Find metadata reference for alias

Author: dibarbet

src/LanguageServer/Protocol/Handler/References/FindUsagesLSPContext.cs

@@ -253,14 +253,20 @@ public override async ValueTask OnReferencesFoundAsync(IAsyncEnumerable<SourceRe
 
         // If we have no document span, our location may be in metadata or may be a namespace.
         var symbol = await SymbolFinder.FindSymbolAtPositionAsync(_document, _position, cancellationToken).ConfigureAwait(false);
-        if (symbol == null || symbol.Locations.IsEmpty || symbol.Kind is SymbolKind.Namespace or SymbolKind.Alias)
+        if (symbol == null || symbol.Locations.IsEmpty || symbol.Kind is SymbolKind.Namespace)
         {
             // Either:
             // (1) We couldn't find the location in metadata and it's not in any of our known documents.
             // (2) The symbol is a namespace (and therefore has no location).
             return null;
         }
 
+        if (symbol is IAliasSymbol aliasSymbol)
+        {
+            // If the location symbol is an alias symbol, we need to get the target symbol to find the original location in metadata.
+            symbol = aliasSymbol.Target;
+        }
+
         var options = _globalOptions.GetMetadataAsSourceOptions();
         var declarationFile = await _metadataAsSourceFileService.GetGeneratedFileAsync(
             _workspace, _document.Project, symbol, signaturesOnly: true, options: options, cancellationToken: cancellationToken).ConfigureAwait(false);

src/LanguageServer/ProtocolUnitTests/References/FindAllReferencesHandlerTests.cs

@@ -318,7 +318,10 @@ void M()
         await using var testLspServer = await CreateTestLspServerAsync(markup, mutatingLspWorkspace, CapabilitiesWithVSExtensions);
 
         var results = await RunFindAllReferencesAsync(testLspServer, testLspServer.GetLocations("caret").First());
-        AssertLocationsEqual(testLspServer.GetLocations("reference"), results.Select(result => result.Location).WhereNotNull());
+        Assert.Equal(3, results.Length);
+        Assert.True(results[0].Location.DocumentUri.ToString().EndsWith("String.cs"));
+
+        AssertLocationsEqual(testLspServer.GetLocations("reference"), results.Skip(1).Select(r => r.Location));
     }
 
     private static LSP.ReferenceParams CreateReferenceParams(LSP.Location caret, IProgress<object> progress)