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.

8 files changed, 14 insertions, 16 deletions

diff --git a/src/libsyntax_ext/deriving/clone.rs b/src/libsyntax_ext/deriving/clone.rs
index 00714002875..1e47ebb8583 100644
--- a/src/libsyntax_ext/deriving/clone.rs
+++ b/src/libsyntax_ext/deriving/clone.rs
@@ -145,12 +145,10 @@ fn cs_clone(
 
     match mode {
         Mode::Shallow => {
-            cx.expr_block(cx.block(trait_span,
-                                   all_fields.iter()
-                                             .map(subcall)
-                                             .map(|e| cx.stmt_expr(e))
-                                             .collect(),
-                                   Some(cx.expr_deref(trait_span, cx.expr_self(trait_span)))))
+            let mut stmts: Vec<_> =
+                all_fields.iter().map(subcall).map(|e| cx.stmt_expr(e)).collect();
+            stmts.push(cx.stmt_expr(cx.expr_deref(trait_span, cx.expr_self(trait_span))));
+            cx.expr_block(cx.block(trait_span, stmts))
         }
         Mode::Deep => {
             match *vdata {
diff --git a/src/libsyntax_ext/deriving/cmp/eq.rs b/src/libsyntax_ext/deriving/cmp/eq.rs
index 4258e152088..9c5072eeb3e 100644
--- a/src/libsyntax_ext/deriving/cmp/eq.rs
+++ b/src/libsyntax_ext/deriving/cmp/eq.rs
@@ -30,7 +30,7 @@ pub fn expand_deriving_eq(cx: &mut ExtCtxt,
                 // create `a.<method>(); b.<method>(); c.<method>(); ...`
                 // (where method is `assert_receiver_is_total_eq`)
                 let stmts = exprs.into_iter().map(|e| cx.stmt_expr(e)).collect();
-                let block = cx.block(span, stmts, None);
+                let block = cx.block(span, stmts);
                 cx.expr_block(block)
             },
             Box::new(|cx, sp, _, _| {
diff --git a/src/libsyntax_ext/deriving/debug.rs b/src/libsyntax_ext/deriving/debug.rs
index dabe234eb9c..34c872bef11 100644
--- a/src/libsyntax_ext/deriving/debug.rs
+++ b/src/libsyntax_ext/deriving/debug.rs
@@ -78,7 +78,7 @@ fn show_substructure(cx: &mut ExtCtxt, span: Span,
 
     let fmt = substr.nonself_args[0].clone();
 
-    let stmts = match *substr.fields {
+    let mut stmts = match *substr.fields {
         Struct(_, ref fields) | EnumMatching(_, _, ref fields) => {
             let mut stmts = vec![];
             if !is_struct {
@@ -136,7 +136,8 @@ fn show_substructure(cx: &mut ExtCtxt, span: Span,
                                    token::str_to_ident("finish"),
                                    vec![]);
 
-    let block = cx.block(span, stmts, Some(expr));
+    stmts.push(cx.stmt_expr(expr));
+    let block = cx.block(span, stmts);
     cx.expr_block(block)
 }
 
diff --git a/src/libsyntax_ext/deriving/encodable.rs b/src/libsyntax_ext/deriving/encodable.rs
index 07a52105deb..ad378621247 100644
--- a/src/libsyntax_ext/deriving/encodable.rs
+++ b/src/libsyntax_ext/deriving/encodable.rs
@@ -285,7 +285,7 @@ fn encodable_substructure(cx: &mut ExtCtxt, trait_span: Span,
                 cx.expr_str(trait_span, substr.type_ident.name.as_str()),
                 blk
             ));
-            cx.expr_block(cx.block(trait_span, vec!(me), Some(ret)))
+            cx.expr_block(cx.block(trait_span, vec![me, cx.stmt_expr(ret)]))
         }
 
         _ => cx.bug("expected Struct or EnumMatching in derive(Encodable)")
diff --git a/src/libsyntax_ext/deriving/generic/mod.rs b/src/libsyntax_ext/deriving/generic/mod.rs
index 7d454fe38cc..647e414a7fd 100644
--- a/src/libsyntax_ext/deriving/generic/mod.rs
+++ b/src/libsyntax_ext/deriving/generic/mod.rs
@@ -1332,8 +1332,8 @@ impl<'a> MethodDef<'a> {
             //  }
             let all_match = cx.expr_match(sp, match_arg, match_arms);
             let arm_expr = cx.expr_if(sp, discriminant_test, all_match, Some(arm_expr));
-            cx.expr_block(
-                cx.block_all(sp, index_let_stmts, Some(arm_expr)))
+            index_let_stmts.push(cx.stmt_expr(arm_expr));
+            cx.expr_block(cx.block(sp, index_let_stmts))
         } else if variants.is_empty() {
             // As an additional wrinkle, For a zero-variant enum A,
             // currently the compiler
diff --git a/src/libsyntax_ext/deriving/hash.rs b/src/libsyntax_ext/deriving/hash.rs
index 245d3f0efa3..0fad96c84ef 100644
--- a/src/libsyntax_ext/deriving/hash.rs
+++ b/src/libsyntax_ext/deriving/hash.rs
@@ -99,5 +99,5 @@ fn hash_substructure(cx: &mut ExtCtxt, trait_span: Span, substr: &Substructure)
         stmts.push(call_hash(span, self_.clone()));
     }
 
-    cx.expr_block(cx.block(trait_span, stmts, None))
+    cx.expr_block(cx.block(trait_span, stmts))
 }
diff --git a/src/libsyntax_ext/deriving/mod.rs b/src/libsyntax_ext/deriving/mod.rs
index f9e0d2c2eae..169e8073661 100644
--- a/src/libsyntax_ext/deriving/mod.rs
+++ b/src/libsyntax_ext/deriving/mod.rs
@@ -298,8 +298,7 @@ fn call_intrinsic(cx: &ExtCtxt,
     let call = cx.expr_call_global(span, path, args);
 
     cx.expr_block(P(ast::Block {
-        stmts: vec![],
-        expr: Some(call),
+        stmts: vec![cx.stmt_expr(call)],
         id: ast::DUMMY_NODE_ID,
         rules: ast::BlockCheckMode::Unsafe(ast::CompilerGenerated),
         span: span }))
diff --git a/src/libsyntax_ext/format.rs b/src/libsyntax_ext/format.rs
index 5be2bf7cdf9..f311f16f11b 100644
--- a/src/libsyntax_ext/format.rs
+++ b/src/libsyntax_ext/format.rs
@@ -449,7 +449,7 @@ impl<'a, 'b> Context<'a, 'b> {
         };
 
         // Wrap the declaration in a block so that it forms a single expression.
-        ecx.expr_block(ecx.block(sp, vec![stmt], Some(ecx.expr_ident(sp, name))))
+        ecx.expr_block(ecx.block(sp, vec![stmt, ecx.stmt_expr(ecx.expr_ident(sp, name))]))
     }
 
     /// Actually builds the expression which the iformat! block will be expanded