Rollup merge of #34436 - jseyfried:no_block_expr, r=eddyb

To allow these braced macro invocation, this PR removes the optional expression from `ast::Block` and instead uses a `StmtKind::Expr` at the end of the statement list.

Currently, braced macro invocations in blocks can expand into statements (and items) except when they are last in a block, in which case they can only expand into expressions.

For example,
```rust
macro_rules! make_stmt {
    () => { let x = 0; }
}

fn f() {
    make_stmt! {} //< This is OK...
    let x = 0; //< ... unless this line is commented out.
}
```

Fixes #34418.

1 files changed, 1 insertions, 4 deletions

diff --git a/src/libsyntax/ast.rs b/src/libsyntax/ast.rs
index dcdc1e60a99..a352715b20b 100644
--- a/src/libsyntax/ast.rs
+++ b/src/libsyntax/ast.rs
@@ -557,9 +557,6 @@ impl PartialEq for MetaItemKind {
 pub struct Block {
     /// Statements in a block
     pub stmts: Vec<Stmt>,
-    /// An expression at the end of the block
-    /// without a semicolon, if any
-    pub expr: Option<P<Expr>>,
     pub id: NodeId,
     /// Distinguishes between `unsafe { ... }` and `{ ... }`
     pub rules: BlockCheckMode,
@@ -832,7 +829,7 @@ pub enum StmtKind {
     /// An item definition.
     Item(P<Item>),
 
-    /// Expr without trailing semi-colon (must have unit type).
+    /// Expr without trailing semi-colon.
     Expr(P<Expr>),
 
     Semi(P<Expr>),