[vala/0.52] vala: NullLiteral is not a valid argument for string concatenation

[Rico Tzschichholz <ricotz src gnome org>]

commit db1ab2cf16e77f5fd9d5c878b4c0f755f4d4f8b7
Author: wxx <769218589 qq com>
Date:   Sat Dec 4 17:17:47 2021 +0800

    vala: NullLiteral is not a valid argument for string concatenation
    
    Fixes https://gitlab.gnome.org/GNOME/vala/issues/1260

 tests/Makefile.am                         | 1 +
 tests/basic-types/string-concat-null.test | 5 +++++
 tests/basic-types/strings.vala            | 6 ++++++
 vala/valabinaryexpression.vala            | 4 +++-
 4 files changed, 15 insertions(+), 1 deletion(-)
---
diff --git a/tests/Makefile.am b/tests/Makefile.am
index 484e0d5be..c097fbc20 100644
--- a/tests/Makefile.am
+++ b/tests/Makefile.am
@@ -50,6 +50,7 @@ TESTS = \
        basic-types/custom-types.vala \
        basic-types/default-gtype.vala \
        basic-types/strings.vala \
+       basic-types/string-concat-null.test \
        basic-types/arrays.vala \
        basic-types/arrays-generics.vala \
        basic-types/arrays-fixed-assignment.vala \
diff --git a/tests/basic-types/string-concat-null.test b/tests/basic-types/string-concat-null.test
new file mode 100644
index 000000000..f12632d8b
--- /dev/null
+++ b/tests/basic-types/string-concat-null.test
@@ -0,0 +1,5 @@
+Invalid Code
+
+void main () {
+       var str = "foo" + null + "bar";
+}
diff --git a/tests/basic-types/strings.vala b/tests/basic-types/strings.vala
index e1cfd9afb..22c96b7f9 100644
--- a/tests/basic-types/strings.vala
+++ b/tests/basic-types/strings.vala
@@ -48,6 +48,11 @@ void test_string () {
        assert (t == s);
 }
 
+void test_string_concat () {
+       var s = "hello" + "world";
+       assert (s == "helloworld");
+}
+
 void test_string_joinv () {
        string[] sa = { "hello", "my", "world" };
 
@@ -139,6 +144,7 @@ void test_string_substring () {
 
 void main () {
        test_string ();
+       test_string_concat ();
        test_string_joinv ();
        test_string_printf ();
        test_string_replace ();
diff --git a/vala/valabinaryexpression.vala b/vala/valabinaryexpression.vala
index d379927c0..6545e1cff 100644
--- a/vala/valabinaryexpression.vala
+++ b/vala/valabinaryexpression.vala
@@ -359,7 +359,9 @@ public class Vala.BinaryExpression : Expression {
                    && left.value_type.compatible (context.analyzer.string_type)) {
                        // string concatenation
 
-                       if (right.value_type == null || !right.value_type.compatible 
(context.analyzer.string_type)) {
+                       if (right.value_type == null || !right.value_type.compatible 
(context.analyzer.string_type)
+                           || left is NullLiteral || right is NullLiteral) {
+                               // operands cannot be null
                                error = true;
                                Report.error (source_reference, "Operands must be strings");
                                return false;