Quotes to wrap XpathExpression should be kept as what it is after serialization

[huyuwen]

We recently found that all Quotes which used to wrap XpathExpression will be removed after serialization. For example, original,
leaf lf2 {
type uint8;
must '. <= ../lf1';
}
After serialization,
leaf lf2 {
type uint8;
must . <= ../lf1;
}
We double checked with RFC 7950, actually, it is valid according to the 'must' and 'when' definition.
But we still propose to wrap XpathExpression with Quotes, or at least keep as what it is. There are a few reasons,

1. The example in RFC 7950, (ex, must statement and when statement) all wrap with quotes. That means according to the spec, they recommend to have the quotes.
2. If there are WS in XpathExpression, Quotes can avoid some parse errors. Actually, pyang doesn't accept 'must' or 'when' expression without quotes if there are WS in expression. Pyang will report it as 'error: unterminated statement definition for keyword "must", looking at...'
3. XpathExpression with quotes has better readability

[JanKoehnlein]

Could you elaborate on the serialization usecase? Do you read in an existing model with an existing XPath or do you create a new UnparsedXpath? Is it in the SerializationIntegrationTest?

[huyuwen]

Hi Jan, You can refer to the test case and data in #119. From Yuwen's iPhone 在 2018年5月17日，下午4:33，Jan Koehnlein <notifications@github.com<mailto:notifications@github.com>> 写道： Could you elaborate on the serialization usecase? Do you read in an existing model with an existing XPath or do you create a new UnparsedXpath? Is it in the SerializationIntegrationTest? — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub<#118 (comment)>, or mute the thread<https://github.com/notifications/unsubscribe-auth/AAxaKXTPr9zu4E5P2mkW_rzTJ3Nats9cks5tzYoogaJpZM4UC_zs>.

[JanKoehnlein]

Depends on eclipse/xtext-core#747

[JanKoehnlein]

Fixed

[huyuwen]

This issue has to be re-opened.
We found if there has '+' in the path string, serialization will be wrong.
Let's still take the xpath-serialize.yang as example.
if we define another leaf node in list (lb),
leaf lfb2 { type leafref { path "/ytest:c1" + "/ytest:l1"; } }
Then the path in lfb2 will be serialized to
{ path "/ytest:c1 "/ytest:l1"; }

[JanKoehnlein]

Fixed

[huyuwen]

Unfortuantely, we found some other strange behaviors.

1. '/' position is the end of a segament. there will be an unnecessary space ' ' append into that segament. See output example.
   Input: leaf lfb2 { type leafref { path "/ytest:c1/" + "ytest:l1"; } }
   Output: leaf lfb2 { type leafref { path "/ytest:c1/ " + "ytest:l1"; } }
2. segament break at ':', whatever it is at the end or at the beginning of a segament, there will be unnecessary space ' ' append into the segament
   Input: leaf lfb2 { type leafref { path "/ytest:" + "c1/ytest" + ":l1"; } }
   Output: leaf lfb2 { type leafref { path "/ytest: " + "c1/ytest " + ":l1"; } }

The space will make xpath totally wrong.

[JanKoehnlein]

Never mind. I've added the missing case and more tests.

[JanKoehnlein]

Hopefully fixed now. Don't hesitate to reopen if you encounter further pecularities.