Adding upstream version 3.1.0+dfsg.

Signed-off-by: Daniel Baumann <daniel@debian.org>

tools/lint/examples/sm-extension.yang

@@ -0,0 +1,39 @@
+module sm-extension {
+    yang-version 1.1;
+    namespace "urn:sm-ext";
+    prefix "sm-ext";
+
+    import ietf-interfaces {
+        prefix if;
+    }
+    import sm-mod {
+        prefix sm-mod;
+    }
+
+    revision 2022-09-15 {
+      description
+        "initial";
+      reference
+        "";
+    }
+
+    list things {
+        key "name";
+        leaf name {
+            type leafref {
+              path "/if:interfaces/if:interface/if:name";
+            }
+        }
+        leaf attribute {
+            type uint32;
+        }
+    }
+
+    augment "/if:interfaces/if:interface" {
+        leaf thing-attribute {
+            type leafref {
+              path "/things/attribute";
+            }
+        }
+    }
+}