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

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

* Update doc.

* Fix test.

1 files changed, 20 insertions, 0 deletions

diff --git a/tests/diagnostics/missing-override.slang b/tests/diagnostics/missing-override.slang
new file mode 100644
index 000000000..cc2cbcad3
--- /dev/null
+++ b/tests/diagnostics/missing-override.slang
@@ -0,0 +1,20 @@
+//DIAGNOSTIC_TEST:SIMPLE(filecheck=CHECK):
+
+interface IFoo
+{
+    int getVal() { return 0; }
+}
+
+struct Impl : IFoo
+{
+    // Missing override for getVal, which should trigger a diagnostic.
+    // CHECK: ([[# @LINE+1]]): error 30853
+    int getVal() { return 1; }
+}
+
+struct Impl2 : IFoo
+{
+    // Overriding getVal with a different signature should also trigger a diagnostic.
+    // CHECK: ([[# @LINE+1]]): error 30854
+    override int getVal(int x) { return x; }
+}
\ No newline at end of file