| //! This file declares the `ScopeTree` type, which describes |
| //! the parent links in the region hierarchy. |
| //! |
| //! For more information about how MIR-based region-checking works, |
| //! see the [rustc dev guide]. |
| //! |
| //! [rustc dev guide]: https://rustc-dev-guide.rust-lang.org/borrow_check.html |
| |
| use std::fmt; |
| |
| use rustc_data_structures::fx::FxIndexMap; |
| use rustc_data_structures::unord::UnordMap; |
| use rustc_hir as hir; |
| use rustc_hir::{HirId, HirIdMap, Node}; |
| use rustc_macros::{HashStable, TyDecodable, TyEncodable}; |
| use rustc_span::{DUMMY_SP, Span}; |
| use tracing::debug; |
| |
| use crate::ty::{self, TyCtxt}; |
| |
| /// Represents a statically-describable scope that can be used to |
| /// bound the lifetime/region for values. |
| /// |
| /// `Node(node_id)`: Any AST node that has any scope at all has the |
| /// `Node(node_id)` scope. Other variants represent special cases not |
| /// immediately derivable from the abstract syntax tree structure. |
| /// |
| /// `DestructionScope(node_id)` represents the scope of destructors |
| /// implicitly-attached to `node_id` that run immediately after the |
| /// expression for `node_id` itself. Not every AST node carries a |
| /// `DestructionScope`, but those that are `terminating_scopes` do; |
| /// see discussion with `ScopeTree`. |
| /// |
| /// `Remainder { block, statement_index }` represents |
| /// the scope of user code running immediately after the initializer |
| /// expression for the indexed statement, until the end of the block. |
| /// |
| /// So: the following code can be broken down into the scopes beneath: |
| /// |
| /// ```text |
| /// let a = f().g( 'b: { let x = d(); let y = d(); x.h(y) } ) ; |
| /// |
| /// +-+ (D12.) |
| /// +-+ (D11.) |
| /// +---------+ (R10.) |
| /// +-+ (D9.) |
| /// +----------+ (M8.) |
| /// +----------------------+ (R7.) |
| /// +-+ (D6.) |
| /// +----------+ (M5.) |
| /// +-----------------------------------+ (M4.) |
| /// +--------------------------------------------------+ (M3.) |
| /// +--+ (M2.) |
| /// +-----------------------------------------------------------+ (M1.) |
| /// |
| /// (M1.): Node scope of the whole `let a = ...;` statement. |
| /// (M2.): Node scope of the `f()` expression. |
| /// (M3.): Node scope of the `f().g(..)` expression. |
| /// (M4.): Node scope of the block labeled `'b:`. |
| /// (M5.): Node scope of the `let x = d();` statement |
| /// (D6.): DestructionScope for temporaries created during M5. |
| /// (R7.): Remainder scope for block `'b:`, stmt 0 (let x = ...). |
| /// (M8.): Node scope of the `let y = d();` statement. |
| /// (D9.): DestructionScope for temporaries created during M8. |
| /// (R10.): Remainder scope for block `'b:`, stmt 1 (let y = ...). |
| /// (D11.): DestructionScope for temporaries and bindings from block `'b:`. |
| /// (D12.): DestructionScope for temporaries created during M1 (e.g., f()). |
| /// ``` |
| /// |
| /// Note that while the above picture shows the destruction scopes |
| /// as following their corresponding node scopes, in the internal |
| /// data structures of the compiler the destruction scopes are |
| /// represented as enclosing parents. This is sound because we use the |
| /// enclosing parent relationship just to ensure that referenced |
| /// values live long enough; phrased another way, the starting point |
| /// of each range is not really the important thing in the above |
| /// picture, but rather the ending point. |
| // |
| // FIXME(pnkfelix): this currently derives `PartialOrd` and `Ord` to |
| // placate the same deriving in `ty::LateParamRegion`, but we may want to |
| // actually attach a more meaningful ordering to scopes than the one |
| // generated via deriving here. |
| #[derive(Clone, PartialEq, PartialOrd, Eq, Ord, Hash, Copy, TyEncodable, TyDecodable)] |
| #[derive(HashStable)] |
| pub struct Scope { |
| pub local_id: hir::ItemLocalId, |
| pub data: ScopeData, |
| } |
| |
| impl fmt::Debug for Scope { |
| fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result { |
| match self.data { |
| ScopeData::Node => write!(fmt, "Node({:?})", self.local_id), |
| ScopeData::CallSite => write!(fmt, "CallSite({:?})", self.local_id), |
| ScopeData::Arguments => write!(fmt, "Arguments({:?})", self.local_id), |
| ScopeData::Destruction => write!(fmt, "Destruction({:?})", self.local_id), |
| ScopeData::IfThen => write!(fmt, "IfThen({:?})", self.local_id), |
| ScopeData::IfThenRescope => write!(fmt, "IfThen[edition2024]({:?})", self.local_id), |
| ScopeData::MatchGuard => write!(fmt, "MatchGuard({:?})", self.local_id), |
| ScopeData::Remainder(fsi) => write!( |
| fmt, |
| "Remainder {{ block: {:?}, first_statement_index: {}}}", |
| self.local_id, |
| fsi.as_u32(), |
| ), |
| } |
| } |
| } |
| |
| #[derive(Clone, PartialEq, PartialOrd, Eq, Ord, Hash, Debug, Copy, TyEncodable, TyDecodable)] |
| #[derive(HashStable)] |
| pub enum ScopeData { |
| Node, |
| |
| /// Scope of the call-site for a function or closure |
| /// (outlives the arguments as well as the body). |
| CallSite, |
| |
| /// Scope of arguments passed to a function or closure |
| /// (they outlive its body). |
| Arguments, |
| |
| /// Scope of destructors for temporaries of node-id. |
| Destruction, |
| |
| /// Scope of the condition and then block of an if expression |
| /// Used for variables introduced in an if-let expression. |
| IfThen, |
| |
| /// Scope of the condition and then block of an if expression |
| /// Used for variables introduced in an if-let expression, |
| /// whose lifetimes do not cross beyond this scope. |
| IfThenRescope, |
| |
| /// Scope of the condition and body of a match arm with a guard |
| /// Used for variables introduced in an if-let guard, |
| /// whose lifetimes do not cross beyond this scope. |
| MatchGuard, |
| |
| /// Scope following a `let id = expr;` binding in a block. |
| Remainder(FirstStatementIndex), |
| } |
| |
| rustc_index::newtype_index! { |
| /// Represents a subscope of `block` for a binding that is introduced |
| /// by `block.stmts[first_statement_index]`. Such subscopes represent |
| /// a suffix of the block. Note that each subscope does not include |
| /// the initializer expression, if any, for the statement indexed by |
| /// `first_statement_index`. |
| /// |
| /// For example, given `{ let (a, b) = EXPR_1; let c = EXPR_2; ... }`: |
| /// |
| /// * The subscope with `first_statement_index == 0` is scope of both |
| /// `a` and `b`; it does not include EXPR_1, but does include |
| /// everything after that first `let`. (If you want a scope that |
| /// includes EXPR_1 as well, then do not use `Scope::Remainder`, |
| /// but instead another `Scope` that encompasses the whole block, |
| /// e.g., `Scope::Node`. |
| /// |
| /// * The subscope with `first_statement_index == 1` is scope of `c`, |
| /// and thus does not include EXPR_2, but covers the `...`. |
| #[derive(HashStable)] |
| #[encodable] |
| #[orderable] |
| pub struct FirstStatementIndex {} |
| } |
| |
| // compilation error if size of `ScopeData` is not the same as a `u32` |
| rustc_data_structures::static_assert_size!(ScopeData, 4); |
| |
| impl Scope { |
| pub fn hir_id(&self, scope_tree: &ScopeTree) -> Option<HirId> { |
| scope_tree.root_body.map(|hir_id| HirId { owner: hir_id.owner, local_id: self.local_id }) |
| } |
| |
| /// Returns the span of this `Scope`. Note that in general the |
| /// returned span may not correspond to the span of any `NodeId` in |
| /// the AST. |
| pub fn span(&self, tcx: TyCtxt<'_>, scope_tree: &ScopeTree) -> Span { |
| let Some(hir_id) = self.hir_id(scope_tree) else { |
| return DUMMY_SP; |
| }; |
| let span = tcx.hir_span(hir_id); |
| if let ScopeData::Remainder(first_statement_index) = self.data |
| // Want span for scope starting after the |
| // indexed statement and ending at end of |
| // `blk`; reuse span of `blk` and shift `lo` |
| // forward to end of indexed statement. |
| // |
| // (This is the special case alluded to in the |
| // doc-comment for this method) |
| && let Node::Block(blk) = tcx.hir_node(hir_id) |
| { |
| let stmt_span = blk.stmts[first_statement_index.index()].span; |
| |
| // To avoid issues with macro-generated spans, the span |
| // of the statement must be nested in that of the block. |
| if span.lo() <= stmt_span.lo() && stmt_span.lo() <= span.hi() { |
| return span.with_lo(stmt_span.lo()); |
| } |
| } |
| span |
| } |
| } |
| |
| /// The region scope tree encodes information about region relationships. |
| #[derive(Default, Debug, HashStable)] |
| pub struct ScopeTree { |
| /// If not empty, this body is the root of this region hierarchy. |
| pub root_body: Option<HirId>, |
| |
| /// Maps from a scope ID to the enclosing scope id; |
| /// this is usually corresponding to the lexical nesting, though |
| /// in the case of closures the parent scope is the innermost |
| /// conditional expression or repeating block. (Note that the |
| /// enclosing scope ID for the block associated with a closure is |
| /// the closure itself.) |
| pub parent_map: FxIndexMap<Scope, Scope>, |
| |
| /// Maps from a variable or binding ID to the block in which that |
| /// variable is declared. |
| var_map: FxIndexMap<hir::ItemLocalId, Scope>, |
| |
| /// Identifies expressions which, if captured into a temporary, ought to |
| /// have a temporary whose lifetime extends to the end of the enclosing *block*, |
| /// and not the enclosing *statement*. Expressions that are not present in this |
| /// table are not rvalue candidates. The set of rvalue candidates is computed |
| /// during type check based on a traversal of the AST. |
| pub rvalue_candidates: HirIdMap<RvalueCandidate>, |
| |
| /// Backwards incompatible scoping that will be introduced in future editions. |
| /// This information is used later for linting to identify locals and |
| /// temporary values that will receive backwards-incompatible drop orders. |
| pub backwards_incompatible_scope: UnordMap<hir::ItemLocalId, Scope>, |
| } |
| |
| /// See the `rvalue_candidates` field for more information on rvalue |
| /// candidates in general. |
| /// The `lifetime` field is None to indicate that certain expressions escape |
| /// into 'static and should have no local cleanup scope. |
| #[derive(Debug, Copy, Clone, HashStable)] |
| pub struct RvalueCandidate { |
| pub target: hir::ItemLocalId, |
| pub lifetime: Option<Scope>, |
| } |
| |
| impl ScopeTree { |
| pub fn record_scope_parent(&mut self, child: Scope, parent: Option<Scope>) { |
| debug!("{:?}.parent = {:?}", child, parent); |
| |
| if let Some(p) = parent { |
| let prev = self.parent_map.insert(child, p); |
| assert!(prev.is_none()); |
| } |
| } |
| |
| pub fn record_var_scope(&mut self, var: hir::ItemLocalId, lifetime: Scope) { |
| debug!("record_var_scope(sub={:?}, sup={:?})", var, lifetime); |
| assert!(var != lifetime.local_id); |
| self.var_map.insert(var, lifetime); |
| } |
| |
| pub fn record_rvalue_candidate(&mut self, var: HirId, candidate: RvalueCandidate) { |
| debug!("record_rvalue_candidate(var={var:?}, candidate={candidate:?})"); |
| if let Some(lifetime) = &candidate.lifetime { |
| assert!(var.local_id != lifetime.local_id) |
| } |
| self.rvalue_candidates.insert(var, candidate); |
| } |
| |
| /// Returns the narrowest scope that encloses `id`, if any. |
| pub fn opt_encl_scope(&self, id: Scope) -> Option<Scope> { |
| self.parent_map.get(&id).cloned() |
| } |
| |
| /// Returns the lifetime of the local variable `var_id`, if any. |
| pub fn var_scope(&self, var_id: hir::ItemLocalId) -> Option<Scope> { |
| self.var_map.get(&var_id).cloned() |
| } |
| |
| /// Returns `true` if `subscope` is equal to or is lexically nested inside `superscope`, and |
| /// `false` otherwise. |
| /// |
| /// Used by clippy. |
| pub fn is_subscope_of(&self, subscope: Scope, superscope: Scope) -> bool { |
| let mut s = subscope; |
| debug!("is_subscope_of({:?}, {:?})", subscope, superscope); |
| while superscope != s { |
| match self.opt_encl_scope(s) { |
| None => { |
| debug!("is_subscope_of({:?}, {:?}, s={:?})=false", subscope, superscope, s); |
| return false; |
| } |
| Some(scope) => s = scope, |
| } |
| } |
| |
| debug!("is_subscope_of({:?}, {:?})=true", subscope, superscope); |
| |
| true |
| } |
| |
| /// Returns the scope of non-lifetime-extended temporaries within a given scope, as well as |
| /// whether we've recorded a potential backwards-incompatible change to lint on. |
| /// Panics if no enclosing temporary scope is found. |
| pub fn default_temporary_scope(&self, inner: Scope) -> (Scope, Option<Scope>) { |
| let mut id = inner; |
| let mut backwards_incompatible = None; |
| |
| while let Some(&p) = self.parent_map.get(&id) { |
| match p.data { |
| ScopeData::Destruction => { |
| debug!("temporary_scope({inner:?}) = {id:?} [enclosing]"); |
| return (id, backwards_incompatible); |
| } |
| ScopeData::IfThenRescope | ScopeData::MatchGuard => { |
| debug!("temporary_scope({inner:?}) = {p:?} [enclosing]"); |
| return (p, backwards_incompatible); |
| } |
| ScopeData::Node |
| | ScopeData::CallSite |
| | ScopeData::Arguments |
| | ScopeData::IfThen |
| | ScopeData::Remainder(_) => { |
| // If we haven't already passed through a backwards-incompatible node, |
| // then check if we are passing through one now and record it if so. |
| // This is for now only working for cases where a temporary lifetime is |
| // *shortened*. |
| if backwards_incompatible.is_none() { |
| backwards_incompatible = |
| self.backwards_incompatible_scope.get(&p.local_id).copied(); |
| } |
| id = p |
| } |
| } |
| } |
| |
| span_bug!(ty::tls::with(|tcx| inner.span(tcx, self)), "no enclosing temporary scope") |
| } |
| } |
