make::expr_field(lhs, &idx);
 759                     let rhs = make::expr_path(make::ext::ident_path("other"));
 760                     let rhs = make::expr_field(rhs, &idx);
 761                     let ord = gen_partial_cmp_call(lhs, rhs);
 762                     exprs.push(ord);
 763                 }
 764                 let tail = exprs.pop();
 765                 let stmts = exprs
 766                     .into_iter()
 767                     .map(gen_partial_eq_match)
 768                     .collect::<Option<Vec<ast::Stmt>>>()?;
 769                 make::block_expr(stmts.into_iter(), tail).indent(ast::edit::IndentLevel(1))
 770             }
 771
 772             // No fields in the body means there's nothing to hash.
 773             None => {
 774                 let expr = make::expr_literal("true").into();
 775                 make::block_expr(None, Some(expr)).indent(ast::edit::IndentLevel(1))
 776             }
 777         },
 778     };
 779
 780     ted::replace(func.body()?.syntax(), body.clone_for_update().syntax());
 781     Some(())
 782 }
 783
 784 fn make_discriminant() -> Option<ast::Expr> {
 785     Some(make::expr_path(make::ext::path_from_idents(["core", "mem", "discriminant"])?))
 786 }