fix(xslt): name the html output method doctype HTML, not the element name (closes output40/48/60) (#259)

* fix(xslt): name the html output method doctype HTML, not the element name

XSLT 1.0 16.2: for the html output method the name following <!DOCTYPE should
be HTML or html, not the document element name (which is the xml method's rule,
16.1). The serializer used the document element name for both methods, so
method=html with a non-html root element (e.g. <root>) emitted
<!DOCTYPE root PUBLIC ...> instead of <!DOCTYPE HTML PUBLIC ...>.

Closes Apache Xalan conformance cases output40, output48, output60.

* fix(xslt): emit no html doctype when the result has no element

Addresses the doctype critic finding: a doctype precedes the first element
(16.2), so a text-only result must emit none even for the html method. The
fixed HTML name made the existing no-element guard unreachable; restore it by
guarding on the document element before choosing the name.

CHANGELOG.md

@@ -52,6 +52,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Fixed
 
+- The `html` output method now names the document type declaration `HTML` rather than the document element name (XSLT 1.0 16.2: "The name following the `<!DOCTYPE` should be HTML or html"). With `method="html"` and a `doctype-public` or `doctype-system`, the emitted declaration is `<!DOCTYPE HTML PUBLIC "...">` regardless of the result's root element; the `xml` method still uses the document element name (16.1). Closes Apache Xalan conformance cases `output40`, `output48`, and `output60`.
+
 - The `html` output method no longer escapes a `<` character in an attribute value (XSLT 1.0 16.2). The HTML output method escapes `&` and `"` in attribute values but leaves `<` and `>` literal, unlike the `xml` method; the serializer was escaping `<` to `&lt;` there. The `xml` output method is unchanged (it still escapes both). Closes Apache Xalan conformance cases `output49` and `output74`.
 
 - A string-form `document()` reference now resolves against the base URI of the stylesheet element holding it (XSLT 1.0 12.1), which for a declaration in an `xsl:include`d or `xsl:import`ed file is that file's URI rather than the top stylesheet's. The parser already tracked each top-level declaration's source-file base; that base is now carried onto the compiled templates and global variables and threaded into expression evaluation, so a relative `document('data.xml')` (or `document('')`, the self-reference) in an included file resolves against the included file, not the importing one. Closes Apache Xalan conformance cases `mdocs12` and `mdocs13`.

Sources/XSLT/XSLTTransform.swift

@@ -186,7 +186,12 @@ public extension PureXML.XSLT {
     /// The `<!DOCTYPE …>` prologue for the result's root element when the output
     /// declares `doctype-system` (optionally with `doctype-public`), else empty.
     private static func doctype(for result: PureXML.Model.Node, _ output: Output, method: String) -> String {
-        guard let name = rootName(of: result) else { return "" }
+        // A doctype precedes the first element, so emit none without one. The
+        // html output method then names it HTML (16.2: "The name following
+        // <!DOCTYPE should be HTML or html"); the xml method uses the document
+        // element name (16.1).
+        guard let elementName = rootName(of: result) else { return "" }
+        let name = method == "html" ? "HTML" : elementName
         if let system = output.doctypeSystem {
             let external = output.doctypePublic.map { "PUBLIC \"\($0)\" \"\(system)\"" } ?? "SYSTEM \"\(system)\""
             return "<!DOCTYPE \(name) \(external)>\n"

Tests/Fixtures/xalan-baseline.txt

@@ -29,9 +29,6 @@ numbering/numbering63
 output/output22
 output/output26
 output/output32
-output/output40
-output/output48
-output/output60
 output/output63
 output/output70
 output/output72

Tests/XSLTDoctypeOutputTests.swift

@@ -20,17 +20,44 @@ struct XSLTDoctypeOutputTests {
         #expect(try transform(style, "<x/>") == "<!DOCTYPE note SYSTEM \"note.dtd\">\n<note/>")
     }
 
-    @Test("doctype-public and doctype-system emit a PUBLIC doctype")
+    @Test("the html method names the doctype HTML regardless of the document element")
     func test_publicAndSystem() throws {
+        // XSLT 1.0 16.2: the html output method's doctype name is HTML, not the
+        // document element name (here `root`), unlike the xml method (Apache
+        // Xalan output40, output48, output60).
         let style = """
         <xsl:stylesheet version="1.0" \(xsl)>
           <xsl:output method="html" doctype-public="-//W3C//DTD HTML 4.01//EN" doctype-system="http://www.w3.org/TR/html4/strict.dtd"/>
-          <xsl:template match="/"><html/></xsl:template>
+          <xsl:template match="/"><root/></xsl:template>
         </xsl:stylesheet>
         """
         let out = try transform(style, "<x/>")
-        #expect(out.hasPrefix("<!DOCTYPE html PUBLIC \"-//W3C//DTD HTML 4.01//EN\" \"http://www.w3.org/TR/html4/strict.dtd\">\n"))
-        #expect(out.contains("<html></html>"))
+        #expect(out.hasPrefix("<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.01//EN\" \"http://www.w3.org/TR/html4/strict.dtd\">\n"))
+        #expect(out.contains("<root></root>"))
+    }
+
+    @Test("the xml method still uses the document element name for the doctype")
+    func test_xmlMethodUsesElementName() throws {
+        let style = """
+        <xsl:stylesheet version="1.0" \(xsl)>
+          <xsl:output method="xml" omit-xml-declaration="yes" doctype-system="note.dtd"/>
+          <xsl:template match="/"><note/></xsl:template>
+        </xsl:stylesheet>
+        """
+        #expect(try transform(style, "<x/>") == "<!DOCTYPE note SYSTEM \"note.dtd\">\n<note/>")
+    }
+
+    @Test("the html method emits no doctype when the result has no element")
+    func test_htmlNoElementNoDoctype() throws {
+        // A doctype precedes the first element (16.2); a text-only result has
+        // none, so even the html method with doctype-public emits nothing.
+        let style = """
+        <xsl:stylesheet version="1.0" \(xsl)>
+          <xsl:output method="html" doctype-public="-//W3C//DTD HTML 4.01//EN"/>
+          <xsl:template match="/">just text</xsl:template>
+        </xsl:stylesheet>
+        """
+        #expect(try transform(style, "<x/>") == "just text")
     }
 
     @Test("Without doctype-system no doctype is emitted")