Add regression tests for parsing non-existent anonymous enums

tests/ui/parser/anon-enums.rs

@@ -0,0 +1,22 @@
+// Output of proposed syntax for anonymous enums from https://github.com/rust-lang/rfcs/issues/294.
+// https://github.com/rust-lang/rust/issues/100741
+
+fn foo(x: bool | i32) -> i32 | f64 {
+    //~^ ERROR: function parameters require top-level or-patterns in parentheses
+    //~| ERROR: expected one of `:`, `@`, or `|`, found `)`
+    //~| ERROR: expected one of `!`, `(`, `)`, `+`, `,`, `::`, or `<`, found `|`
+    //~| ERROR: expected one of `!`, `(`, `+`, `::`, `<`, `where`, or `{`, found `|`
+    match x {
+        x: i32 => x,
+        true => 42.,
+        false => 0.333,
+    }
+}
+
+fn main() {
+    match foo(true) {
+        42: i32 => (),
+        _: f64 => (),
+        x: i32 => (),
+    }
+}

tests/ui/parser/anon-enums.stderr

@@ -0,0 +1,28 @@
+error: function parameters require top-level or-patterns in parentheses
+  --> $DIR/anon-enums.rs:4:16
+   |
+LL | fn foo(x: bool | i32) -> i32 | f64 {
+   |                ^^^^^
+
+error: expected one of `:`, `@`, or `|`, found `)`
+  --> $DIR/anon-enums.rs:4:21
+   |
+LL | fn foo(x: bool | i32) -> i32 | f64 {
+   |                     ^ expected one of `:`, `@`, or `|`
+
+error: expected one of `!`, `(`, `)`, `+`, `,`, `::`, or `<`, found `|`
+  --> $DIR/anon-enums.rs:4:16
+   |
+LL | fn foo(x: bool | i32) -> i32 | f64 {
+   |               -^ expected one of 7 possible tokens
+   |               |
+   |               help: missing `,`
+
+error: expected one of `!`, `(`, `+`, `::`, `<`, `where`, or `{`, found `|`
+  --> $DIR/anon-enums.rs:4:30
+   |
+LL | fn foo(x: bool | i32) -> i32 | f64 {
+   |                              ^ expected one of 7 possible tokens
+
+error: aborting due to 4 previous errors
+

tests/ui/parser/fake-anon-enums-in-expressions.rs

@@ -0,0 +1,22 @@
+//@ build-pass
+// Regression test for https://github.com/rust-lang/rust/issues/107461, where anon enum syntax
+// proposed in https://github.com/rust-lang/rfcs/issues/294 being parsed in a naïve way fails with
+// exisitng valid syntax for closures.
+
+struct A;
+struct B;
+
+#[derive(Debug)]
+#[allow(unused)]
+struct MyStruct {
+    x: f32,
+}
+
+fn main() {
+    let x = |_: fn() -> A | B;
+    let B = x(|| A);
+
+    let y = 1.0;
+    let closure = |f: fn(&f32) -> f32| MyStruct { x: f(&y) };
+    println!("foo: {:?}", closure(|x| *x + 3.0));
+}

tests/ui/parser/fake-anon-enums-in-macros.rs

@@ -0,0 +1,23 @@
+//@ build-pass
+// If we ever introduce anonymous enums (https://github.com/rust-lang/rfcs/issues/294) we need to
+// ensure that we don't break existing macros that expect types with `|` between them.
+
+macro_rules! check_ty {
+    ($Z:ty) => { compile_error!("triggered"); };
+    ($X:ty | $Y:ty) => { $X };
+}
+
+macro_rules! check {
+    ($Z:ty) => { compile_error!("triggered"); };
+    ($X:ty | $Y:ty) => { };
+}
+
+check! { i32 | u8 }
+
+fn foo(x: check_ty! { i32 | u8 }) -> check_ty! { i32 | u8 } {
+    x
+}
+fn main() {
+    let x: check_ty! { i32 | u8 } = 42;
+    let _: check_ty! { i32 | u8 } = foo(x);
+}