Use Official Cross-Version (xver) Packages

[cmoesel]

Description: SUSHI implemented cross-version extensions in 2021 by allowing authors to put special cross-version extension packages in their dependencies. The package names and versions followed the conventions described in the spec here and we interpreted it as hl7.fhir.extensions.r5:4.0.1 indicating the R5 extensions in the R4 format. We processed cross-version extensions by using pattern-matching to find the corresponding targeted element in the target version of FHIR (which we loaded as "supplemental" FHIR definitions).

Now that official cross-version packages are available (see FAQs and #IG creation > issue with link to xver extension @ 💬), SUSHI's old implementation is no longer necessary. This PR makes the following changes:

• Removes all code for the old implementation of cross-version extensions (often called "implied" extensions in the code) and "supplemental" FHIR definitions (which are no longer needed).
• Replaces old cross-version package dependencies (e.g., hl7.fhir.extensions.r5:4.0.1) with the corresponding new cross-version package dependencies (e.g., hl7.fhir.uv.xver-r5.r4) and logs a warning telling the user to fix it in their sushi-config.yaml.
• Detects use of cross-version choice extensions ending in [x] or URL-encoded %5Bx%5D and strips the [x] suffix since the new cross-version packages do not expect it. In this case, SUSHI also warns the user to fix it in their source code.
• Detects use of cross-version extensions that are not valid according to the new cross-version package (i.e., the cross-version package is loaded but the extension can't be found) and issues an error directing the user to the cross-version package IG documentation.
• Detects use of cross-version extensions with no cross-version extension package loaded and issues an error directing the user to add the appropriate cross-version extension package to their dependencies.

Since SUSHI implemented cross-version extensions before all of the rules were worked out, there are differences between SUSHI's implementation and the final implementation. As a result, some IGs will see new errors for cross-version extensions that differ between the two implementations.

I ran a regression over 1000+ existing SUSHI projects and found there were 61 projects that used the old SUSHI cross-version extension packages. Of those 61, here are how the regression results turned out:

• 13 projects with new errors and changes in output
• 7 projects with no new errors and with incompatible output changes due to use of extensions ending in [x]
• 9 projects with no new errors and with compatible output changes
• 32 projects with no new errors and with the only output change being the new xver dependency in the IG JSON file

I've attached a zip of the regression results. You may review them if you'd like by unzipping it and opening the index.html file in your browser: xver-regression.zip

I'm also including a screenshot of the affect projects below:

Testing Instructions:

Review the regression results above to ensure they are as expected.

Create a project with cross-version extensions using SUSHI's old cross-version extension packages or clone one of the affected projects from the regression. Run this version of SUSHI against it to determine it works as expected (ts-node src/app.ts build /path/to/project).

Related Issue: N/A

[jduteau]

argh, this affects one of my guides! But a good PR in any case.