How xslint checks

The full list of checks with descriptions and examples is available at the check catalog.

xslint runs in two stages. Validators first establish that the input is valid; linters then run over the stylesheets that pass, catching stylistic, semantic, and logical problems. A stylesheet that does not parse is reported once and skipped, so one broken file never hides the feedback on the rest.

Validators:

• XML well-formedness — a stylesheet that is not well-formed XML, or that spells a namespace prefix it never declares, is reported at the line and column the parser stopped on and excluded from linting.
• XPath syntax — every bare XPath expression (in select, test, use, value, group-by, group-adjacent, and the XSLT 3.0 key, initial-value, xpath, context-item, with-params, namespace-context, for-each-item, for-each-source and use-when) is parsed, on an XSLT element or — spelled xsl:use-when, the only spelling a simplified stylesheet has — on a literal result element; the ones the processor cannot parse are reported.

Linters:

• Per-file checks evaluate one stylesheet at a time (most checks).
• Cross-file checks reason across all the stylesheets you lint together. For example, a named template defined in one file but invoked from another (via xsl:import/xsl:include) is not reported as unused, an xsl:import/xsl:include cycle across files is flagged (circular-import), and the same module imported twice in one stylesheet is flagged (redundant-import). Lint the whole project at once so these checks can see every caller and every imported module.
• Formatting checks are written in code rather than as a declarative selector — their YAML tunes only severity and message. Most read the parse tree of one expression; the rest read the document or the import graph. The check catalog teaches every one of them.

Every check that reads an expression reads it from an XPath or pattern attribute of an XSLT element (select, test, match, …) or from an attribute value template — <div class="{count(item) = 0}"/> is checked, and fixed, inside the braces. An attribute of your own output vocabulary that happens to share a name with an XSLT one, as in <widget test="count(item) = 0"/>, holds text destined for the result tree, so it is never read as XPath and never rewritten. And each of them is handed the expressions the validator kept, so a malformed one is reported once rather than nagged about its spacing, its axes and its count(...) calls on top of that.