Always : XSLT: instruction: xsl:YYYYYY not valid in this context

[GMo7944]

Hello,
I hope I have looked sufficiently before bothering you.

Even with a simple example like the one below, the top-level instructions are in error:
"XSLT: instruction: xsl:output not valid in this context" for example.

Is it a problem with my configuration or is it simply a bug?

Thank you for your tool.
Best regards.

I rename the extension to import the file :
test.xsl.txt

[SchabaJo]

Somehow syntax highlighting breaks if the file extension is not .xslt. Try renaming the file to test.xslt. This has the potential to break other addons, though.

[pgfearo]

As suggested by @SchabaJo , you can fix the problem by renaming the file to test.xsl

Further details

'Problems' indicated by the red squiggly lines come from one of the two 'diagnostics providers' for this extension, which are:

1. The XSLT diagnostics provider checks XML well-formedness but also checks XSLT instructions and XPath expression syntax for basic errors.
2. The XML diagnostics provider is intended for checking well-formedness of XML files that are not XSLT

From your screenshot it appears that the VS Code Language Mode for the editor shown in the screenshot is set to 'XML' not 'XSLT'. To fix the problem, you need to change the language mode to XSLT. You can either rename the file with a .xsl or .xslt extension to change the Language Mode to XSLT or you can manually do this by clicking on the Language Mode shown in the status bar at the bottom of the IDE and selecting XSLT (not XSL).

The screenshot below shows the file you've submitted loaded in two editors side-by-side. The left-hand editor is in XML language mode because of its .xml file extension, while the right-hand editor is in XSLT language mode because of its .xsl file extension. Because the left-hand editor is selected, the status bar shows its language mode 'XML' in the status bar.

Screenshot showing the file opened in two editors, the XML language mode (left) and the XSLT language mode (right)

A bug causes you to see incorrect XSLT diagnostics errors when viewing XSLT in the XML language mode. In a way the bug is a useful prompt to fix the language mode, but a fix for this bug would add a less confusing notification message to switch to the XSLT language mode.

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As a side note: @SchabaJo suggests, the XSLT language mode does not work well with other extensions, like Red Hat's XML extensions. I have found this too, the workaround is to use a different VS Code profile when working with XSLT that does not include other XML related extensions.

Unfortunately, for this extension to be compatible for other XML extensions, the VS Code team at Microsoft would first need to remove the built-in XML/XSLT extension for VS Code which is out of date and mostly relies on code developed for HTML, not XML, hence it is unsuitable for XML anyway. Repeated requests for this removal have been declined, sadly there are always higher priorities for the team.