Fix expression tree nesting with await bug

Summary:
The lowerer introduces lambdas to allow lists of statements in expression trees, e.g. ``ExampleDsl`{$x = 1; $y = 2;}` `` lowers to ``ExampleDsl`(() ==> {$x = 1; $y = 2;})()` `` before desugaring. This is an expression tree lambda, not a Hack lambda, and thus processing it shouldn't interfere with the code looking for awaits and yields should they appear in splices, nor should we forget if we are in an enclosing async Hack function. However, the call to `reset_for_function_body` was doing exactly that.

Improve error message if a yield appears in an expression tree

Reviewed By: andrewjkennedy

Differential Revision: D66822415

fbshipit-source-id: 1b89af3ab838473c51d641331fdce73bdab010a4

hphp/hack/src/parser/lowerer/desugar_expression_tree.rs

@@ -1609,6 +1609,11 @@ impl RewriteState {
                 ));
                 unchanged_result
             }
+            Yield(_) => {
+                self.errors
+                    .push((pos, "`yield` is not supported in expression trees.".into()));
+                unchanged_result
+            }
             _ => {
                 self.errors
                     .push((pos, "Unsupported expression tree syntax.".into()));

hphp/hack/src/parser/lowerer/lowerer.rs

@@ -187,7 +187,7 @@ pub struct Env<'a> {
     pub empty_ns_env: Arc<NamespaceEnv>,
 
     // Whether we have encountered an yield expression
-    pub found_yield: bool,
+    found_yield: bool,
     // Whether we have encountered an await expression
     found_await: bool,
     // Whether we are in the body of an async function
@@ -2377,8 +2377,7 @@ fn p_prefixed_code_expr<'a>(
         let pos = p_pos(&c.body, env);
         let suspension_kind = SuspensionKind::SKSync;
         // Take the body and create a no argument lambda expression
-        let (body, yield_) =
-            env.reset_for_function_body(&c.body, suspension_kind, p_function_body)?;
+        let body = p_function_body(&c.body, env)?;
         let external = c.body.is_external();
         let fun = ast::Fun_ {
             span: pos.clone(),
@@ -2387,7 +2386,7 @@ fn p_prefixed_code_expr<'a>(
             readonly_ret: None,
             ret: ast::TypeHint((), None),
             body: ast::FuncBody { fb_ast: body },
-            fun_kind: mk_fun_kind(suspension_kind, yield_),
+            fun_kind: mk_fun_kind(suspension_kind, false),
             params: vec![],
             ctxs: None,
             unsafe_ctxs: None,

hphp/hack/test/typecheck/expression_trees/async_generator.php.exp

@@ -3,7 +3,7 @@ Internal error: Return type is not a generator (Other[0000])
 ERROR: File "async_generator.php", line 6, characters 14-38:
 Expression trees only support simple lambdas, without features like `async`, generators or capabilities. (Parsing[1002])
 ERROR: File "async_generator.php", line 6, characters 29-35:
-Unsupported expression tree syntax. (Parsing[1002])
+`yield` is not supported in expression trees. (Parsing[1002])
 ERROR: File "async_generator.php", line 6, characters 14-38:
 You cannot return a value in a generator (a generator is a function that uses `yield`) (NastCheck[3019])
 ERROR: File "async_generator.php", line 6, characters 14-38:

hphp/hack/test/typecheck/expression_trees/generator.php.exp

@@ -3,7 +3,7 @@ Internal error: Return type is not a generator (Other[0000])
 ERROR: File "generator.php", line 6, characters 14-32:
 Expression trees only support simple lambdas, without features like `async`, generators or capabilities. (Parsing[1002])
 ERROR: File "generator.php", line 6, characters 23-29:
-Unsupported expression tree syntax. (Parsing[1002])
+`yield` is not supported in expression trees. (Parsing[1002])
 ERROR: File "generator.php", line 6, characters 14-32:
 You cannot return a value in a generator (a generator is a function that uses `yield`) (NastCheck[3019])
 ERROR: File "generator.php", line 6, characters 14-32:

hphp/hack/test/typecheck/expression_trees/nesting/await.php

@@ -0,0 +1,33 @@
+<?hh
+<<file: __EnableUnstableFeatures('expression_trees')>>
+
+async function g(): Awaitable<ExampleDslExpression<ExampleInt>> {
+  return ExampleDsl`1`;
+}
+
+async function f(): Awaitable<void> {
+  ExampleDsl`${ExampleDsl`${await g()}`}`;
+  ExampleDsl`{
+    ${await g()};
+  }`;
+  ExampleDsl`${
+    ExampleDsl`{
+      1;
+      ${await g()};
+    }`
+  }`;
+  ExampleDsl`{
+    ${ExampleDsl`${await g()}`};
+  }`;
+  ExampleDsl`{
+    ${await g()};
+    ${ExampleDsl`${await g()}`};
+  }`;
+  ExampleDsl`{
+    ${
+      ExampleDsl`{
+        ${await g()};
+      }`
+    };
+  }`;
+}

hphp/hack/test/typecheck/expression_trees/nesting/await.php.exp

@@ -0,0 +1 @@
+No errors

hphp/test/slow/expression_trees/blocks_yield.php.expectf

@@ -1 +1 @@
-Fatal error: Expression trees only support simple lambdas, without features like `async`, generators or capabilities. in %s/blocks_yield.php on line 14
+Fatal error: `yield` is not supported in expression trees. in %s/blocks_yield.php on line 12