compiler/rustc_expand/src/placeholders.rs

   1 use crate::expand::{AstFragment, AstFragmentKind};
   2
   3 use rustc_ast as ast;
   4 use rustc_ast::mut_visit::*;
   5 use rustc_ast::ptr::P;
   6 use rustc_span::source_map::DUMMY_SP;
   7 use rustc_span::symbol::Ident;
   8
   9 use smallvec::{smallvec, SmallVec};
  10
  11 use rustc_data_structures::fx::FxHashMap;
  12
  13 pub fn placeholder(
  14     kind: AstFragmentKind,
  15     id: ast::NodeId,
  16     vis: Option<ast::Visibility>,
  17 ) -> AstFragment {
  18     fn mac_placeholder() -> ast::MacCall {
  19         ast::MacCall {
  20             path: ast::Path { span: DUMMY_SP, segments: Vec::new(), tokens: None },
  21             args: P(ast::MacArgs::Empty),
  22             prior_type_ascription: None,
  23         }
  24     }
  25
  26     let ident = Ident::empty();
  27     let attrs = Vec::new();
  28     let vis = vis.unwrap_or(ast::Visibility {
  29         span: DUMMY_SP,
  30         kind: ast::VisibilityKind::Inherited,
  31         tokens: None,
  32     });
  33     let span = DUMMY_SP;
  34     let expr_placeholder = || {
  35         P(ast::Expr {
  36             id,
  37             span,
  38             attrs: ast::AttrVec::new(),
  39             kind: ast::ExprKind::MacCall(mac_placeholder()),
  40             tokens: None,
  41         })
  42     };
  43     let ty =
  44         || P(ast::Ty { id, kind: ast::TyKind::MacCall(mac_placeholder()), span, tokens: None });
  45     let pat =
  46         || P(ast::Pat { id, kind: ast::PatKind::MacCall(mac_placeholder()), span, tokens: None });
  47
  48     match kind {
  49         AstFragmentKind::Crate => AstFragment::Crate(ast::Crate {
  50             attrs: Default::default(),
  51             items: Default::default(),
  52             spans: ast::ModSpans { inner_span: span, ..Default::default() },
  53             id,
  54             is_placeholder: true,
  55         }),
  56         AstFragmentKind::Expr => AstFragment::Expr(expr_placeholder()),
  57         AstFragmentKind::OptExpr => AstFragment::OptExpr(Some(expr_placeholder())),
  58         AstFragmentKind::Items => AstFragment::Items(smallvec![P(ast::Item {
  59             id,
  60             span,
  61             ident,
  62             vis,
  63             attrs,
  64             kind: ast::ItemKind::MacCall(mac_placeholder()),
  65             tokens: None,
  66         })]),
  67         AstFragmentKind::TraitItems => AstFragment::TraitItems(smallvec![P(ast::AssocItem {
  68             id,
  69             span,
  70             ident,
  71             vis,
  72             attrs,
  73             kind: ast::AssocItemKind::MacCall(mac_placeholder()),
  74             tokens: None,
  75         })]),
  76         AstFragmentKind::ImplItems => AstFragment::ImplItems(smallvec![P(ast::AssocItem {
  77             id,
  78             span,
  79             ident,
  80             vis,
  81             attrs,
  82             kind: ast::AssocItemKind::MacCall(mac_placeholder()),
  83             tokens: None,
  84         })]),
  85         AstFragmentKind::ForeignItems => {
  86             AstFragment::ForeignItems(smallvec![P(ast::ForeignItem {
  87                 id,
  88                 span,
  89                 ident,
  90                 vis,
  91                 attrs,
  92                 kind: ast::ForeignItemKind::MacCall(mac_placeholder()),
  93                 tokens: None,
  94             })])
  95         }
  96         AstFragmentKind::Pat => AstFragment::Pat(P(ast::Pat {
  97             id,
  98             span,
  99             kind: ast::PatKind::MacCall(mac_placeholder()),
 100             tokens: None,
 101         })),
 102         AstFragmentKind::Ty => AstFragment::Ty(P(ast::Ty {
 103             id,
 104             span,
 105             kind: ast::TyKind::MacCall(mac_placeholder()),
 106             tokens: None,
 107         })),
 108         AstFragmentKind::Stmts => AstFragment::Stmts(smallvec![{
 109             let mac = P(ast::MacCallStmt {
 110                 mac: mac_placeholder(),
 111                 style: ast::MacStmtStyle::Braces,
 112                 attrs: ast::AttrVec::new(),
 113                 tokens: None,
 114             });
 115             ast::Stmt { id, span, kind: ast::StmtKind::MacCall(mac) }
 116         }]),
 117         AstFragmentKind::Arms => AstFragment::Arms(smallvec![ast::Arm {
 118             attrs: Default::default(),
 119             body: expr_placeholder(),
 120             guard: None,
 121             id,
 122             pat: pat(),
 123             span,
 124             is_placeholder: true,
 125         }]),
 126         AstFragmentKind::ExprFields => AstFragment::ExprFields(smallvec![ast::ExprField {
 127             attrs: Default::default(),
 128             expr: expr_placeholder(),
 129             id,
 130             ident,
 131             is_shorthand: false,
 132             span,
 133             is_placeholder: true,
 134         }]),
 135         AstFragmentKind::PatFields => AstFragment::PatFields(smallvec![ast::PatField {
 136             attrs: Default::default(),
 137             id,
 138             ident,
 139             is_shorthand: false,
 140             pat: pat(),
 141             span,
 142             is_placeholder: true,
 143         }]),
 144         AstFragmentKind::GenericParams => AstFragment::GenericParams(smallvec![{
 145             ast::GenericParam {
 146                 attrs: Default::default(),
 147                 bounds: Default::default(),
 148                 id,
 149                 ident,
 150                 is_placeholder: true,
 151                 kind: ast::GenericParamKind::Lifetime,
 152             }
 153         }]),
 154         AstFragmentKind::Params => AstFragment::Params(smallvec![ast::Param {
 155             attrs: Default::default(),
 156             id,
 157             pat: pat(),
 158             span,
 159             ty: ty(),
 160             is_placeholder: true,
 161         }]),
 162         AstFragmentKind::FieldDefs => AstFragment::FieldDefs(smallvec![ast::FieldDef {
 163             attrs: Default::default(),
 164             id,
 165             ident: None,
 166             span,
 167             ty: ty(),
 168             vis,
 169             is_placeholder: true,
 170         }]),
 171         AstFragmentKind::Variants => AstFragment::Variants(smallvec![ast::Variant {
 172             attrs: Default::default(),
 173             data: ast::VariantData::Struct(Default::default(), false),
 174             disr_expr: None,
 175             id,
 176             ident,
 177             span,
 178             vis,
 179             is_placeholder: true,
 180         }]),
 181     }
 182 }
 183
 184 #[derive(Default)]
 185 pub struct PlaceholderExpander {
 186     expanded_fragments: FxHashMap<ast::NodeId, AstFragment>,
 187 }
 188
 189 impl PlaceholderExpander {
 190     pub fn add(&mut self, id: ast::NodeId, mut fragment: AstFragment) {
 191         fragment.mut_visit_with(self);
 192         self.expanded_fragments.insert(id, fragment);
 193     }
 194
 195     fn remove(&mut self, id: ast::NodeId) -> AstFragment {
 196         self.expanded_fragments.remove(&id).unwrap()
 197     }
 198 }
 199
 200 impl MutVisitor for PlaceholderExpander {
 201     fn flat_map_arm(&mut self, arm: ast::Arm) -> SmallVec<[ast::Arm; 1]> {
 202         if arm.is_placeholder {
 203             self.remove(arm.id).make_arms()
 204         } else {
 205             noop_flat_map_arm(arm, self)
 206         }
 207     }
 208
 209     fn flat_map_expr_field(&mut self, field: ast::ExprField) -> SmallVec<[ast::ExprField; 1]> {
 210         if field.is_placeholder {
 211             self.remove(field.id).make_expr_fields()
 212         } else {
 213             noop_flat_map_expr_field(field, self)
 214         }
 215     }
 216
 217     fn flat_map_pat_field(&mut self, fp: ast::PatField) -> SmallVec<[ast::PatField; 1]> {
 218         if fp.is_placeholder {
 219             self.remove(fp.id).make_pat_fields()
 220         } else {
 221             noop_flat_map_pat_field(fp, self)
 222         }
 223     }
 224
 225     fn flat_map_generic_param(
 226         &mut self,
 227         param: ast::GenericParam,
 228     ) -> SmallVec<[ast::GenericParam; 1]> {
 229         if param.is_placeholder {
 230             self.remove(param.id).make_generic_params()
 231         } else {
 232             noop_flat_map_generic_param(param, self)
 233         }
 234     }
 235
 236     fn flat_map_param(&mut self, p: ast::Param) -> SmallVec<[ast::Param; 1]> {
 237         if p.is_placeholder {
 238             self.remove(p.id).make_params()
 239         } else {
 240             noop_flat_map_param(p, self)
 241         }
 242     }
 243
 244     fn flat_map_field_def(&mut self, sf: ast::FieldDef) -> SmallVec<[ast::FieldDef; 1]> {
 245         if sf.is_placeholder {
 246             self.remove(sf.id).make_field_defs()
 247         } else {
 248             noop_flat_map_field_def(sf, self)
 249         }
 250     }
 251
 252     fn flat_map_variant(&mut self, variant: ast::Variant) -> SmallVec<[ast::Variant; 1]> {
 253         if variant.is_placeholder {
 254             self.remove(variant.id).make_variants()
 255         } else {
 256             noop_flat_map_variant(variant, self)
 257         }
 258     }
 259
 260     fn flat_map_item(&mut self, item: P<ast::Item>) -> SmallVec<[P<ast::Item>; 1]> {
 261         match item.kind {
 262             ast::ItemKind::MacCall(_) => self.remove(item.id).make_items(),
 263             _ => noop_flat_map_item(item, self),
 264         }
 265     }
 266
 267     fn flat_map_trait_item(&mut self, item: P<ast::AssocItem>) -> SmallVec<[P<ast::AssocItem>; 1]> {
 268         match item.kind {
 269             ast::AssocItemKind::MacCall(_) => self.remove(item.id).make_trait_items(),
 270             _ => noop_flat_map_assoc_item(item, self),
 271         }
 272     }
 273
 274     fn flat_map_impl_item(&mut self, item: P<ast::AssocItem>) -> SmallVec<[P<ast::AssocItem>; 1]> {
 275         match item.kind {
 276             ast::AssocItemKind::MacCall(_) => self.remove(item.id).make_impl_items(),
 277             _ => noop_flat_map_assoc_item(item, self),
 278         }
 279     }
 280
 281     fn flat_map_foreign_item(
 282         &mut self,
 283         item: P<ast::ForeignItem>,
 284     ) -> SmallVec<[P<ast::ForeignItem>; 1]> {
 285         match item.kind {
 286             ast::ForeignItemKind::MacCall(_) => self.remove(item.id).make_foreign_items(),
 287             _ => noop_flat_map_foreign_item(item, self),
 288         }
 289     }
 290
 291     fn visit_expr(&mut self, expr: &mut P<ast::Expr>) {
 292         match expr.kind {
 293             ast::ExprKind::MacCall(_) => *expr = self.remove(expr.id).make_expr(),
 294             _ => noop_visit_expr(expr, self),
 295         }
 296     }
 297
 298     fn filter_map_expr(&mut self, expr: P<ast::Expr>) -> Option<P<ast::Expr>> {
 299         match expr.kind {
 300             ast::ExprKind::MacCall(_) => self.remove(expr.id).make_opt_expr(),
 301             _ => noop_filter_map_expr(expr, self),
 302         }
 303     }
 304
 305     fn flat_map_stmt(&mut self, stmt: ast::Stmt) -> SmallVec<[ast::Stmt; 1]> {
 306         let (style, mut stmts) = match stmt.kind {
 307             ast::StmtKind::MacCall(mac) => (mac.style, self.remove(stmt.id).make_stmts()),
 308             _ => return noop_flat_map_stmt(stmt, self),
 309         };
 310
 311         if style == ast::MacStmtStyle::Semicolon {
 312             // Implement the proposal described in
 313             // https://github.com/rust-lang/rust/issues/61733#issuecomment-509626449
 314             //
 315             // The macro invocation expands to the list of statements. If the
 316             // list of statements is empty, then 'parse' the trailing semicolon
 317             // on the original invocation as an empty statement. That is:
 318             //
 319             // `empty();` is parsed as a single `StmtKind::Empty`
 320             //
 321             // If the list of statements is non-empty, see if the final
 322             // statement already has a trailing semicolon.
 323             //
 324             // If it doesn't have a semicolon, then 'parse' the trailing
 325             // semicolon from the invocation as part of the final statement,
 326             // using `stmt.add_trailing_semicolon()`
 327             //
 328             // If it does have a semicolon, then 'parse' the trailing semicolon
 329             // from the invocation as a new StmtKind::Empty
 330
 331             // FIXME: We will need to preserve the original semicolon token and
 332             // span as part of #15701
 333             let empty_stmt =
 334                 ast::Stmt { id: ast::DUMMY_NODE_ID, kind: ast::StmtKind::Empty, span: DUMMY_SP };
 335
 336             if let Some(stmt) = stmts.pop() {
 337                 if stmt.has_trailing_semicolon() {
 338                     stmts.push(stmt);
 339                     stmts.push(empty_stmt);
 340                 } else {
 341                     stmts.push(stmt.add_trailing_semicolon());
 342                 }
 343             } else {
 344                 stmts.push(empty_stmt);
 345             }
 346         }
 347
 348         stmts
 349     }
 350
 351     fn visit_pat(&mut self, pat: &mut P<ast::Pat>) {
 352         match pat.kind {
 353             ast::PatKind::MacCall(_) => *pat = self.remove(pat.id).make_pat(),
 354             _ => noop_visit_pat(pat, self),
 355         }
 356     }
 357
 358     fn visit_ty(&mut self, ty: &mut P<ast::Ty>) {
 359         match ty.kind {
 360             ast::TyKind::MacCall(_) => *ty = self.remove(ty.id).make_ty(),
 361             _ => noop_visit_ty(ty, self),
 362         }
 363     }
 364
 365     fn visit_crate(&mut self, krate: &mut ast::Crate) {
 366         if krate.is_placeholder {
 367             *krate = self.remove(krate.id).make_crate();
 368         } else {
 369             noop_visit_crate(krate, self)
 370         }
 371     }
 372 }