Stop invalidating resolution when file stays open

Author: Benjamin Lichtman

src/compiler/resolutionCache.ts

@@ -54,6 +54,7 @@ namespace ts {
         writeLog(s: string): void;
         maxNumberOfFilesToIterateForInvalidation?: number;
         getCurrentProgram(): Program | undefined;
+        fileIsOpen(filePath: Path): boolean;
     }
 
     interface DirectoryWatchesOfFailedLookup {
@@ -713,6 +714,10 @@ namespace ts {
                     if (!isPathWithDefaultFailedLookupExtension(fileOrDirectoryPath) && !customFailedLookupPaths.has(fileOrDirectoryPath)) {
                         return false;
                     }
+                    // prevent saving an open file from over-eagerly triggering invalidation
+                    if (resolutionHost.fileIsOpen(fileOrDirectoryPath)) {
+                        return;
+                    }
                     // Ignore emits from the program
                     if (isEmittedFileOfProgram(resolutionHost.getCurrentProgram(), fileOrDirectoryPath)) {
                         return false;

src/compiler/watch.ts

@@ -691,6 +691,7 @@ namespace ts {
             hasChangedAutomaticTypeDirectiveNames = true;
             scheduleProgramUpdate();
         };
+        compilerHost.fileIsOpen = () => false;
         compilerHost.maxNumberOfFilesToIterateForInvalidation = host.maxNumberOfFilesToIterateForInvalidation;
         compilerHost.getCurrentProgram = getCurrentProgram;
         compilerHost.writeLog = writeLog;

src/server/project.ts

@@ -457,6 +457,11 @@ namespace ts.server {
             return this.getTypeAcquisition().enable ? this.projectService.typingsInstaller.globalTypingsCacheLocation : undefined;
         }
 
+        /*@internal*/
+        fileIsOpen(filePath: Path) {
+            return this.projectService.openFiles.has(filePath);
+        }
+
         /*@internal*/
         writeLog(s: string) {
             this.projectService.logger.info(s);