use rustc_errors::struct_span_err;
use rustc_hir as hir;
use rustc_hir::def::Res;
+use rustc_session::parse::feature_err;
use rustc_span::hygiene::ForLoopLoc;
use rustc_span::source_map::{respan, DesugaringKind, Span, Spanned};
use rustc_span::symbol::{sym, Ident, Symbol};
hir::ExprKind::Block(self.lower_block(blk, opt_label.is_some()), opt_label)
}
ExprKind::Assign(ref el, ref er, span) => {
- hir::ExprKind::Assign(self.lower_expr(el), self.lower_expr(er), span)
+ self.lower_expr_assign(el, er, span, e.span)
}
ExprKind::AssignOp(op, ref el, ref er) => hir::ExprKind::AssignOp(
self.lower_binop(op),
ExprKind::Range(ref e1, ref e2, lims) => {
self.lower_expr_range(e.span, e1.as_deref(), e2.as_deref(), lims)
}
+ ExprKind::Underscore => {
+ self.sess
+ .struct_span_err(
+ e.span,
+ "in expressions, `_` can only be used on the left-hand side of an assignment",
+ )
+ .span_label(e.span, "`_` not allowed here")
+ .emit();
+ hir::ExprKind::Err
+ }
ExprKind::Path(ref qself, ref path) => {
let qpath = self.lower_qpath(
e.id,
}
ExprKind::InlineAsm(ref asm) => self.lower_expr_asm(e.span, asm),
ExprKind::LlvmInlineAsm(ref asm) => self.lower_expr_llvm_asm(asm),
- ExprKind::Struct(ref path, ref fields, ref maybe_expr) => {
- let maybe_expr = maybe_expr.as_ref().map(|x| self.lower_expr(x));
+ ExprKind::Struct(ref path, ref fields, ref rest) => {
+ let rest = match rest {
+ StructRest::Base(e) => Some(self.lower_expr(e)),
+ StructRest::Rest(sp) => {
+ self.sess
+ .struct_span_err(*sp, "base expression required after `..`")
+ .span_label(*sp, "add a base expression here")
+ .emit();
+ Some(&*self.arena.alloc(self.expr_err(*sp)))
+ }
+ StructRest::None => None,
+ };
hir::ExprKind::Struct(
self.arena.alloc(self.lower_qpath(
e.id,
ImplTraitContext::disallowed(),
)),
self.arena.alloc_from_iter(fields.iter().map(|x| self.lower_field(x))),
- maybe_expr,
+ rest,
)
}
ExprKind::Yield(ref opt_expr) => self.lower_expr_yield(e.span, opt_expr.as_deref()),
})
}
+ /// Destructure the LHS of complex assignments.
+ /// For instance, lower `(a, b) = t` to `{ let (lhs1, lhs2) = t; a = lhs1; b = lhs2; }`.
+ fn lower_expr_assign(
+ &mut self,
+ lhs: &Expr,
+ rhs: &Expr,
+ eq_sign_span: Span,
+ whole_span: Span,
+ ) -> hir::ExprKind<'hir> {
+ // Return early in case of an ordinary assignment.
+ fn is_ordinary(lower_ctx: &mut LoweringContext<'_, '_>, lhs: &Expr) -> bool {
+ match &lhs.kind {
+ ExprKind::Array(..)
+ | ExprKind::Struct(..)
+ | ExprKind::Tup(..)
+ | ExprKind::Underscore => false,
+ // Check for tuple struct constructor.
+ ExprKind::Call(callee, ..) => lower_ctx.extract_tuple_struct_path(callee).is_none(),
+ ExprKind::Paren(e) => {
+ match e.kind {
+ // We special-case `(..)` for consistency with patterns.
+ ExprKind::Range(None, None, RangeLimits::HalfOpen) => false,
+ _ => is_ordinary(lower_ctx, e),
+ }
+ }
+ _ => true,
+ }
+ }
+ if is_ordinary(self, lhs) {
+ return hir::ExprKind::Assign(self.lower_expr(lhs), self.lower_expr(rhs), eq_sign_span);
+ }
+ if !self.sess.features_untracked().destructuring_assignment {
+ feature_err(
+ &self.sess.parse_sess,
+ sym::destructuring_assignment,
+ eq_sign_span,
+ "destructuring assignments are unstable",
+ )
+ .span_label(lhs.span, "cannot assign to this expression")
+ .emit();
+ }
+
+ let mut assignments = vec![];
+
+ // The LHS becomes a pattern: `(lhs1, lhs2)`.
+ let pat = self.destructure_assign(lhs, eq_sign_span, &mut assignments);
+ let rhs = self.lower_expr(rhs);
+
+ // Introduce a `let` for destructuring: `let (lhs1, lhs2) = t`.
+ let destructure_let = self.stmt_let_pat(
+ ThinVec::new(),
+ whole_span,
+ Some(rhs),
+ pat,
+ hir::LocalSource::AssignDesugar(eq_sign_span),
+ );
+
+ // `a = lhs1; b = lhs2;`.
+ let stmts = self
+ .arena
+ .alloc_from_iter(std::iter::once(destructure_let).chain(assignments.into_iter()));
+
+ // Wrap everything in a block.
+ hir::ExprKind::Block(&self.block_all(whole_span, stmts, None), None)
+ }
+
+ /// If the given expression is a path to a tuple struct, returns that path.
+ /// It is not a complete check, but just tries to reject most paths early
+ /// if they are not tuple structs.
+ /// Type checking will take care of the full validation later.
+ fn extract_tuple_struct_path<'a>(&mut self, expr: &'a Expr) -> Option<&'a Path> {
+ // For tuple struct destructuring, it must be a non-qualified path (like in patterns).
+ if let ExprKind::Path(None, path) = &expr.kind {
+ // Does the path resolves to something disallowed in a tuple struct/variant pattern?
+ if let Some(partial_res) = self.resolver.get_partial_res(expr.id) {
+ if partial_res.unresolved_segments() == 0
+ && !partial_res.base_res().expected_in_tuple_struct_pat()
+ {
+ return None;
+ }
+ }
+ return Some(path);
+ }
+ None
+ }
+
+ /// Convert the LHS of a destructuring assignment to a pattern.
+ /// Each sub-assignment is recorded in `assignments`.
+ fn destructure_assign(
+ &mut self,
+ lhs: &Expr,
+ eq_sign_span: Span,
+ assignments: &mut Vec<hir::Stmt<'hir>>,
+ ) -> &'hir hir::Pat<'hir> {
+ match &lhs.kind {
+ // Underscore pattern.
+ ExprKind::Underscore => {
+ return self.pat_without_dbm(lhs.span, hir::PatKind::Wild);
+ }
+ // Slice patterns.
+ ExprKind::Array(elements) => {
+ let (pats, rest) =
+ self.destructure_sequence(elements, "slice", eq_sign_span, assignments);
+ let slice_pat = if let Some((i, span)) = rest {
+ let (before, after) = pats.split_at(i);
+ hir::PatKind::Slice(
+ before,
+ Some(self.pat_without_dbm(span, hir::PatKind::Wild)),
+ after,
+ )
+ } else {
+ hir::PatKind::Slice(pats, None, &[])
+ };
+ return self.pat_without_dbm(lhs.span, slice_pat);
+ }
+ // Tuple structs.
+ ExprKind::Call(callee, args) => {
+ if let Some(path) = self.extract_tuple_struct_path(callee) {
+ let (pats, rest) = self.destructure_sequence(
+ args,
+ "tuple struct or variant",
+ eq_sign_span,
+ assignments,
+ );
+ let qpath = self.lower_qpath(
+ callee.id,
+ &None,
+ path,
+ ParamMode::Optional,
+ ImplTraitContext::disallowed(),
+ );
+ // Destructure like a tuple struct.
+ let tuple_struct_pat =
+ hir::PatKind::TupleStruct(qpath, pats, rest.map(|r| r.0));
+ return self.pat_without_dbm(lhs.span, tuple_struct_pat);
+ }
+ }
+ // Structs.
+ ExprKind::Struct(path, fields, rest) => {
+ let field_pats = self.arena.alloc_from_iter(fields.iter().map(|f| {
+ let pat = self.destructure_assign(&f.expr, eq_sign_span, assignments);
+ hir::FieldPat {
+ hir_id: self.next_id(),
+ ident: f.ident,
+ pat,
+ is_shorthand: f.is_shorthand,
+ span: f.span,
+ }
+ }));
+ let qpath = self.lower_qpath(
+ lhs.id,
+ &None,
+ path,
+ ParamMode::Optional,
+ ImplTraitContext::disallowed(),
+ );
+ let fields_omitted = match rest {
+ StructRest::Base(e) => {
+ self.sess
+ .struct_span_err(
+ e.span,
+ "functional record updates are not allowed in destructuring \
+ assignments",
+ )
+ .span_suggestion(
+ e.span,
+ "consider removing the trailing pattern",
+ String::new(),
+ rustc_errors::Applicability::MachineApplicable,
+ )
+ .emit();
+ true
+ }
+ StructRest::Rest(_) => true,
+ StructRest::None => false,
+ };
+ let struct_pat = hir::PatKind::Struct(qpath, field_pats, fields_omitted);
+ return self.pat_without_dbm(lhs.span, struct_pat);
+ }
+ // Tuples.
+ ExprKind::Tup(elements) => {
+ let (pats, rest) =
+ self.destructure_sequence(elements, "tuple", eq_sign_span, assignments);
+ let tuple_pat = hir::PatKind::Tuple(pats, rest.map(|r| r.0));
+ return self.pat_without_dbm(lhs.span, tuple_pat);
+ }
+ ExprKind::Paren(e) => {
+ // We special-case `(..)` for consistency with patterns.
+ if let ExprKind::Range(None, None, RangeLimits::HalfOpen) = e.kind {
+ let tuple_pat = hir::PatKind::Tuple(&[], Some(0));
+ return self.pat_without_dbm(lhs.span, tuple_pat);
+ } else {
+ return self.destructure_assign(e, eq_sign_span, assignments);
+ }
+ }
+ _ => {}
+ }
+ // Treat all other cases as normal lvalue.
+ let ident = Ident::new(sym::lhs, lhs.span);
+ let (pat, binding) = self.pat_ident(lhs.span, ident);
+ let ident = self.expr_ident(lhs.span, ident, binding);
+ let assign = hir::ExprKind::Assign(self.lower_expr(lhs), ident, eq_sign_span);
+ let expr = self.expr(lhs.span, assign, ThinVec::new());
+ assignments.push(self.stmt_expr(lhs.span, expr));
+ pat
+ }
+
+ /// Destructure a sequence of expressions occurring on the LHS of an assignment.
+ /// Such a sequence occurs in a tuple (struct)/slice.
+ /// Return a sequence of corresponding patterns, and the index and the span of `..` if it
+ /// exists.
+ /// Each sub-assignment is recorded in `assignments`.
+ fn destructure_sequence(
+ &mut self,
+ elements: &[AstP<Expr>],
+ ctx: &str,
+ eq_sign_span: Span,
+ assignments: &mut Vec<hir::Stmt<'hir>>,
+ ) -> (&'hir [&'hir hir::Pat<'hir>], Option<(usize, Span)>) {
+ let mut rest = None;
+ let elements =
+ self.arena.alloc_from_iter(elements.iter().enumerate().filter_map(|(i, e)| {
+ // Check for `..` pattern.
+ if let ExprKind::Range(None, None, RangeLimits::HalfOpen) = e.kind {
+ if let Some((_, prev_span)) = rest {
+ self.ban_extra_rest_pat(e.span, prev_span, ctx);
+ } else {
+ rest = Some((i, e.span));
+ }
+ None
+ } else {
+ Some(self.destructure_assign(e, eq_sign_span, assignments))
+ }
+ }));
+ (elements, rest)
+ }
+
/// Desugar `<start>..=<end>` into `std::ops::RangeInclusive::new(<start>, <end>)`.
fn lower_expr_range_closed(&mut self, span: Span, e1: &Expr, e2: &Expr) -> hir::ExprKind<'hir> {
let e1 = self.lower_expr_mut(e1);
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