[yang-model] Using 'leafref' instead of 'must' for loopback (#9535)

#### Why I did it Fix issue sonic-net/sonic-utilities#1962 The problem is current implementation of [sonic-yang-mgmt::find_data_dependencies](https://github.com/Azure/sonic-buildimage/blob/f2774b635dee2d5c0e30489632b47e0210a712dd/src/sonic-yang-mgmt/sonic_yang.py#L518) does not get referrers if they are using `must` statement, it has to use `leafref`. For now we can convert `must` to `leafref` if possible. In the future we will investigate get referrers by `must` statements as well #9534 #### How I did it Instead of `must` use `leafref` #### How to verify it unit-test #### Which release branch to backport (provide reason below if selected) - [ ] 201811 - [ ] 201911 - [ ] 202006 - [ ] 202012 - [ ] 202106
sonic-net · Dec 16, 2021 · 2c5794f · 2c5794f
1 parent 6a0bb3a
commit 2c5794f
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diff --git a/src/sonic-yang-models/tests/yang_model_tests/tests/loopback.json b/src/sonic-yang-models/tests/yang_model_tests/tests/loopback.json
@@ -1,7 +1,7 @@
 {
-    "LOOPBACK_IPPREFIX_PORT_MUST_CONDITION_FALSE": {
-	"desc": "Loopback Ip-prefix port-name must condition failure.",
-	"eStrKey" : "Must"
+    "LOOPBACK_IPPREFIX_PORT_FOR_NON_EXIST_INTERFACE": {
+        "desc": "Configure Loopback Ip-prefix for non-existing Loopback interface.",
+        "eStrKey" : "LeafRef"
     },
     "LOOPBACK_INTERFACE_WRONG_NAT_ZONE_RANGE": {
         "desc": "Configure wrong value for nat zone.",

diff --git a/src/sonic-yang-models/tests/yang_model_tests/tests_config/loopback.json b/src/sonic-yang-models/tests/yang_model_tests/tests_config/loopback.json
@@ -1,5 +1,5 @@
 {
-    "LOOPBACK_IPPREFIX_PORT_MUST_CONDITION_FALSE": {
+    "LOOPBACK_IPPREFIX_PORT_FOR_NON_EXIST_INTERFACE": {
         "sonic-loopback-interface:sonic-loopback-interface": {
             "sonic-loopback-interface:LOOPBACK_INTERFACE": {
                 "LOOPBACK_INTERFACE_IPPREFIX_LIST": [

diff --git a/src/sonic-yang-models/yang-models/sonic-loopback-interface.yang b/src/sonic-yang-models/yang-models/sonic-loopback-interface.yang
@@ -63,12 +63,11 @@ module sonic-loopback-interface {
                 key "name ip-prefix";
 
                 leaf name{
-                    /* This node must be present in LOOPBACK_INTERFACE_LIST */
-                    must "(current() = ../../LOOPBACK_INTERFACE_LIST[name=current()]/name)"
-                    {
-                        error-message "Must condition not satisfied, Try adding lo<>: {}, Example: 'lo1': {}";
+                    description "Loopback interface name";
+
+                    type leafref {
+                        path "../../LOOPBACK_INTERFACE_LIST/name";
                     }
-                    type string;
                 }
 
                 leaf ip-prefix {