XSLT and XPath

for Visual Studio Code

Editing XSLT/XPath

With DeltaXML's XSLT/XPath extension , Visual Studio Code is now a fully featured XSLT 3.0 editor. Standalone XPath 3.1 files are also fully supported. Visual Studio Code's rich ecosystem is now available to XSLT and XPath developers.

Comprehensive, but language-neutral, descriptions of Visual Studio Code can be found in Microsoft's Visual Studio Code User Guide. Links to key sections are below:

The documentation here focuses on XSLT and XPath language features. More general XML features are covered on the Editing XML page. Help on navigating code in the editor is provided in the Code Navigation page.

Syntax Highlighting

Eva Dark Theme

For improved performance and precision, this extension eschews the default but problematic TM Grammar and instead uses Visual Studio Code's Semantic Highlighting introduced in 2020. feature. For external color themes you should explicitly enable Semantic Highlighting. See the Settings page for more information.

Github Light Theme

The extension provides syntax highlighting for XSLT instructions, XML Literal Result Elements, XML attributes, XML character references, CDATA sections and all tokens within XPath expressions. XPath expressions within Attribute Value Templates (AVTs) and Text Value Templates are syntax highlighted also.

Formatting

Two commands are provided for formatting XML, XSLT or XPath expressions:

As well as explicitly invoking commands, formatting can be triggered as you type, when you save a file, or when you paste content from the clipboard. The following settings control this:

The XPath formatter indents code blocks within {}, [] and () bracket-pairs. Indentation is also adjusted for if/else blocks and range-variable blocks.

Folding

Folding with this extension uses indentation to determine fold regions. To set a region code-folding block, surround it with <?region?> and <?endregion?> processing instructions. You may optionally include a label for the processing instructions, for example:

<?region modeA?> ... <?endregion modeA?>

For more detail and a full list of Folding-related actions see the Folding section in Visual Studio Code's User Guide.

Intellisense (Auto Complete)

Intellisense suggestions include all in-scope XSLT and XPath symbols from xsl:accumulator names to xsl:variable names, to anonymous XPath function parameters. There is intellisense also for XSLT and XPath functions - help for built-in functions is shown alongside the suggestions list. Symbols from included/imported files are included in the suggestions list.

Intellisense for XPath Locations

An XML source file is used for context to provide XML node-names when editing XPath location steps. This is the last non-XSLT file opened in Visual Studio Code.

XPath is evaluated as you type so node-names in the auto-completion list are filtered to be just those that are possible given previous XPath steps such as axes and node-name tests.

Triggering the auto-complete list

For XSLT intellisense, the < character triggers suggestions. XSLT instruction suggestions fit the context of the curstor location. On accepting a suggestion a Code Snippet is inserted which will include common attributes for the selected instruction.

Intellisense is manually triggered with ⌃Space, with Tab or Enter used to accept suggestions. These key bindings are fully customizable.

XSLT Instruction Snippets

The special xsl:stylesheet suggestion includes a boiler plate 'identity transform' stylesheet complete with namespace declarations.

The xsl:message suggestions include a Watch Variables snippet that lists the names and values of all the immediate in-scope variables or parameters.

More Snippets

You can define your own snippets in Visual Studio Code in a declarative way, without writing an extension. See the Visual Studio Code documentation: Create your own snippets.

Emmet Snippets provide a useful shorthand for inserting literal result elements. They can be enabled for XSLT in Visual Studio Code Settings.

Bracket Matching

Matching brackets in XPath expressions are highlighted when the cursor is near one of them. You can jump to the matching bracket with ⇧⌘\

Symbol Renaming

There's currently no explicit language support for Visual Studio Code's Symbol Renaming feature. A good substitute, however, is the multi-select feature for the selected name ⇧⌘L . All other occurrences of the selected name are editing simultaneously. Pressing Escape quits the multi-select mode.

Code Checking

The XSLT/XPath extension performs a comprehensive set of checks on your code as you type. Any syntax warning or error problems are highlighted with a squiggly underline for the token in question. Reference checks attempt to resolve symbol names through all imported/include stylesheets and packages. Here is a summary of the key checks:

  1. XML Syntax
  2. XSLT/XPath Variable name references
  3. XSLT/XPath Parameter name references
  4. All other symbol name refererences
  5. Function name and arity (number of params)
  6. xsl:with-param names
  7. File locations in xsl:import xsl:include xsl:use-package
  8. Order of operators/operands in XPath
  9. Matching of brackets in XPath
  10. XSLT instructions and their attributes
  11. Duplicate global symbol names
  12. Attribute Value Template Syntax
  13. Text Value Template Syntax
'Non-Standalone' Stylesheets

Non-standalone XSLT stylesheet modules have missing imports because they are imported by a parent module that declares the required imports. If no knowledge of the parent module is available, spurious problems can be reported. In such cases, the spurious problems are annoying and may obscure reported problems that are actually relevant.

The Inferred Imports feature prevents spurious problems being highlighted in the editor. With this featue, a search is made to find if the active XSLT stylesheet has been declared as an import by another stylesheet opened recently in Visual Studio Code. If such a 'parent' stylesheet is found (the most recently opened example is used) it is imported along with any other imports. Functions and, variables etc. used in the active stylehseet can therefore be resolved.

Unused Variables

The Code Checker detects unused variables and parameters declared in either XSLT or XPath expressions. These are highlighted by being 'grayed out' in the editor. Global variables are shown as unused if they are not referenced in the current file, the 'unused' state is not affected by imported stylesheets thay may reference the same variable.

Compile-time and Run-time problems

The Code Checking feature is designed to find most basic code problems due to typos or changes to referenced symbols. When XSLT is run, an attempt is made to parse error messages from the Saxon XSLT procesor (shown in the Task tab of the Terminal View) so that the problem token is highlighted, and the error message is shown in the Problems View.

You can quickly create a new XSLT file when adding a xsl:import, xsl:use-package or xsl:include XSLT instruction. Simply enter the file path in the href, press ⌘+click and then, in the 'Unable to Open...' dialog press the Create File button.