Update tcSigEnv instead of overriding it in the callback for a signature file.

Author: nojaf

src/Compiler/Driver/ParseAndCheckInputs.fs

@@ -1470,6 +1470,8 @@ let CheckOneInputAux'
                     // printfn $"Applying Sig {file.FileName}"
                     let fsiPartialResult, tcState =
                         let rootSigs = Zmap.add qualNameOfFile sigFileType tcState.tcsRootSigs
+                        let tcSigEnv =
+                            AddLocalRootModuleOrNamespace TcResultsSink.NoSink tcGlobals amap m tcState.tcsTcSigEnv sigFileType
 
                         // Add the signature to the signature env (unless it had an explicit signature)
                         let ccuSigForFile = CombineCcuContentFragments [ sigFileType; tcState.tcsCcuSig ]
@@ -1478,8 +1480,7 @@ let CheckOneInputAux'
 
                         let tcState =
                             { tcState with
-                                tcsTcSigEnv = tcEnv
-                                tcsTcImplEnv = tcState.tcsTcImplEnv
+                                tcsTcSigEnv = tcSigEnv
                                 tcsRootSigs = rootSigs
                                 tcsCreatesGeneratedProvidedTypes = tcState.tcsCreatesGeneratedProvidedTypes || createsGeneratedProvidedTypes
                             }