Open existential on arguments after overload resolution. (#4982)

* Open existential on arguments after overload resolution.

* Fix.

* Update source/slang/slang-check-overload.cpp

Co-authored-by: ArielG-NV <159081215+ArielG-NV@users.noreply.github.com>

---------

Co-authored-by: ArielG-NV <159081215+ArielG-NV@users.noreply.github.com>

1 files changed, 43 insertions, 0 deletions

diff --git a/tests/bugs/gh-4467.slang b/tests/bugs/gh-4467.slang
new file mode 100644
index 000000000..dc97b9890
--- /dev/null
+++ b/tests/bugs/gh-4467.slang
@@ -0,0 +1,43 @@
+//TEST(compute):COMPARE_COMPUTE_EX(filecheck-buffer=CHK): -d3d12 -compute -shaderobj -output-using-type
+//TEST(compute, vulkan):COMPARE_COMPUTE_EX(filecheck-buffer=CHK): -vk -compute -shaderobj -output-using-type
+
+
+// Test that we can synthesize a [mutating] interface requirement from a nonmutating implementation,
+// and the interface requirement signature contains an output interface-typed parameter.
+
+//TEST_INPUT: ubuffer(data=[0 0], stride=4):out,name outputBuffer
+RWStructuredBuffer<int> outputBuffer;
+
+interface IFoo
+{
+    int getVal();
+};
+
+interface IBar
+{
+    [mutating] void method(out IFoo o);
+};
+
+struct FooImpl : IFoo
+{
+    int x;
+    int getVal() { return x; }
+}
+
+struct BarImpl : IBar
+{
+    void method(out IFoo o)
+    {
+        o = FooImpl(1);
+    }
+};
+
+[numthreads(1,1,1)]
+void computeMain()
+{
+    BarImpl bar;
+    IFoo foo;
+    bar.method(foo);
+    // CHK: 1
+    outputBuffer[0] = foo.getVal();
+}
\ No newline at end of file