Yangtools fails to parse following augmentation present in
ietf-mpls@2017-07-02.yang:

augment
"/rt:routing-state/rt:ribs/rt:rib/rt:active-route/rt:input"

{ description "This augment adds the input parameter of the 'active-route' action."; uses nhlfe-contents; }

augment "/rt:routing-state/rt:ribs/rt:rib/rt:active-route/"
+ "rt:output/rt:route"

{ description "This augment adds the destination prefix to the reply of the 'active-route' action."; uses nhlfe-contents; }

where active-route is defined as(ietf-routing@2016-08-18.yang):

action active-route {
description
"Return the active RIB route that is used for the
destination address.

Address family specific modules MUST augment input
parameters with a leaf named 'destination-address'.";
output {

container route {
description
"The active RIB route for the specified destination.

If no route exists in the RIB for the destination
address, no output is returned.

Address family specific modules MUST augment this
container with appropriate route contents.";
container next-hop

{ description "Route's next-hop attribute."; uses next-hop-state-content; }

uses route-metadata;
}
}
}

with following exception:
[ERROR] Failed to parse YANG from source SourceSpecificContext [source=META-INF/yang/ietf-mpls@2017-07-02.yang, current=EFFECTIVE_MODEL, finished=FULL_DECLARATION]: Augment target 'Absolute

{path=[(urn:ietf:params:xml:ns:yang:ietf-routing?revision=2016-08-18)routing-state, (urn:ietf:params:xml:ns:yang:ietf-routing?revision=2016-08-18)ribs, (urn:ietf:params:xml:ns:yang:ietf-routing?revision=2016-08-18)rib, (urn:ietf:params:xml:ns:yang:ietf-routing?revision=2016-08-18)active-route, (urn:ietf:params:xml:ns:yang:ietf-routing?revision=2016-08-18)input]}

' not found [at META-INF/yang/ietf-mpls@2017-07-02.yang:366:2]
[ERROR] yang-to-sources: Unable to parse yang files from /home/m/hc2vpp/mpls/api/src/main/yang
org.opendaylight.yangtools.yang.parser.spi.meta.SomeModifiersUnresolvedException: Some of EFFECTIVE_MODEL modifiers for statements were not resolved.
[...]
Caused by: org.opendaylight.yangtools.yang.parser.spi.meta.InferenceException: Augment target 'Absolute

{path=[(urn:ietf:params:xml:ns:yang:ietf-routing?revision=2016-08-18)routing-state, (urn:ietf:params:xml:ns:yang:ietf-routing?revision=2016-08-18)ribs, (urn:ietf:params:xml:ns:yang:ietf-routing?revision=2016-08-18)rib, (urn:ietf:params:xml:ns:yang:ietf-routing?revision=2016-08-18)active-route, (urn:ietf:params:xml:ns:yang:ietf-routing?revision=2016-08-18)input]}

' not found [at META-INF/yang/ietf-mpls@2017-07-02.yang:366:2]
at org.opendaylight.yangtools.yang.parser.stmt.rfc6020.AugmentStatementImpl$Definition$1.prerequisiteFailed(AugmentStatementImpl.java:187)
at org.opendaylight.yangtools.yang.parser.stmt.reactor.ModifierImpl.failModifier(ModifierImpl.java:87)
at org.opendaylight.yangtools.yang.parser.stmt.reactor.SourceSpecificContext.failModifiers(SourceSpecificContext.java:341)
... 35 more