Rollup of 9 pull requests

src/libcore/benches/fmt.rs

@@ -0,0 +1,110 @@
+use std::io::{self, Write as IoWrite};
+use std::fmt::{self, Write as FmtWrite};
+use test::Bencher;
+
+#[bench]
+fn write_vec_value(bh: &mut Bencher) {
+    bh.iter(|| {
+        let mut mem = Vec::new();
+        for _ in 0..1000 {
+            mem.write_all("abc".as_bytes()).unwrap();
+        }
+    });
+}
+
+#[bench]
+fn write_vec_ref(bh: &mut Bencher) {
+    bh.iter(|| {
+        let mut mem = Vec::new();
+        let wr = &mut mem as &mut dyn io::Write;
+        for _ in 0..1000 {
+            wr.write_all("abc".as_bytes()).unwrap();
+        }
+    });
+}
+
+#[bench]
+fn write_vec_macro1(bh: &mut Bencher) {
+    bh.iter(|| {
+        let mut mem = Vec::new();
+        let wr = &mut mem as &mut dyn io::Write;
+        for _ in 0..1000 {
+            write!(wr, "abc").unwrap();
+        }
+    });
+}
+
+#[bench]
+fn write_vec_macro2(bh: &mut Bencher) {
+    bh.iter(|| {
+        let mut mem = Vec::new();
+        let wr = &mut mem as &mut dyn io::Write;
+        for _ in 0..1000 {
+            write!(wr, "{}", "abc").unwrap();
+        }
+    });
+}
+
+#[bench]
+fn write_vec_macro_debug(bh: &mut Bencher) {
+    bh.iter(|| {
+        let mut mem = Vec::new();
+        let wr = &mut mem as &mut dyn io::Write;
+        for _ in 0..1000 {
+            write!(wr, "{:?}", "☃").unwrap();
+        }
+    });
+}
+
+#[bench]
+fn write_str_value(bh: &mut Bencher) {
+    bh.iter(|| {
+        let mut mem = String::new();
+        for _ in 0..1000 {
+            mem.write_str("abc").unwrap();
+        }
+    });
+}
+
+#[bench]
+fn write_str_ref(bh: &mut Bencher) {
+    bh.iter(|| {
+        let mut mem = String::new();
+        let wr = &mut mem as &mut dyn fmt::Write;
+        for _ in 0..1000 {
+            wr.write_str("abc").unwrap();
+        }
+    });
+}
+
+#[bench]
+fn write_str_macro1(bh: &mut Bencher) {
+    bh.iter(|| {
+        let mut mem = String::new();
+        for _ in 0..1000 {
+            write!(mem, "abc").unwrap();
+        }
+    });
+}
+
+#[bench]
+fn write_str_macro2(bh: &mut Bencher) {
+    bh.iter(|| {
+        let mut mem = String::new();
+        let wr = &mut mem as &mut dyn fmt::Write;
+        for _ in 0..1000 {
+            write!(wr, "{}", "abc").unwrap();
+        }
+    });
+}
+
+#[bench]
+fn write_str_macro_debug(bh: &mut Bencher) {
+    bh.iter(|| {
+        let mut mem = String::new();
+        let wr = &mut mem as &mut dyn fmt::Write;
+        for _ in 0..1000 {
+            write!(wr, "{:?}", "☃").unwrap();
+        }
+    });
+}

src/libcore/benches/lib.rs

@@ -11,3 +11,4 @@ mod iter;
 mod num;
 mod ops;
 mod slice;
+mod fmt;

src/libcore/fmt/mod.rs

@@ -1006,28 +1006,30 @@ pub fn write(output: &mut dyn Write, args: Arguments) -> Result {
         curarg: args.args.iter(),
     };
 
-    let mut pieces = args.pieces.iter();
+    let mut idx = 0;
 
     match args.fmt {
         None => {
             // We can use default formatting parameters for all arguments.
-            for (arg, piece) in args.args.iter().zip(pieces.by_ref()) {
+            for (arg, piece) in args.args.iter().zip(args.pieces.iter()) {
                 formatter.buf.write_str(*piece)?;
                 (arg.formatter)(arg.value, &mut formatter)?;
+                idx += 1;
             }
         }
         Some(fmt) => {
             // Every spec has a corresponding argument that is preceded by
             // a string piece.
-            for (arg, piece) in fmt.iter().zip(pieces.by_ref()) {
+            for (arg, piece) in fmt.iter().zip(args.pieces.iter()) {
                 formatter.buf.write_str(*piece)?;
                 formatter.run(arg)?;
+                idx += 1;
             }
         }
     }
 
     // There can be only one trailing string piece left.
-    if let Some(piece) = pieces.next() {
+    if let Some(piece) = args.pieces.get(idx) {
         formatter.buf.write_str(*piece)?;
     }
 

src/libcore/ops/index.rs

@@ -51,21 +51,6 @@
 /// ```
 #[lang = "index"]
 #[rustc_on_unimplemented(
-    on(
-        _Self="&str",
-        note="you can use `.chars().nth()` or `.bytes().nth()`
-see chapter in The Book <https://doc.rust-lang.org/book/ch08-02-strings.html#indexing-into-strings>"
-    ),
-    on(
-        _Self="str",
-        note="you can use `.chars().nth()` or `.bytes().nth()`
-see chapter in The Book <https://doc.rust-lang.org/book/ch08-02-strings.html#indexing-into-strings>"
-    ),
-    on(
-        _Self="std::string::String",
-        note="you can use `.chars().nth()` or `.bytes().nth()`
-see chapter in The Book <https://doc.rust-lang.org/book/ch08-02-strings.html#indexing-into-strings>"
-    ),
     message="the type `{Self}` cannot be indexed by `{Idx}`",
     label="`{Self}` cannot be indexed by `{Idx}`",
 )]

src/libcore/slice/mod.rs

@@ -2383,7 +2383,6 @@ impl [u8] {
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-#[rustc_on_unimplemented = "slice indices are of type `usize` or ranges of `usize`"]
 impl<T, I> ops::Index<I> for [T]
     where I: SliceIndex<[T]>
 {
@@ -2396,7 +2395,6 @@ impl<T, I> ops::Index<I> for [T]
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-#[rustc_on_unimplemented = "slice indices are of type `usize` or ranges of `usize`"]
 impl<T, I> ops::IndexMut<I> for [T]
     where I: SliceIndex<[T]>
 {
@@ -2447,7 +2445,19 @@ mod private_slice_index {
 
 /// A helper trait used for indexing operations.
 #[stable(feature = "slice_get_slice", since = "1.28.0")]
-#[rustc_on_unimplemented = "slice indices are of type `usize` or ranges of `usize`"]
+#[rustc_on_unimplemented(
+    on(
+        T = "str",
+        label = "string indices are ranges of `usize`",
+    ),
+    on(
+        all(any(T = "str", T = "&str", T = "std::string::String"), _Self="{integer}"),
+        note="you can use `.chars().nth()` or `.bytes().nth()`
+see chapter in The Book <https://doc.rust-lang.org/book/ch08-02-strings.html#indexing-into-strings>"
+    ),
+    message = "the type `{T}` cannot be indexed by `{Self}`",
+    label = "slice indices are of type `usize` or ranges of `usize`",
+)]
 pub trait SliceIndex<T: ?Sized>: private_slice_index::Sealed {
     /// The output type returned by methods.
     #[stable(feature = "slice_get_slice", since = "1.28.0")]