Merging upstream version 1.68.2+dfsg1.

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

10 files changed, 1299 insertions, 0 deletions

diff --git a/tests/ui/macros/rfc-3086-metavar-expr/count-and-length-are-distinct.rs b/tests/ui/macros/rfc-3086-metavar-expr/count-and-length-are-distinct.rs
new file mode 100644
index 000000000..ab8d95a41
--- /dev/null
+++ b/tests/ui/macros/rfc-3086-metavar-expr/count-and-length-are-distinct.rs
@@ -0,0 +1,271 @@
+// run-pass
+
+#![feature(macro_metavar_expr)]
+
+fn main() {
+    macro_rules! one_nested_count_and_length {
+        ( $( [ $( $l:literal ),* ] ),* ) => {
+            [
+                // outer-most repetition
+                $(
+                    // inner-most repetition
+                    $(
+                        ${ignore(l)} ${index()}, ${length()},
+                    )*
+                    ${count(l)}, ${index()}, ${length()},
+                )*
+                ${count(l)},
+            ]
+        };
+    }
+    assert_eq!(
+        one_nested_count_and_length!(["foo"], ["bar", "baz"]),
+        [
+            // # ["foo"]
+
+            // ## inner-most repetition (first iteration)
+            //
+            // `index` is 0 because this is the first inner-most iteration.
+            // `length` is 1 because there is only one inner-most repetition, "foo".
+            0, 1,
+
+            // ## outer-most repetition (first iteration)
+            //
+            // `count` is 1 because of "foo", i,e, `$l` has only one repetition,
+            // `index` is 0 because this is the first outer-most iteration.
+            // `length` is 2 because there are 2 outer-most repetitions, ["foo"] and ["bar", "baz"]
+            1, 0, 2,
+
+            // # ["bar", "baz"]
+
+            // ## inner-most repetition (first iteration)
+            //
+            // `index` is 0 because this is the first inner-most iteration
+            // `length` is 2 because there are repetitions, "bar" and "baz"
+            0, 2,
+
+            // ## inner-most repetition (second iteration)
+            //
+            // `index` is 1 because this is the second inner-most iteration
+            // `length` is 2 because there are repetitions, "bar" and "baz"
+            1, 2,
+
+            // ## outer-most repetition (second iteration)
+            //
+            // `count` is 2 because of "bar" and "baz", i,e, `$l` has two repetitions,
+            // `index` is 1 because this is the second outer-most iteration
+            // `length` is 2 because there are 2 outer-most repetitions, ["foo"] and ["bar", "baz"]
+            2, 1, 2,
+
+            // # last count
+
+            // Because there are a total of 3 repetitions of `$l`, "foo", "bar" and "baz"
+            3,
+        ]
+    );
+
+    // Based on the above explanation, the following macros should be straightforward
+
+    // Grouped from the outer-most to the inner-most
+    macro_rules! three_nested_count {
+        ( $( { $( [ $( ( $( $i:ident )* ) )* ] )* } )* ) => {
+            &[
+                $( $( $(
+                    &[
+                        ${ignore(i)} ${count(i, 0)},
+                    ][..],
+                )* )* )*
+
+                $( $(
+                    &[
+                        ${ignore(i)} ${count(i, 0)},
+                        ${ignore(i)} ${count(i, 1)},
+                    ][..],
+                )* )*
+
+                $(
+                    &[
+                        ${ignore(i)} ${count(i, 0)},
+                        ${ignore(i)} ${count(i, 1)},
+                        ${ignore(i)} ${count(i, 2)},
+                    ][..],
+                )*
+
+                &[
+                    ${count(i, 0)},
+                    ${count(i, 1)},
+                    ${count(i, 2)},
+                    ${count(i, 3)},
+                ][..]
+            ][..]
+        }
+    }
+    assert_eq!(
+        three_nested_count!(
+            {
+                [ (a b c) (d e f) ]
+                [ (g h) (i j k l m) ]
+                [ (n) ]
+            }
+            {
+                [ (o) (p q) (r s) ]
+                [ (t u v w x y z) ]
+            }
+        ),
+        &[
+            // a b c
+            &[3][..],
+            // d e f
+            &[3][..],
+            // g h
+            &[2][..],
+            // i j k l m
+            &[5][..],
+            // n
+            &[1][..],
+            // o
+            &[1][..],
+            // p q
+            &[2][..],
+            // r s
+            &[2][..],
+            // t u v w x y z
+            &[7][..],
+
+            // (a b c) (d e f)
+            &[2, 6][..],
+            // (g h) (i j k l m)
+            &[2, 7][..],
+            // (n)
+            &[1, 1][..],
+            // (o) (p q) (r s)
+            &[3, 5][..],
+            // (t u v w x y z)
+            &[1, 7][..],
+
+            // [ (a b c) (d e f) ]
+            // [ (g h) (i j k l m) ]
+            // [ (n) ]
+            &[3, 5, 14][..],
+            // [ (o) (p q) (r s) ]
+            // [ (t u v w x y z) ]
+            &[2, 4, 12][..],
+
+            // {
+            //     [ (a b c) (d e f) ]
+            //     [ (g h) (i j k l m) ]
+            //     [ (n) ]
+            // }
+            // {
+            //     [ (o) (p q) (r s) ]
+            //     [ (t u v w x y z) ]
+            // }
+            &[2, 5, 9, 26][..]
+        ][..]
+    );
+
+    // Grouped from the outer-most to the inner-most
+    macro_rules! three_nested_length {
+        ( $( { $( [ $( ( $( $i:ident )* ) )* ] )* } )* ) => {
+            &[
+                $( $( $( $(
+                    &[
+                        ${ignore(i)} ${length(3)},
+                        ${ignore(i)} ${length(2)},
+                        ${ignore(i)} ${length(1)},
+                        ${ignore(i)} ${length(0)},
+                    ][..],
+                )* )* )* )*
+
+                $( $( $(
+                    &[
+                        ${ignore(i)} ${length(2)},
+                        ${ignore(i)} ${length(1)},
+                        ${ignore(i)} ${length(0)},
+                    ][..],
+                )* )* )*
+
+                $( $(
+                    &[
+                        ${ignore(i)} ${length(1)},
+                        ${ignore(i)} ${length(0)},
+                    ][..],
+                )* )*
+
+                $(
+                    &[
+                        ${ignore(i)} ${length(0)},
+                    ][..],
+                )*
+            ][..]
+        }
+    }
+    assert_eq!(
+        three_nested_length!(
+            {
+                [ (a b c) (d e f) ]
+                [ (g h) (i j k l m) ]
+                [ (n) ]
+            }
+            {
+                [ (o) (p q) (r s) ]
+                [ (t u v w x y z) ]
+            }
+        ),
+        &[
+            // a b c
+            &[2, 3, 2, 3][..], &[2, 3, 2, 3][..], &[2, 3, 2, 3][..],
+            // d e f
+            &[2, 3, 2, 3][..], &[2, 3, 2, 3][..], &[2, 3, 2, 3][..],
+            // g h
+            &[2, 3, 2, 2][..], &[2, 3, 2, 2][..],
+            // i j k l m
+            &[2, 3, 2, 5][..], &[2, 3, 2, 5][..], &[2, 3, 2, 5][..], &[2, 3, 2, 5][..],
+            &[2, 3, 2, 5][..],
+            // n
+            &[2, 3, 1, 1][..],
+            // o
+            &[2, 2, 3, 1][..],
+            // p q
+            &[2, 2, 3, 2][..], &[2, 2, 3, 2][..],
+            // r s
+            &[2, 2, 3, 2][..], &[2, 2, 3, 2][..],
+            // t u v w x y z
+            &[2, 2, 1, 7][..], &[2, 2, 1, 7][..], &[2, 2, 1, 7][..], &[2, 2, 1, 7][..],
+            &[2, 2, 1, 7][..], &[2, 2, 1, 7][..], &[2, 2, 1, 7][..],
+
+            // (a b c) (d e f)
+            &[2, 3, 2][..], &[2, 3, 2][..],
+            // (g h) (i j k l m)
+            &[2, 3, 2][..], &[2, 3, 2][..],
+            // (n)
+            &[2, 3, 1][..],
+            // (o) (p q) (r s)
+            &[2, 2, 3][..], &[2, 2, 3][..], &[2, 2, 3][..],
+            // (t u v w x y z)
+            &[2, 2, 1][..],
+
+            // [ (a b c) (d e f) ]
+            // [ (g h) (i j k l m) ]
+            // [ (n) ]
+            &[2, 3][..], &[2, 3][..],  &[2, 3,][..],
+            // [ (o) (p q) (r s) ]
+            // [ (t u v w x y z) ]
+            &[2, 2][..], &[2, 2][..],
+
+            // {
+            //     [ (a b c) (d e f) ]
+            //     [ (g h) (i j k l m) ]
+            //     [ (n) ]
+            // }
+            // {
+            //     [ (o) (p q) (r s) ]
+            //     [ (t u v w x y z) ]
+            // }
+            &[2][..], &[2][..]
+        ][..]
+    );
+
+    // It is possible to say, to some degree, that count is an "amalgamation" of length (see
+    // each length line result and compare them with the count results)
+}
diff --git a/tests/ui/macros/rfc-3086-metavar-expr/dollar-dollar-has-correct-behavior.rs b/tests/ui/macros/rfc-3086-metavar-expr/dollar-dollar-has-correct-behavior.rs
new file mode 100644
index 000000000..ed94c27cf
--- /dev/null
+++ b/tests/ui/macros/rfc-3086-metavar-expr/dollar-dollar-has-correct-behavior.rs
@@ -0,0 +1,28 @@
+// run-pass
+
+#![feature(macro_metavar_expr)]
+
+macro_rules! nested {
+    ( $a:ident ) => {
+        macro_rules! $a {
+            ( $$( $b:ident ),* ) => {
+                $$(
+                    macro_rules! $b {
+                        ( $$$$( $c:ident ),* ) => {
+                            $$$$(
+                                fn $c() -> &'static str { stringify!($c) }
+                            ),*
+                        };
+                    }
+                )*
+            };
+        }
+    };
+}
+
+fn main() {
+    nested!(a);
+    a!(b);
+    b!(c);
+    assert_eq!(c(), "c");
+}
diff --git a/tests/ui/macros/rfc-3086-metavar-expr/feature-gate-macro_metavar_expr.rs b/tests/ui/macros/rfc-3086-metavar-expr/feature-gate-macro_metavar_expr.rs
new file mode 100644
index 000000000..d05cd1b31
--- /dev/null
+++ b/tests/ui/macros/rfc-3086-metavar-expr/feature-gate-macro_metavar_expr.rs
@@ -0,0 +1,148 @@
+// run-pass
+
+#![feature(macro_metavar_expr)]
+
+/// Count the number of idents in a macro repetition.
+macro_rules! count_idents {
+    ( $( $i:ident ),* ) => {
+        ${count(i)}
+    };
+}
+
+/// Count the number of idents in a 2-dimensional macro repetition.
+macro_rules! count_idents_2 {
+    ( $( [ $( $i:ident ),* ] ),* ) => {
+        ${count(i)}
+    };
+}
+
+/// Mostly counts the number of OUTER-MOST repetitions
+macro_rules! count_depth_limits {
+    ( $( { $( [ $( $outer:ident : ( $( $inner:ident )* ) )* ] )* } )* ) => {
+        (
+            (
+                ${count(inner)},
+                ${count(inner, 0)},
+                ${count(inner, 1)},
+                ${count(inner, 2)},
+                ${count(inner, 3)},
+            ),
+            (
+                ${count(outer)},
+                ${count(outer, 0)},
+                ${count(outer, 1)},
+                ${count(outer, 2)},
+            ),
+        )
+    };
+}
+
+/// Produce (index, length) pairs for literals in a macro repetition.
+/// The literal is not included in the output, so this macro uses the
+/// `ignore` meta-variable expression to create a non-expanding
+/// repetition binding.
+macro_rules! enumerate_literals {
+    ( $( ($l:stmt) ),* ) => {
+        [$( ${ignore(l)} (${index()}, ${length()}) ),*]
+    };
+}
+
+/// Produce index and length tuples for literals in a 2-dimensional
+/// macro repetition.
+macro_rules! enumerate_literals_2 {
+    ( $( [ $( ($l:literal) ),* ] ),* ) => {
+        [
+            $(
+                $(
+                    (
+                        ${index(1)},
+                        ${length(1)},
+                        ${index(0)},
+                        ${length(0)},
+                        $l
+                    ),
+                )*
+            )*
+        ]
+    };
+}
+
+/// Generate macros that count idents and then add a constant number
+/// to the count.
+///
+/// This macro uses dollar escaping to make it unambiguous as to which
+/// macro the repetition belongs to.
+macro_rules! make_count_adders {
+    ( $( $i:ident, $b:literal );* ) => {
+        $(
+            macro_rules! $i {
+                ( $$( $$j:ident ),* ) => {
+                    $b + $${count(j)}
+                };
+            }
+        )*
+    };
+}
+
+make_count_adders! { plus_one, 1; plus_five, 5 }
+
+/// Generate a macro that allows selection of a particular literal
+/// from a sequence of inputs by their identifier.
+///
+/// This macro uses dollar escaping to make it unambiguous as to which
+/// macro the repetition belongs to, and to allow expansion of an
+/// identifier the name of which is not known in the definition
+/// of `make_picker`.
+macro_rules! make_picker {
+    ( $m:ident => $( $i:ident ),* ; $p:ident ) => {
+        macro_rules! $m {
+            ( $( $$ $i:literal ),* ) => {
+                $$ $p
+            };
+        }
+    };
+}
+
+make_picker!(first => a, b; a);
+
+make_picker!(second => a, b; b);
+
+fn main() {
+    assert_eq!(count_idents!(a, b, c), 3);
+    assert_eq!(count_idents_2!([a, b, c], [d, e], [f]), 6);
+    assert_eq!(
+        count_depth_limits! {
+            {
+                [ A: (a b c) D: (d e f) ]
+                [ G: (g h) I: (i j k l m) ]
+                [ N: (n) ]
+            }
+            {
+                [ O: (o) P: (p q) R: (r s) ]
+                [ T: (t u v w x y z) ]
+            }
+        },
+        ((26, 2, 5, 9, 26), (9, 2, 5, 9))
+    );
+    assert_eq!(enumerate_literals![("foo"), ("bar")], [(0, 2), (1, 2)]);
+    assert_eq!(
+        enumerate_literals_2![
+            [("foo"), ("bar"), ("baz")],
+            [("qux"), ("quux"), ("quuz"), ("xyzzy")]
+        ],
+        [
+            (0, 2, 0, 3, "foo"),
+            (0, 2, 1, 3, "bar"),
+            (0, 2, 2, 3, "baz"),
+
+            (1, 2, 0, 4, "qux"),
+            (1, 2, 1, 4, "quux"),
+            (1, 2, 2, 4, "quuz"),
+            (1, 2, 3, 4, "xyzzy"),
+        ]
+    );
+    assert_eq!(plus_one!(a, b, c), 4);
+    assert_eq!(plus_five!(a, b), 7);
+    assert_eq!(first!(1, 2), 1);
+    assert_eq!(second!(1, 2), 2);
+}
diff --git a/tests/ui/macros/rfc-3086-metavar-expr/macro-expansion.rs b/tests/ui/macros/rfc-3086-metavar-expr/macro-expansion.rs
new file mode 100644
index 000000000..b954967c4
--- /dev/null
+++ b/tests/ui/macros/rfc-3086-metavar-expr/macro-expansion.rs
@@ -0,0 +1,102 @@
+// run-pass
+
+#![feature(macro_metavar_expr)]
+
+#[derive(Debug)]
+struct Example<'a> {
+    _indexes: &'a [(u32, u32)],
+    _counts: &'a [u32],
+    _nested: Vec<Example<'a>>,
+}
+
+macro_rules! example {
+    ( $( [ $( ( $( $x:ident )* ) )* ] )* ) => {
+        Example {
+            _indexes: &[],
+            _counts: &[${count(x, 0)}, ${count(x, 1)}, ${count(x, 2)}],
+            _nested: vec![
+            $(
+                Example {
+                    _indexes: &[(${index()}, ${length()})],
+                    _counts: &[${count(x, 0)}, ${count(x, 1)}],
+                    _nested: vec![
+                    $(
+                        Example {
+                            _indexes: &[(${index(1)}, ${length(1)}), (${index()}, ${length()})],
+                            _counts: &[${count(x)}],
+                            _nested: vec![
+                            $(
+                                Example {
+                                    _indexes: &[
+                                        (${index(2)}, ${length(2)}),
+                                        (${index(1)}, ${length(1)}),
+                                        (${index()}, ${length()})
+                                    ],
+                                    _counts: &[],
+                                    _nested: vec![],
+                                    ${ignore(x)}
+                                }
+                            ),*
+                            ]
+                        }
+                    ),*
+                    ]
+                }
+            ),*
+            ]
+        }
+    };
+}
+
+static EXPECTED: &str = concat!(
+    "Example { _indexes: [], _counts: [2, 4, 13], _nested: [",
+    concat!(
+        "Example { _indexes: [(0, 2)], _counts: [3, 10], _nested: [",
+        concat!(
+            "Example { _indexes: [(0, 2), (0, 3)], _counts: [4], _nested: [",
+            concat!(
+                "Example { _indexes: [(0, 2), (0, 3), (0, 4)], _counts: [], _nested: [] }, ",
+                "Example { _indexes: [(0, 2), (0, 3), (1, 4)], _counts: [], _nested: [] }, ",
+                "Example { _indexes: [(0, 2), (0, 3), (2, 4)], _counts: [], _nested: [] }, ",
+                "Example { _indexes: [(0, 2), (0, 3), (3, 4)], _counts: [], _nested: [] }",
+            ),
+            "] }, ",
+            "Example { _indexes: [(0, 2), (1, 3)], _counts: [4], _nested: [",
+            concat!(
+                "Example { _indexes: [(0, 2), (1, 3), (0, 4)], _counts: [], _nested: [] }, ",
+                "Example { _indexes: [(0, 2), (1, 3), (1, 4)], _counts: [], _nested: [] }, ",
+                "Example { _indexes: [(0, 2), (1, 3), (2, 4)], _counts: [], _nested: [] }, ",
+                "Example { _indexes: [(0, 2), (1, 3), (3, 4)], _counts: [], _nested: [] }",
+            ),
+            "] }, ",
+            "Example { _indexes: [(0, 2), (2, 3)], _counts: [2], _nested: [",
+            concat!(
+                "Example { _indexes: [(0, 2), (2, 3), (0, 2)], _counts: [], _nested: [] }, ",
+                "Example { _indexes: [(0, 2), (2, 3), (1, 2)], _counts: [], _nested: [] }",
+            ),
+            "] }",
+        ),
+        "] }, ",
+        "Example { _indexes: [(1, 2)], _counts: [1, 3], _nested: [",
+        concat!(
+            "Example { _indexes: [(1, 2), (0, 1)], _counts: [3], _nested: [",
+            concat!(
+                "Example { _indexes: [(1, 2), (0, 1), (0, 3)], _counts: [], _nested: [] }, ",
+                "Example { _indexes: [(1, 2), (0, 1), (1, 3)], _counts: [], _nested: [] }, ",
+                "Example { _indexes: [(1, 2), (0, 1), (2, 3)], _counts: [], _nested: [] }",
+            ),
+            "] }",
+        ),
+        "] }",
+    ),
+    "] }",
+);
+
+fn main() {
+    let e = example! {
+        [ ( A B C D ) ( E F G H ) ( I J ) ]
+        [ ( K L M ) ]
+    };
+    let debug = format!("{:?}", e);
+    assert_eq!(debug, EXPECTED);
+}
diff --git a/tests/ui/macros/rfc-3086-metavar-expr/out-of-bounds-arguments.rs b/tests/ui/macros/rfc-3086-metavar-expr/out-of-bounds-arguments.rs
new file mode 100644
index 000000000..6a0d68bd6
--- /dev/null
+++ b/tests/ui/macros/rfc-3086-metavar-expr/out-of-bounds-arguments.rs
@@ -0,0 +1,43 @@
+#![feature(macro_metavar_expr)]
+
+macro_rules! a {
+    ( $( { $( [ $( ( $( $foo:ident )* ) )* ] )* } )* ) => {
+        (
+            ${count(foo, 0)},
+            ${count(foo, 10)},
+            //~^ ERROR depth parameter on meta-variable expression `count` must be less than 4
+        )
+    };
+}
+
+macro_rules! b {
+    ( $( { $( [ $( $foo:ident )* ] )* } )* ) => {
+        (
+            $( $( $(
+                ${ignore(foo)}
+                ${index(0)},
+                ${index(10)},
+                //~^ ERROR depth parameter on meta-variable expression `index` must be less than 3
+            )* )* )*
+        )
+    };
+}
+
+macro_rules! c {
+    ( $( { $( $foo:ident )* } )* ) => {
+        (
+            $( $(
+                ${ignore(foo)}
+                ${length(0)}
+                ${length(10)}
+                //~^ ERROR depth parameter on meta-variable expression `length` must be less than 2
+            )* )*
+        )
+    };
+}
+
+fn main() {
+    a!( { [ (a) ] [ (b c) ] } );
+    b!( { [ a b ] } );
+    c!({ a });
+}
diff --git a/tests/ui/macros/rfc-3086-metavar-expr/out-of-bounds-arguments.stderr b/tests/ui/macros/rfc-3086-metavar-expr/out-of-bounds-arguments.stderr
new file mode 100644
index 000000000..236122b64
--- /dev/null
+++ b/tests/ui/macros/rfc-3086-metavar-expr/out-of-bounds-arguments.stderr
@@ -0,0 +1,20 @@
+error: depth parameter on meta-variable expression `count` must be less than 4
+  --> $DIR/out-of-bounds-arguments.rs:7:14
+   |
+LL |             ${count(foo, 10)},
+   |              ^^^^^^^^^^^^^^^^
+
+error: depth parameter on meta-variable expression `index` must be less than 3
+  --> $DIR/out-of-bounds-arguments.rs:19:18
+   |
+LL |                 ${index(10)},
+   |                  ^^^^^^^^^^^
+
+error: depth parameter on meta-variable expression `length` must be less than 2
+  --> $DIR/out-of-bounds-arguments.rs:32:18
+   |
+LL |                 ${length(10)}
+   |                  ^^^^^^^^^^^^
+
+error: aborting due to 3 previous errors
+
diff --git a/tests/ui/macros/rfc-3086-metavar-expr/required-feature.rs b/tests/ui/macros/rfc-3086-metavar-expr/required-feature.rs
new file mode 100644
index 000000000..b4fef11f1
--- /dev/null
+++ b/tests/ui/macros/rfc-3086-metavar-expr/required-feature.rs
@@ -0,0 +1,44 @@
+macro_rules! count {
+    ( $( $e:stmt ),* ) => {
+        ${ count(e) }
+        //~^ ERROR meta-variable expressions are unstable
+    };
+}
+
+macro_rules! dollar_dollar {
+    () => {
+        macro_rules! bar {
+            ( $$( $$any:tt )* ) => { $$( $$any )* };
+            //~^ ERROR meta-variable expressions are unstable
+            //~| ERROR meta-variable expressions are unstable
+            //~| ERROR meta-variable expressions are unstable
+            //~| ERROR meta-variable expressions are unstable
+        }
+    };
+}
+
+macro_rules! index {
+    ( $( $e:stmt ),* ) => {
+        $( ${ignore(e)} ${index()} )*
+        //~^ ERROR meta-variable expressions are unstable
+        //~| ERROR meta-variable expressions are unstable
+    };
+}
+
+macro_rules! ignore {
+    ( $( $i:stmt ),* ) => {{
+        0 $( + 1 ${ignore(i)} )*
+        //~^ ERROR meta-variable expressions are unstable
+    }};
+}
+
+macro_rules! length {
+    ( $( $e:stmt ),* ) => {
+        $( ${ignore(e)} ${length()} )*
+        //~^ ERROR meta-variable expressions are unstable
+        //~| ERROR meta-variable expressions are unstable
+    };
+}
+
+fn main() {
+}
diff --git a/tests/ui/macros/rfc-3086-metavar-expr/required-feature.stderr b/tests/ui/macros/rfc-3086-metavar-expr/required-feature.stderr
new file mode 100644
index 000000000..ecf598b10
--- /dev/null
+++ b/tests/ui/macros/rfc-3086-metavar-expr/required-feature.stderr
@@ -0,0 +1,93 @@
+error[E0658]: meta-variable expressions are unstable
+  --> $DIR/required-feature.rs:3:10
+   |
+LL |         ${ count(e) }
+   |          ^^^^^^^^^^^^
+   |
+   = note: see issue #83527 <https://github.com/rust-lang/rust/issues/83527> for more information
+   = help: add `#![feature(macro_metavar_expr)]` to the crate attributes to enable
+
+error[E0658]: meta-variable expressions are unstable
+  --> $DIR/required-feature.rs:11:16
+   |
+LL |             ( $$( $$any:tt )* ) => { $$( $$any )* };
+   |                ^
+   |
+   = note: see issue #83527 <https://github.com/rust-lang/rust/issues/83527> for more information
+   = help: add `#![feature(macro_metavar_expr)]` to the crate attributes to enable
+
+error[E0658]: meta-variable expressions are unstable
+  --> $DIR/required-feature.rs:11:20
+   |
+LL |             ( $$( $$any:tt )* ) => { $$( $$any )* };
+   |                    ^
+   |
+   = note: see issue #83527 <https://github.com/rust-lang/rust/issues/83527> for more information
+   = help: add `#![feature(macro_metavar_expr)]` to the crate attributes to enable
+
+error[E0658]: meta-variable expressions are unstable
+  --> $DIR/required-feature.rs:11:39
+   |
+LL |             ( $$( $$any:tt )* ) => { $$( $$any )* };
+   |                                       ^
+   |
+   = note: see issue #83527 <https://github.com/rust-lang/rust/issues/83527> for more information
+   = help: add `#![feature(macro_metavar_expr)]` to the crate attributes to enable
+
+error[E0658]: meta-variable expressions are unstable
+  --> $DIR/required-feature.rs:11:43
+   |
+LL |             ( $$( $$any:tt )* ) => { $$( $$any )* };
+   |                                           ^
+   |
+   = note: see issue #83527 <https://github.com/rust-lang/rust/issues/83527> for more information
+   = help: add `#![feature(macro_metavar_expr)]` to the crate attributes to enable
+
+error[E0658]: meta-variable expressions are unstable
+  --> $DIR/required-feature.rs:22:13
+   |
+LL |         $( ${ignore(e)} ${index()} )*
+   |             ^^^^^^^^^^^
+   |
+   = note: see issue #83527 <https://github.com/rust-lang/rust/issues/83527> for more information
+   = help: add `#![feature(macro_metavar_expr)]` to the crate attributes to enable
+
+error[E0658]: meta-variable expressions are unstable
+  --> $DIR/required-feature.rs:22:26
+   |
+LL |         $( ${ignore(e)} ${index()} )*
+   |                          ^^^^^^^^^
+   |
+   = note: see issue #83527 <https://github.com/rust-lang/rust/issues/83527> for more information
+   = help: add `#![feature(macro_metavar_expr)]` to the crate attributes to enable
+
+error[E0658]: meta-variable expressions are unstable
+  --> $DIR/required-feature.rs:30:19
+   |
+LL |         0 $( + 1 ${ignore(i)} )*
+   |                   ^^^^^^^^^^^
+   |
+   = note: see issue #83527 <https://github.com/rust-lang/rust/issues/83527> for more information
+   = help: add `#![feature(macro_metavar_expr)]` to the crate attributes to enable
+
+error[E0658]: meta-variable expressions are unstable
+  --> $DIR/required-feature.rs:37:13
+   |
+LL |         $( ${ignore(e)} ${length()} )*
+   |             ^^^^^^^^^^^
+   |
+   = note: see issue #83527 <https://github.com/rust-lang/rust/issues/83527> for more information
+   = help: add `#![feature(macro_metavar_expr)]` to the crate attributes to enable
+
+error[E0658]: meta-variable expressions are unstable
+  --> $DIR/required-feature.rs:37:26
+   |
+LL |         $( ${ignore(e)} ${length()} )*
+   |                          ^^^^^^^^^^
+   |
+   = note: see issue #83527 <https://github.com/rust-lang/rust/issues/83527> for more information
+   = help: add `#![feature(macro_metavar_expr)]` to the crate attributes to enable
+
+error: aborting due to 10 previous errors
+
+For more information about this error, try `rustc --explain E0658`.
diff --git a/tests/ui/macros/rfc-3086-metavar-expr/syntax-errors.rs b/tests/ui/macros/rfc-3086-metavar-expr/syntax-errors.rs
new file mode 100644
index 000000000..fdf16442d
--- /dev/null
+++ b/tests/ui/macros/rfc-3086-metavar-expr/syntax-errors.rs
@@ -0,0 +1,165 @@
+#![feature(macro_metavar_expr)]
+
+// `curly` = Right hand side curly brackets
+// `no_rhs_dollar` = No dollar sign at the right hand side meta variable "function"
+// `round` = Left hand side round brackets
+
+macro_rules! curly__no_rhs_dollar__round {
+    ( $( $i:ident ),* ) => { ${ count(i) } };
+}
+
+macro_rules! curly__no_rhs_dollar__no_round {
+    ( $i:ident ) => { ${ count(i) } };
+    //~^ ERROR `count` can not be placed inside the inner-most repetition
+}
+
+macro_rules! curly__rhs_dollar__round {
+    ( $( $i:ident ),* ) => { ${ count($i) } };
+    //~^ ERROR expected identifier, found `$`
+    //~| ERROR expected expression, found `$`
+}
+
+macro_rules! curly__rhs_dollar__no_round {
+    ( $i:ident ) => { ${ count($i) } };
+    //~^ ERROR expected identifier, found `$`
+    //~| ERROR expected expression, found `$`
+}
+
+macro_rules! no_curly__no_rhs_dollar__round {
+    ( $( $i:ident ),* ) => { count(i) };
+    //~^ ERROR cannot find function `count` in this scope
+    //~| ERROR cannot find value `i` in this scope
+}
+
+macro_rules! no_curly__no_rhs_dollar__no_round {
+    ( $i:ident ) => { count(i) };
+    //~^ ERROR cannot find function `count` in this scope
+    //~| ERROR cannot find value `i` in this scope
+}
+
+macro_rules! no_curly__rhs_dollar__round {
+    ( $( $i:ident ),* ) => { count($i) };
+    //~^ ERROR variable 'i' is still repeating at this depth
+}
+
+macro_rules! no_curly__rhs_dollar__no_round {
+    ( $i:ident ) => { count($i) };
+    //~^ ERROR cannot find function `count` in this scope
+}
+
+// Other scenarios
+
+macro_rules! dollar_dollar_in_the_lhs {
+    ( $$ $a:ident ) => {
+    //~^ ERROR unexpected token: $
+    };
+}
+
+macro_rules! extra_garbage_after_metavar {
+    ( $( $i:ident ),* ) => {
+        ${count() a b c}
+        //~^ ERROR unexpected token: a
+        //~| ERROR expected expression, found `$`
+        ${count(i a b c)}
+        //~^ ERROR unexpected token: a
+        ${count(i, 1 a b c)}
+        //~^ ERROR unexpected token: a
+        ${count(i) a b c}
+        //~^ ERROR unexpected token: a
+
+        ${ignore(i) a b c}
+        //~^ ERROR unexpected token: a
+        ${ignore(i a b c)}
+        //~^ ERROR unexpected token: a
+
+        ${index() a b c}
+        //~^ ERROR unexpected token: a
+        ${index(1 a b c)}
+        //~^ ERROR unexpected token: a
+
+        ${index() a b c}
+        //~^ ERROR unexpected token: a
+        ${index(1 a b c)}
+        //~^ ERROR unexpected token: a
+    };
+}
+
+const IDX: usize = 1;
+macro_rules! metavar_depth_is_not_literal {
+    ( $( $i:ident ),* ) => { ${ index(IDX) } };
+    //~^ ERROR meta-variable expression depth must be a literal
+    //~| ERROR expected expression, found `$`
+}
+
+macro_rules! metavar_in_the_lhs {
+    ( ${ length() } ) => {
+        //~^ ERROR unexpected token: {
+        //~| ERROR expected one of: `*`, `+`, or `?`
+    };
+}
+
+macro_rules! metavar_token_without_ident {
+    ( $( $i:ident ),* ) => { ${ ignore() } };
+    //~^ ERROR expected identifier
+    //~| ERROR expected expression, found `$`
+}
+
+macro_rules! metavar_with_literal_suffix {
+    ( $( $i:ident ),* ) => { ${ index(1u32) } };
+    //~^ ERROR only unsuffixes integer literals are supported in meta-variable expressions
+    //~| ERROR expected expression, found `$`
+}
+
+macro_rules! metavar_without_parens {
+    ( $( $i:ident ),* ) => { ${ count{i} } };
+    //~^ ERROR meta-variable expression parameter must be wrapped in parentheses
+    //~| ERROR expected expression, found `$`
+}
+
+macro_rules! open_brackets_without_tokens {
+    ( $( $i:ident ),* ) => { ${ {} } };
+    //~^ ERROR expected expression, found `$`
+    //~| ERROR expected identifier
+}
+
+macro_rules! unknown_count_ident {
+    ( $( $i:ident )* ) => {
+        ${count(foo)}
+        //~^ ERROR variable `foo` is not recognized in meta-variable expression
+    };
+}
+
+macro_rules! unknown_ignore_ident {
+    ( $( $i:ident )* ) => {
+        ${ignore(bar)}
+        //~^ ERROR variable `bar` is not recognized in meta-variable expression
+    };
+}
+
+macro_rules! unknown_metavar {
+    ( $( $i:ident ),* ) => { ${ aaaaaaaaaaaaaa(i) } };
+    //~^ ERROR unrecognized meta-variable expression
+    //~| ERROR expected expression
+}
+
+fn main() {
+    curly__no_rhs_dollar__round!(a, b, c);
+    curly__no_rhs_dollar__no_round!(a);
+    curly__rhs_dollar__round!(a, b, c);
+    curly__rhs_dollar__no_round!(a);
+    no_curly__no_rhs_dollar__round!(a, b, c);
+    no_curly__no_rhs_dollar__no_round!(a);
+    no_curly__rhs_dollar__round!(a, b, c);
+    no_curly__rhs_dollar__no_round!(a);
+    //~^ ERROR cannot find value `a` in this scope
+
+    extra_garbage_after_metavar!(a);
+    metavar_depth_is_not_literal!(a);
+    metavar_token_without_ident!(a);
+    metavar_with_literal_suffix!(a);
+    metavar_without_parens!(a);
+    open_brackets_without_tokens!(a);
+    unknown_count_ident!(a);
+    unknown_ignore_ident!(a);
+    unknown_metavar!(a);
+}
diff --git a/tests/ui/macros/rfc-3086-metavar-expr/syntax-errors.stderr b/tests/ui/macros/rfc-3086-metavar-expr/syntax-errors.stderr
new file mode 100644
index 000000000..a6cff95fd
--- /dev/null
+++ b/tests/ui/macros/rfc-3086-metavar-expr/syntax-errors.stderr
@@ -0,0 +1,385 @@
+error: expected identifier, found `$`
+  --> $DIR/syntax-errors.rs:17:33
+   |
+LL |     ( $( $i:ident ),* ) => { ${ count($i) } };
+   |                                 ^^^^^ - help: try removing `$`
+
+error: expected identifier, found `$`
+  --> $DIR/syntax-errors.rs:23:26
+   |
+LL |     ( $i:ident ) => { ${ count($i) } };
+   |                          ^^^^^ - help: try removing `$`
+
+error: unexpected token: $
+  --> $DIR/syntax-errors.rs:53:8
+   |
+LL |     ( $$ $a:ident ) => {
+   |        ^
+
+note: `$$` and meta-variable expressions are not allowed inside macro parameter definitions
+  --> $DIR/syntax-errors.rs:53:8
+   |
+LL |     ( $$ $a:ident ) => {
+   |        ^
+
+error: unexpected token: a
+  --> $DIR/syntax-errors.rs:60:19
+   |
+LL |         ${count() a b c}
+   |                   ^
+   |
+note: meta-variable expression must not have trailing tokens
+  --> $DIR/syntax-errors.rs:60:19
+   |
+LL |         ${count() a b c}
+   |                   ^
+
+error: unexpected token: a
+  --> $DIR/syntax-errors.rs:63:19
+   |
+LL |         ${count(i a b c)}
+   |                   ^
+   |
+note: meta-variable expression must not have trailing tokens
+  --> $DIR/syntax-errors.rs:63:19
+   |
+LL |         ${count(i a b c)}
+   |                   ^
+
+error: unexpected token: a
+  --> $DIR/syntax-errors.rs:65:22
+   |
+LL |         ${count(i, 1 a b c)}
+   |                      ^
+   |
+note: meta-variable expression must not have trailing tokens
+  --> $DIR/syntax-errors.rs:65:22
+   |
+LL |         ${count(i, 1 a b c)}
+   |                      ^
+
+error: unexpected token: a
+  --> $DIR/syntax-errors.rs:67:20
+   |
+LL |         ${count(i) a b c}
+   |                    ^
+   |
+note: meta-variable expression must not have trailing tokens
+  --> $DIR/syntax-errors.rs:67:20
+   |
+LL |         ${count(i) a b c}
+   |                    ^
+
+error: unexpected token: a
+  --> $DIR/syntax-errors.rs:70:21
+   |
+LL |         ${ignore(i) a b c}
+   |                     ^
+   |
+note: meta-variable expression must not have trailing tokens
+  --> $DIR/syntax-errors.rs:70:21
+   |
+LL |         ${ignore(i) a b c}
+   |                     ^
+
+error: unexpected token: a
+  --> $DIR/syntax-errors.rs:72:20
+   |
+LL |         ${ignore(i a b c)}
+   |                    ^
+   |
+note: meta-variable expression must not have trailing tokens
+  --> $DIR/syntax-errors.rs:72:20
+   |
+LL |         ${ignore(i a b c)}
+   |                    ^
+
+error: unexpected token: a
+  --> $DIR/syntax-errors.rs:75:19
+   |
+LL |         ${index() a b c}
+   |                   ^
+   |
+note: meta-variable expression must not have trailing tokens
+  --> $DIR/syntax-errors.rs:75:19
+   |
+LL |         ${index() a b c}
+   |                   ^
+
+error: unexpected token: a
+  --> $DIR/syntax-errors.rs:77:19
+   |
+LL |         ${index(1 a b c)}
+   |                   ^
+   |
+note: meta-variable expression must not have trailing tokens
+  --> $DIR/syntax-errors.rs:77:19
+   |
+LL |         ${index(1 a b c)}
+   |                   ^
+
+error: unexpected token: a
+  --> $DIR/syntax-errors.rs:80:19
+   |
+LL |         ${index() a b c}
+   |                   ^
+   |
+note: meta-variable expression must not have trailing tokens
+  --> $DIR/syntax-errors.rs:80:19
+   |
+LL |         ${index() a b c}
+   |                   ^
+
+error: unexpected token: a
+  --> $DIR/syntax-errors.rs:82:19
+   |
+LL |         ${index(1 a b c)}
+   |                   ^
+   |
+note: meta-variable expression must not have trailing tokens
+  --> $DIR/syntax-errors.rs:82:19
+   |
+LL |         ${index(1 a b c)}
+   |                   ^
+
+error: meta-variable expression depth must be a literal
+  --> $DIR/syntax-errors.rs:89:33
+   |
+LL |     ( $( $i:ident ),* ) => { ${ index(IDX) } };
+   |                                 ^^^^^
+
+error: unexpected token: {
+  --> $DIR/syntax-errors.rs:95:8
+   |
+LL |     ( ${ length() } ) => {
+   |        ^^^^^^^^^^^^
+
+note: `$$` and meta-variable expressions are not allowed inside macro parameter definitions
+  --> $DIR/syntax-errors.rs:95:8
+   |
+LL |     ( ${ length() } ) => {
+   |        ^^^^^^^^^^^^
+
+error: expected one of: `*`, `+`, or `?`
+  --> $DIR/syntax-errors.rs:95:8
+   |
+LL |     ( ${ length() } ) => {
+   |        ^^^^^^^^^^^^
+
+error: expected identifier
+  --> $DIR/syntax-errors.rs:102:33
+   |
+LL |     ( $( $i:ident ),* ) => { ${ ignore() } };
+   |                                 ^^^^^^
+
+error: only unsuffixes integer literals are supported in meta-variable expressions
+  --> $DIR/syntax-errors.rs:108:33
+   |
+LL |     ( $( $i:ident ),* ) => { ${ index(1u32) } };
+   |                                 ^^^^^
+
+error: meta-variable expression parameter must be wrapped in parentheses
+  --> $DIR/syntax-errors.rs:114:33
+   |
+LL |     ( $( $i:ident ),* ) => { ${ count{i} } };
+   |                                 ^^^^^
+
+error: expected identifier
+  --> $DIR/syntax-errors.rs:120:31
+   |
+LL |     ( $( $i:ident ),* ) => { ${ {} } };
+   |                               ^^^^^^
+
+error: unrecognized meta-variable expression
+  --> $DIR/syntax-errors.rs:140:33
+   |
+LL |     ( $( $i:ident ),* ) => { ${ aaaaaaaaaaaaaa(i) } };
+   |                                 ^^^^^^^^^^^^^^ help: supported expressions are count, ignore, index and length
+
+error: `count` can not be placed inside the inner-most repetition
+  --> $DIR/syntax-errors.rs:12:24
+   |
+LL |     ( $i:ident ) => { ${ count(i) } };
+   |                        ^^^^^^^^^^^^
+
+error: expected expression, found `$`
+  --> $DIR/syntax-errors.rs:17:30
+   |
+LL |     ( $( $i:ident ),* ) => { ${ count($i) } };
+   |                              ^ expected expression
+...
+LL |     curly__rhs_dollar__round!(a, b, c);
+   |     ---------------------------------- in this macro invocation
+   |
+   = note: this error originates in the macro `curly__rhs_dollar__round` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: expected expression, found `$`
+  --> $DIR/syntax-errors.rs:23:23
+   |
+LL |     ( $i:ident ) => { ${ count($i) } };
+   |                       ^ expected expression
+...
+LL |     curly__rhs_dollar__no_round!(a);
+   |     ------------------------------- in this macro invocation
+   |
+   = note: this error originates in the macro `curly__rhs_dollar__no_round` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: variable 'i' is still repeating at this depth
+  --> $DIR/syntax-errors.rs:41:36
+   |
+LL |     ( $( $i:ident ),* ) => { count($i) };
+   |                                    ^^
+
+error: expected expression, found `$`
+  --> $DIR/syntax-errors.rs:60:9
+   |
+LL |         ${count() a b c}
+   |         ^ expected expression
+...
+LL |     extra_garbage_after_metavar!(a);
+   |     ------------------------------- in this macro invocation
+   |
+   = note: this error originates in the macro `extra_garbage_after_metavar` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: expected expression, found `$`
+  --> $DIR/syntax-errors.rs:89:30
+   |
+LL |     ( $( $i:ident ),* ) => { ${ index(IDX) } };
+   |                              ^ expected expression
+...
+LL |     metavar_depth_is_not_literal!(a);
+   |     -------------------------------- in this macro invocation
+   |
+   = note: this error originates in the macro `metavar_depth_is_not_literal` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: expected expression, found `$`
+  --> $DIR/syntax-errors.rs:102:30
+   |
+LL |     ( $( $i:ident ),* ) => { ${ ignore() } };
+   |                              ^ expected expression
+...
+LL |     metavar_token_without_ident!(a);
+   |     ------------------------------- in this macro invocation
+   |
+   = note: this error originates in the macro `metavar_token_without_ident` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: expected expression, found `$`
+  --> $DIR/syntax-errors.rs:108:30
+   |
+LL |     ( $( $i:ident ),* ) => { ${ index(1u32) } };
+   |                              ^ expected expression
+...
+LL |     metavar_with_literal_suffix!(a);
+   |     ------------------------------- in this macro invocation
+   |
+   = note: this error originates in the macro `metavar_with_literal_suffix` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: expected expression, found `$`
+  --> $DIR/syntax-errors.rs:114:30
+   |
+LL |     ( $( $i:ident ),* ) => { ${ count{i} } };
+   |                              ^ expected expression
+...
+LL |     metavar_without_parens!(a);
+   |     -------------------------- in this macro invocation
+   |
+   = note: this error originates in the macro `metavar_without_parens` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: expected expression, found `$`
+  --> $DIR/syntax-errors.rs:120:30
+   |
+LL |     ( $( $i:ident ),* ) => { ${ {} } };
+   |                              ^ expected expression
+...
+LL |     open_brackets_without_tokens!(a);
+   |     -------------------------------- in this macro invocation
+   |
+   = note: this error originates in the macro `open_brackets_without_tokens` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: variable `foo` is not recognized in meta-variable expression
+  --> $DIR/syntax-errors.rs:127:17
+   |
+LL |         ${count(foo)}
+   |                 ^^^
+
+error: variable `bar` is not recognized in meta-variable expression
+  --> $DIR/syntax-errors.rs:134:18
+   |
+LL |         ${ignore(bar)}
+   |                  ^^^
+
+error: expected expression, found `$`
+  --> $DIR/syntax-errors.rs:140:30
+   |
+LL |     ( $( $i:ident ),* ) => { ${ aaaaaaaaaaaaaa(i) } };
+   |                              ^ expected expression
+...
+LL |     unknown_metavar!(a);
+   |     ------------------- in this macro invocation
+   |
+   = note: this error originates in the macro `unknown_metavar` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0425]: cannot find value `i` in this scope
+  --> $DIR/syntax-errors.rs:29:36
+   |
+LL |     ( $( $i:ident ),* ) => { count(i) };
+   |                                    ^ not found in this scope
+...
+LL |     no_curly__no_rhs_dollar__round!(a, b, c);
+   |     ---------------------------------------- in this macro invocation
+   |
+   = note: this error originates in the macro `no_curly__no_rhs_dollar__round` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0425]: cannot find value `i` in this scope
+  --> $DIR/syntax-errors.rs:35:29
+   |
+LL |     ( $i:ident ) => { count(i) };
+   |                             ^ not found in this scope
+...
+LL |     no_curly__no_rhs_dollar__no_round!(a);
+   |     ------------------------------------- in this macro invocation
+   |
+   = note: this error originates in the macro `no_curly__no_rhs_dollar__no_round` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0425]: cannot find value `a` in this scope
+  --> $DIR/syntax-errors.rs:153:37
+   |
+LL |     no_curly__rhs_dollar__no_round!(a);
+   |                                     ^ not found in this scope
+
+error[E0425]: cannot find function `count` in this scope
+  --> $DIR/syntax-errors.rs:29:30
+   |
+LL |     ( $( $i:ident ),* ) => { count(i) };
+   |                              ^^^^^ not found in this scope
+...
+LL |     no_curly__no_rhs_dollar__round!(a, b, c);
+   |     ---------------------------------------- in this macro invocation
+   |
+   = note: this error originates in the macro `no_curly__no_rhs_dollar__round` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0425]: cannot find function `count` in this scope
+  --> $DIR/syntax-errors.rs:35:23
+   |
+LL |     ( $i:ident ) => { count(i) };
+   |                       ^^^^^ not found in this scope
+...
+LL |     no_curly__no_rhs_dollar__no_round!(a);
+   |     ------------------------------------- in this macro invocation
+   |
+   = note: this error originates in the macro `no_curly__no_rhs_dollar__no_round` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0425]: cannot find function `count` in this scope
+  --> $DIR/syntax-errors.rs:46:23
+   |
+LL |     ( $i:ident ) => { count($i) };
+   |                       ^^^^^ not found in this scope
+...
+LL |     no_curly__rhs_dollar__no_round!(a);
+   |     ---------------------------------- in this macro invocation
+   |
+   = note: this error originates in the macro `no_curly__rhs_dollar__no_round` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: aborting due to 40 previous errors
+
+For more information about this error, try `rustc --explain E0425`.