Handle WatchCompilerHost without timeout methods to retrieve correct Program (#37308)

Author: sheetalkamat

src/compiler/watchPublic.ts

@@ -320,8 +320,8 @@ namespace ts {
         watchConfigFileWildCardDirectories();
 
         return configFileName ?
-            { getCurrentProgram: getCurrentBuilderProgram, getProgram: synchronizeProgram, close } :
-            { getCurrentProgram: getCurrentBuilderProgram, getProgram: synchronizeProgram, updateRootFileNames, close };
+            { getCurrentProgram: getCurrentBuilderProgram, getProgram: updateProgram, close } :
+            { getCurrentProgram: getCurrentBuilderProgram, getProgram: updateProgram, updateRootFileNames, close };
 
         function close() {
             resolutionCache.clear();
@@ -553,7 +553,7 @@ namespace ts {
                 host.clearTimeout(timerToUpdateProgram);
             }
             writeLog("Scheduling update");
-            timerToUpdateProgram = host.setTimeout(updateProgram, 250);
+            timerToUpdateProgram = host.setTimeout(updateProgramWithWatchStatus, 250);
         }
 
         function scheduleProgramReload() {
@@ -562,10 +562,13 @@ namespace ts {
             scheduleProgramUpdate();
         }
 
-        function updateProgram() {
+        function updateProgramWithWatchStatus() {
             timerToUpdateProgram = undefined;
             reportWatchDiagnostic(Diagnostics.File_change_detected_Starting_incremental_compilation);
+            updateProgram();
+        }
 
+        function updateProgram() {
             switch (reloadLevel) {
                 case ConfigFileProgramReloadLevel.Partial:
                     perfLogger.logStartUpdateProgram("PartialConfigReload");
@@ -581,6 +584,7 @@ namespace ts {
                     break;
             }
             perfLogger.logStopUpdateProgram("Done");
+            return getCurrentBuilderProgram();
         }
 
         function reloadFileNamesFromConfigFile() {

src/testRunner/unittests/tscWatch/watchApi.ts

@@ -63,4 +63,27 @@ namespace ts.tscWatch {
             assert.equal(watchedErrorCount, 2, "The error count was expected to be 2 for the file change");
         });
     });
+
+    describe("unittests:: tsc-watch:: watchAPI:: when watchHost does not implement setTimeout or clearTimeout", () => {
+        it("verifies that getProgram gets updated program if new file is added to the program", () => {
+            const config: File = {
+                path: `${projectRoot}/tsconfig.json`,
+                content: "{}"
+            };
+            const mainFile: File = {
+                path: `${projectRoot}/main.ts`,
+                content: "const x = 10;"
+            };
+            const sys = createWatchedSystem([config, mainFile, libFile]);
+            const watchCompilerHost = createWatchCompilerHost(config.path, {}, sys);
+            watchCompilerHost.setTimeout = undefined;
+            watchCompilerHost.clearTimeout = undefined;
+            const watch = createWatchProgram(watchCompilerHost);
+            checkProgramActualFiles(watch.getProgram().getProgram(), [mainFile.path, libFile.path]);
+            // Write new file
+            const barPath = `${projectRoot}/bar.ts`;
+            sys.writeFile(barPath, "const y =10;");
+            checkProgramActualFiles(watch.getProgram().getProgram(), [mainFile.path, barPath, libFile.path]);
+        });
+    });
 }