1 files changed, 52 insertions, 0 deletions
diff --git a/compiler/rustc_ast/src/util/classify.rs b/compiler/rustc_ast/src/util/classify.rs
new file mode 100644
index 000000000..6ea3db6d3
--- /dev/null
+++ b/compiler/rustc_ast/src/util/classify.rs
@@ -0,0 +1,52 @@
+//! Routines the parser uses to classify AST nodes
+
+// Predicates on exprs and stmts that the pretty-printer and parser use
+
+use crate::ast;
+
+/// Does this expression require a semicolon to be treated
+/// as a statement? The negation of this: 'can this expression
+/// be used as a statement without a semicolon' -- is used
+/// as an early-bail-out in the parser so that, for instance,
+///     if true {...} else {...}
+///      |x| 5
+/// isn't parsed as (if true {...} else {...} | x) | 5
+pub fn expr_requires_semi_to_be_stmt(e: &ast::Expr) -> bool {
+    !matches!(
+        e.kind,
+        ast::ExprKind::If(..)
+            | ast::ExprKind::Match(..)
+            | ast::ExprKind::Block(..)
+            | ast::ExprKind::While(..)
+            | ast::ExprKind::Loop(..)
+            | ast::ExprKind::ForLoop(..)
+            | ast::ExprKind::TryBlock(..)
+    )
+}
+
+/// If an expression ends with `}`, returns the innermost expression ending in the `}`
+pub fn expr_trailing_brace(mut expr: &ast::Expr) -> Option<&ast::Expr> {
+    use ast::ExprKind::*;
+
+    loop {
+        match &expr.kind {
+            AddrOf(_, _, e)
+            | Assign(_, e, _)
+            | AssignOp(_, _, e)
+            | Binary(_, _, e)
+            | Box(e)
+            | Break(_, Some(e))
+            | Closure(.., e, _)
+            | Let(_, e, _)
+            | Range(_, Some(e), _)
+            | Ret(Some(e))
+            | Unary(_, e)
+            | Yield(Some(e)) => {
+                expr = e;
+            }
+            Async(..) | Block(..) | ForLoop(..) | If(..) | Loop(..) | Match(..) | Struct(..)
+            | TryBlock(..) | While(..) => break Some(expr),
+            _ => break None,
+        }
+    }
+}