Add Icon. (#184)

Part of #25.

Sources/Slipstream/Documentation.docc/Guides/SlipstreamForWebDevelopers.md

@@ -36,7 +36,7 @@ provided below is an organized table of W3C HTML tags and their equivalent Slips
 [`<link rel="expect">`](https://html.spec.whatwg.org/multipage/links.html#link-type-expect) | [Not implemented yet](https://github.com/jverkoey/slipstream/issues/25) 
 [`<link rel="external">`](https://html.spec.whatwg.org/multipage/links.html#link-type-external) | [Not implemented yet](https://github.com/jverkoey/slipstream/issues/25) 
 [`<link rel="help">`](https://html.spec.whatwg.org/multipage/links.html#link-type-help) | [Not implemented yet](https://github.com/jverkoey/slipstream/issues/25)   
-[`<link rel="icon">`](https://html.spec.whatwg.org/multipage/links.html#rel-icon) | [Not implemented yet](https://github.com/jverkoey/slipstream/issues/25)   
+[`<link rel="icon">`](https://html.spec.whatwg.org/multipage/links.html#rel-icon) | ``Icon``   
 [`<link rel="manifest">`](https://html.spec.whatwg.org/multipage/links.html#link-type-manifest) | [Not implemented yet](https://github.com/jverkoey/slipstream/issues/25) 
 [`<link rel="modulepreload">`](https://html.spec.whatwg.org/multipage/links.html#link-type-modulepreload) | [Not implemented yet](https://github.com/jverkoey/slipstream/issues/25) 
 [`<link rel="license">`](https://html.spec.whatwg.org/multipage/links.html#link-type-license) | [Not implemented yet](https://github.com/jverkoey/slipstream/issues/25) 

Sources/Slipstream/Documentation.docc/W3C/W3CViews.md

@@ -14,6 +14,7 @@ The complete W3C HTML elements standard can be found [here](https://html.spec.wh
 
 - ``Head``
 - ``Title``
+- ``Icon``
 - ``Preload``
 - ``Preconnect``
 - ``Stylesheet``

Sources/Slipstream/W3C/Elements/DocumentMetadata/Icon.swift

@@ -0,0 +1,51 @@
+import Foundation
+
+import SwiftSoup
+
+/// A view that is an icon representing the page or site/.
+///
+/// ```swift
+/// struct MySiteMetadata: View {
+///   var body: some View {
+///     Head {
+///       Icon(URL(string: "/favicon.ico"))
+///     }
+///   }
+/// }
+/// ```
+///
+/// - SeeAlso: W3C [rel="icon"](https://html.spec.whatwg.org/multipage/links.html#rel-icon) specification.
+@available(iOS 17.0, macOS 14.0, *)
+public struct Icon: View {
+  /// Creates an Icon view.
+  ///
+  /// - Parameters:
+  ///   - url: The icon will be loaded from this URL.
+  ///   - sizes: Gives the sizes of icons for visual media. If present, is only advisory.
+  ///   - type: The MIME type of the linked resource. If present, is only advisory and must be a valid MIME type.
+  public init(_ url: URL?, sizes: String? = nil, type: String? = nil) {
+    self.url = url
+    self.sizes = sizes
+    self.type = type
+  }
+
+  @_documentation(visibility: private)
+  public func render(_ container: Element, environment: EnvironmentValues) throws {
+    guard let url else {
+      return
+    }
+    let element = try container.appendElement("link")
+    try element.attr("rel", "icon")
+    try element.attr("href", url.absoluteString)
+    if let sizes {
+      try element.attr("sizes", sizes)
+    }
+    if let type {
+      try element.attr("type", type)
+    }
+  }
+
+  private let url: URL?
+  private let sizes: String?
+  private let type: String?
+}

Tests/SlipstreamTests/W3C/IconTests.swift

@@ -0,0 +1,22 @@
+import Foundation
+import Testing
+
+import Slipstream
+
+struct IconTests {
+  @Test func nilURL() throws {
+    try #expect(renderHTML(Icon(nil)) == "")
+  }
+
+  @Test func validURL() throws {
+    try #expect(renderHTML(Icon(URL(string: "/favicon.ico"))) == #"<link rel="icon" href="/favicon.ico" />"#)
+  }
+
+  @Test func sizes() throws {
+    try #expect(renderHTML(Icon(URL(string: "/favicon.ico"), sizes: "16x16")) == #"<link rel="icon" href="/favicon.ico" sizes="16x16" />"#)
+  }
+
+  @Test func type() throws {
+    try #expect(renderHTML(Icon(URL(string: "/favicon.ico"), type: "image/png")) == #"<link rel="icon" href="/favicon.ico" type="image/png" />"#)
+  }
+}