unified/swift: Use tree! instead of ctx.node

Cleans up a few places where we were constructing trees piece by piece
rather than using the `tree!` macro.

In the process, Copilot noticed an issue that should probably be
addressed: the labeled_statement rule can never fire, since there are no
such nodes in the input. This is possibly a simple as making
_labeled_statement (which _does_ exist) named, but I haven't attempted
this.

Finally, a small change to yeast makes it so that the contents of a {}
interpolation can be a Rust block (previously it could only be a single
expression). This avoids the need to double-wrap instances where you
want to interpolate a single node produced as the final value of some
block.

shared/yeast-macros/src/parse.rs

@@ -359,7 +359,7 @@ fn parse_direct_node(tokens: &mut Tokens, ctx: &Ident) -> Result<TokenStream> {
         Some(TokenTree::Group(g)) if g.delimiter() == Delimiter::Brace => {
             let group = expect_group(tokens, Delimiter::Brace)?;
             let expr = group.stream();
-            Ok(quote! { ::std::convert::Into::<usize>::into(#expr) })
+            Ok(quote! { ::std::convert::Into::<usize>::into({ #expr }) })
         }
         Some(TokenTree::Group(g)) if g.delimiter() == Delimiter::Parenthesis => {
             let group = expect_group(tokens, Delimiter::Parenthesis)?;
@@ -396,7 +396,7 @@ fn parse_direct_node_inner(tokens: &mut Tokens, ctx: &Ident) -> Result<TokenStre
         let expr = group.stream();
         return Ok(quote! {
             {
-                let __expr = (#expr);
+                let __expr = { #expr };
                 let __value = yeast::YeastDisplay::yeast_to_string(&__expr, &*#ctx.ast);
                 let __source_range = yeast::YeastSourceRange::yeast_source_range(&__expr, &*#ctx.ast);
                 #ctx.literal_with_source_range(#kind_str, &__value, __source_range)
@@ -448,11 +448,11 @@ fn parse_direct_node_inner(tokens: &mut Tokens, ctx: &Ident) -> Result<TokenStre
                         inner.next(); // consume second .
                         let expr: TokenStream = inner.collect();
                         quote! {
-                            (#expr).into_iter().map(::std::convert::Into::<usize>::into)
+                            { #expr }.into_iter().map(::std::convert::Into::<usize>::into)
                         }
                     } else {
                         let expr = group.stream();
-                        quote! { (#expr).into_iter() }
+                        quote! { { #expr }.into_iter() }
                     };
                     let chained = parse_chain_suffix(tokens, ctx, base)?;
                     stmts.push(quote! {
@@ -617,11 +617,11 @@ fn parse_direct_list(tokens: &mut Tokens, ctx: &Ident) -> Result<Vec<TokenStream
                     inner.next(); // consume second .
                     let expr: TokenStream = inner.collect();
                     quote! {
-                        (#expr).into_iter().map(::std::convert::Into::<usize>::into)
+                        { #expr }.into_iter().map(::std::convert::Into::<usize>::into)
                     }
                 } else {
                     let expr = group.stream();
-                    quote! { (#expr).into_iter() }
+                    quote! { { #expr }.into_iter() }
                 };
                 let chained = parse_chain_suffix(tokens, ctx, base)?;
                 items.push(quote! {
@@ -630,7 +630,7 @@ fn parse_direct_list(tokens: &mut Tokens, ctx: &Ident) -> Result<Vec<TokenStream
             } else {
                 let expr = group.stream();
                 items.push(quote! {
-                    __nodes.push(::std::convert::Into::<usize>::into(#expr));
+                    __nodes.push(::std::convert::Into::<usize>::into({ #expr }));
                 });
             }
             continue;

shared/yeast/doc/yeast.md

@@ -265,7 +265,21 @@ occurrences of the same `$name` within one `BuildCtx` share the same value:
 )
 ```
 
-`{..expr}` splices a `Vec<Id>` (or any iterable of `Id`):
+The contents of `{…}` are treated as a Rust block, so multi-statement
+expressions (with `let` bindings) work too:
+
+```rust
+(assignment
+    left: {tmp}
+    right: {
+        let lit = ctx.literal("integer", "0");
+        tree!((binary_expr op: (operator "+") left: {tmp} right: {lit}))
+    })
+```
+
+`{..expr}` splices a `Vec<Id>` (or any iterable of `Id`); the contents
+are likewise a Rust block, so the splice can be the result of arbitrary
+computation:
 
 ```rust
 yeast::trees!(ctx,

unified/extractor/src/languages/swift/swift.rs

@@ -725,11 +725,11 @@ fn translation_rules() -> Vec<Rule<SwiftContext>> {
                 body: (block stmt: {..body}))
         ),
         // Labeled statement (e.g. `outer: for ...`). Strip the trailing ':' from the label token.
-        rule!((labeled_statement label: (statement_label) @lbl statement: @stmt) => {..{
+        rule!((labeled_statement label: (statement_label) @lbl statement: @stmt) => {
             let text = ctx.ast.source_text(lbl.into());
-            let name = ctx.literal("identifier", &text[..text.len() - 1]);
-            vec![ctx.node("labeled_stmt", vec![("label", vec![name]), ("stmt", vec![stmt.into()])])]
-        }}),
+            let name = &text[..text.len() - 1];
+            tree!((labeled_stmt label: (identifier #{name}) stmt: {stmt}))
+        }),
         // ---- Collections ----
         // Array literal
         rule!((array_literal element: _* @elems) => (array_literal element: {..elems})),
@@ -739,16 +739,9 @@ fn translation_rules() -> Vec<Rule<SwiftContext>> {
         rule!(
             (dictionary_literal key: _* @keys value: _* @vals)
             =>
-            (map_literal element: {..{
-                keys.iter().zip(vals.iter()).map(|(&k, &v)| {
-                    let k_id: usize = k.into();
-                    let v_id: usize = v.into();
-                    ctx.node("key_value_pair", vec![
-                        ("key", vec![k_id]),
-                        ("value", vec![v_id]),
-                    ])
-                }).collect::<Vec<_>>()
-            }})
+            (map_literal element: {..keys.into_iter().zip(vals).map(|(k, v)|
+                tree!((key_value_pair key: {k} value: {v}))
+            )})
         ),
         rule!((dictionary_literal element: _* @elems) => (map_literal element: {..elems})),
         rule!((dictionary_literal_item key: @k value: @v) => (key_value_pair key: {k} value: {v})),