lower let-else in MIR instead

GuillaumeGomez · Jul 11, 2022 · 6c529de · 6c529de
1 parent 38b7215
commit 6c529de
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Showing 71 changed files with 421 additions and 264 deletions.
diff --git a/compiler/rustc_ast_lowering/src/block.rs b/compiler/rustc_ast_lowering/src/block.rs
@@ -1,8 +1,8 @@
 use crate::{ImplTraitContext, ImplTraitPosition, LoweringContext};
-use rustc_ast::{AttrVec, Block, BlockCheckMode, Expr, Local, LocalKind, Stmt, StmtKind};
+use rustc_ast::{Block, BlockCheckMode, Local, LocalKind, Stmt, StmtKind};
 use rustc_hir as hir;
 use rustc_session::parse::feature_err;
-use rustc_span::{sym, DesugaringKind};
+use rustc_span::sym;
 
 use smallvec::SmallVec;
 
@@ -36,21 +36,25 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
             match s.kind {
                 StmtKind::Local(ref local) => {
                     let hir_id = self.lower_node_id(s.id);
-                    match &local.kind {
-                        LocalKind::InitElse(init, els) => {
-                            let e = self.lower_let_else(hir_id, local, init, els, tail);
-                            expr = Some(e);
-                            // remaining statements are in let-else expression
-                            break;
+                    let els = if let LocalKind::InitElse(_, els) = &local.kind {
+                        if !self.tcx.features().let_else {
+                            feature_err(
+                                &self.tcx.sess.parse_sess,
+                                sym::let_else,
+                                s.span,
+                                "`let...else` statements are unstable",
+                            )
+                            .emit();
                         }
-                        _ => {
-                            let local = self.lower_local(local);
-                            self.alias_attrs(hir_id, local.hir_id);
-                            let kind = hir::StmtKind::Local(local);
-                            let span = self.lower_span(s.span);
-                            stmts.push(hir::Stmt { hir_id, kind, span });
-                        }
-                    }
+                        Some(self.lower_block(els, false))
+                    } else {
+                        None
+                    };
+                    let local = self.lower_local(local);
+                    self.alias_attrs(hir_id, local.hir_id);
+                    let kind = hir::StmtKind::Local(local, els);
+                    let span = self.lower_span(s.span);
+                    stmts.push(hir::Stmt { hir_id, kind, span });
                 }
                 StmtKind::Item(ref it) => {
                     stmts.extend(self.lower_item_ref(it).into_iter().enumerate().map(
@@ -115,59 +119,4 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
             }
         }
     }
-
-    fn lower_let_else(
-        &mut self,
-        stmt_hir_id: hir::HirId,
-        local: &Local,
-        init: &Expr,
-        els: &Block,
-        tail: &[Stmt],
-    ) -> &'hir hir::Expr<'hir> {
-        let ty = local
-            .ty
-            .as_ref()
-            .map(|t| self.lower_ty(t, ImplTraitContext::Disallowed(ImplTraitPosition::Variable)));
-        let span = self.lower_span(local.span);
-        let span = self.mark_span_with_reason(DesugaringKind::LetElse, span, None);
-        let init = self.lower_expr(init);
-        let local_hir_id = self.lower_node_id(local.id);
-        self.lower_attrs(local_hir_id, &local.attrs);
-        let let_expr = {
-            let lex = self.arena.alloc(hir::Let {
-                hir_id: local_hir_id,
-                pat: self.lower_pat(&local.pat),
-                ty,
-                init,
-                span,
-            });
-            self.arena.alloc(self.expr(span, hir::ExprKind::Let(lex), AttrVec::new()))
-        };
-        let then_expr = {
-            let (stmts, expr) = self.lower_stmts(tail);
-            let block = self.block_all(span, stmts, expr);
-            self.arena.alloc(self.expr_block(block, AttrVec::new()))
-        };
-        let else_expr = {
-            let block = self.lower_block(els, false);
-            self.arena.alloc(self.expr_block(block, AttrVec::new()))
-        };
-        self.alias_attrs(let_expr.hir_id, local_hir_id);
-        self.alias_attrs(else_expr.hir_id, local_hir_id);
-        let if_expr = self.arena.alloc(hir::Expr {
-            hir_id: stmt_hir_id,
-            span,
-            kind: hir::ExprKind::If(let_expr, then_expr, Some(else_expr)),
-        });
-        if !self.tcx.features().let_else {
-            feature_err(
-                &self.tcx.sess.parse_sess,
-                sym::let_else,
-                local.span,
-                "`let...else` statements are unstable",
-            )
-            .emit();
-        }
-        if_expr
-    }
 }
diff --git a/compiler/rustc_ast_lowering/src/index.rs b/compiler/rustc_ast_lowering/src/index.rs
@@ -284,10 +284,10 @@ impl<'a, 'hir> Visitor<'hir> for NodeCollector<'a, 'hir> {
         });
     }
 
-    fn visit_local(&mut self, l: &'hir Local<'hir>) {
+    fn visit_local(&mut self, l: &'hir Local<'hir>, e: Option<&'hir Block<'hir>>) {
         self.insert(l.span, l.hir_id, Node::Local(l));
         self.with_parent(l.hir_id, |this| {
-            intravisit::walk_local(this, l);
+            intravisit::walk_local(this, l, e);
         })
     }
 

diff --git a/compiler/rustc_ast_lowering/src/lib.rs b/compiler/rustc_ast_lowering/src/lib.rs
@@ -2147,7 +2147,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
             self.attrs.insert(hir_id.local_id, a);
         }
         let local = hir::Local { hir_id, init, pat, source, span: self.lower_span(span), ty: None };
-        self.stmt(span, hir::StmtKind::Local(self.arena.alloc(local)))
+        self.stmt(span, hir::StmtKind::Local(self.arena.alloc(local), None))
     }
 
     fn block_expr(&mut self, expr: &'hir hir::Expr<'hir>) -> &'hir hir::Block<'hir> {

diff --git a/compiler/rustc_hir/src/hir.rs b/compiler/rustc_hir/src/hir.rs
@@ -1296,7 +1296,8 @@ pub struct Stmt<'hir> {
 #[derive(Debug, HashStable_Generic)]
 pub enum StmtKind<'hir> {
     /// A local (`let`) binding.
-    Local(&'hir Local<'hir>),
+    /// FIXME: bundle the last two components into another `struct`
+    Local(&'hir Local<'hir>, Option<&'hir Block<'hir>>),
 
     /// An item binding.
     Item(ItemId),

diff --git a/compiler/rustc_hir/src/intravisit.rs b/compiler/rustc_hir/src/intravisit.rs
@@ -310,8 +310,8 @@ pub trait Visitor<'v>: Sized {
     fn visit_foreign_item(&mut self, i: &'v ForeignItem<'v>) {
         walk_foreign_item(self, i)
     }
-    fn visit_local(&mut self, l: &'v Local<'v>) {
-        walk_local(self, l)
+    fn visit_local(&mut self, l: &'v Local<'v>, els: Option<&'v Block<'v>>) {
+        walk_local(self, l, els)
     }
     fn visit_block(&mut self, b: &'v Block<'v>) {
         walk_block(self, b)
@@ -466,12 +466,19 @@ pub fn walk_body<'v, V: Visitor<'v>>(visitor: &mut V, body: &'v Body<'v>) {
     visitor.visit_expr(&body.value);
 }
 
-pub fn walk_local<'v, V: Visitor<'v>>(visitor: &mut V, local: &'v Local<'v>) {
+pub fn walk_local<'v, V: Visitor<'v>>(
+    visitor: &mut V,
+    local: &'v Local<'v>,
+    els: Option<&'v Block<'v>>,
+) {
     // Intentionally visiting the expr first - the initialization expr
     // dominates the local's definition.
     walk_list!(visitor, visit_expr, &local.init);
     visitor.visit_id(local.hir_id);
     visitor.visit_pat(&local.pat);
+    if let Some(els) = els {
+        visitor.visit_block(els);
+    }
     walk_list!(visitor, visit_ty, &local.ty);
 }
 
@@ -1055,9 +1062,9 @@ pub fn walk_block<'v, V: Visitor<'v>>(visitor: &mut V, block: &'v Block<'v>) {
 
 pub fn walk_stmt<'v, V: Visitor<'v>>(visitor: &mut V, statement: &'v Stmt<'v>) {
     visitor.visit_id(statement.hir_id);
-    match statement.kind {
-        StmtKind::Local(ref local) => visitor.visit_local(local),
-        StmtKind::Item(item) => visitor.visit_nested_item(item),
+    match &statement.kind {
+        StmtKind::Local(ref local, els) => visitor.visit_local(local, *els),
+        StmtKind::Item(item) => visitor.visit_nested_item(*item),
         StmtKind::Expr(ref expression) | StmtKind::Semi(ref expression) => {
             visitor.visit_expr(expression)
         }

diff --git a/compiler/rustc_hir_pretty/src/lib.rs b/compiler/rustc_hir_pretty/src/lib.rs
@@ -883,7 +883,12 @@ impl<'a> State<'a> {
         self.ann.post(self, AnnNode::SubItem(ii.hir_id()))
     }
 
-    pub fn print_local(&mut self, init: Option<&hir::Expr<'_>>, decl: impl Fn(&mut Self)) {
+    pub fn print_local(
+        &mut self,
+        init: Option<&hir::Expr<'_>>,
+        els: Option<&hir::Block<'_>>,
+        decl: impl Fn(&mut Self),
+    ) {
         self.space_if_not_bol();
         self.ibox(INDENT_UNIT);
         self.word_nbsp("let");
@@ -897,14 +902,21 @@ impl<'a> State<'a> {
             self.word_space("=");
             self.print_expr(init);
         }
+
+        if let Some(els) = els {
+            self.nbsp();
+            self.word_space("else");
+            self.print_block(els);
+        }
+
         self.end()
     }
 
     pub fn print_stmt(&mut self, st: &hir::Stmt<'_>) {
         self.maybe_print_comment(st.span.lo());
         match st.kind {
-            hir::StmtKind::Local(loc) => {
-                self.print_local(loc.init, |this| this.print_local_decl(loc));
+            hir::StmtKind::Local(loc, els) => {
+                self.print_local(loc.init, els, |this| this.print_local_decl(loc));
             }
             hir::StmtKind::Item(item) => self.ann.nested(self, Nested::Item(item)),
             hir::StmtKind::Expr(expr) => {
@@ -1404,7 +1416,7 @@ impl<'a> State<'a> {
 
                 // Print `let _t = $init;`:
                 let temp = Ident::from_str("_t");
-                self.print_local(Some(init), |this| this.print_ident(temp));
+                self.print_local(Some(init), None, |this| this.print_ident(temp));
                 self.word(";");
 
                 // Print `_t`:
@@ -2293,7 +2305,7 @@ fn expr_requires_semi_to_be_stmt(e: &hir::Expr<'_>) -> bool {
 /// seen the semicolon, and thus don't need another.
 fn stmt_ends_with_semi(stmt: &hir::StmtKind<'_>) -> bool {
     match *stmt {
-        hir::StmtKind::Local(_) => true,
+        hir::StmtKind::Local(_, _) => true,
         hir::StmtKind::Item(_) => false,
         hir::StmtKind::Expr(e) => expr_requires_semi_to_be_stmt(e),
         hir::StmtKind::Semi(..) => false,

diff --git a/compiler/rustc_infer/src/infer/error_reporting/need_type_info.rs b/compiler/rustc_infer/src/infer/error_reporting/need_type_info.rs
@@ -1,12 +1,13 @@
 use crate::infer::type_variable::TypeVariableOriginKind;
 use crate::infer::InferCtxt;
+use hir::{Block, LocalSource};
 use rustc_errors::{pluralize, struct_span_err, Applicability, DiagnosticBuilder, ErrorGuaranteed};
 use rustc_hir as hir;
 use rustc_hir::def::Res;
 use rustc_hir::def::{CtorOf, DefKind, Namespace};
 use rustc_hir::def_id::DefId;
 use rustc_hir::intravisit::{self, Visitor};
-use rustc_hir::{Body, Expr, ExprKind, FnRetTy, HirId, Local, LocalSource};
+use rustc_hir::{Body, Expr, ExprKind, FnRetTy, HirId, Local};
 use rustc_middle::hir::nested_filter;
 use rustc_middle::infer::unify_key::ConstVariableOriginKind;
 use rustc_middle::ty::adjustment::{Adjust, Adjustment, AutoBorrow, AutoBorrowMutability};
@@ -952,8 +953,8 @@ impl<'a, 'tcx> Visitor<'tcx> for FindInferSourceVisitor<'a, 'tcx> {
         self.infcx.tcx.hir()
     }
 
-    fn visit_local(&mut self, local: &'tcx Local<'tcx>) {
-        intravisit::walk_local(self, local);
+    fn visit_local(&mut self, local: &'tcx Local<'tcx>, els: Option<&'tcx Block<'tcx>>) {
+        intravisit::walk_local(self, local, els);
 
         if let Some(ty) = self.opt_node_type(local.hir_id) {
             if self.generic_arg_contains_target(ty.into()) {

diff --git a/compiler/rustc_lint/src/late.rs b/compiler/rustc_lint/src/late.rs
@@ -251,10 +251,10 @@ impl<'tcx, T: LateLintPass<'tcx>> hir_visit::Visitor<'tcx> for LateContextAndPas
         }
     }
 
-    fn visit_local(&mut self, l: &'tcx hir::Local<'tcx>) {
+    fn visit_local(&mut self, l: &'tcx hir::Local<'tcx>, e: Option<&'tcx hir::Block<'tcx>>) {
         self.with_lint_attrs(l.hir_id, |cx| {
-            lint_callback!(cx, check_local, l);
-            hir_visit::walk_local(cx, l);
+            lint_callback!(cx, check_local, l, e);
+            hir_visit::walk_local(cx, l, e);
         })
     }
 

diff --git a/compiler/rustc_lint/src/levels.rs b/compiler/rustc_lint/src/levels.rs
@@ -783,9 +783,9 @@ impl<'tcx> intravisit::Visitor<'tcx> for LintLevelMapBuilder<'tcx> {
         })
     }
 
-    fn visit_local(&mut self, l: &'tcx hir::Local<'tcx>) {
+    fn visit_local(&mut self, l: &'tcx hir::Local<'tcx>, e: Option<&'tcx hir::Block<'tcx>>) {
         self.with_lint_attrs(l.hir_id, |builder| {
-            intravisit::walk_local(builder, l);
+            intravisit::walk_local(builder, l, e);
         })
     }
 

diff --git a/compiler/rustc_lint/src/passes.rs b/compiler/rustc_lint/src/passes.rs
@@ -24,7 +24,7 @@ macro_rules! late_lint_methods {
             fn check_foreign_item_post(a: &$hir hir::ForeignItem<$hir>);
             fn check_item(a: &$hir hir::Item<$hir>);
             fn check_item_post(a: &$hir hir::Item<$hir>);
-            fn check_local(a: &$hir hir::Local<$hir>);
+            fn check_local(a: &$hir hir::Local<$hir>, b: Option<&$hir hir::Block<$hir>>);
             fn check_block(a: &$hir hir::Block<$hir>);
             fn check_block_post(a: &$hir hir::Block<$hir>);
             fn check_stmt(a: &$hir hir::Stmt<$hir>);

diff --git a/compiler/rustc_middle/src/hir/map/mod.rs b/compiler/rustc_middle/src/hir/map/mod.rs
@@ -789,7 +789,7 @@ impl<'hir> Map<'hir> {
                 | Node::ForeignItem(_)
                 | Node::TraitItem(_)
                 | Node::ImplItem(_)
-                | Node::Stmt(Stmt { kind: StmtKind::Local(_), .. }) => break,
+                | Node::Stmt(Stmt { kind: StmtKind::Local(_, _), .. }) => break,
                 Node::Expr(expr @ Expr { kind: ExprKind::If(..) | ExprKind::Match(..), .. }) => {
                     return Some(expr);
                 }

diff --git a/compiler/rustc_middle/src/thir.rs b/compiler/rustc_middle/src/thir.rs
@@ -182,6 +182,9 @@ pub enum StmtKind<'tcx> {
         /// `let pat: ty = <INIT>`
         initializer: Option<ExprId>,
 
+        /// `let pat: ty = <INIT> else { <ELSE> }
+        else_block: Option<Block>,
+
         /// The lint level for this `let` statement.
         lint_level: LintLevel,
     },

diff --git a/compiler/rustc_middle/src/thir/visit.rs b/compiler/rustc_middle/src/thir/visit.rs
@@ -167,11 +167,15 @@ pub fn walk_stmt<'a, 'tcx: 'a, V: Visitor<'a, 'tcx>>(visitor: &mut V, stmt: &Stm
             init_scope: _,
             ref pattern,
             lint_level: _,
+            else_block,
         } => {
             if let Some(init) = initializer {
                 visitor.visit_expr(&visitor.thir()[*init]);
             }
             visitor.visit_pat(pattern);
+            if let Some(block) = else_block {
+                visitor.visit_block(block)
+            }
         }
     }
 }

diff --git a/compiler/rustc_mir_build/src/build/block.rs b/compiler/rustc_mir_build/src/build/block.rs
@@ -99,6 +99,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                     ref pattern,
                     initializer,
                     lint_level,
+                    else_block,
                 } => {
                     let ignores_expr_result = matches!(*pattern.kind, PatKind::Wild);
                     this.block_context.push(BlockFrame::Statement { ignores_expr_result });
@@ -124,18 +125,30 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                                 |this| {
                                     let scope = (*init_scope, source_info);
                                     this.in_scope(scope, *lint_level, |this| {
-                                        this.declare_bindings(
-                                            visibility_scope,
-                                            remainder_span,
-                                            pattern,
-                                            ArmHasGuard(false),
-                                            Some((None, initializer_span)),
-                                        );
-                                        this.expr_into_pattern(block, pattern.clone(), init)
+                                        if let Some(else_block) = else_block {
+                                            this.ast_let_else(
+                                                block,
+                                                init,
+                                                initializer_span,
+                                                else_block,
+                                                visibility_scope,
+                                                remainder_span,
+                                                pattern,
+                                            )
+                                        } else {
+                                            this.declare_bindings(
+                                                visibility_scope,
+                                                remainder_span,
+                                                pattern,
+                                                ArmHasGuard(false),
+                                                Some((None, initializer_span)),
+                                            );
+                                            this.expr_into_pattern(block, pattern.clone(), init) // irrefutable pattern
+                                        }
                                     })
-                                }
+                                },
                             )
-                        );
+                        )
                     } else {
                         let scope = (*init_scope, source_info);
                         unpack!(this.in_scope(scope, *lint_level, |this| {