Experiment using caches to answer readFile, fileExists

src/compiler/program.ts

@@ -217,6 +217,7 @@ import {
     maybeBind,
     memoize,
     MethodDeclaration,
+    missingFileModifiedTime,
     ModeAwareCache,
     ModeAwareCacheKey,
     ModifierFlags,
@@ -515,6 +516,7 @@ export function changeCompilerHostLikeToUseCache(
     host: CompilerHostLikeForCache,
     toPath: (fileName: string) => Path,
     getSourceFile?: CompilerHost["getSourceFile"],
+    getModifiedTime?: (path: Path) => Date | undefined,
 ) {
     const originalReadFile = host.readFile;
     const originalFileExists = host.fileExists;
@@ -533,7 +535,7 @@ export function changeCompilerHostLikeToUseCache(
         return setReadFileCache(key, fileName);
     };
     const setReadFileCache = (key: Path, fileName: string) => {
-        const newValue = originalReadFile.call(host, fileName);
+        const newValue = readFile(key, fileName);
         readFileCache.set(key, newValue !== undefined ? newValue : false);
         return newValue;
     };
@@ -543,7 +545,7 @@ export function changeCompilerHostLikeToUseCache(
         if (value !== undefined) return value !== false ? value : undefined; // could be .d.ts from output
         // Cache json or buildInfo
         if (!fileExtensionIs(fileName, Extension.Json) && !isBuildInfoFile(fileName)) {
-            return originalReadFile.call(host, fileName);
+            return readFile(key, fileName);
         }
 
         return setReadFileCache(key, fileName);
@@ -568,7 +570,7 @@ export function changeCompilerHostLikeToUseCache(
         const key = toPath(fileName);
         const value = fileExistsCache.get(key);
         if (value !== undefined) return value;
-        const newValue = originalFileExists.call(host, fileName);
+        const newValue = fileExists(key, fileName);
         fileExistsCache.set(key, !!newValue);
         return newValue;
     };
@@ -623,6 +625,21 @@ export function changeCompilerHostLikeToUseCache(
         getSourceFileWithCache,
         readFileWithCache,
     };
+
+    function readFile(key: Path, fileName: string) {
+        return fileExistsCache.get(key) !== false || getModifiedTime?.(key) !== missingFileModifiedTime ?
+            originalReadFile.call(host, fileName) :
+            undefined;
+    }
+
+    function fileExists(key: Path, fileName: string) {
+        const text = readFileCache.get(key);
+        if (text !== undefined) return text !== false;
+        const modifiedTime = getModifiedTime?.(key);
+        return modifiedTime === undefined ?
+            originalFileExists.call(host, fileName) :
+            modifiedTime !== missingFileModifiedTime;
+    }
 }
 
 export function getPreEmitDiagnostics(program: Program, sourceFile?: SourceFile, cancellationToken?: CancellationToken): readonly Diagnostic[];

src/compiler/tsbuildPublic.ts

@@ -759,6 +759,13 @@ function enableCache<T extends BuilderProgram>(state: SolutionBuilderState<T>) {
         host,
         fileName => toPath(state, fileName),
         (...args) => originalGetSourceFile.call(compilerHost, ...args),
+        path => {
+            const existing = state.filesWatched.get(path);
+            if (!!existing) {
+                if (!isFileWatcherWithModifiedTime(existing)) return existing;
+                if (existing.modifiedTime) return existing.modifiedTime;
+            }
+        },
     );
     state.readFileWithCache = readFileWithCache;
     compilerHost.getSourceFile = getSourceFileWithCache!;
@@ -786,6 +793,7 @@ function disableCache<T extends BuilderProgram>(state: SolutionBuilderState<T>)
     host.writeFile = cache.originalWriteFile;
     compilerHost.getSourceFile = cache.originalGetSourceFile;
     state.readFileWithCache = cache.originalReadFileWithCache;
+    if (!state.watch) state.filesWatched.clear();
     extendedConfigCache.clear();
     moduleResolutionCache?.clear();
     typeReferenceDirectiveResolutionCache?.clear();
@@ -1597,7 +1605,7 @@ function isFileWatcherWithModifiedTime(value: FileWatcherWithModifiedTime | Date
 function getModifiedTime<T extends BuilderProgram>(state: SolutionBuilderState<T>, fileName: string): Date {
     const path = toPath(state, fileName);
     const existing = state.filesWatched.get(path);
-    if (state.watch && !!existing) {
+    if (!!existing) {
         if (!isFileWatcherWithModifiedTime(existing)) return existing;
         if (existing.modifiedTime) return existing.modifiedTime;
     }
@@ -1605,10 +1613,8 @@ function getModifiedTime<T extends BuilderProgram>(state: SolutionBuilderState<T
     // This is either Date | FileWatcherWithModifiedTime because we query modified times first and
     // then after complete compilation of the project, watch the files so we dont want to loose these modified times.
     const result = ts_getModifiedTime(state.host, fileName);
-    if (state.watch) {
-        if (existing) (existing as FileWatcherWithModifiedTime).modifiedTime = result;
-        else state.filesWatched.set(path, result);
-    }
+    if (existing) existing.modifiedTime = result;
+    else state.filesWatched.set(path, result);
     return result;
 }