Use an explicit type

Author: amcasey

src/server/session.ts

@@ -689,7 +689,7 @@ namespace ts.server {
             this.logErrorWorker(err, cmd);
         }
 
-        private logErrorWorker(err: Error, cmd: string, fileRequest?: protocol.FileRequestArgs): void {
+        private logErrorWorker(err: Error & PossibleProgramFileInfo, cmd: string, fileRequest?: protocol.FileRequestArgs): void {
             let msg = "Exception on executing command " + cmd;
             if (err.message) {
                 msg += ":\n" + indent(err.message);
@@ -711,8 +711,9 @@ namespace ts.server {
                     catch { } // tslint:disable-line no-empty
                 }
 
-                if (err.hasOwnProperty("ProgramFiles")) {
-                    msg += `\n\nProgram files: {(err as any)["ProgramFiles"]}\n`;
+
+                if (err.ProgramFiles) {
+                    msg += `\n\nProgram files: {JSON.stringify(error.ProgramFiles}}\n`;
                     msg += `\n\nProjects::\n`;
                     let counter = 0;
                     const addProjectInfo = (project: Project) => {

src/services/services.ts

@@ -1158,10 +1158,11 @@ namespace ts {
         function getValidSourceFile(fileName: string): SourceFile {
             const sourceFile = program.getSourceFile(fileName);
             if (!sourceFile) {
-                let error = new Error(`Could not find sourceFile: '${fileName}'.`);
+                const error: Error & PossibleProgramFileInfo = new Error(`Could not find sourceFile: '${fileName}'.`);
 
-                // Attach sidecar data for the server log
-                (error as any)["ProgramFiles"] = program && JSON.stringify(program.getSourceFiles().map(f => f.fileName));
+                // We've been having trouble debugging this, so attach sidecar data for the tsserver log.
+                // See https://github.com/microsoft/TypeScript/issues/30180.
+                error.ProgramFiles = program.getSourceFiles().map(f => f.fileName);
 
                 throw error;
             }

src/services/utilities.ts

@@ -967,6 +967,11 @@ namespace ts {
         readonly called: Identifier;
         readonly nTypeArguments: number;
     }
+
+    export interface PossibleProgramFileInfo {
+        ProgramFiles?: string[];
+    }
+
     // Get info for an expression like `f <` that may be the start of type arguments.
     export function getPossibleTypeArgumentsInfo(tokenIn: Node, sourceFile: SourceFile): PossibleTypeArgumentInfo | undefined {
         let token: Node | undefined = tokenIn;

src/testRunner/unittests/tsserver/cachingFileSystemInformation.ts

@@ -139,7 +139,7 @@ namespace ts.projectSystem {
                 assert.isTrue(false, `should not find file '${imported.path}'`);
             }
             catch (e) {
-                assert.isTrue(e.message.indexOf(`Could not find sourceFile: '${imported.path}' in ["${root.path}"].`) === 0, `Actual: ${e.message}`);
+                assert.isTrue(e.message.indexOf(`Could not find sourceFile: '${imported.path}'.`) === 0, `Actual: ${e.message}`);
             }
             const f2Lookups = getLocationsForModuleLookup("f2");
             callsTrackingHost.verifyCalledOnEachEntryNTimes(CalledMapsWithSingleArg.fileExists, f2Lookups, 1);