fix(typescript-estree): hash code to reduce update frequency (typescript-eslint#1179)

yoyo930021 · bradzacher · commit 96d1cc3039e2 · 2019-11-09T08:47:02.000-08:00
diff --git a/packages/typescript-estree/src/create-program/createWatchProgram.ts b/packages/typescript-estree/src/create-program/createWatchProgram.ts
@@ -45,7 +45,7 @@ const programFileListCache = new Map<CanonicalPath, Set<CanonicalPath>>();
  */
 const tsconfigLastModifiedTimestampCache = new Map<CanonicalPath, number>();
 
-const parsedFilesSeen = new Set<CanonicalPath>();
+const parsedFilesSeenHash = new Map<CanonicalPath, string>();
 
 /**
  * Clear all of the parser caches.
@@ -55,7 +55,7 @@ function clearCaches(): void {
   knownWatchProgramMap.clear();
   fileWatchCallbackTrackingMap.clear();
   folderWatchCallbackTrackingMap.clear();
-  parsedFilesSeen.clear();
+  parsedFilesSeenHash.clear();
   programFileListCache.clear();
   tsconfigLastModifiedTimestampCache.clear();
 }
@@ -104,6 +104,19 @@ function diagnosticReporter(diagnostic: ts.Diagnostic): void {
   );
 }
 
+/**
+ * Hash content for compare content.
+ * @param content hashed contend
+ * @returns hashed result
+ */
+function createHash(content: string): string {
+  // No ts.sys in browser environments.
+  if (ts.sys && ts.sys.createHash) {
+    return ts.sys.createHash(content);
+  }
+  return content;
+}
+
 /**
  * Calculate project environments using options provided by consumer and paths from config
  * @param code The code being linted
@@ -125,10 +138,10 @@ function getProgramsForProjects(
   currentLintOperationState.filePath = filePath;
 
   // Update file version if necessary
-  // TODO: only update when necessary, currently marks as changed on every lint
   const fileWatchCallbacks = fileWatchCallbackTrackingMap.get(filePath);
+  const codeHash = createHash(code);
   if (
-    parsedFilesSeen.has(filePath) &&
+    parsedFilesSeenHash.get(filePath) !== codeHash &&
     fileWatchCallbacks &&
     fileWatchCallbacks.size > 0
   ) {
@@ -232,11 +245,15 @@ function createWatchProgram(
   const oldReadFile = watchCompilerHost.readFile;
   watchCompilerHost.readFile = (filePathIn, encoding): string | undefined => {
     const filePath = getCanonicalFileName(filePathIn);
-    parsedFilesSeen.add(filePath);
-    return path.normalize(filePath) ===
+    const fileContent =
+      path.normalize(filePath) ===
       path.normalize(currentLintOperationState.filePath)
-      ? currentLintOperationState.code
-      : oldReadFile(filePath, encoding);
+        ? currentLintOperationState.code
+        : oldReadFile(filePath, encoding);
+    if (fileContent) {
+      parsedFilesSeenHash.set(filePath, createHash(fileContent));
+    }
+    return fileContent;
   };
 
   // ensure process reports error on failure instead of exiting process immediately
