diff --git a/src/compiler/commandLineParser.ts b/src/compiler/commandLineParser.ts
index 8005aabcc3538..4e37395f41e50 100644
--- a/src/compiler/commandLineParser.ts
+++ b/src/compiler/commandLineParser.ts
@@ -1345,7 +1345,7 @@ namespace ts {
         configFileName: string,
         optionsToExtend: CompilerOptions,
         host: ParseConfigFileHost,
-        /*@internal*/ extendedConfigCache?: Map<ExtendedConfigCacheEntry>
+        extendedConfigCache?: Map<ExtendedConfigCacheEntry>
     ): ParsedCommandLine | undefined {
         let configFileText: string | undefined;
         try {
@@ -2183,7 +2183,7 @@ namespace ts {
         return existingErrors !== configParseDiagnostics.length;
     }
 
-    interface ParsedTsconfig {
+    export interface ParsedTsconfig {
         raw: any;
         options?: CompilerOptions;
         typeAcquisition?: TypeAcquisition;
@@ -2370,7 +2370,6 @@ namespace ts {
         return undefined;
     }
 
-    /*@internal*/
     export interface ExtendedConfigCacheEntry {
         extendedResult: TsConfigSourceFile;
         extendedConfig: ParsedTsconfig | undefined;
@@ -2398,7 +2397,6 @@ namespace ts {
                 const extendedDirname = getDirectoryPath(extendedConfigPath);
                 extendedConfig = parseConfig(/*json*/ undefined, extendedResult, host, extendedDirname,
                     getBaseFileName(extendedConfigPath), resolutionStack, errors, extendedConfigCache);
-                
 
                 if (isSuccessfulParsedTsconfig(extendedConfig)) {
                     // Update the paths to reflect base path
@@ -2423,7 +2421,7 @@ namespace ts {
         if (sourceFile) {
             sourceFile.extendedSourceFiles = [extendedResult.fileName];
             if (extendedResult.extendedSourceFiles) {
-                sourceFile.extendedSourceFiles!.push(...extendedResult.extendedSourceFiles);
+                sourceFile.extendedSourceFiles.push(...extendedResult.extendedSourceFiles);
             }
         }
         if (extendedResult.parseDiagnostics.length) {
diff --git a/src/compiler/program.ts b/src/compiler/program.ts
index 9103ca2432d74..61030ed39feaf 100644
--- a/src/compiler/program.ts
+++ b/src/compiler/program.ts
@@ -2682,10 +2682,12 @@ namespace ts {
             if (host.getParsedCommandLine) {
                 commandLine = host.getParsedCommandLine(refPath);
                 if (!commandLine) {
+                    addFileToFilesByName(/*sourceFile*/ undefined, sourceFilePath, /*redirectedPath*/ undefined);
                     projectReferenceRedirects.set(sourceFilePath, false);
                     return undefined;
                 }
                 sourceFile = Debug.assertDefined(commandLine.options.configFile);
+                addFileToFilesByName(sourceFile, sourceFilePath, /*redirectedPath*/ undefined);
             }
             else {
                 // An absolute path pointing to the containing directory of the config file
diff --git a/src/compiler/types.ts b/src/compiler/types.ts
index 36b1a32e54a6a..da5ab5a677263 100644
--- a/src/compiler/types.ts
+++ b/src/compiler/types.ts
@@ -5130,7 +5130,7 @@ namespace ts {
         /* @internal */ hasInvalidatedResolution?: HasInvalidatedResolution;
         /* @internal */ hasChangedAutomaticTypeDirectiveNames?: boolean;
         createHash?(data: string): string;
-        /*@internal*/getParsedCommandLine?(fileName: string): ParsedCommandLine | undefined;
+        getParsedCommandLine?(fileName: string): ParsedCommandLine | undefined;
 
         // TODO: later handle this in better way in builder host instead once the api for tsbuild finalizes and doesnt use compilerHost as base
         /*@internal*/createDirectory?(directory: string): void;
diff --git a/tests/baselines/reference/api/tsserverlibrary.d.ts b/tests/baselines/reference/api/tsserverlibrary.d.ts
index 5d5472e840592..c0cc90efdc770 100644
--- a/tests/baselines/reference/api/tsserverlibrary.d.ts
+++ b/tests/baselines/reference/api/tsserverlibrary.d.ts
@@ -2760,6 +2760,7 @@ declare namespace ts {
         resolveTypeReferenceDirectives?(typeReferenceDirectiveNames: string[], containingFile: string, redirectedReference?: ResolvedProjectReference): (ResolvedTypeReferenceDirective | undefined)[];
         getEnvironmentVariable?(name: string): string | undefined;
         createHash?(data: string): string;
+        getParsedCommandLine?(fileName: string): ParsedCommandLine | undefined;
     }
     interface SourceMapRange extends TextRange {
         source?: SourceMapSource;
@@ -3631,7 +3632,7 @@ declare namespace ts {
     /**
      * Reads the config file, reports errors if any and exits if the config file cannot be found
      */
-    function getParsedCommandLineOfConfigFile(configFileName: string, optionsToExtend: CompilerOptions, host: ParseConfigFileHost): ParsedCommandLine | undefined;
+    function getParsedCommandLineOfConfigFile(configFileName: string, optionsToExtend: CompilerOptions, host: ParseConfigFileHost, extendedConfigCache?: Map<ExtendedConfigCacheEntry>): ParsedCommandLine | undefined;
     /**
      * Read tsconfig.json file
      * @param fileName The path to the config file
@@ -3673,7 +3674,20 @@ declare namespace ts {
      * @param basePath A root directory to resolve relative path entries in the config
      *    file to. e.g. outDir
      */
-    function parseJsonSourceFileConfigFileContent(sourceFile: TsConfigSourceFile, host: ParseConfigHost, basePath: string, existingOptions?: CompilerOptions, configFileName?: string, resolutionStack?: Path[], extraFileExtensions?: ReadonlyArray<FileExtensionInfo>): ParsedCommandLine;
+    function parseJsonSourceFileConfigFileContent(sourceFile: TsConfigSourceFile, host: ParseConfigHost, basePath: string, existingOptions?: CompilerOptions, configFileName?: string, resolutionStack?: Path[], extraFileExtensions?: ReadonlyArray<FileExtensionInfo>, /*@internal*/ extendedConfigCache?: Map<ExtendedConfigCacheEntry>): ParsedCommandLine;
+    interface ParsedTsconfig {
+        raw: any;
+        options?: CompilerOptions;
+        typeAcquisition?: TypeAcquisition;
+        /**
+         * Note that the case of the config path has not yet been normalized, as no files have been imported into the project yet
+         */
+        extendedConfigPath?: string;
+    }
+    interface ExtendedConfigCacheEntry {
+        extendedResult: TsConfigSourceFile;
+        extendedConfig: ParsedTsconfig | undefined;
+    }
     function convertCompilerOptionsFromJson(jsonOptions: any, basePath: string, configFileName?: string): {
         options: CompilerOptions;
         errors: Diagnostic[];
diff --git a/tests/baselines/reference/api/typescript.d.ts b/tests/baselines/reference/api/typescript.d.ts
index e8e2bed3bb8f9..61f5919396d74 100644
--- a/tests/baselines/reference/api/typescript.d.ts
+++ b/tests/baselines/reference/api/typescript.d.ts
@@ -2760,6 +2760,7 @@ declare namespace ts {
         resolveTypeReferenceDirectives?(typeReferenceDirectiveNames: string[], containingFile: string, redirectedReference?: ResolvedProjectReference): (ResolvedTypeReferenceDirective | undefined)[];
         getEnvironmentVariable?(name: string): string | undefined;
         createHash?(data: string): string;
+        getParsedCommandLine?(fileName: string): ParsedCommandLine | undefined;
     }
     interface SourceMapRange extends TextRange {
         source?: SourceMapSource;
@@ -3631,7 +3632,7 @@ declare namespace ts {
     /**
      * Reads the config file, reports errors if any and exits if the config file cannot be found
      */
-    function getParsedCommandLineOfConfigFile(configFileName: string, optionsToExtend: CompilerOptions, host: ParseConfigFileHost): ParsedCommandLine | undefined;
+    function getParsedCommandLineOfConfigFile(configFileName: string, optionsToExtend: CompilerOptions, host: ParseConfigFileHost, extendedConfigCache?: Map<ExtendedConfigCacheEntry>): ParsedCommandLine | undefined;
     /**
      * Read tsconfig.json file
      * @param fileName The path to the config file
@@ -3673,7 +3674,20 @@ declare namespace ts {
      * @param basePath A root directory to resolve relative path entries in the config
      *    file to. e.g. outDir
      */
-    function parseJsonSourceFileConfigFileContent(sourceFile: TsConfigSourceFile, host: ParseConfigHost, basePath: string, existingOptions?: CompilerOptions, configFileName?: string, resolutionStack?: Path[], extraFileExtensions?: ReadonlyArray<FileExtensionInfo>): ParsedCommandLine;
+    function parseJsonSourceFileConfigFileContent(sourceFile: TsConfigSourceFile, host: ParseConfigHost, basePath: string, existingOptions?: CompilerOptions, configFileName?: string, resolutionStack?: Path[], extraFileExtensions?: ReadonlyArray<FileExtensionInfo>, /*@internal*/ extendedConfigCache?: Map<ExtendedConfigCacheEntry>): ParsedCommandLine;
+    interface ParsedTsconfig {
+        raw: any;
+        options?: CompilerOptions;
+        typeAcquisition?: TypeAcquisition;
+        /**
+         * Note that the case of the config path has not yet been normalized, as no files have been imported into the project yet
+         */
+        extendedConfigPath?: string;
+    }
+    interface ExtendedConfigCacheEntry {
+        extendedResult: TsConfigSourceFile;
+        extendedConfig: ParsedTsconfig | undefined;
+    }
     function convertCompilerOptionsFromJson(jsonOptions: any, basePath: string, configFileName?: string): {
         options: CompilerOptions;
         errors: Diagnostic[];