From e1f7dd437ca0c7754427b5f4ccb4d620932b1052 Mon Sep 17 00:00:00 2001
From: Dmitry Vasilev <dmitry.vasil@gmail.com>
Date: Fri, 2 Feb 2024 03:13:21 +0800
Subject: [PATCH] bare return statements

---
 src/cmd.js      |  7 ++++++-
 src/eval.js     | 15 ++++++++++++++-
 src/parse_js.js | 23 +++++++++++++++--------
 test/test.js    | 22 +++++++++++++++++++---
 4 files changed, 54 insertions(+), 13 deletions(-)

diff --git a/src/cmd.js b/src/cmd.js
index d07a79e..ca38072 100644
--- a/src/cmd.js
+++ b/src/cmd.js
@@ -624,7 +624,12 @@ const get_stmt_value_explorer = (state, stmt) => {
 
   if(stmt.result.ok) {
     if(stmt.type == 'return') {
-      result = stmt.children[0].result
+      if(stmt.expr == null) {
+        // add fake version number
+        result = {ok: true, value: undefined, version_number: 0}
+      } else {
+        result = stmt.children[0].result
+      }
     } else if(['let', 'const', 'assignment'].includes(stmt.type)) {
 
       if(stmt.children.find(c => c.type == 'assignment_pair') != null) {
diff --git a/src/eval.js b/src/eval.js
index 6407629..cd36646 100644
--- a/src/eval.js
+++ b/src/eval.js
@@ -192,7 +192,11 @@ const codegen = (node, node_cxt) => {
         ''
       )
   } else if(node.type == 'return') {
-    return 'return ' + do_codegen(node.expr) + ';'
+    if(node.expr == null) {
+      return 'return ;'
+    } else {
+      return 'return ' + do_codegen(node.expr) + ';'
+    }
   } else if(node.type == 'throw') {
     return 'throw ' + do_codegen(node.expr) + ';'
   } else if(node.type == 'if') {
@@ -1278,6 +1282,15 @@ const eval_statement = (s, eval_cxt, frame_cxt) => {
     }
   } else if(s.type == 'return') {
 
+    if(s.expr == null) {
+      return {
+        ok: true,
+        returned: true,
+        node: {...s, result: {ok: true}},
+        eval_cxt,
+      }
+    }
+
     const {node, eval_cxt: next_eval_cxt} = 
       eval_frame_expr(s.expr, eval_cxt, frame_cxt)
 
diff --git a/src/parse_js.js b/src/parse_js.js
index b7d5e0a..3c01822 100644
--- a/src/parse_js.js
+++ b/src/parse_js.js
@@ -1225,15 +1225,10 @@ const assignment = if_ok(
 )
 
 
-const return_statement =
+const return_statement = either(
+  // return expr
   if_ok(
     seq_select(1, [
-
-      // We forbid bare return statement
-      // TODO bare return statement
-      // TODO implement bare return statement compatible with ASI
-      // see https://riptutorial.com/javascript/example/15248/rules-of-automatic-semicolon-insertion
-      // see ASI_restrited unit test
       not_followed_by(
         literal('return'),
         newline,
@@ -1245,7 +1240,19 @@ const return_statement =
       type: 'return',
       children: [value],
     })
-  )
+  ),
+
+  // bare return statement 
+  if_ok(
+    literal('return'),
+    node => ({
+      ...node,
+      type: 'return',
+      children: [],
+      value: null,
+    })
+  ),
+)
 
 const if_branch = if_ok(
   seq_select(1, [
diff --git a/test/test.js b/test/test.js
index f743450..36a9e1e 100644
--- a/test/test.js
+++ b/test/test.js
@@ -487,14 +487,13 @@ export const tests = [
     )
   }),
 
-  test('ASI_restrited', () => {
-    // Currently we forbid bare return statement, TODO
+  test('ASI_restricted', () => {
     assert_equal(
       do_parse(`
         return
         1
       `).ok,
-      false
+      true
     )
     assert_equal(
       do_parse(`
@@ -945,6 +944,23 @@ export const tests = [
     assert_equal(x.result.version_number, 0)
   }),
 
+  test('bare return statement', () => {
+    const code = `
+      function test() {
+        return
+      }
+      test() /*call*/
+    `
+    assert_value_explorer(
+      test_initial_state(code, code.indexOf('test() /*call*/')),
+      undefined,
+    )
+    assert_value_explorer(
+      test_initial_state(code, code.indexOf('return')),
+      undefined,
+    )
+  }),
+
   test('array spread not iterable', () => {
     assert_code_error(
       `[...null]`,