Auto merge of rust-lang#60435 - Centril:rollup-aa5lmuw, r=Centril

Rollup of 7 pull requests

Successful merges:

 - rust-lang#60287 (Use references for variances_of)
 - rust-lang#60327 (Search for incompatible universes in borrow errors)
 - rust-lang#60330 (Suggest using an inclusive range instead of an exclusive range when the endpoint overflows by 1)
 - rust-lang#60366 (build-gcc: Create missing cc symlink)
 - rust-lang#60369 (Support ZSTs in DispatchFromDyn)
 - rust-lang#60404 (Implement `BorrowMut<str>` for `String`)
 - rust-lang#60417 (Rename hir::ExprKind::Use to ::DropTemps and improve docs.)

Failed merges:

r? @ghost

Author: bors

src/ci/docker/dist-x86_64-linux/build-gcc.sh

@@ -32,6 +32,7 @@ hide_output ../gcc-$GCC/configure \
     --enable-languages=c,c++
 hide_output make -j10
 hide_output make install
+ln -s gcc /rustroot/bin/cc
 
 cd ..
 rm -rf gcc-build

src/liballoc/str.rs

@@ -28,7 +28,7 @@
 // It's cleaner to just turn off the unused_imports warning than to fix them.
 #![allow(unused_imports)]
 
-use core::borrow::Borrow;
+use core::borrow::{Borrow, BorrowMut};
 use core::str::pattern::{Pattern, Searcher, ReverseSearcher, DoubleEndedSearcher};
 use core::mem;
 use core::ptr;
@@ -190,6 +190,14 @@ impl Borrow<str> for String {
     }
 }
 
+#[stable(feature = "string_borrow_mut", since = "1.36.0")]
+impl BorrowMut<str> for String {
+    #[inline]
+    fn borrow_mut(&mut self) -> &mut str {
+        &mut self[..]
+    }
+}
+
 #[stable(feature = "rust1", since = "1.0.0")]
 impl ToOwned for str {
     type Owned = String;

src/librustc/arena.rs

@@ -144,6 +144,14 @@ impl<'tcx> Arena<'tcx> {
         }
     }
 
+    #[inline]
+    pub fn alloc_slice<T: Copy>(&self, value: &[T]) -> &mut [T] {
+        if value.len() == 0 {
+            return &mut []
+        }
+        self.dropless.alloc_slice(value)
+    }
+
     pub fn alloc_from_iter<
         T: ArenaAllocatable,
         I: IntoIterator<Item = T>

src/librustc/cfg/construct.rs

@@ -369,7 +369,7 @@ impl<'a, 'tcx> CFGBuilder<'a, 'tcx> {
             hir::ExprKind::AddrOf(_, ref e) |
             hir::ExprKind::Cast(ref e, _) |
             hir::ExprKind::Type(ref e, _) |
-            hir::ExprKind::Use(ref e) |
+            hir::ExprKind::DropTemps(ref e) |
             hir::ExprKind::Unary(_, ref e) |
             hir::ExprKind::Field(ref e, _) |
             hir::ExprKind::Yield(ref e) |

src/librustc/hir/intravisit.rs

@@ -1029,7 +1029,7 @@ pub fn walk_expr<'v, V: Visitor<'v>>(visitor: &mut V, expression: &'v Expr) {
             visitor.visit_expr(subexpression);
             visitor.visit_ty(typ)
         }
-        ExprKind::Use(ref subexpression) => {
+        ExprKind::DropTemps(ref subexpression) => {
             visitor.visit_expr(subexpression);
         }
         ExprKind::If(ref head_expression, ref if_block, ref optional_else) => {

src/librustc/hir/lowering.rs

@@ -4671,7 +4671,7 @@ impl<'a> LoweringContext<'a> {
                 // The construct was introduced in #21984.
                 // FIXME(60253): Is this still necessary?
                 // Also, add the attributes to the outer returned expr node.
-                return self.expr_use(head_sp, match_expr, e.attrs.clone())
+                return self.expr_drop_temps(head_sp, match_expr, e.attrs.clone())
             }
 
             // Desugar `ExprKind::Try`
@@ -5030,15 +5030,19 @@ impl<'a> LoweringContext<'a> {
         )
     }
 
-    /// Wrap the given `expr` in `hir::ExprKind::Use`.
+    /// Wrap the given `expr` in a terminating scope using `hir::ExprKind::DropTemps`.
     ///
-    /// In terms of drop order, it has the same effect as
-    /// wrapping `expr` in `{ let _t = $expr; _t }` but
-    /// should provide better compile-time performance.
+    /// In terms of drop order, it has the same effect as wrapping `expr` in
+    /// `{ let _t = $expr; _t }` but should provide better compile-time performance.
     ///
     /// The drop order can be important in e.g. `if expr { .. }`.
-    fn expr_use(&mut self, span: Span, expr: P<hir::Expr>, attrs: ThinVec<Attribute>) -> hir::Expr {
-        self.expr(span, hir::ExprKind::Use(expr), attrs)
+    fn expr_drop_temps(
+        &mut self,
+        span: Span,
+        expr: P<hir::Expr>,
+        attrs: ThinVec<Attribute>
+    ) -> hir::Expr {
+        self.expr(span, hir::ExprKind::DropTemps(expr), attrs)
     }
 
     fn expr_match(
@@ -5400,3 +5404,65 @@ fn body_ids(bodies: &BTreeMap<hir::BodyId, hir::Body>) -> Vec<hir::BodyId> {
     body_ids.sort_by_key(|b| bodies[b].value.span);
     body_ids
 }
+
+/// Checks if the specified expression is a built-in range literal.
+/// (See: `LoweringContext::lower_expr()`).
+pub fn is_range_literal(sess: &Session, expr: &hir::Expr) -> bool {
+    use hir::{Path, QPath, ExprKind, TyKind};
+
+    // Returns whether the given path represents a (desugared) range,
+    // either in std or core, i.e. has either a `::std::ops::Range` or
+    // `::core::ops::Range` prefix.
+    fn is_range_path(path: &Path) -> bool {
+        let segs: Vec<_> = path.segments.iter().map(|seg| seg.ident.as_str().to_string()).collect();
+        let segs: Vec<_> = segs.iter().map(|seg| &**seg).collect();
+
+        // "{{root}}" is the equivalent of `::` prefix in `Path`.
+        if let ["{{root}}", std_core, "ops", range] = segs.as_slice() {
+            (*std_core == "std" || *std_core == "core") && range.starts_with("Range")
+        } else {
+            false
+        }
+    };
+
+    // Check whether a span corresponding to a range expression is a
+    // range literal, rather than an explicit struct or `new()` call.
+    fn is_lit(sess: &Session, span: &Span) -> bool {
+        let source_map = sess.source_map();
+        let end_point = source_map.end_point(*span);
+
+        if let Ok(end_string) = source_map.span_to_snippet(end_point) {
+            !(end_string.ends_with("}") || end_string.ends_with(")"))
+        } else {
+            false
+        }
+    };
+
+    match expr.node {
+        // All built-in range literals but `..=` and `..` desugar to `Struct`s.
+        ExprKind::Struct(ref qpath, _, _) => {
+            if let QPath::Resolved(None, ref path) = **qpath {
+                return is_range_path(&path) && is_lit(sess, &expr.span);
+            }
+        }
+
+        // `..` desugars to its struct path.
+        ExprKind::Path(QPath::Resolved(None, ref path)) => {
+            return is_range_path(&path) && is_lit(sess, &expr.span);
+        }
+
+        // `..=` desugars into `::std::ops::RangeInclusive::new(...)`.
+        ExprKind::Call(ref func, _) => {
+            if let ExprKind::Path(QPath::TypeRelative(ref ty, ref segment)) = func.node {
+                if let TyKind::Path(QPath::Resolved(None, ref path)) = ty.node {
+                    let new_call = segment.ident.as_str() == "new";
+                    return is_range_path(&path) && is_lit(sess, &expr.span) && new_call;
+                }
+            }
+        }
+
+        _ => {}
+    }
+
+    false
+}

src/librustc/hir/mod.rs

@@ -1366,7 +1366,7 @@ impl Expr {
             ExprKind::Unary(..) => ExprPrecedence::Unary,
             ExprKind::Lit(_) => ExprPrecedence::Lit,
             ExprKind::Type(..) | ExprKind::Cast(..) => ExprPrecedence::Cast,
-            ExprKind::Use(ref expr, ..) => expr.precedence(),
+            ExprKind::DropTemps(ref expr, ..) => expr.precedence(),
             ExprKind::If(..) => ExprPrecedence::If,
             ExprKind::While(..) => ExprPrecedence::While,
             ExprKind::Loop(..) => ExprPrecedence::Loop,
@@ -1438,7 +1438,7 @@ impl Expr {
             ExprKind::Binary(..) |
             ExprKind::Yield(..) |
             ExprKind::Cast(..) |
-            ExprKind::Use(..) |
+            ExprKind::DropTemps(..) |
             ExprKind::Err => {
                 false
             }
@@ -1488,10 +1488,12 @@ pub enum ExprKind {
     Cast(P<Expr>, P<Ty>),
     /// A type reference (e.g., `Foo`).
     Type(P<Expr>, P<Ty>),
-    /// Semantically equivalent to `{ let _t = expr; _t }`.
-    /// Maps directly to `hair::ExprKind::Use`.
-    /// Only exists to tweak the drop order in HIR.
-    Use(P<Expr>),
+    /// Wraps the expression in a terminating scope.
+    /// This makes it semantically equivalent to `{ let _t = expr; _t }`.
+    ///
+    /// This construct only exists to tweak the drop order in HIR lowering.
+    /// An example of that is the desugaring of `for` loops.
+    DropTemps(P<Expr>),
     /// An `if` block, with an optional else block.
     ///
     /// I.e., `if <expr> { <expr> } else { <expr> }`.

src/librustc/hir/print.rs

@@ -1388,7 +1388,7 @@ impl<'a> State<'a> {
                 self.word_space(":")?;
                 self.print_type(&ty)?;
             }
-            hir::ExprKind::Use(ref init) => {
+            hir::ExprKind::DropTemps(ref init) => {
                 // Print `{`:
                 self.cbox(indent_unit)?;
                 self.ibox(0)?;

src/librustc/middle/expr_use_visitor.rs

@@ -520,7 +520,7 @@ impl<'a, 'gcx, 'tcx> ExprUseVisitor<'a, 'gcx, 'tcx> {
                 self.consume_expr(&base);
             }
 
-            hir::ExprKind::Use(ref expr) => {
+            hir::ExprKind::DropTemps(ref expr) => {
                 self.consume_expr(&expr);
             }
 

src/librustc/middle/liveness.rs

@@ -521,7 +521,7 @@ fn visit_expr<'a, 'tcx>(ir: &mut IrMaps<'a, 'tcx>, expr: &'tcx Expr) {
       hir::ExprKind::Binary(..) |
       hir::ExprKind::AddrOf(..) |
       hir::ExprKind::Cast(..) |
-      hir::ExprKind::Use(..) |
+      hir::ExprKind::DropTemps(..) |
       hir::ExprKind::Unary(..) |
       hir::ExprKind::Break(..) |
       hir::ExprKind::Continue(_) |
@@ -1222,7 +1222,7 @@ impl<'a, 'tcx> Liveness<'a, 'tcx> {
             hir::ExprKind::AddrOf(_, ref e) |
             hir::ExprKind::Cast(ref e, _) |
             hir::ExprKind::Type(ref e, _) |
-            hir::ExprKind::Use(ref e) |
+            hir::ExprKind::DropTemps(ref e) |
             hir::ExprKind::Unary(_, ref e) |
             hir::ExprKind::Yield(ref e) |
             hir::ExprKind::Repeat(ref e, _) => {
@@ -1526,7 +1526,7 @@ fn check_expr<'a, 'tcx>(this: &mut Liveness<'a, 'tcx>, expr: &'tcx Expr) {
         hir::ExprKind::Match(..) | hir::ExprKind::While(..) | hir::ExprKind::Loop(..) |
         hir::ExprKind::Index(..) | hir::ExprKind::Field(..) |
         hir::ExprKind::Array(..) | hir::ExprKind::Tup(..) | hir::ExprKind::Binary(..) |
-        hir::ExprKind::Cast(..) | hir::ExprKind::Use(..) | hir::ExprKind::Unary(..) |
+        hir::ExprKind::Cast(..) | hir::ExprKind::DropTemps(..) | hir::ExprKind::Unary(..) |
         hir::ExprKind::Ret(..) | hir::ExprKind::Break(..) | hir::ExprKind::Continue(..) |
         hir::ExprKind::Lit(_) | hir::ExprKind::Block(..) | hir::ExprKind::AddrOf(..) |
         hir::ExprKind::Struct(..) | hir::ExprKind::Repeat(..) |