Rollup merge of #87599 - Smittyvb:concat_bytes, r=Mark-Simulacrum

Implement concat_bytes!

This implements the unstable `concat_bytes!` macro, which has tracking issue #87555. It can be used like:
```rust
#![feature(concat_bytes)]

fn main() {
    assert_eq!(concat_bytes!(), &[]);
    assert_eq!(concat_bytes!(b'A', b"BC", [68, b'E', 70]), b"ABCDEF");
}
```
If strings or characters are used where byte strings or byte characters are required, it suggests adding a `b` prefix. If a number is used outside of an array it suggests arrayifying it. If a boolean is used it suggests replacing it with the numeric value of that number. Doubly nested arrays of bytes are disallowed.

src/test/ui/feature-gates/feature-gate-concat_bytes.rs

@@ -0,0 +1,4 @@
+fn main() {
+    let a = concat_bytes!(b'A', b"BC"); //~ ERROR use of unstable library feature 'concat_bytes'
+    assert_eq!(a, &[65, 66, 67]);
+}

src/test/ui/feature-gates/feature-gate-concat_bytes.stderr

@@ -0,0 +1,12 @@
+error[E0658]: use of unstable library feature 'concat_bytes'
+  --> $DIR/feature-gate-concat_bytes.rs:2:13
+   |
+LL |     let a = concat_bytes!(b'A', b"BC");
+   |             ^^^^^^^^^^^^
+   |
+   = note: see issue #87555 <https://github.com/rust-lang/rust/issues/87555> for more information
+   = help: add `#![feature(concat_bytes)]` to the crate attributes to enable
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0658`.

src/test/ui/macros/concat-bytes-error.rs

@@ -0,0 +1,42 @@
+#![feature(concat_bytes)]
+
+fn main() {
+    concat_bytes!(pie); //~ ERROR expected a byte literal
+    concat_bytes!(pie, pie); //~ ERROR expected a byte literal
+    concat_bytes!("tnrsi", "tnri"); //~ ERROR cannot concatenate string literals
+    concat_bytes!(2.8); //~ ERROR cannot concatenate float literals
+    concat_bytes!(300); //~ ERROR cannot concatenate numeric literals
+    concat_bytes!('a'); //~ ERROR cannot concatenate character literals
+    concat_bytes!(true, false); //~ ERROR cannot concatenate boolean literals
+    concat_bytes!(42, b"va", b'l'); //~ ERROR cannot concatenate numeric literals
+    concat_bytes!(42, b"va", b'l', [1, 2]); //~ ERROR cannot concatenate numeric literals
+    concat_bytes!([
+        "hi", //~ ERROR cannot concatenate string literals
+    ]);
+    concat_bytes!([
+        'a', //~ ERROR cannot concatenate character literals
+    ]);
+    concat_bytes!([
+        true, //~ ERROR cannot concatenate boolean literals
+    ]);
+    concat_bytes!([
+        false, //~ ERROR cannot concatenate boolean literals
+    ]);
+    concat_bytes!([
+        2.6, //~ ERROR cannot concatenate float literals
+    ]);
+    concat_bytes!([
+        265, //~ ERROR numeric literal is out of bounds
+    ]);
+    concat_bytes!([
+        -33, //~ ERROR expected a byte literal
+    ]);
+    concat_bytes!([
+        b"hi!", //~ ERROR cannot concatenate doubly nested array
+    ]);
+    concat_bytes!([
+        [5, 6, 7], //~ ERROR cannot concatenate doubly nested array
+    ]);
+    concat_bytes!(5u16); //~ ERROR cannot concatenate numeric literals
+    concat_bytes!([5u16]); //~ ERROR numeric literal is not a `u8`
+}

src/test/ui/macros/concat-bytes-error.stderr

@@ -0,0 +1,131 @@
+error: expected a byte literal
+  --> $DIR/concat-bytes-error.rs:4:19
+   |
+LL |     concat_bytes!(pie);
+   |                   ^^^
+   |
+   = note: only byte literals (like `b"foo"`, `b's'`, and `[3, 4, 5]`) can be passed to `concat_bytes!()`
+
+error: expected a byte literal
+  --> $DIR/concat-bytes-error.rs:5:19
+   |
+LL |     concat_bytes!(pie, pie);
+   |                   ^^^  ^^^
+   |
+   = note: only byte literals (like `b"foo"`, `b's'`, and `[3, 4, 5]`) can be passed to `concat_bytes!()`
+
+error: cannot concatenate string literals
+  --> $DIR/concat-bytes-error.rs:6:19
+   |
+LL |     concat_bytes!("tnrsi", "tnri");
+   |                   ^^^^^^^ help: try using a byte string: `b"tnrsi"`
+
+error: cannot concatenate float literals
+  --> $DIR/concat-bytes-error.rs:7:19
+   |
+LL |     concat_bytes!(2.8);
+   |                   ^^^
+
+error: cannot concatenate numeric literals
+  --> $DIR/concat-bytes-error.rs:8:19
+   |
+LL |     concat_bytes!(300);
+   |                   ^^^ help: try wrapping the number in an array: `[300]`
+
+error: cannot concatenate character literals
+  --> $DIR/concat-bytes-error.rs:9:19
+   |
+LL |     concat_bytes!('a');
+   |                   ^^^ help: try using a byte character: `b'a'`
+
+error: cannot concatenate boolean literals
+  --> $DIR/concat-bytes-error.rs:10:19
+   |
+LL |     concat_bytes!(true, false);
+   |                   ^^^^
+
+error: cannot concatenate numeric literals
+  --> $DIR/concat-bytes-error.rs:11:19
+   |
+LL |     concat_bytes!(42, b"va", b'l');
+   |                   ^^ help: try wrapping the number in an array: `[42]`
+
+error: cannot concatenate numeric literals
+  --> $DIR/concat-bytes-error.rs:12:19
+   |
+LL |     concat_bytes!(42, b"va", b'l', [1, 2]);
+   |                   ^^ help: try wrapping the number in an array: `[42]`
+
+error: cannot concatenate string literals
+  --> $DIR/concat-bytes-error.rs:14:9
+   |
+LL |         "hi",
+   |         ^^^^
+
+error: cannot concatenate character literals
+  --> $DIR/concat-bytes-error.rs:17:9
+   |
+LL |         'a',
+   |         ^^^ help: try using a byte character: `b'a'`
+
+error: cannot concatenate boolean literals
+  --> $DIR/concat-bytes-error.rs:20:9
+   |
+LL |         true,
+   |         ^^^^
+
+error: cannot concatenate boolean literals
+  --> $DIR/concat-bytes-error.rs:23:9
+   |
+LL |         false,
+   |         ^^^^^
+
+error: cannot concatenate float literals
+  --> $DIR/concat-bytes-error.rs:26:9
+   |
+LL |         2.6,
+   |         ^^^
+
+error: numeric literal is out of bounds
+  --> $DIR/concat-bytes-error.rs:29:9
+   |
+LL |         265,
+   |         ^^^
+
+error: expected a byte literal
+  --> $DIR/concat-bytes-error.rs:32:9
+   |
+LL |         -33,
+   |         ^^^
+   |
+   = note: only byte literals (like `b"foo"`, `b's'`, and `[3, 4, 5]`) can be passed to `concat_bytes!()`
+
+error: cannot concatenate doubly nested array
+  --> $DIR/concat-bytes-error.rs:35:9
+   |
+LL |         b"hi!",
+   |         ^^^^^^
+   |
+   = note: byte strings are treated as arrays of bytes
+   = help: try flattening the array
+
+error: cannot concatenate doubly nested array
+  --> $DIR/concat-bytes-error.rs:38:9
+   |
+LL |         [5, 6, 7],
+   |         ^^^^^^^^^
+
+error: cannot concatenate numeric literals
+  --> $DIR/concat-bytes-error.rs:40:19
+   |
+LL |     concat_bytes!(5u16);
+   |                   ^^^^ help: try wrapping the number in an array: `[5u16]`
+
+error: numeric literal is not a `u8`
+  --> $DIR/concat-bytes-error.rs:41:20
+   |
+LL |     concat_bytes!([5u16]);
+   |                    ^^^^
+
+error: aborting due to 20 previous errors
+

src/test/ui/macros/concat-bytes.rs

@@ -0,0 +1,7 @@
+// run-pass
+#![feature(concat_bytes)]
+
+fn main() {
+    assert_eq!(concat_bytes!(), &[]);
+    assert_eq!(concat_bytes!(b'A', b"BC", [68, b'E', 70]), b"ABCDEF");
+}