Auto merge of rust-lang#42396 - venkatagiri:remove_lifetime_extn, r=arielb1

rustc: remove temporary lifetime extension by borrow hint

closes rust-lang#39283.

Thanks to @nikomatsakis for mentoring on this one.

r? @arielb1

Author: bors

src/librustc/middle/expr_use_visitor.rs

@@ -303,7 +303,6 @@ impl<'a, 'gcx, 'tcx> ExprUseVisitor<'a, 'gcx, 'tcx> {
                 arg.id,
                 arg.pat.span,
                 fn_body_scope_r, // Args live only as long as the fn body.
-                fn_body_scope_r,
                 arg_ty);
 
             self.walk_irrefutable_pat(arg_cmt, &arg.pat);

src/librustc/middle/mem_categorization.rs

@@ -88,8 +88,7 @@ use std::rc::Rc;
 
 #[derive(Clone, PartialEq)]
 pub enum Categorization<'tcx> {
-    // temporary val, argument is its scope
-    Rvalue(ty::Region<'tcx>, ty::Region<'tcx>),
+    Rvalue(ty::Region<'tcx>),              // temporary val, argument is its scope
     StaticItem,
     Upvar(Upvar),                          // upvar referenced by closure env
     Local(ast::NodeId),                    // local variable
@@ -827,18 +826,13 @@ impl<'a, 'gcx, 'tcx> MemCategorizationContext<'a, 'gcx, 'tcx> {
 
     /// Returns the lifetime of a temporary created by expr with id `id`.
     /// This could be `'static` if `id` is part of a constant expression.
-    pub fn temporary_scope(&self, id: ast::NodeId) -> (ty::Region<'tcx>, ty::Region<'tcx>)
+    pub fn temporary_scope(&self, id: ast::NodeId) -> ty::Region<'tcx>
     {
-        let (scope, old_scope) =
-            self.region_maps.old_and_new_temporary_scope(id);
-        (self.tcx().mk_region(match scope {
+        let scope = self.region_maps.temporary_scope(id);
+        self.tcx().mk_region(match scope {
             Some(scope) => ty::ReScope(scope),
             None => ty::ReStatic
-        }),
-         self.tcx().mk_region(match old_scope {
-            Some(scope) => ty::ReScope(scope),
-            None => ty::ReStatic
-        }))
+        })
     }
 
     pub fn cat_rvalue_node(&self,
@@ -858,13 +852,12 @@ impl<'a, 'gcx, 'tcx> MemCategorizationContext<'a, 'gcx, 'tcx> {
         // Compute maximum lifetime of this rvalue. This is 'static if
         // we can promote to a constant, otherwise equal to enclosing temp
         // lifetime.
-        let (re, old_re) = if promotable {
-            (self.tcx().types.re_static,
-             self.tcx().types.re_static)
+        let re = if promotable {
+            self.tcx().types.re_static
         } else {
             self.temporary_scope(id)
         };
-        let ret = self.cat_rvalue(id, span, re, old_re, expr_ty);
+        let ret = self.cat_rvalue(id, span, re, expr_ty);
         debug!("cat_rvalue_node ret {:?}", ret);
         ret
     }
@@ -873,12 +866,11 @@ impl<'a, 'gcx, 'tcx> MemCategorizationContext<'a, 'gcx, 'tcx> {
                       cmt_id: ast::NodeId,
                       span: Span,
                       temp_scope: ty::Region<'tcx>,
-                      old_temp_scope: ty::Region<'tcx>,
                       expr_ty: Ty<'tcx>) -> cmt<'tcx> {
         let ret = Rc::new(cmt_ {
             id:cmt_id,
             span:span,
-            cat:Categorization::Rvalue(temp_scope, old_temp_scope),
+            cat:Categorization::Rvalue(temp_scope),
             mutbl:McDeclared,
             ty:expr_ty,
             note: NoteNone
@@ -1415,9 +1407,7 @@ impl<'tcx> fmt::Debug for Categorization<'tcx> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         match *self {
             Categorization::StaticItem => write!(f, "static"),
-            Categorization::Rvalue(r, or) => {
-                write!(f, "rvalue({:?}, {:?})", r, or)
-            }
+            Categorization::Rvalue(r) => { write!(f, "rvalue({:?})", r) }
             Categorization::Local(id) => {
                let name = ty::tls::with(|tcx| tcx.local_var_name_str(id));
                write!(f, "local({})", name)

src/librustc/middle/region.rs

@@ -223,13 +223,6 @@ pub struct RegionMaps {
     /// block (see `terminating_scopes`).
     rvalue_scopes: NodeMap<CodeExtent>,
 
-    /// Records the value of rvalue scopes before they were shrunk by
-    /// #36082, for error reporting.
-    ///
-    /// FIXME: this should be temporary. Remove this by 1.18.0 or
-    /// so.
-    shrunk_rvalue_scopes: NodeMap<CodeExtent>,
-
     /// Encodes the hierarchy of fn bodies. Every fn body (including
     /// closures) forms its own distinct region hierarchy, rooted in
     /// the block that is the fn body. This map points from the id of
@@ -301,7 +294,6 @@ impl<'tcx> RegionMaps {
             destruction_scopes: FxHashMap(),
             var_map: NodeMap(),
             rvalue_scopes: NodeMap(),
-            shrunk_rvalue_scopes: NodeMap(),
             fn_tree: NodeMap(),
         }
     }
@@ -370,12 +362,6 @@ impl<'tcx> RegionMaps {
         self.rvalue_scopes.insert(var, lifetime);
     }
 
-    fn record_shrunk_rvalue_scope(&mut self, var: ast::NodeId, lifetime: CodeExtent) {
-        debug!("record_rvalue_scope(sub={:?}, sup={:?})", var, lifetime);
-        assert!(var != lifetime.node_id());
-        self.shrunk_rvalue_scopes.insert(var, lifetime);
-    }
-
     pub fn opt_encl_scope(&self, id: CodeExtent) -> Option<CodeExtent> {
         //! Returns the narrowest scope that encloses `id`, if any.
         self.scope_map.get(&id).cloned()
@@ -395,32 +381,6 @@ impl<'tcx> RegionMaps {
         }
     }
 
-    pub fn temporary_scope2(&self, expr_id: ast::NodeId)
-                            -> (Option<CodeExtent>, bool) {
-        let temporary_scope = self.temporary_scope(expr_id);
-        let was_shrunk = match self.shrunk_rvalue_scopes.get(&expr_id) {
-            Some(&s) => {
-                info!("temporary_scope2({:?}, scope={:?}, shrunk={:?})",
-                      expr_id, temporary_scope, s);
-                temporary_scope != Some(s)
-            }
-            _ => false
-        };
-        info!("temporary_scope2({:?}) - was_shrunk={:?}", expr_id, was_shrunk);
-        (temporary_scope, was_shrunk)
-    }
-
-    pub fn old_and_new_temporary_scope(&self, expr_id: ast::NodeId)
-                                       -> (Option<CodeExtent>,
-                                           Option<CodeExtent>)
-    {
-        let temporary_scope = self.temporary_scope(expr_id);
-        (temporary_scope,
-         self.shrunk_rvalue_scopes
-             .get(&expr_id).cloned()
-             .or(temporary_scope))
-    }
-
     pub fn temporary_scope(&self, expr_id: ast::NodeId) -> Option<CodeExtent> {
         //! Returns the scope when temp created by expr_id will be cleaned up
 
@@ -896,10 +856,7 @@ fn resolve_local<'a, 'tcx>(visitor: &mut RegionResolutionVisitor<'a, 'tcx>,
     // Rule A. `let (ref x, ref y) = (foo().x, 44)`. The rvalue `(22, 44)`
     // would have an extended lifetime, but not `foo()`.
     //
-    // Rule B. `let x: &[...] = [foo().x]`. The rvalue `[foo().x]`
-    // would have an extended lifetime, but not `foo()`.
-    //
-    // Rule C. `let x = &foo().x`. The rvalue ``foo()` would have extended
+    // Rule B. `let x = &foo().x`. The rvalue ``foo()` would have extended
     // lifetime.
     //
     // In some cases, multiple rules may apply (though not to the same
@@ -916,13 +873,8 @@ fn resolve_local<'a, 'tcx>(visitor: &mut RegionResolutionVisitor<'a, 'tcx>,
     if let Some(ref expr) = local.init {
         record_rvalue_scope_if_borrow_expr(visitor, &expr, blk_scope);
 
-        let is_borrow =
-            if let Some(ref ty) = local.ty { is_borrowed_ty(&ty) } else { false };
-
         if is_binding_pat(&local.pat) {
-            record_rvalue_scope(visitor, &expr, blk_scope, false);
-        } else if is_borrow {
-            record_rvalue_scope(visitor, &expr, blk_scope, true);
+            record_rvalue_scope(visitor, &expr, blk_scope);
         }
     }
 
@@ -963,14 +915,6 @@ fn resolve_local<'a, 'tcx>(visitor: &mut RegionResolutionVisitor<'a, 'tcx>,
         }
     }
 
-    /// True if `ty` is a borrowed pointer type like `&int` or `&[...]`.
-    fn is_borrowed_ty(ty: &hir::Ty) -> bool {
-        match ty.node {
-            hir::TyRptr(..) => true,
-            _ => false
-        }
-    }
-
     /// If `expr` matches the `E&` grammar, then records an extended rvalue scope as appropriate:
     ///
     ///     E& = & ET
@@ -989,7 +933,7 @@ fn resolve_local<'a, 'tcx>(visitor: &mut RegionResolutionVisitor<'a, 'tcx>,
         match expr.node {
             hir::ExprAddrOf(_, ref subexpr) => {
                 record_rvalue_scope_if_borrow_expr(visitor, &subexpr, blk_id);
-                record_rvalue_scope(visitor, &subexpr, blk_id, false);
+                record_rvalue_scope(visitor, &subexpr, blk_id);
             }
             hir::ExprStruct(_, ref fields, _) => {
                 for field in fields {
@@ -1034,21 +978,15 @@ fn resolve_local<'a, 'tcx>(visitor: &mut RegionResolutionVisitor<'a, 'tcx>,
     /// Note: ET is intended to match "rvalues or lvalues based on rvalues".
     fn record_rvalue_scope<'a, 'tcx>(visitor: &mut RegionResolutionVisitor<'a, 'tcx>,
                                      expr: &hir::Expr,
-                                     blk_scope: CodeExtent,
-                                     is_shrunk: bool) {
+                                     blk_scope: CodeExtent) {
         let mut expr = expr;
         loop {
             // Note: give all the expressions matching `ET` with the
             // extended temporary lifetime, not just the innermost rvalue,
             // because in trans if we must compile e.g. `*rvalue()`
             // into a temporary, we request the temporary scope of the
             // outer expression.
-            if is_shrunk {
-                // this changed because of #36082
-                visitor.region_maps.record_shrunk_rvalue_scope(expr.id, blk_scope);
-            } else {
-                visitor.region_maps.record_rvalue_scope(expr.id, blk_scope);
-            }
+            visitor.region_maps.record_rvalue_scope(expr.id, blk_scope);
 
             match expr.node {
                 hir::ExprAddrOf(_, ref subexpr) |

src/librustc_borrowck/borrowck/gather_loans/lifetime.rs

@@ -108,7 +108,7 @@ impl<'a, 'tcx> GuaranteeLifetimeContext<'a, 'tcx> {
         //! rooting etc, and presuming `cmt` is not mutated.
 
         match cmt.cat {
-            Categorization::Rvalue(temp_scope, _) => {
+            Categorization::Rvalue(temp_scope) => {
                 temp_scope
             }
             Categorization::Upvar(..) => {

src/librustc_borrowck/borrowck/mod.rs

@@ -1125,17 +1125,6 @@ impl<'a, 'tcx> BorrowckCtxt<'a, 'tcx> {
                 if let Some(_) = statement_scope_span(self.tcx, super_scope) {
                     db.note("consider using a `let` binding to increase its lifetime");
                 }
-
-
-
-                match err.cmt.cat {
-                    mc::Categorization::Rvalue(r, or) if r != or => {
-                        db.note("\
-before rustc 1.16, this temporary lived longer - see issue #39283 \
-(https://github.com/rust-lang/rust/issues/39283)");
-                    }
-                    _ => {}
-                }
             }
 
             err_borrowed_pointer_too_short(loan_scope, ptr_scope) => {

src/librustc_mir/build/expr/as_constant.rs

@@ -26,7 +26,7 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
 
     fn expr_as_constant(&mut self, expr: Expr<'tcx>) -> Constant<'tcx> {
         let this = self;
-        let Expr { ty, temp_lifetime: _, temp_lifetime_was_shrunk: _, span, kind }
+        let Expr { ty, temp_lifetime: _, span, kind }
             = expr;
         match kind {
             ExprKind::Scope { extent: _, value } =>

src/librustc_mir/build/expr/as_temp.rs

@@ -50,13 +50,6 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
         let temp = this.temp(expr_ty.clone(), expr_span);
         let source_info = this.source_info(expr_span);
 
-        if expr.temp_lifetime_was_shrunk && this.hir.needs_drop(expr_ty) {
-            this.hir.tcx().sess.span_warn(
-                expr_span,
-                "this temporary used to live longer - see issue #39283 \
-(https://github.com/rust-lang/rust/issues/39283)");
-        }
-
         if !expr_ty.is_never() && temp_lifetime.is_some() {
             this.cfg.push(block, Statement {
                 source_info: source_info,

src/librustc_mir/hair/cx/block.rs

@@ -82,11 +82,10 @@ pub fn to_expr_ref<'a, 'gcx, 'tcx>(cx: &mut Cx<'a, 'gcx, 'tcx>,
                                    block: &'tcx hir::Block)
                                    -> ExprRef<'tcx> {
     let block_ty = cx.tables().node_id_to_type(block.id);
-    let (temp_lifetime, was_shrunk) = cx.region_maps.temporary_scope2(block.id);
+    let temp_lifetime = cx.region_maps.temporary_scope(block.id);
     let expr = Expr {
         ty: block_ty,
         temp_lifetime: temp_lifetime,
-        temp_lifetime_was_shrunk: was_shrunk,
         span: block.span,
         kind: ExprKind::Block { body: block },
     };