Parse 'return' correctly if followed by newline

The following snippet should be interpreted as two statements, but
quick-lint-js interprets them as one:

    return
    x;

Fix quick-lint-js to respec da rules.

Author: strager

src/quick-lint-js/parse.h

@@ -394,8 +394,12 @@ class parser {
         break;
 
       default:
-        this->parse_and_visit_expression(v);
-        parse_expression_end();
+        if (this->peek().has_leading_newline) {
+          // Insert a semicolon, then consume it.
+        } else {
+          this->parse_and_visit_expression(v);
+          parse_expression_end();
+        }
         break;
       }
       break;

test/test-parse-statement.cpp

@@ -86,6 +86,35 @@ TEST(test_parse, return_statement) {
   }
 }
 
+TEST(test_parse, return_statement_disallows_newline) {
+  {
+    padded_string code(u8"return\nx"_sv);
+    spy_visitor v;
+    parser p(&code, &v);
+
+    // Parse 'return'.
+    EXPECT_TRUE(p.parse_and_visit_statement(v));
+    EXPECT_THAT(v.variable_uses, IsEmpty());
+
+    // Parse 'x' (separate statement from 'return')
+    EXPECT_TRUE(p.parse_and_visit_statement(v));
+    EXPECT_THAT(v.variable_uses,
+                ElementsAre(spy_visitor::visited_variable_use{u8"x"}));
+
+    EXPECT_THAT(v.errors, IsEmpty());
+  }
+
+  {
+    spy_visitor v = parse_and_visit_module(u8"for (let x of []) return\nx"_sv);
+    EXPECT_THAT(v.visits,
+                ElementsAre("visit_enter_for_scope",       //
+                            "visit_variable_declaration",  // x
+                            "visit_exit_for_scope",        //
+                            "visit_variable_use",          // x
+                            "visit_end_of_module"));
+  }
+}
+
 TEST(test_parse, throw_statement) {
   {
     spy_visitor v = parse_and_visit_statement(u8"throw new Error('ouch');"_sv);