Require `override` keyword for overriding default interface methods. (#7458)

* Require `override` keyword for overriding default interface methods.

* Update doc.

* Fix test.

1 files changed, 40 insertions, 0 deletions

diff --git a/tests/language-feature/interfaces/override-default-method.slang b/tests/language-feature/interfaces/override-default-method.slang
new file mode 100644
index 000000000..22ae48311
--- /dev/null
+++ b/tests/language-feature/interfaces/override-default-method.slang
@@ -0,0 +1,40 @@
+//TEST(compute):COMPARE_COMPUTE(filecheck-buffer=CHECK): -shaderobj -output-using-type
+
+// Test that a generic interface method can have a body providing default implementation.
+
+interface IFoo
+{
+    int getVal();
+    int getGreaterVal<int x>()
+    {
+        return getVal() + x;
+    }
+}
+
+struct Impl : IFoo
+{
+    int getVal()
+    {
+        return 42;
+    }
+    
+    // override default implementation for getGreaterVal.
+    override int getGreaterVal<int x>()
+    {
+        return getVal() + x + 1; // Adding 1 to differentiate from the default implementation.
+    }
+}
+
+int test<T:IFoo>(T v) { return v.getGreaterVal<1>(); }
+
+//TEST_INPUT: set resultBuffer = out ubuffer(data=[0 0 0 0], stride=4)
+RWStructuredBuffer<int> resultBuffer;
+
+[numthreads(1,1,1)]
+void computeMain()
+{
+    Impl impl = {};
+    int result = test(impl);
+    resultBuffer[0] = result;
+    // CHECK: 44
+}
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