Fix ContainsGlobalUsingAlias when the file starts with a global using directive

Author: sharwell

StyleCop.Analyzers/StyleCop.Analyzers.Test.CSharp11/ReadabilityRules/SA1121CSharp11UnitTests.cs

@@ -41,5 +41,28 @@ class TestClass
                 FixedSources = { source1, newSource2 },
             }.RunAsync(CancellationToken.None).ConfigureAwait(false);
         }
+
+        [Fact]
+        [WorkItem(3594, "https://github.com/DotNetAnalyzers/StyleCopAnalyzers/issues/3594")]
+        public async Task TestUsingNameChangeInGlobalUsingInSameFileAsync()
+        {
+            var source = @"global using MyDouble = System.Double;
+class TestClass
+{
+    private [|MyDouble|] x;
+}";
+
+            var newSource = @"global using MyDouble = System.Double;
+class TestClass
+{
+    private double x;
+}";
+
+            await new CSharpTest()
+            {
+                TestSources = { source },
+                FixedSources = { newSource },
+            }.RunAsync(CancellationToken.None).ConfigureAwait(false);
+        }
     }
 }

StyleCop.Analyzers/StyleCop.Analyzers/Helpers/UsingAliasCache.cs

@@ -71,8 +71,10 @@ private bool ContainsGlobalUsingAlias(SemanticModel semanticModel, CancellationT
         {
             if (this.perCompilationCache == -1)
             {
-                // Check for global using aliases
-                var scopes = semanticModel.GetImportScopes(0, cancellationToken);
+                // Check for global using aliases. We check at the end of the file since GetImportScopes is observed to
+                // omit global using directives in the current file at position 0 for the specific case where there is
+                // no whitespace preceding the global using directives.
+                var scopes = semanticModel.GetImportScopes(semanticModel.SyntaxTree.Length, cancellationToken);
                 Interlocked.CompareExchange(ref this.perCompilationCache, scopes.Any(x => x.Aliases.Length > 0) ? 1 : 0, -1);
             }