use HashSet for usedSnippets and usedIncludes (#747)

Author: SimonCropp

src/MarkdownSnippets/Processing/IncludeProcessor.cs

@@ -21,7 +21,7 @@ public IncludeProcessor(
         this.allFiles = allFiles;
     }
 
-    public bool TryProcessInclude(List<Line> lines, Line line, List<Include> used, int index, List<MissingInclude> missing, string? relativePath)
+    public bool TryProcessInclude(List<Line> lines, Line line, ICollection<Include> used, int index, List<MissingInclude> missing, string? relativePath)
     {
         var current = line.Current;
 
@@ -79,7 +79,7 @@ static string GetIncludeKey(CharSpan substring)
         return false;
     }
 
-    void Inner(List<Line> lines, Line line, List<Include> used, int index, List<MissingInclude> missing, string includeKey, string? relativePath)
+    void Inner(List<Line> lines, Line line, ICollection<Include> used, int index, List<MissingInclude> missing, string includeKey, string? relativePath)
     {
         if (includesLookup.TryGetValue(includeKey, out var include))
         {
@@ -125,7 +125,7 @@ void Inner(List<Line> lines, Line line, List<Include> used, int index, List<Miss
         line.Current = $"** Could not find include '{includeKey}' ** <!-- singleLineInclude: {includeKey} -->";
     }
 
-    void AddInclude(List<Line> lines, Line line, List<Include> used, int index, Include include, bool writePath)
+    void AddInclude(List<Line> lines, Line line, ICollection<Include> used, int index, Include include, bool writePath)
     {
         used.Add(include);
         var linesToInject = BuildIncludes(line, include, writePath).ToList();

src/MarkdownSnippets/Processing/MarkdownProcessor.cs

@@ -129,8 +129,8 @@ internal ProcessResult Apply(List<Line> lines, string newLine, string? relativeP
         var missingSnippets = new List<MissingSnippet>();
         var validationErrors = new List<ValidationError>();
         var missingIncludes = new List<MissingInclude>();
-        var usedSnippets = new List<Snippet>();
-        var usedIncludes = new List<Include>();
+        var usedSnippets = new HashSet<Snippet>();
+        var usedIncludes = new HashSet<Include>();
         var builder = new StringBuilder();
         Line? tocLine = null;
 
@@ -263,8 +263,8 @@ void AppendWebSnippet(string url, string snippetKey, string? viewUrl = null)
 
         return new(
             missingSnippets: missingSnippets,
-            usedSnippets: usedSnippets.Distinct().ToList(),
-            usedIncludes: usedIncludes.Distinct().ToList(),
+            usedSnippets: usedSnippets.ToList(),
+            usedIncludes: usedIncludes.ToList(),
             missingIncludes: missingIncludes,
             validationErrors: validationErrors);
     }
@@ -292,15 +292,15 @@ bool ValidateContent(string? relativePath, Line line, List<ValidationError> vali
         return found;
     }
 
-    void ProcessSnippetLine(Action<string> appendLine, List<MissingSnippet> missings, List<Snippet> used, string key, string? relativePath, Line line)
+    void ProcessSnippetLine(Action<string> appendLine, List<MissingSnippet> missings, HashSet<Snippet> used, string key, string? relativePath, Line line)
     {
         appendLine($"<!-- snippet: {key} -->");
 
         if (TryGetSnippets(key, relativePath, line.Path, out var snippetsForKey))
         {
             appendSnippets(key, snippetsForKey, appendLine);
             appendLine("<!-- endSnippet -->");
-            used.AddRange(snippetsForKey);
+            used.UnionWith(snippetsForKey);
             return;
         }
 
@@ -312,7 +312,7 @@ void ProcessSnippetLine(Action<string> appendLine, List<MissingSnippet> missings
         appendLine("<!-- endSnippet -->");
     }
 
-    void ProcessWebSnippetLine(Action<string> appendLine, List<MissingSnippet> missings, List<Snippet> used, string url, string snippetKey, string? viewUrl, Line line)
+    void ProcessWebSnippetLine(Action<string> appendLine, List<MissingSnippet> missings, HashSet<Snippet> used, string url, string snippetKey, string? viewUrl, Line line)
     {
         var commentText = viewUrl == null
             ? $"<!-- web-snippet: {url}#{snippetKey} -->"