Add more information when getValidSourceFile cant find the file in question.

src/server/session.ts

@@ -659,16 +659,32 @@ namespace ts.server {
                 }
             }
 
-            if (fileRequest && this.logger.hasLevel(LogLevel.verbose)) {
-                try {
-                    const { file, project } = this.getFileAndProject(fileRequest);
-                    const scriptInfo = project.getScriptInfoForNormalizedPath(file);
-                    if (scriptInfo) {
-                        const text = getSnapshotText(scriptInfo.getSnapshot());
-                        msg += `\n\nFile text of ${fileRequest.file}:${indent(text)}\n`;
+            if (this.logger.hasLevel(LogLevel.verbose)) {
+                if (fileRequest) {
+                    try {
+                        const { file, project } = this.getFileAndProject(fileRequest);
+                        const scriptInfo = project.getScriptInfoForNormalizedPath(file);
+                        if (scriptInfo) {
+                            const text = getSnapshotText(scriptInfo.getSnapshot());
+                            msg += `\n\nFile text of ${fileRequest.file}:${indent(text)}\n`;
+                        }
                     }
+                    catch { } // tslint:disable-line no-empty
+                }
+
+                if (err.message && err.message.indexOf(`Could not find sourceFile:`) !== -1) {
+                    msg += `\n\nProjects::\n`;
+                    let counter = 0;
+                    const addProjectInfo = (project: Project) => {
+                        msg += `\nProject '${project.projectName}' (${ProjectKind[project.projectKind]}) ${counter}\n`;
+                        msg += project.filesToString(/*writeProjectFileNames*/ true);
+                        msg += "\n-----------------------------------------------\n";
+                        counter++;
+                    };
+                    this.projectService.externalProjects.forEach(addProjectInfo);
+                    this.projectService.configuredProjects.forEach(addProjectInfo);
+                    this.projectService.inferredProjects.forEach(addProjectInfo);
                 }
-                catch {} // tslint:disable-line no-empty
             }
 
             this.logger.msg(msg, Msg.Err);

src/services/services.ts

@@ -1158,7 +1158,7 @@ namespace ts {
         function getValidSourceFile(fileName: string): SourceFile {
             const sourceFile = program.getSourceFile(fileName);
             if (!sourceFile) {
-                throw new Error("Could not find file: '" + fileName + "'.");
+                throw new Error(`Could not find sourceFile: '${fileName}' in ${program && JSON.stringify(program.getSourceFiles().map(f => f.fileName))}.`);
             }
             return sourceFile;
         }

src/testRunner/unittests/tsserver/cachingFileSystemInformation.ts

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