Handle empty string when getting file version (#51689)

* Test for empty string change

* Fix empty string for file versioning

src/compiler/tsbuildPublic.ts

@@ -1811,7 +1811,7 @@ function getUpToDateStatusWorker(state: SolutionBuilderState, project: ParsedCom
                 if (!buildInfoVersionMap) buildInfoVersionMap = getBuildInfoFileVersionMap(buildInfoProgram, buildInfoPath!, host);
                 version = buildInfoVersionMap.get(toPath(state, inputFile));
                 const text = version ? state.readFileWithCache(inputFile) : undefined;
-                currentVersion = text && getSourceFileVersionAsHashFromText(host, text);
+                currentVersion = text !== undefined ? getSourceFileVersionAsHashFromText(host, text) : undefined;
                 if (version && version === currentVersion) pseudoInputUpToDate = true;
             }
 

src/compiler/watchPublic.ts

@@ -715,7 +715,7 @@ export function createWatchProgram<T extends BuilderProgram>(host: WatchCompiler
         if (hostSourceFile.version) return hostSourceFile.version;
         // Read file and get new version
         const text = readFileWithCache(path);
-        return text ? getSourceFileVersionAsHashFromText(compilerHost, text) : undefined;
+        return text !== undefined ? getSourceFileVersionAsHashFromText(compilerHost, text) : undefined;
     }
 
     function onReleaseOldSourceFile(oldSourceFile: SourceFile, _oldOptions: CompilerOptions, hasSourceFileByPath: boolean) {

src/testRunner/unittests/tscWatch/watchEnvironment.ts

@@ -717,6 +717,16 @@ describe("unittests:: tsc-watch:: watchEnvironment:: tsc-watch with different po
                 change: sys => sys.replaceFileText("/user/username/projects/project/main.ts", "Hello", "Hello World"),
                 timeouts: sys => sys.runQueuedTimeoutCallbacks(),
             },
+            {
+                caption: "receive another change event without modifying the file",
+                change: sys => sys.invokeFsWatches("/user/username/projects/project/main.ts", "change", /*modifiedTime*/ undefined, /*useTildeSuffix*/ undefined),
+                timeouts: sys => sys.runQueuedTimeoutCallbacks(),
+            },
+            {
+                caption: "change main.ts to empty text",
+                change: sys => sys.writeFile("/user/username/projects/project/main.ts", ""),
+                timeouts: sys => sys.runQueuedTimeoutCallbacks(),
+            },
             {
                 caption: "receive another change event without modifying the file",
                 change: sys => sys.invokeFsWatches("/user/username/projects/project/main.ts", "change", /*modifiedTime*/ undefined, /*useTildeSuffix*/ undefined),