Auto merge of #65053 - Centril:rollup-nwp0wgf, r=Centril

Rollup of 5 pull requests

Successful merges:

 - #64690 (proc_macro API: Expose `macro_rules` hygiene)
 - #64749 (Fix most remaining Polonius test differences)
 - #64938 (Avoid ICE on ReFree region on where clause)
 - #64999 (extract expected return type for async fn generators)
 - #65037 (`#[track_caller]` feature gate (RFC 2091))

Failed merges:

r? @ghost

Author: bors

src/doc/unstable-book/src/language-features/track-caller.md

@@ -0,0 +1,5 @@
+# `track_caller`
+
+The tracking issue for this feature is: [#47809](https://github.com/rust-lang/rust/issues/47809).
+
+------------------------

src/libproc_macro/bridge/mod.rs

@@ -148,6 +148,7 @@ macro_rules! with_api {
                 fn debug($self: $S::Span) -> String;
                 fn def_site() -> $S::Span;
                 fn call_site() -> $S::Span;
+                fn mixed_site() -> $S::Span;
                 fn source_file($self: $S::Span) -> $S::SourceFile;
                 fn parent($self: $S::Span) -> Option<$S::Span>;
                 fn source($self: $S::Span) -> $S::Span;

src/libproc_macro/lib.rs

@@ -271,6 +271,15 @@ impl Span {
         Span(bridge::client::Span::call_site())
     }
 
+    /// A span that represents `macro_rules` hygiene, and sometimes resolves at the macro
+    /// definition site (local variables, labels, `$crate`) and sometimes at the macro
+    /// call site (everything else).
+    /// The span location is taken from the call-site.
+    #[unstable(feature = "proc_macro_mixed_site", issue = "65049")]
+    pub fn mixed_site() -> Span {
+        Span(bridge::client::Span::mixed_site())
+    }
+
     /// The original source file into which this span points.
     #[unstable(feature = "proc_macro_span", issue = "54725")]
     pub fn source_file(&self) -> SourceFile {

src/librustc/error_codes.rs

@@ -2234,6 +2234,15 @@ These attributes are meant to only be used by the standard library and are
 rejected in your own crates.
 "##,
 
+E0736: r##"
+#[track_caller] and #[naked] cannot be applied to the same function.
+
+This is primarily due to ABI incompatibilities between the two attributes.
+See [RFC 2091] for details on this and other limitations.
+
+[RFC 2091]: https://github.com/rust-lang/rfcs/blob/master/text/2091-inline-semantic.md
+"##,
+
 ;
 //  E0006, // merged with E0005
 //  E0101, // replaced with E0282
@@ -2296,4 +2305,5 @@ rejected in your own crates.
     E0726, // non-explicit (not `'_`) elided lifetime in unsupported position
     E0727, // `async` generators are not yet supported
     E0728, // `await` must be in an `async` function or block
+    E0735, // invalid track_caller application/syntax
 }

src/librustc/hir/check_attr.rs

@@ -11,7 +11,7 @@ use crate::ty::TyCtxt;
 use crate::ty::query::Providers;
 
 use std::fmt::{self, Display};
-use syntax::symbol::sym;
+use syntax::{attr, symbol::sym};
 use syntax_pos::Span;
 
 #[derive(Copy, Clone, PartialEq)]
@@ -103,6 +103,8 @@ impl CheckAttrVisitor<'tcx> {
                 self.check_marker(attr, item, target)
             } else if attr.check_name(sym::target_feature) {
                 self.check_target_feature(attr, item, target)
+            } else if attr.check_name(sym::track_caller) {
+                self.check_track_caller(attr, &item, target)
             } else {
                 true
             };
@@ -135,6 +137,32 @@ impl CheckAttrVisitor<'tcx> {
         }
     }
 
+    /// Checks if a `#[track_caller]` is applied to a non-naked function. Returns `true` if valid.
+    fn check_track_caller(&self, attr: &hir::Attribute, item: &hir::Item, target: Target) -> bool {
+        if target != Target::Fn {
+            struct_span_err!(
+                self.tcx.sess,
+                attr.span,
+                E0735,
+                "attribute should be applied to function"
+            )
+            .span_label(item.span, "not a function")
+            .emit();
+            false
+        } else if attr::contains_name(&item.attrs, sym::naked) {
+            struct_span_err!(
+                self.tcx.sess,
+                attr.span,
+                E0736,
+                "cannot use `#[track_caller]` with `#[naked]`",
+            )
+            .emit();
+            false
+        } else {
+            true
+        }
+    }
+
     /// Checks if the `#[non_exhaustive]` attribute on an `item` is valid. Returns `true` if valid.
     fn check_non_exhaustive(
         &self,

src/librustc/hir/lowering/expr.rs

@@ -89,9 +89,14 @@ impl LoweringContext<'_> {
                 hir::MatchSource::Normal,
             ),
             ExprKind::Async(capture_clause, closure_node_id, ref block) => {
-                self.make_async_expr(capture_clause, closure_node_id, None, block.span, |this| {
-                    this.with_new_scopes(|this| this.lower_block_expr(block))
-                })
+                self.make_async_expr(
+                    capture_clause,
+                    closure_node_id,
+                    None,
+                    block.span,
+                    hir::AsyncGeneratorKind::Block,
+                    |this| this.with_new_scopes(|this| this.lower_block_expr(block)),
+                )
             }
             ExprKind::Await(ref expr) => self.lower_expr_await(e.span, expr),
             ExprKind::Closure(
@@ -457,6 +462,7 @@ impl LoweringContext<'_> {
         closure_node_id: NodeId,
         ret_ty: Option<AstP<Ty>>,
         span: Span,
+        async_gen_kind: hir::AsyncGeneratorKind,
         body: impl FnOnce(&mut LoweringContext<'_>) -> hir::Expr,
     ) -> hir::ExprKind {
         let capture_clause = self.lower_capture_clause(capture_clause);
@@ -470,7 +476,7 @@ impl LoweringContext<'_> {
         };
         let decl = self.lower_fn_decl(&ast_decl, None, /* impl trait allowed */ false, None);
         let body_id = self.lower_fn_body(&ast_decl, |this| {
-            this.generator_kind = Some(hir::GeneratorKind::Async);
+            this.generator_kind = Some(hir::GeneratorKind::Async(async_gen_kind));
             body(this)
         });
 
@@ -522,7 +528,7 @@ impl LoweringContext<'_> {
     /// ```
     fn lower_expr_await(&mut self, await_span: Span, expr: &Expr) -> hir::ExprKind {
         match self.generator_kind {
-            Some(hir::GeneratorKind::Async) => {},
+            Some(hir::GeneratorKind::Async(_)) => {},
             Some(hir::GeneratorKind::Gen) |
             None => {
                 let mut err = struct_span_err!(
@@ -727,7 +733,7 @@ impl LoweringContext<'_> {
                     Movability::Static => hir::GeneratorMovability::Static,
                 })
             },
-            Some(hir::GeneratorKind::Async) => {
+            Some(hir::GeneratorKind::Async(_)) => {
                 bug!("non-`async` closure body turned `async` during lowering");
             },
             None => {
@@ -786,10 +792,12 @@ impl LoweringContext<'_> {
                     None
                 };
                 let async_body = this.make_async_expr(
-                    capture_clause, closure_id, async_ret_ty, body.span,
-                    |this| {
-                        this.with_new_scopes(|this| this.lower_expr(body))
-                    }
+                    capture_clause,
+                    closure_id,
+                    async_ret_ty,
+                    body.span,
+                    hir::AsyncGeneratorKind::Closure,
+                    |this| this.with_new_scopes(|this| this.lower_expr(body)),
                 );
                 this.expr(fn_decl_span, async_body, ThinVec::new())
             });
@@ -1005,7 +1013,7 @@ impl LoweringContext<'_> {
     fn lower_expr_yield(&mut self, span: Span, opt_expr: Option<&Expr>) -> hir::ExprKind {
         match self.generator_kind {
             Some(hir::GeneratorKind::Gen) => {},
-            Some(hir::GeneratorKind::Async) => {
+            Some(hir::GeneratorKind::Async(_)) => {
                 span_err!(
                     self.sess,
                     span,

src/librustc/hir/lowering/item.rs

@@ -1222,7 +1222,11 @@ impl LoweringContext<'_> {
             }
 
             let async_expr = this.make_async_expr(
-                CaptureBy::Value, closure_id, None, body.span,
+                CaptureBy::Value,
+                closure_id,
+                None,
+                body.span,
+                hir::AsyncGeneratorKind::Fn,
                 |this| {
                     // Create a block from the user's function body:
                     let user_body = this.lower_block_expr(body);

src/librustc/hir/mod.rs

@@ -1362,21 +1362,49 @@ impl Body {
 }
 
 /// The type of source expression that caused this generator to be created.
-// Not `IsAsync` because we want to eventually add support for `AsyncGen`
 #[derive(Clone, PartialEq, Eq, PartialOrd, Ord, HashStable,
          RustcEncodable, RustcDecodable, Hash, Debug, Copy)]
 pub enum GeneratorKind {
-    /// An `async` block or function.
-    Async,
+    /// An explicit `async` block or the body of an async function.
+    Async(AsyncGeneratorKind),
+
     /// A generator literal created via a `yield` inside a closure.
     Gen,
 }
 
 impl fmt::Display for GeneratorKind {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            GeneratorKind::Async(k) => fmt::Display::fmt(k, f),
+            GeneratorKind::Gen => f.write_str("generator"),
+        }
+    }
+}
+
+/// In the case of a generator created as part of an async construct,
+/// which kind of async construct caused it to be created?
+///
+/// This helps error messages but is also used to drive coercions in
+/// type-checking (see #60424).
+#[derive(Clone, PartialEq, Eq, PartialOrd, Ord, HashStable,
+         RustcEncodable, RustcDecodable, Hash, Debug, Copy)]
+pub enum AsyncGeneratorKind {
+    /// An explicit `async` block written by the user.
+    Block,
+
+    /// An explicit `async` block written by the user.
+    Closure,
+
+    /// The `async` block generated as the body of an async function.
+    Fn,
+}
+
+impl fmt::Display for AsyncGeneratorKind {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         f.write_str(match self {
-            GeneratorKind::Async => "`async` object",
-            GeneratorKind::Gen => "generator",
+            AsyncGeneratorKind::Block => "`async` block",
+            AsyncGeneratorKind::Closure => "`async` closure body",
+            AsyncGeneratorKind::Fn => "`async fn` body",
         })
     }
 }
@@ -1758,6 +1786,7 @@ pub struct Destination {
 pub enum GeneratorMovability {
     /// May contain self-references, `!Unpin`.
     Static,
+
     /// Must not contain self-references, `Unpin`.
     Movable,
 }
@@ -2687,7 +2716,9 @@ bitflags! {
         const USED                      = 1 << 9;
         /// #[ffi_returns_twice], indicates that an extern function can return
         /// multiple times
-        const FFI_RETURNS_TWICE = 1 << 10;
+        const FFI_RETURNS_TWICE         = 1 << 10;
+        /// #[track_caller]: allow access to the caller location
+        const TRACK_CALLER              = 1 << 11;
     }
 }
 

src/librustc/infer/mod.rs

@@ -1319,6 +1319,14 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
         }
     }
 
+    /// Resolve any type variables found in `value` -- but only one
+    /// level.  So, if the variable `?X` is bound to some type
+    /// `Foo<?Y>`, then this would return `Foo<?Y>` (but `?Y` may
+    /// itself be bound to a type).
+    ///
+    /// Useful when you only need to inspect the outermost level of
+    /// the type and don't care about nested types (or perhaps you
+    /// will be resolving them as well, e.g. in a loop).
     pub fn shallow_resolve<T>(&self, value: T) -> T
     where
         T: TypeFoldable<'tcx>,
@@ -1579,6 +1587,9 @@ impl<'a, 'tcx> ShallowResolver<'a, 'tcx> {
         ShallowResolver { infcx }
     }
 
+    /// If `typ` is a type variable of some kind, resolve it one level
+    /// (but do not resolve types found in the result). If `typ` is
+    /// not a type variable, just return it unmodified.
     pub fn shallow_resolve(&mut self, typ: Ty<'tcx>) -> Ty<'tcx> {
         match typ.kind {
             ty::Infer(ty::TyVar(v)) => {

src/librustc_mir/borrow_check/nll/type_check/liveness/local_use_map.rs

@@ -70,6 +70,10 @@ impl LocalUseMap {
             appearances: IndexVec::new(),
         };
 
+        if live_locals.is_empty() {
+            return local_use_map;
+        }
+
         let mut locals_with_use_data: IndexVec<Local, bool> =
             IndexVec::from_elem_n(false, body.local_decls.len());
         live_locals.iter().for_each(|&local| locals_with_use_data[local] = true);