Add parser tests for statement boundary insertion

tests/ui/parser/macro/statement-boundaries.rs

@@ -0,0 +1,104 @@
+//@ run-pass
+//@ edition:2021
+
+// This is a test of several uses of rustc_ast::util::classify::expr_requires_semi_to_be_stmt
+// by the Rust parser, which relates to the insertion of statement boundaries
+// after certain kinds of expressions if they appear at the head of a statement.
+
+#![allow(unused_braces, unused_unsafe)]
+
+macro_rules! unit {
+    () => {
+        { () }
+    };
+}
+
+#[derive(Copy, Clone)]
+struct X;
+
+fn main() {
+    let x = X;
+
+    // There is a statement boundary before `|x| x`, so it's a closure.
+    let _: fn(X) -> X = { if true {} |x| x };
+    let _: fn(X) -> X = { if true {} else {} |x| x };
+    let _: fn(X) -> X = { match () { () => {} } |x| x };
+    let _: fn(X) -> X = { { () } |x| x };
+    let _: fn(X) -> X = { unsafe {} |x| x };
+    let _: fn(X) -> X = { while false {} |x| x };
+    let _: fn(X) -> X = { loop { break; } |x| x };
+    let _: fn(X) -> X = { for _ in 0..0 {} |x| x };
+    let _: fn(X) -> X = { const {} |x| x };
+    let _: fn(X) -> X = { unit! {} |x| x };
+
+    // No statement boundary, so `|x| x` is 2× BitOr operation.
+    () = { "" |x| x };
+    () = { ("") |x| x };
+    () = { [""] |x| x };
+    () = { unit!() |x| x };
+    () = { unit![] |x| x };
+
+    // All the same cases, but as a match arm.
+    () = match x {
+        // Statement boundary before `| X`, which becomes a new arm with leading vert.
+        X if false => if true {} | X if false => {}
+        X if false => if true {} else {} | X if false => {}
+        X if false => match () { () => {} } | X if false => {}
+        X if false => { () } | X if false => {}
+        X if false => unsafe {} | X if false => {}
+        X if false => while false {} | X if false => {}
+        X if false => loop { break; } | X if false => {}
+        X if false => for _ in 0..0 {} | X if false => {}
+        X if false => const {} | X if false => {}
+
+        // No statement boundary, so `| X` is BitOr.
+        X if false => "" | X,
+        X if false => ("") | X,
+        X if false => [""] | X,
+        X if false => unit! {} | X, // !! inconsistent with braced mac call in statement position
+        X if false => unit!() | X,
+        X if false => unit![] | X,
+
+        X => {}
+    };
+
+    // Test how the statement boundary logic interacts with macro metavariables /
+    // "invisible delimiters".
+    macro_rules! assert_statement_boundary {
+        ($expr:expr) => {
+            let _: fn(X) -> X = { $expr |x| x };
+
+            () = match X {
+                X if false => $expr | X if false => {}
+                X => {}
+            };
+        };
+    }
+    macro_rules! assert_no_statement_boundary {
+        ($expr:expr) => {
+            () = { $expr |x| x };
+
+            () = match x {
+                X if false => $expr | X,
+                X => {}
+            };
+        };
+    }
+    assert_statement_boundary!(if true {});
+    assert_no_statement_boundary!("");
+}
+
+impl std::ops::BitOr<X> for () {
+    type Output = ();
+    fn bitor(self, _: X) {}
+}
+
+impl std::ops::BitOr<X> for &str {
+    type Output = ();
+    fn bitor(self, _: X) {}
+}
+
+impl<T, const N: usize> std::ops::BitOr<X> for [T; N] {
+    type Output = ();
+    fn bitor(self, _: X) {}
+}