Inline legacy local link parsing to drop obsolete HtmlLocalLinkParser API (#1004)

HtmlLocalLinkParser.FindLegacyLocalLinkIds and its LocalLinkTag model
are obsolete (CS0618) and scheduled for removal in Umbraco 18, but
uSync still needs to detect un-migrated {localLink:x} references when
mapping RTE content. Copies the regex and parsing logic directly into
SyncLocalLinkProcessor (verified against the Umbraco 18 source) so we
own it going forward instead of depending on removed API surface.

Co-authored-by: Claude Sonnet 5 <noreply@anthropic.com>

Author: KevinJump

uSync.Core/Versions/18.0/SyncLocalLinkProcessor.cs

@@ -1,11 +1,12 @@
 using System;
 using System.Collections.Generic;
+using System.Globalization;
 using System.Text;
+using System.Text.RegularExpressions;
 
 using Umbraco.Cms.Core;
 using Umbraco.Cms.Core.Models;
 using Umbraco.Cms.Core.Services;
-using Umbraco.Cms.Core.Templates;
 
 namespace uSync.Core.Versions._18._0;
 
@@ -18,19 +19,27 @@ public interface ISyncTypedLocalLinkProcessor
     public Func<object?, Func<object?, bool>, Func<string, string>, bool> Process { get; }
 }
 
-
-public class SyncLocalLinkProcessor
+/// <summary>
+///  Finds and replaces the legacy {localLink:x} syntax within values, mapping ids/UDIs to keys.
+/// </summary>
+/// <remarks>
+///  Umbraco's own <c>HtmlLocalLinkParser.FindLegacyLocalLinkIds</c> (and its <c>LocalLinkTag</c> model)
+///  are obsolete and scheduled for removal in Umbraco 18, but uSync still needs to detect these
+///  legacy (un-migrated) links when mapping content, so the parsing logic lives here instead.
+/// </remarks>
+public partial class SyncLocalLinkProcessor
 {
-    private readonly HtmlLocalLinkParser _localLinkParser;
+    // copied from Umbraco.Cms.Core.Templates.HtmlLocalLinkParser.LocalLinkPattern
+    [GeneratedRegex(@"href=['""](?<locallink>\/?(?:\{|\%7B)localLink:(?<guid>[a-zA-Z0-9-://]+)(?:\}|\%7D))", RegexOptions.IgnoreCase | RegexOptions.Compiled | RegexOptions.IgnorePatternWhitespace, "en-GB")]
+    private static partial Regex LegacyLocalLinkPattern();
+
     private readonly IIdKeyMap _idKeyMap;
     private readonly IEnumerable<ISyncTypedLocalLinkProcessor> _localLinkProcessors;
 
     public SyncLocalLinkProcessor(
-        HtmlLocalLinkParser localLinkParser,
         IIdKeyMap idKeyMap,
         IEnumerable<ISyncTypedLocalLinkProcessor> localLinkProcessors)
     {
-        _localLinkParser = localLinkParser;
         _idKeyMap = idKeyMap;
         _localLinkProcessors = localLinkProcessors;
     }
@@ -49,9 +58,9 @@ public bool ProcessToEditorValue(object? editorValue)
     public string ProcessStringValue(string input)
     {
         // find all legacy tags
-        var tags = _localLinkParser.FindLegacyLocalLinkIds(input).ToList();
+        var tags = FindLegacyLocalLinkIds(input).ToList();
 
-        foreach (HtmlLocalLinkParser.LocalLinkTag tag in tags)
+        foreach (LocalLinkTag tag in tags)
         {
             string newTagHref;
             if (tag.Udi is not null)
@@ -101,4 +110,49 @@ public string ProcessStringValue(string input)
         return null;
     }
 
+    // copied from Umbraco.Cms.Core.Templates.HtmlLocalLinkParser.FindLegacyLocalLinkIds
+    private static IEnumerable<LocalLinkTag> FindLegacyLocalLinkIds(string text)
+    {
+        MatchCollection tags = LegacyLocalLinkPattern().Matches(text);
+        foreach (Match tag in tags)
+        {
+            if (tag.Groups.Count <= 0)
+            {
+                continue;
+            }
+
+            var id = tag.Groups["guid"].Value;
+
+            // The id could be an int or a UDI
+            if (UdiParser.TryParse(id, out Udi? udi))
+            {
+                if (udi is GuidUdi guidUdi)
+                {
+                    yield return new LocalLinkTag(null, guidUdi, tag.Groups["locallink"].Value);
+                }
+            }
+
+            if (int.TryParse(id, NumberStyles.Integer, CultureInfo.InvariantCulture, out var intId))
+            {
+                yield return new LocalLinkTag(intId, null, tag.Groups["locallink"].Value);
+            }
+        }
+    }
+
+    // copied from Umbraco.Cms.Core.Templates.HtmlLocalLinkParser.LocalLinkTag
+    private sealed class LocalLinkTag
+    {
+        public LocalLinkTag(int? intId, GuidUdi? udi, string tagHref)
+        {
+            IntId = intId;
+            Udi = udi;
+            TagHref = tagHref;
+        }
+
+        public int? IntId { get; }
+
+        public GuidUdi? Udi { get; }
+
+        public string TagHref { get; }
+    }
 }