speed up hot-path utf8 processing

Sources/Elementary/Core/AttributeStorage.swift

@@ -100,6 +100,10 @@ public struct _MergedAttributes: Sequence, Sendable {
         Iterator(storage)
     }
 
+    public var isEmpty: Bool {
+        storage.isEmpty
+    }
+
     public struct Iterator: IteratorProtocol {
         enum State {
             case empty

Sources/Elementary/Core/Html+Elements.swift

@@ -166,7 +166,7 @@ extension HTMLComment: Sendable {}
 extension HTMLRaw: Sendable {}
 
 extension HTMLTagDefinition {
-    @usableFromInline
+    @usableFromInline @inline(__always)
     static var renderingType: _HTMLRenderToken.RenderingType {
         _rendersInline ? .inline : .block
     }

Sources/Elementary/Rendering/RenderingUtils.swift

@@ -23,61 +23,99 @@ extension _RenderingContext {
 // I do not know why this function does not work in embedded, but currently it crashes the compiler
 #if !hasFeature(Embedded)
 extension [UInt8] {
+    @inline(__always)
     mutating func appendToken(_ token: consuming _HTMLRenderToken) {
         // avoid strings and append each component directly
         switch token {
         case let .startTag(tagName, attributes: attributes, isUnpaired: _, type: _):
             append(60) // <
-            append(contentsOf: tagName.utf8)
-            for attribute in attributes {
-                append(32) // space
-                append(contentsOf: attribute.name.utf8)
-                if let value = attribute.value {
-                    append(contentsOf: [61, 34]) // ="
-                    appendEscapedAttributeValue(value)
-                    append(34) // "
+            appendString(tagName)
+            if !attributes.isEmpty {
+                for attribute in attributes {
+                    append(32) // space
+                    appendString(attribute.name)
+                    if let value = attribute.value {
+                        append(contentsOf: [61, 34]) // ="
+                        appendEscapedAttributeValue(value)
+                        append(34) // "
+                    }
                 }
             }
             append(62) // >
         case let .endTag(tagName, _):
             append(contentsOf: [60, 47]) // </
-            append(contentsOf: tagName.utf8)
+            appendString(tagName)
             append(62) // >
         case let .text(text):
             appendEscapedText(text)
         case let .raw(raw):
-            append(contentsOf: raw.utf8)
+            appendString(raw)
         case let .comment(comment):
-            append(contentsOf: "<!--".utf8)
+            appendString("<!--")
             appendEscapedText(comment)
-            append(contentsOf: "-->".utf8)
+            appendString("-->")
+        }
+    }
+
+    @inline(__always)
+    mutating func appendString(_ string: consuming String) {
+        string.withUTF8 { utf8 in
+            append(contentsOf: utf8)
         }
     }
 
+    @inline(__always)
     mutating func appendEscapedAttributeValue(_ value: consuming String) {
-        for byte in value.utf8 {
-            switch byte {
-            case 38: // &
-                append(contentsOf: "&amp;".utf8)
-            case 34: // "
-                append(contentsOf: "&quot;".utf8)
-            default:
-                append(byte)
+        value.withUTF8 { utf8 in
+            var start = utf8.startIndex
+
+            for current in utf8.indices {
+                switch utf8[current] {
+                case 38: // &
+                    append(contentsOf: utf8[start ..< current])
+                    appendString("&amp;")
+                    start = utf8.index(after: current)
+                case 34: // "
+                    append(contentsOf: utf8[start ..< current])
+                    appendString("&quot;")
+                    start = utf8.index(after: current)
+                default:
+                    ()
+                }
+            }
+
+            if start < utf8.endIndex {
+                append(contentsOf: utf8[start ..< utf8.endIndex])
             }
         }
     }
 
+    @inline(__always)
     mutating func appendEscapedText(_ value: consuming String) {
-        for byte in value.utf8 {
-            switch byte {
-            case 38: // &
-                append(contentsOf: "&amp;".utf8)
-            case 60: // <
-                append(contentsOf: "&lt;".utf8)
-            case 62: // >
-                append(contentsOf: "&gt;".utf8)
-            default:
-                append(byte)
+        value.withUTF8 { utf8 in
+            var start = utf8.startIndex
+
+            for current in utf8.indices {
+                switch utf8[current] {
+                case 38: // &
+                    append(contentsOf: utf8[start ..< current])
+                    appendString("&amp;")
+                    start = utf8.index(after: current)
+                case 60: // <
+                    append(contentsOf: utf8[start ..< current])
+                    appendString("&lt;")
+                    start = utf8.index(after: current)
+                case 62: // >
+                    append(contentsOf: utf8[start ..< current])
+                    appendString("&gt;")
+                    start = utf8.index(after: current)
+                default:
+                    ()
+                }
+            }
+
+            if start < utf8.endIndex {
+                append(contentsOf: utf8[start ..< utf8.endIndex])
             }
         }
     }

Tests/ElementaryTests/Utilities.swift

@@ -15,6 +15,3 @@ func HTMLAssertEqualAsyncOnly(_ html: some HTML, _ expected: String, file: Stati
 func HTMLFormattedAssertEqual(_ html: some HTML, _ expected: String, file: StaticString = #filePath, line: UInt = #line) {
     XCTAssertEqual(expected, html.renderFormatted(), file: file, line: line)
 }
-
-@inline(never)
-func blackHole<T>(_: T) {}