Add x:variable to schema and improve compiler support for x:variable

[galtm]

Per issue #60, x:variable is missing from the schema. This change adds it
and fixes some bugs in the compiler related to handling of variables.

A few questions and comments

• I debated about x:variable interspersed with x:expect. It seems handy; for example, if you store the expected value in a variable, you might want the variable definition near the x:expect element that references the variable. However, if you have to put several x:expect elements inside x:pending, you won't want to have to move x:variable out of the way. Instead, you'll want x:pending to allow x:variable as a child. Since I've seen some issues with x:pending, I hesitate to allow x:variable inside x:pending at the moment. That could be a later enhancement, if there is enough interest. In practice, I rarely use x:pending with x:expect as a child.
• The issue writeup is about both x:variable and x:apply. This pull request addresses x:variable only, and I have not done any work on x:apply.
• Variables should be documented in one of the wikis for users. I will update the wiki soon after this pull request is merged in.

[galtm]

Regarding the 1.0 stylesheet, https://saxonica.plan.io/issues/4266 may help.

Thanks for the reference. I believe I don't need to do anything special to react to or mention XSLT 1.0 differences with regard to redefinition of variables. Redefined XSpec variables compile to redefined XSLT variables, which work fine in multiple recent Saxon versions because they operate as XSLT 2 or XSLT 3 processors.

[AirQuick]

I've reviewed all the files. We're quite close to the end of the game. 😃

[galtm]

I've reviewed all the files. We're quite close to the end of the game. 😃

Happy to hear that! Thanks, @AirQuick and @cirulls , for all your help and diligence along the way. :)

[AirQuick]

#475 (comment)

• I debated about x:variable interspersed with x:expect. It seems handy; ... I hesitate to allow x:variable inside x:pending at the moment. That could be a later enhancement, if there is enough interest. In practice, I rarely use x:pending with x:expect as a child.

I totally agree.

[AirQuick]

What should we say about Schematron?
I vaguely remember @galtm mentioned somewhere that Schematron was out of scope. And I think it's perfectly ok. I'm just wondering about Release Note, Wiki or any other documentation.

[galtm]

When drafting the wiki content, I considered saying "XSLT and XQuery" explicitly somewhere. Then I saw that the entire Writing Scenarios wiki makes no mention of Schematron. How about having that wiki say near the top that the whole topic is about XSpec for XSLT and XQuery, and linking to the separate topic, Writing Scenarios for Schematron? Maybe something like the following, in the Introduction section:

Scenarios fall into four main types:

• [keep the three bulleted items that are already there]
• Schematron scenarios, covered in Writing Scenarios for Schematron

If there's a concise way to make the Release Notes indicate that the support for variables is in XSpec tests for XSLT and XQuery only, that sounds good.

[AirQuick]

How about having that wiki say near the top...

Sounds like a nice idea. Can you make those changes?

[galtm]

Yes, I updated the Writing Scenarios wiki with the extra Schematron bullet and the new XSpec Variables section. Thanks for merging this pull request!

[AirQuick]

@cirulls
Merged this substantial improvement of x:variable (for XSLT and XQuery only), a long-standing but lesser-known feature.
I'd like the release note to highlight it and express big thanks to @galtm for this extraordinary contribution.

[cirulls]

This is awesome! Thanks @galtm for the major contribution and @AirQuick for shepherding this improvement into the code base.

Absolutely, this will be the highlight of the next release. If you want to write a specific paragraph, post i here and I will include it in the release notes.

[galtm]

@AirQuick and @cirulls : You're very welcome, and thanks for the compliments. I enjoyed working with you both on this, and it was a super learning experience!

About the release notes, how about something like the following? Feel free to change anything, especially to make it fit in better with surrounding content. The 2nd sentence, in particular, can be removed if you think it is obvious or want to save space.

A useful enhancement in v1.4.0 is the ability to define your own variables in an XSpec test for XSLT or XQuery (#475). Reasons for using XSpec variables can include reusing data within the XSpec file and naming intermediate results for clarity. This feature had an incomplete implementation in earlier releases. For more information on using variables, see XSpec Variables.

(FYI, I will be away from the Internet until Tuesday.)

[cirulls]

@galtm: it looks good to me, I added it to the draft release notes.

[galtm]

I added it to the draft release notes

Thanks, @cirulls !