[vala/wip/issue/658: 34/34] Fixed crash: anonymous delegate returning a. del.

[Rico Tzschichholz <ricotz src gnome org>]

commit c28cbf4e7bb70fc131e3f151e888c02e9fb5140c
Author: Nick Schrader <nick schrader mailbox org>
Date:   Thu Nov 5 23:11:50 2020 -0300

    Fixed crash: anonymous delegate returning a. del.

 tests/Makefile.am                               |  1 +
 tests/delegates/anonymous-return-anonymous.test | 18 ++++++++++++++++++
 vala/valaparser.vala                            | 12 +++++++-----
 3 files changed, 26 insertions(+), 5 deletions(-)
---
diff --git a/tests/Makefile.am b/tests/Makefile.am
index b43ab00b9..16d9c3459 100644
--- a/tests/Makefile.am
+++ b/tests/Makefile.am
@@ -371,6 +371,7 @@ TESTS = \
        delegates/anonymous-params.test \
        delegates/anonymous-param-attrs.vala \
        delegates/anonymous-ref.test \
+       delegates/anonymous-return-anonymous.test \
        delegates/anonymous-throws.test \
        delegates/anonymous-type-param.vala \
        delegates/anonymous-variadic.test \
diff --git a/tests/delegates/anonymous-return-anonymous.test b/tests/delegates/anonymous-return-anonymous.test
new file mode 100644
index 000000000..47be7785f
--- /dev/null
+++ b/tests/delegates/anonymous-return-anonymous.test
@@ -0,0 +1,18 @@
+Invalid Code
+ 
+ /*
+  * 9.26-9.33: error: syntax error, anonymous delegate not allowed here
+  * void f (delegate(int) => delegate() => int d) {
+  *                          ^^^^^^^^
+  */
+
+void f (delegate(int) => delegate() => int d) {
+    var r = d (14);
+    stdout.printf("%d\n", r ());
+}
+
+void main () {
+    f ((a) => {
+        return () => a;
+    });
+}
diff --git a/vala/valaparser.vala b/vala/valaparser.vala
index 056289961..fcb6774b4 100644
--- a/vala/valaparser.vala
+++ b/vala/valaparser.vala
@@ -509,15 +509,17 @@ public class Vala.Parser : CodeVisitor {
 
                DataType type;
 
-               var begin2 = get_location ();
-               if (accept (TokenType.DELEGATE)) {
-                       rollback (begin2);
+               var begin_delegate_token = get_location ();
+               var is_delegate_token = accept (TokenType.DELEGATE);
+               rollback (begin_delegate_token);
+
+               if (is_delegate_token && method == null) {
+                       throw new ParseError.SYNTAX ("anonymous delegate not allowed here");
+               } else if (is_delegate_token) {
                        type = parse_anonymous_delegate (parent, method);
                        type.value_owned = value_owned;
                        type.is_dynamic = is_dynamic;
                        return type;
-               } else {
-                       rollback (begin2);
                }
 
                bool inner_type_owned = true;