crates/ide/src/syntax_highlighting/highlight.rs

   1 //! Computes color for a single element.
   2
   3 use hir::{AsAssocItem, AssocItemContainer, Semantics, VariantDef};
   4 use ide_db::{
   5     defs::{Definition, NameClass, NameRefClass},
   6     RootDatabase, SymbolKind,
   7 };
   8 use rustc_hash::FxHashMap;
   9 use syntax::{
  10     ast, AstNode, AstToken, NodeOrToken, SyntaxElement,
  11     SyntaxKind::{self, *},
  12     SyntaxNode, SyntaxToken, T,
  13 };
  14
  15 use crate::{
  16     syntax_highlighting::tags::{HlOperator, HlPunct},
  17     Highlight, HlMod, HlTag,
  18 };
  19
  20 pub(super) fn element(
  21     sema: &Semantics<RootDatabase>,
  22     bindings_shadow_count: &mut FxHashMap<hir::Name, u32>,
  23     syntactic_name_ref_highlighting: bool,
  24     element: SyntaxElement,
  25 ) -> Option<(Highlight, Option<u64>)> {
  26     let db = sema.db;
  27     let mut binding_hash = None;
  28     let highlight: Highlight = match element.kind() {
  29         FN => {
  30             bindings_shadow_count.clear();
  31             return None;
  32         }
  33
  34         // Highlight definitions depending on the "type" of the definition.
  35         NAME => {
  36             let name = element.into_node().and_then(ast::Name::cast).unwrap();
  37             let name_kind = NameClass::classify(sema, &name);
  38
  39             if let Some(NameClass::Definition(Definition::Local(local))) = &name_kind {
  40                 if let Some(name) = local.name(db) {
  41                     let shadow_count = bindings_shadow_count.entry(name.clone()).or_default();
  42                     *shadow_count += 1;
  43                     binding_hash = Some(calc_binding_hash(&name, *shadow_count))
  44                 }
  45             };
  46
  47             match name_kind {
  48                 Some(NameClass::ExternCrate(_)) => HlTag::Symbol(SymbolKind::Module).into(),
  49                 Some(NameClass::Definition(def)) => highlight_def(db, def) | HlMod::Definition,
  50                 Some(NameClass::ConstReference(def)) => highlight_def(db, def),
  51                 Some(NameClass::PatFieldShorthand { field_ref, .. }) => {
  52                     let mut h = HlTag::Symbol(SymbolKind::Field).into();
  53                     if let Definition::Field(field) = field_ref {
  54                         if let VariantDef::Union(_) = field.parent_def(db) {
  55                             h |= HlMod::Unsafe;
  56                         }
  57                     }
  58
  59                     h
  60                 }
  61                 None => highlight_name_by_syntax(name) | HlMod::Definition,
  62             }
  63         }
  64
  65         // Highlight references like the definitions they resolve to
  66         NAME_REF if element.ancestors().any(|it| it.kind() == ATTR) => {
  67             // even though we track whether we are in an attribute or not we still need this special case
  68             // as otherwise we would emit unresolved references for name refs inside attributes
  69             Highlight::from(HlTag::Symbol(SymbolKind::Function))
  70         }
  71         NAME_REF => {
  72             let name_ref = element.into_node().and_then(ast::NameRef::cast).unwrap();
  73             highlight_func_by_name_ref(sema, &name_ref).unwrap_or_else(|| {
  74                 let is_self = name_ref.self_token().is_some();
  75                 let h = match NameRefClass::classify(sema, &name_ref) {
  76                     Some(name_kind) => match name_kind {
  77                         NameRefClass::ExternCrate(_) => HlTag::Symbol(SymbolKind::Module).into(),
  78                         NameRefClass::Definition(def) => {
  79                             if let Definition::Local(local) = &def {
  80                                 if let Some(name) = local.name(db) {
  81                                     let shadow_count =
  82                                         bindings_shadow_count.entry(name.clone()).or_default();
  83                                     binding_hash = Some(calc_binding_hash(&name, *shadow_count))
  84                                 }
  85                             };
  86
  87                             let mut h = highlight_def(db, def);
  88
  89                             if let Definition::Local(local) = &def {
  90                                 if is_consumed_lvalue(name_ref.syntax().clone().into(), local, db) {
  91                                     h |= HlMod::Consuming;
  92                                 }
  93                             }
  94
  95                             if let Some(parent) = name_ref.syntax().parent() {
  96                                 if matches!(parent.kind(), FIELD_EXPR | RECORD_PAT_FIELD) {
  97                                     if let Definition::Field(field) = def {
  98                                         if let VariantDef::Union(_) = field.parent_def(db) {
  99                                             h |= HlMod::Unsafe;
 100                                         }
 101                                     }
 102                                 }
 103                             }
 104
 105                             h
 106                         }
 107                         NameRefClass::FieldShorthand { .. } => {
 108                             HlTag::Symbol(SymbolKind::Field).into()
 109                         }
 110                     },
 111                     None if syntactic_name_ref_highlighting => {
 112                         highlight_name_ref_by_syntax(name_ref, sema)
 113                     }
 114                     None => HlTag::UnresolvedReference.into(),
 115                 };
 116                 if h.tag == HlTag::Symbol(SymbolKind::Module) && is_self {
 117                     HlTag::Symbol(SymbolKind::SelfParam).into()
 118                 } else {
 119                     h
 120                 }
 121             })
 122         }
 123
 124         // Simple token-based highlighting
 125         COMMENT => {
 126             let comment = element.into_token().and_then(ast::Comment::cast)?;
 127             let h = HlTag::Comment;
 128             match comment.kind().doc {
 129                 Some(_) => h | HlMod::Documentation,
 130                 None => h.into(),
 131             }
 132         }
 133         STRING | BYTE_STRING => HlTag::StringLiteral.into(),
 134         ATTR => HlTag::Attribute.into(),
 135         INT_NUMBER | FLOAT_NUMBER => HlTag::NumericLiteral.into(),
 136         BYTE => HlTag::ByteLiteral.into(),
 137         CHAR => HlTag::CharLiteral.into(),
 138         QUESTION => Highlight::new(HlTag::Operator(HlOperator::Other)) | HlMod::ControlFlow,
 139         LIFETIME => {
 140             let lifetime = element.into_node().and_then(ast::Lifetime::cast).unwrap();
 141
 142             match NameClass::classify_lifetime(sema, &lifetime) {
 143                 Some(NameClass::Definition(def)) => highlight_def(db, def) | HlMod::Definition,
 144                 None => match NameRefClass::classify_lifetime(sema, &lifetime) {
 145                     Some(NameRefClass::Definition(def)) => highlight_def(db, def),
 146                     _ => Highlight::new(HlTag::Symbol(SymbolKind::LifetimeParam)),
 147                 },
 148                 _ => Highlight::new(HlTag::Symbol(SymbolKind::LifetimeParam)) | HlMod::Definition,
 149             }
 150         }
 151         p if p.is_punct() => match p {
 152             T![&] if element.parent().and_then(ast::BinExpr::cast).is_some() => {
 153                 HlTag::Operator(HlOperator::Bitwise).into()
 154             }
 155             T![&] => {
 156                 let h = HlTag::Operator(HlOperator::Other).into();
 157                 let is_unsafe = element
 158                     .parent()
 159                     .and_then(ast::RefExpr::cast)
 160                     .map(|ref_expr| sema.is_unsafe_ref_expr(&ref_expr))
 161                     .unwrap_or(false);
 162                 if is_unsafe {
 163                     h | HlMod::Unsafe
 164                 } else {
 165                     h
 166                 }
 167             }
 168             T![::] | T![->] | T![=>] | T![..] | T![=] | T![@] | T![.] => {
 169                 HlTag::Operator(HlOperator::Other).into()
 170             }
 171             T![!] if element.parent().and_then(ast::MacroCall::cast).is_some() => {
 172                 HlTag::Symbol(SymbolKind::Macro).into()
 173             }
 174             T![!] if element.parent().and_then(ast::NeverType::cast).is_some() => {
 175                 HlTag::BuiltinType.into()
 176             }
 177             T![!] if element.parent().and_then(ast::PrefixExpr::cast).is_some() => {
 178                 HlTag::Operator(HlOperator::Logical).into()
 179             }
 180             T![*] if element.parent().and_then(ast::PtrType::cast).is_some() => {
 181                 HlTag::Keyword.into()
 182             }
 183             T![*] if element.parent().and_then(ast::PrefixExpr::cast).is_some() => {
 184                 let prefix_expr = element.parent().and_then(ast::PrefixExpr::cast)?;
 185
 186                 let expr = prefix_expr.expr()?;
 187                 let ty = sema.type_of_expr(&expr)?;
 188                 if ty.is_raw_ptr() {
 189                     HlTag::Operator(HlOperator::Other) | HlMod::Unsafe
 190                 } else if let Some(ast::PrefixOp::Deref) = prefix_expr.op_kind() {
 191                     HlTag::Operator(HlOperator::Other).into()
 192                 } else {
 193                     HlTag::Punctuation(HlPunct::Other).into()
 194                 }
 195             }
 196             T![-] if element.parent().and_then(ast::PrefixExpr::cast).is_some() => {
 197                 let prefix_expr = element.parent().and_then(ast::PrefixExpr::cast)?;
 198
 199                 let expr = prefix_expr.expr()?;
 200                 match expr {
 201                     ast::Expr::Literal(_) => HlTag::NumericLiteral,
 202                     _ => HlTag::Operator(HlOperator::Other),
 203                 }
 204                 .into()
 205             }
 206             _ if element.parent().and_then(ast::PrefixExpr::cast).is_some() => {
 207                 HlTag::Operator(HlOperator::Other).into()
 208             }
 209             T![+] | T![-] | T![*] | T![/] | T![+=] | T![-=] | T![*=] | T![/=]
 210                 if element.parent().and_then(ast::BinExpr::cast).is_some() =>
 211             {
 212                 HlTag::Operator(HlOperator::Arithmetic).into()
 213             }
 214             T![|] | T![&] | T![!] | T![^] | T![|=] | T![&=] | T![^=]
 215                 if element.parent().and_then(ast::BinExpr::cast).is_some() =>
 216             {
 217                 HlTag::Operator(HlOperator::Bitwise).into()
 218             }
 219             T![&&] | T![||] if element.parent().and_then(ast::BinExpr::cast).is_some() => {
 220                 HlTag::Operator(HlOperator::Logical).into()
 221             }
 222             T![>] | T![<] | T![==] | T![>=] | T![<=] | T![!=]
 223                 if element.parent().and_then(ast::BinExpr::cast).is_some() =>
 224             {
 225                 HlTag::Operator(HlOperator::Comparison).into()
 226             }
 227             _ if element.parent().and_then(ast::BinExpr::cast).is_some() => {
 228                 HlTag::Operator(HlOperator::Other).into()
 229             }
 230             _ if element.parent().and_then(ast::RangeExpr::cast).is_some() => {
 231                 HlTag::Operator(HlOperator::Other).into()
 232             }
 233             _ if element.parent().and_then(ast::RangePat::cast).is_some() => {
 234                 HlTag::Operator(HlOperator::Other).into()
 235             }
 236             _ if element.parent().and_then(ast::RestPat::cast).is_some() => {
 237                 HlTag::Operator(HlOperator::Other).into()
 238             }
 239             _ if element.parent().and_then(ast::Attr::cast).is_some() => HlTag::Attribute.into(),
 240             kind => HlTag::Punctuation(match kind {
 241                 T!['['] | T![']'] => HlPunct::Bracket,
 242                 T!['{'] | T!['}'] => HlPunct::Brace,
 243                 T!['('] | T![')'] => HlPunct::Parenthesis,
 244                 T![<] | T![>] => HlPunct::Angle,
 245                 T![,] => HlPunct::Comma,
 246                 T![:] => HlPunct::Colon,
 247                 T![;] => HlPunct::Semi,
 248                 T![.] => HlPunct::Dot,
 249                 _ => HlPunct::Other,
 250             })
 251             .into(),
 252         },
 253
 254         k if k.is_keyword() => {
 255             let h = Highlight::new(HlTag::Keyword);
 256             match k {
 257                 T![break]
 258                 | T![continue]
 259                 | T![else]
 260                 | T![if]
 261                 | T![loop]
 262                 | T![match]
 263                 | T![return]
 264                 | T![while]
 265                 | T![in] => h | HlMod::ControlFlow,
 266                 T![for] if !is_child_of_impl(&element) => h | HlMod::ControlFlow,
 267                 T![unsafe] => h | HlMod::Unsafe,
 268                 T![true] | T![false] => HlTag::BoolLiteral.into(),
 269                 // self is handled as either a Name or NameRef already
 270                 T![self] => return None,
 271                 T![ref] => element
 272                     .parent()
 273                     .and_then(ast::IdentPat::cast)
 274                     .and_then(|ident_pat| {
 275                         if sema.is_unsafe_ident_pat(&ident_pat) {
 276                             Some(HlMod::Unsafe)
 277                         } else {
 278                             None
 279                         }
 280                     })
 281                     .map(|modifier| h | modifier)
 282                     .unwrap_or(h),
 283                 _ => h,
 284             }
 285         }
 286
 287         _ => return None,
 288     };
 289
 290     return Some((highlight, binding_hash));
 291
 292     fn calc_binding_hash(name: &hir::Name, shadow_count: u32) -> u64 {
 293         fn hash<T: std::hash::Hash + std::fmt::Debug>(x: T) -> u64 {
 294             use std::{collections::hash_map::DefaultHasher, hash::Hasher};
 295
 296             let mut hasher = DefaultHasher::new();
 297             x.hash(&mut hasher);
 298             hasher.finish()
 299         }
 300
 301         hash((name, shadow_count))
 302     }
 303 }
 304
 305 fn highlight_def(db: &RootDatabase, def: Definition) -> Highlight {
 306     match def {
 307         Definition::Macro(_) => HlTag::Symbol(SymbolKind::Macro),
 308         Definition::Field(_) => HlTag::Symbol(SymbolKind::Field),
 309         Definition::ModuleDef(def) => match def {
 310             hir::ModuleDef::Module(_) => HlTag::Symbol(SymbolKind::Module),
 311             hir::ModuleDef::Function(func) => {
 312                 let mut h = Highlight::new(HlTag::Symbol(SymbolKind::Function));
 313                 if let Some(item) = func.as_assoc_item(db) {
 314                     h |= HlMod::Associated;
 315                     if func.self_param(db).is_none() {
 316                         h |= HlMod::Static
 317                     }
 318
 319                     match item.container(db) {
 320                         AssocItemContainer::Impl(i) => {
 321                             if i.trait_(db).is_some() {
 322                                 h |= HlMod::Trait;
 323                             }
 324                         }
 325                         AssocItemContainer::Trait(_t) => {
 326                             h |= HlMod::Trait;
 327                         }
 328                     }
 329                 }
 330
 331                 if func.is_unsafe(db) {
 332                     h |= HlMod::Unsafe;
 333                 }
 334                 return h;
 335             }
 336             hir::ModuleDef::Adt(hir::Adt::Struct(_)) => HlTag::Symbol(SymbolKind::Struct),
 337             hir::ModuleDef::Adt(hir::Adt::Enum(_)) => HlTag::Symbol(SymbolKind::Enum),
 338             hir::ModuleDef::Adt(hir::Adt::Union(_)) => HlTag::Symbol(SymbolKind::Union),
 339             hir::ModuleDef::Variant(_) => HlTag::Symbol(SymbolKind::Variant),
 340             hir::ModuleDef::Const(konst) => {
 341                 let mut h = Highlight::new(HlTag::Symbol(SymbolKind::Const));
 342                 if let Some(item) = konst.as_assoc_item(db) {
 343                     h |= HlMod::Associated;
 344                     match item.container(db) {
 345                         AssocItemContainer::Impl(i) => {
 346                             if i.trait_(db).is_some() {
 347                                 h |= HlMod::Trait;
 348                             }
 349                         }
 350                         AssocItemContainer::Trait(_t) => {
 351                             h |= HlMod::Trait;
 352                         }
 353                     }
 354                 }
 355
 356                 return h;
 357             }
 358             hir::ModuleDef::Trait(_) => HlTag::Symbol(SymbolKind::Trait),
 359             hir::ModuleDef::TypeAlias(type_) => {
 360                 let mut h = Highlight::new(HlTag::Symbol(SymbolKind::TypeAlias));
 361                 if let Some(item) = type_.as_assoc_item(db) {
 362                     h |= HlMod::Associated;
 363                     match item.container(db) {
 364                         AssocItemContainer::Impl(i) => {
 365                             if i.trait_(db).is_some() {
 366                                 h |= HlMod::Trait;
 367                             }
 368                         }
 369                         AssocItemContainer::Trait(_t) => {
 370                             h |= HlMod::Trait;
 371                         }
 372                     }
 373                 }
 374                 return h;
 375             }
 376             hir::ModuleDef::BuiltinType(_) => HlTag::BuiltinType,
 377             hir::ModuleDef::Static(s) => {
 378                 let mut h = Highlight::new(HlTag::Symbol(SymbolKind::Static));
 379                 if s.is_mut(db) {
 380                     h |= HlMod::Mutable;
 381                     h |= HlMod::Unsafe;
 382                 }
 383                 return h;
 384             }
 385         },
 386         Definition::SelfType(_) => HlTag::Symbol(SymbolKind::Impl),
 387         Definition::GenericParam(it) => match it {
 388             hir::GenericParam::TypeParam(_) => HlTag::Symbol(SymbolKind::TypeParam),
 389             hir::GenericParam::ConstParam(_) => HlTag::Symbol(SymbolKind::ConstParam),
 390             hir::GenericParam::LifetimeParam(_) => HlTag::Symbol(SymbolKind::LifetimeParam),
 391         },
 392         Definition::Local(local) => {
 393             let tag = if local.is_self(db) {
 394                 HlTag::Symbol(SymbolKind::SelfParam)
 395             } else if local.is_param(db) {
 396                 HlTag::Symbol(SymbolKind::ValueParam)
 397             } else {
 398                 HlTag::Symbol(SymbolKind::Local)
 399             };
 400             let mut h = Highlight::new(tag);
 401             let ty = local.ty(db);
 402             if local.is_mut(db) || ty.is_mutable_reference() {
 403                 h |= HlMod::Mutable;
 404             }
 405             if ty.as_callable(db).is_some() || ty.impls_fnonce(db) {
 406                 h |= HlMod::Callable;
 407             }
 408             return h;
 409         }
 410         Definition::Label(_) => HlTag::Symbol(SymbolKind::Label),
 411     }
 412     .into()
 413 }
 414
 415 fn highlight_func_by_name_ref(
 416     sema: &Semantics<RootDatabase>,
 417     name_ref: &ast::NameRef,
 418 ) -> Option<Highlight> {
 419     let mc = name_ref.syntax().parent().and_then(ast::MethodCallExpr::cast)?;
 420     highlight_method_call(sema, &mc)
 421 }
 422
 423 fn highlight_method_call(
 424     sema: &Semantics<RootDatabase>,
 425     method_call: &ast::MethodCallExpr,
 426 ) -> Option<Highlight> {
 427     let func = sema.resolve_method_call(&method_call)?;
 428     let mut h = HlTag::Symbol(SymbolKind::Function).into();
 429     h |= HlMod::Associated;
 430     if func.is_unsafe(sema.db) || sema.is_unsafe_method_call(&method_call) {
 431         h |= HlMod::Unsafe;
 432     }
 433     if func.as_assoc_item(sema.db).and_then(|it| it.containing_trait(sema.db)).is_some() {
 434         h |= HlMod::Trait
 435     }
 436
 437     if let Some(self_param) = func.self_param(sema.db) {
 438         match self_param.access(sema.db) {
 439             hir::Access::Shared => (),
 440             hir::Access::Exclusive => h |= HlMod::Mutable,
 441             hir::Access::Owned => {
 442                 if let Some(receiver_ty) =
 443                     method_call.receiver().and_then(|it| sema.type_of_expr(&it))
 444                 {
 445                     if !receiver_ty.is_copy(sema.db) {
 446                         h |= HlMod::Consuming
 447                     }
 448                 }
 449             }
 450         }
 451     }
 452     Some(h)
 453 }
 454
 455 fn highlight_name_by_syntax(name: ast::Name) -> Highlight {
 456     let default = HlTag::UnresolvedReference;
 457
 458     let parent = match name.syntax().parent() {
 459         Some(it) => it,
 460         _ => return default.into(),
 461     };
 462
 463     let tag = match parent.kind() {
 464         STRUCT => HlTag::Symbol(SymbolKind::Struct),
 465         ENUM => HlTag::Symbol(SymbolKind::Enum),
 466         VARIANT => HlTag::Symbol(SymbolKind::Variant),
 467         UNION => HlTag::Symbol(SymbolKind::Union),
 468         TRAIT => HlTag::Symbol(SymbolKind::Trait),
 469         TYPE_ALIAS => HlTag::Symbol(SymbolKind::TypeAlias),
 470         TYPE_PARAM => HlTag::Symbol(SymbolKind::TypeParam),
 471         RECORD_FIELD => HlTag::Symbol(SymbolKind::Field),
 472         MODULE => HlTag::Symbol(SymbolKind::Module),
 473         FN => HlTag::Symbol(SymbolKind::Function),
 474         CONST => HlTag::Symbol(SymbolKind::Const),
 475         STATIC => HlTag::Symbol(SymbolKind::Static),
 476         IDENT_PAT => HlTag::Symbol(SymbolKind::Local),
 477         _ => default,
 478     };
 479
 480     tag.into()
 481 }
 482
 483 fn highlight_name_ref_by_syntax(name: ast::NameRef, sema: &Semantics<RootDatabase>) -> Highlight {
 484     let default = HlTag::UnresolvedReference;
 485
 486     let parent = match name.syntax().parent() {
 487         Some(it) => it,
 488         _ => return default.into(),
 489     };
 490
 491     match parent.kind() {
 492         METHOD_CALL_EXPR => {
 493             return ast::MethodCallExpr::cast(parent)
 494                 .and_then(|it| highlight_method_call(sema, &it))
 495                 .unwrap_or_else(|| HlTag::Symbol(SymbolKind::Function).into());
 496         }
 497         FIELD_EXPR => {
 498             let h = HlTag::Symbol(SymbolKind::Field);
 499             let is_union = ast::FieldExpr::cast(parent)
 500                 .and_then(|field_expr| {
 501                     let field = sema.resolve_field(&field_expr)?;
 502                     Some(if let VariantDef::Union(_) = field.parent_def(sema.db) {
 503                         true
 504                     } else {
 505                         false
 506                     })
 507                 })
 508                 .unwrap_or(false);
 509             if is_union {
 510                 h | HlMod::Unsafe
 511             } else {
 512                 h.into()
 513             }
 514         }
 515         PATH_SEGMENT => {
 516             let path = match parent.parent().and_then(ast::Path::cast) {
 517                 Some(it) => it,
 518                 _ => return default.into(),
 519             };
 520             let expr = match path.syntax().parent().and_then(ast::PathExpr::cast) {
 521                 Some(it) => it,
 522                 _ => {
 523                     // within path, decide whether it is module or adt by checking for uppercase name
 524                     return if name.text().chars().next().unwrap_or_default().is_uppercase() {
 525                         HlTag::Symbol(SymbolKind::Struct)
 526                     } else {
 527                         HlTag::Symbol(SymbolKind::Module)
 528                     }
 529                     .into();
 530                 }
 531             };
 532             let parent = match expr.syntax().parent() {
 533                 Some(it) => it,
 534                 None => return default.into(),
 535             };
 536
 537             match parent.kind() {
 538                 CALL_EXPR => HlTag::Symbol(SymbolKind::Function).into(),
 539                 _ => if name.text().chars().next().unwrap_or_default().is_uppercase() {
 540                     HlTag::Symbol(SymbolKind::Struct)
 541                 } else {
 542                     HlTag::Symbol(SymbolKind::Const)
 543                 }
 544                 .into(),
 545             }
 546         }
 547         _ => default.into(),
 548     }
 549 }
 550
 551 fn is_consumed_lvalue(
 552     node: NodeOrToken<SyntaxNode, SyntaxToken>,
 553     local: &hir::Local,
 554     db: &RootDatabase,
 555 ) -> bool {
 556     // When lvalues are passed as arguments and they're not Copy, then mark them as Consuming.
 557     parents_match(node, &[PATH_SEGMENT, PATH, PATH_EXPR, ARG_LIST]) && !local.ty(db).is_copy(db)
 558 }
 559
 560 /// Returns true if the parent nodes of `node` all match the `SyntaxKind`s in `kinds` exactly.
 561 fn parents_match(mut node: NodeOrToken<SyntaxNode, SyntaxToken>, mut kinds: &[SyntaxKind]) -> bool {
 562     while let (Some(parent), [kind, rest @ ..]) = (&node.parent(), kinds) {
 563         if parent.kind() != *kind {
 564             return false;
 565         }
 566
 567         // FIXME: Would be nice to get parent out of the match, but binding by-move and by-value
 568         // in the same pattern is unstable: rust-lang/rust#68354.
 569         node = node.parent().unwrap().into();
 570         kinds = rest;
 571     }
 572
 573     // Only true if we matched all expected kinds
 574     kinds.len() == 0
 575 }
 576
 577 fn is_child_of_impl(element: &SyntaxElement) -> bool {
 578     match element.parent() {
 579         Some(e) => e.kind() == IMPL,
 580         _ => false,
 581     }
 582 }