feat: implement analyzer and code fixer for identifying and fixing when a sync flag is not propagated correctly.

samples/StevanFreeborn.AsyncSyncFlagAnalyzer.Demo/Program.cs

@@ -0,0 +1,70 @@
+internal static class Program
+{
+  public static async Task Main()
+  {
+    await Task.CompletedTask;
+  }
+}
+
+internal interface IDataService
+{
+  Task<string> GetDataAsync(string name, bool sync = false);
+  Task<string> GetMoreDataAsync(bool runSynchronously, string name);
+  Task<string> FetchAsync(int id, bool sync = false, bool cache = true);
+}
+
+internal class BusinessLogic(IDataService dataService)
+{
+  private readonly IDataService _dataService = dataService;
+
+  // ── Good patterns (no SYNC001) ──────────────────────────
+
+  /// <summary>Passes the default 'sync' variable positionally.</summary>
+  public async Task<string> Good_ForwardSync(bool sync)
+  {
+    return await _dataService.GetDataAsync("Stevan", sync);
+  }
+
+  /// <summary>Passes a custom 'runSynchronously' variable positionally.</summary>
+  public async Task<string> Good_ForwardCustomFlag(bool runSynchronously)
+  {
+    return await _dataService.GetMoreDataAsync(runSynchronously, "Freeborn");
+  }
+
+  // ── Bad patterns (SYNC001, demonstrating code fix) ──────
+
+  /// <summary>Omits the sync argument entirely.
+  /// Code fix: inserts `sync` at ordinal 1.</summary>
+  public async Task<string> Bad_OmittedSync(bool sync)
+  {
+    return await _dataService.GetDataAsync("Stevan");
+  }
+
+  /// <summary>Hardcodes `false` as a positional argument.
+  /// Code fix: replaces arg at ordinal 1 with `sync`.</summary>
+  public async Task<string> Bad_HardcodedValue(bool sync)
+  {
+    return await _dataService.GetDataAsync("Stevan", false);
+  }
+
+  /// <summary>Hardcodes a value using a named argument.
+  /// Code fix: replaces expression in the named arg, keeping `sync:`.</summary>
+  public async Task<string> Bad_NamedHardcoded(bool sync)
+  {
+    return await _dataService.GetDataAsync("Stevan", sync: false);
+  }
+
+  /// <summary>Omits sync when it's not the last parameter.
+  /// Code fix: inserts `sync` at ordinal 1 (before `cache`).</summary>
+  public async Task<string> Bad_OmittedSyncNotLast(bool sync)
+  {
+    return await _dataService.FetchAsync(17);
+  }
+
+  /// <summary>Hardcodes `false` at ordinal 0 where the target expects `runSynchronously`.
+  /// Code fix: replaces arg at ordinal 0 with `sync` (value = enclosing name).</summary>
+  public async Task<string> Bad_HardcodedAtOrdinalZero(bool sync)
+  {
+    return await _dataService.GetMoreDataAsync(false, "Freeborn");
+  }
+}