Auto merge of #66686 - Centril:rollup-07slyoo, r=Centril

Rollup of 5 pull requests

Successful merges:

 - #64856 (Scope format! temporaries)
 - #66411 (mem::forget docs: mention ManuallyDrop)
 - #66594 (Fix cycle when debug-printing opaque types)
 - #66641 (parser: recover on nested ADTs as enum variants)
 - #66659 (make `./x.py bench` again)

Failed merges:

r? @ghost

Author: bors

src/liballoc/macros.rs

@@ -98,5 +98,8 @@ macro_rules! vec {
 #[macro_export]
 #[stable(feature = "rust1", since = "1.0.0")]
 macro_rules! format {
-    ($($arg:tt)*) => ($crate::fmt::format($crate::__export::format_args!($($arg)*)))
+    ($($arg:tt)*) => {{
+        let res = $crate::fmt::format($crate::__export::format_args!($($arg)*));
+        res
+    }}
 }

src/libcore/benches/num/mod.rs

@@ -35,7 +35,7 @@ macro_rules! from_str_bench {
                     .iter()
                     .cycle()
                     .take(5_000)
-                    .filter_map(|s| <($t)>::from_str(s).ok())
+                    .filter_map(|s| <$t>::from_str(s).ok())
                     .max()
             })
         }
@@ -51,7 +51,7 @@ macro_rules! from_str_radix_bench {
                     .iter()
                     .cycle()
                     .take(5_000)
-                    .filter_map(|s| <($t)>::from_str_radix(s, $radix).ok())
+                    .filter_map(|s| <$t>::from_str_radix(s, $radix).ok())
                     .max()
             })
         }

src/libcore/mem/mod.rs

@@ -45,8 +45,9 @@ pub use crate::intrinsics::transmute;
 /// `mem::forget` from safe code does not fundamentally change Rust's safety
 /// guarantees.
 ///
-/// That said, leaking resources such as memory or I/O objects is usually undesirable,
-/// so `forget` is only recommended for specialized use cases like those shown below.
+/// That said, leaking resources such as memory or I/O objects is usually undesirable.
+/// The need comes up in some specialized use cases for FFI or unsafe code, but even
+/// then, [`ManuallyDrop`] is typically preferred.
 ///
 /// Because forgetting a value is allowed, any `unsafe` code you write must
 /// allow for this possibility. You cannot return a value and expect that the
@@ -68,7 +69,35 @@ pub use crate::intrinsics::transmute;
 /// ```
 ///
 /// The practical use cases for `forget` are rather specialized and mainly come
-/// up in unsafe or FFI code.
+/// up in unsafe or FFI code. However, [`ManuallyDrop`] is usually preferred
+/// for such cases, e.g.:
+///
+/// ```
+/// use std::mem::ManuallyDrop;
+///
+/// let v = vec![65, 122];
+/// // Before we disassemble `v` into its raw parts, make sure it
+/// // does not get dropped!
+/// let mut v = ManuallyDrop::new(v);
+/// // Now disassemble `v`. These operations cannot panic, so there cannot be a leak.
+/// let ptr = v.as_mut_ptr();
+/// let cap = v.capacity();
+/// // Finally, build a `String`.
+/// let s = unsafe { String::from_raw_parts(ptr, 2, cap) };
+/// assert_eq!(s, "Az");
+/// // `s` is implicitly dropped and its memory deallocated.
+/// ```
+///
+/// Using `ManuallyDrop` here has two advantages:
+///
+/// * We do not "touch" `v` after disassembling it. For some types, operations
+///   such as passing ownership (to a funcion like `mem::forget`) requires them to actually
+///   be fully owned right now; that is a promise we do not want to make here as we are
+///   in the process of transferring ownership to the new `String` we are building.
+/// * In case of an unexpected panic, `ManuallyDrop` is not dropped, but if the panic
+///   occurs before `mem::forget` was called we might end up dropping invalid data,
+///   or double-dropping. In other words, `ManuallyDrop` errs on the side of leaking
+///   instead of erring on the side of dropping.
 ///
 /// [drop]: fn.drop.html
 /// [uninit]: fn.uninitialized.html
@@ -78,6 +107,7 @@ pub use crate::intrinsics::transmute;
 /// [leak]: ../../std/boxed/struct.Box.html#method.leak
 /// [into_raw]: ../../std/boxed/struct.Box.html#method.into_raw
 /// [ub]: ../../reference/behavior-considered-undefined.html
+/// [`ManuallyDrop`]: struct.ManuallyDrop.html
 #[inline]
 #[stable(feature = "rust1", since = "1.0.0")]
 pub fn forget<T>(t: T) {

src/librustc/benches/dispatch.rs

@@ -1,6 +1,63 @@
+#![feature(slice_patterns)]
 #![feature(test)]
 
 extern crate test;
 
-mod dispatch;
-mod pattern;
+use test::Bencher;
+
+// Static/dynamic method dispatch
+
+struct Struct {
+    field: isize
+}
+
+trait Trait {
+    fn method(&self) -> isize;
+}
+
+impl Trait for Struct {
+    fn method(&self) -> isize {
+        self.field
+    }
+}
+
+#[bench]
+fn trait_vtable_method_call(b: &mut Bencher) {
+    let s = Struct { field: 10 };
+    let t = &s as &dyn Trait;
+    b.iter(|| {
+        t.method()
+    });
+}
+
+#[bench]
+fn trait_static_method_call(b: &mut Bencher) {
+    let s = Struct { field: 10 };
+    b.iter(|| {
+        s.method()
+    });
+}
+
+// Overhead of various match forms
+
+#[bench]
+fn option_some(b: &mut Bencher) {
+    let x = Some(10);
+    b.iter(|| {
+        match x {
+            Some(y) => y,
+            None => 11
+        }
+    });
+}
+
+#[bench]
+fn vec_pattern(b: &mut Bencher) {
+    let x = [1,2,3,4,5,6];
+    b.iter(|| {
+        match x {
+            [1,2,3,..] => 10,
+            _ => 11,
+        }
+    });
+}

src/librustc/benches/lib.rs

@@ -49,6 +49,24 @@ macro_rules! define_scoped_cx {
 thread_local! {
     static FORCE_IMPL_FILENAME_LINE: Cell<bool> = Cell::new(false);
     static SHOULD_PREFIX_WITH_CRATE: Cell<bool> = Cell::new(false);
+    static NO_QUERIES: Cell<bool> = Cell::new(false);
+}
+
+/// Avoids running any queries during any prints that occur
+/// during the closure. This may alter the apperance of some
+/// types (e.g. forcing verbose printing for opaque types).
+/// This method is used during some queries (e.g. `predicates_of`
+/// for opaque types), to ensure that any debug printing that
+/// occurs during the query computation does not end up recursively
+/// calling the same query.
+pub fn with_no_queries<F: FnOnce() -> R, R>(f: F) -> R {
+    NO_QUERIES.with(|no_queries| {
+        let old = no_queries.get();
+        no_queries.set(true);
+        let result = f();
+        no_queries.set(old);
+        result
+    })
 }
 
 /// Force us to name impls with just the filename/line number. We
@@ -556,52 +574,61 @@ pub trait PrettyPrinter<'tcx>:
             }
             ty::Opaque(def_id, substs) => {
                 // FIXME(eddyb) print this with `print_def_path`.
-                if self.tcx().sess.verbose() {
+                // We use verbose printing in 'NO_QUERIES' mode, to
+                // avoid needing to call `predicates_of`. This should
+                // only affect certain debug messages (e.g. messages printed
+                // from `rustc::ty` during the computation of `tcx.predicates_of`),
+                // and should have no effect on any compiler output.
+                if self.tcx().sess.verbose() || NO_QUERIES.with(|q| q.get())  {
                     p!(write("Opaque({:?}, {:?})", def_id, substs));
                     return Ok(self);
                 }
 
-                let def_key = self.tcx().def_key(def_id);
-                if let Some(name) = def_key.disambiguated_data.data.get_opt_name() {
-                    p!(write("{}", name));
-                    let mut substs = substs.iter();
-                    // FIXME(eddyb) print this with `print_def_path`.
-                    if let Some(first) = substs.next() {
-                        p!(write("::<"));
-                        p!(print(first));
-                        for subst in substs {
-                            p!(write(", "), print(subst));
+                return Ok(with_no_queries(|| {
+
+                    let def_key = self.tcx().def_key(def_id);
+                    if let Some(name) = def_key.disambiguated_data.data.get_opt_name() {
+                        p!(write("{}", name));
+                        let mut substs = substs.iter();
+                        // FIXME(eddyb) print this with `print_def_path`.
+                        if let Some(first) = substs.next() {
+                            p!(write("::<"));
+                            p!(print(first));
+                            for subst in substs {
+                                p!(write(", "), print(subst));
+                            }
+                            p!(write(">"));
                         }
-                        p!(write(">"));
+                        return Ok(self);
                     }
-                    return Ok(self);
-                }
-                // Grab the "TraitA + TraitB" from `impl TraitA + TraitB`,
-                // by looking up the projections associated with the def_id.
-                let bounds = self.tcx().predicates_of(def_id).instantiate(self.tcx(), substs);
-
-                let mut first = true;
-                let mut is_sized = false;
-                p!(write("impl"));
-                for predicate in bounds.predicates {
-                    if let Some(trait_ref) = predicate.to_opt_poly_trait_ref() {
-                        // Don't print +Sized, but rather +?Sized if absent.
-                        if Some(trait_ref.def_id()) == self.tcx().lang_items().sized_trait() {
-                            is_sized = true;
-                            continue;
-                        }
+                    // Grab the "TraitA + TraitB" from `impl TraitA + TraitB`,
+                    // by looking up the projections associated with the def_id.
+                    let bounds = self.tcx().predicates_of(def_id).instantiate(self.tcx(), substs);
+
+                    let mut first = true;
+                    let mut is_sized = false;
+                    p!(write("impl"));
+                    for predicate in bounds.predicates {
+                        if let Some(trait_ref) = predicate.to_opt_poly_trait_ref() {
+                            // Don't print +Sized, but rather +?Sized if absent.
+                            if Some(trait_ref.def_id()) == self.tcx().lang_items().sized_trait() {
+                                is_sized = true;
+                                continue;
+                            }
 
-                        p!(
-                                write("{}", if first { " " } else { "+" }),
-                                print(trait_ref));
-                        first = false;
+                            p!(
+                                    write("{}", if first { " " } else { "+" }),
+                                    print(trait_ref));
+                            first = false;
+                        }
                     }
-                }
-                if !is_sized {
-                    p!(write("{}?Sized", if first { " " } else { "+" }));
-                } else if first {
-                    p!(write(" Sized"));
-                }
+                    if !is_sized {
+                        p!(write("{}?Sized", if first { " " } else { "+" }));
+                    } else if first {
+                        p!(write(" Sized"));
+                    }
+                    Ok(self)
+                })?);
             }
             ty::Str => p!(write("str")),
             ty::Generator(did, substs, movability) => {

src/librustc/benches/pattern.rs

@@ -52,7 +52,7 @@ fn test_minimize2() {
 fn test_rpath_relative() {
     if cfg!(target_os = "macos") {
         let config = &mut RPathConfig {
-            used_crates: Vec::new(),
+            used_crates: &[],
             has_rpath: true,
             is_like_osx: true,
             linker_is_gnu: false,
@@ -64,7 +64,7 @@ fn test_rpath_relative() {
         assert_eq!(res, "@loader_path/../lib");
     } else {
         let config = &mut RPathConfig {
-            used_crates: Vec::new(),
+            used_crates: &[],
             out_filename: PathBuf::from("bin/rustc"),
             get_install_prefix_lib_path: &mut || panic!(),
             has_rpath: true,