Implement and use optimisticReadJsonOrNull for better caching.

The problem with optimisticReadFile is that it doesn't cache anything when
the file is missing, because files.readFile throws an ENOENT exception.

tools/fs/optimistic.js

@@ -122,9 +122,9 @@ export const optimisticStatOrNull = makeOptimistic("statOrNull", statOrNull);
 export const optimisticLStat = makeOptimistic("lstat", lstat);
 export const optimisticReadFile = makeOptimistic("readFile", readFile);
 export const optimisticReaddir = makeOptimistic("readdir", readdir);
-export const optimisticHashOrNull = makeOptimistic("hashOrNull", path => {
+export const optimisticHashOrNull = makeOptimistic("hashOrNull", (...args) => {
   try {
-    return sha1(optimisticReadFile(path));
+    return sha1(optimisticReadFile(...args));
 
   } catch (e) {
     if (e.code !== "EISDIR" &&
@@ -135,3 +135,16 @@ export const optimisticHashOrNull = makeOptimistic("hashOrNull", path => {
 
   return null;
 });
+
+export const optimisticReadJsonOrNull =
+makeOptimistic("readJsonOrNull", (...args) => {
+  try {
+    return JSON.parse(optimisticReadFile(...args));
+  } catch (e) {
+    if (! (e instanceof SyntaxError ||
+           e.code === "ENOENT")) {
+      throw e;
+    }
+  }
+  return null;
+});

tools/isobuild/meteor-npm.js

@@ -27,7 +27,7 @@ import {
   dirtyNpmPackageByName,
   optimisticLStat,
   optimisticStatOrNull,
-  optimisticReadFile,
+  optimisticReadJsonOrNull,
   optimisticReaddir,
 } from "../fs/optimistic.js";
 
@@ -146,7 +146,7 @@ export function getProdPackageNames(nodeModulesDir) {
 
     if (packageJsonStat &&
         packageJsonStat.isFile()) {
-      const pkg = JSON.parse(optimisticReadFile(packageJsonPath));
+      const pkg = optimisticReadJsonOrNull(packageJsonPath);
       const nodeModulesDir = files.pathJoin(dir, "node_modules");
       nodeModulesDirStack.push(nodeModulesDir);
 
@@ -268,16 +268,8 @@ function rebuildVersionsAreCompatible(pkgPath) {
   const versionFile =
     files.pathJoin(pkgPath, lastRebuildJSONFilename);
 
-  try {
-    var versions = JSON.parse(files.readFile(versionFile));
-  } catch (e) {
-    if (! (e instanceof SyntaxError ||
-           e.code === "ENOENT")) {
-      throw e;
-    }
-  }
-
-  return versionsAreCompatible(versions);
+  return versionsAreCompatible(
+    optimisticReadJsonOrNull(versionFile));
 }
 
 // Rebuilds any binary dependencies in the given node_modules directory,
@@ -458,13 +450,9 @@ const isPortable = Profile("meteorNpm.isPortable", dir => {
     // put .meteor-portable files only in the individual top-level package
     // directories, so that they will get cleared away the next time those
     // packages are (re)installed.
-    try {
-      return JSON.parse(optimisticReadFile(portableFile));
-    } catch (e) {
-      if (! (e instanceof SyntaxError ||
-             e.code === "ENOENT")) {
-        throw e;
-      }
+    const result = optimisticReadJsonOrNull(portableFile);
+    if (result) {
+      return result;
     }
   } else {
     // Clean up any .meteor-portable files we mistakenly wrote in

tools/isobuild/resolver.js

@@ -21,7 +21,7 @@ import LRU from "lru-cache";
 import { wrap } from "optimism";
 import {
   optimisticStatOrNull,
-  optimisticReadFile,
+  optimisticReadJsonOrNull,
 } from "../fs/optimistic.js";
 
 const nativeModulesMap = Object.create(null);
@@ -279,26 +279,9 @@ export default class Resolver {
     return resolved || "missing";
   }
 
-  _readPkgJson(path) {
-    if (! optimisticStatOrNull(path)) {
-      return null;
-    }
-
-    try {
-      return JSON.parse(optimisticReadFile(path));
-    } catch (e) {
-      if (! (e instanceof SyntaxError ||
-             e.code === "ENOENT")) {
-        throw e;
-      }
-    }
-
-    return null;
-  }
-
   _resolvePkgJsonMain(dirPath, _seenDirPaths) {
     const pkgJsonPath = pathJoin(dirPath, "package.json");
-    const pkg = this._readPkgJson(pkgJsonPath);
+    const pkg = optimisticReadJsonOrNull(pkgJsonPath);
     if (! pkg) {
       return null;
     }