Update: Implement eslint/rfcs#63

conf/default-cli-options.js

@@ -24,6 +24,7 @@ module.exports = {
      */
     cacheLocation: "",
     cacheFile: ".eslintcache",
+    cacheStrategy: "metadata",
     fix: false,
     allowInlineConfig: true,
     reportUnusedDisableDirectives: void 0,

docs/user-guide/command-line-interface.md

@@ -75,6 +75,7 @@ Caching:
   --cache                        Only check changed files - default: false
   --cache-file path::String      Path to the cache file. Deprecated: use --cache-location - default: .eslintcache
   --cache-location path::String  Path to the cache file or directory
+  --cache-strategy String        Strategy to use for detecting changed files - either: metadata or content - default: metadata
 
 Miscellaneous:
   --init                         Run config initialization wizard - default: false
@@ -440,6 +441,16 @@ Example:
 
     eslint "src/**/*.js" --cache --cache-location "/Users/user/.eslintcache/"
 
+#### `--cache-strategy`
+
+Strategy for the cache to use for detecting changed files. Can be either `metadata` or `content`. If no strategy is specified, `metadata` will be used.
+
+The `content` strategy can be useful in cases where the modification time of your files change even if their contents have not.
+
+Examples:
+
+    eslint "src/**/*.js" --cache --cache-strategy content
+
 ### Miscellaneous
 
 #### `--init`

lib/cli-engine/cli-engine.js

@@ -589,7 +589,7 @@ class CLIEngine {
             ignore: options.ignore
         });
         const lintResultCache =
-            options.cache ? new LintResultCache(cacheFilePath) : null;
+            options.cache ? new LintResultCache(cacheFilePath, { options }) : null;
         const linter = new Linter({ cwd: options.cwd });
 
         /** @type {ConfigArray[]} */

lib/cli-engine/lint-result-cache.js

@@ -15,13 +15,31 @@ const stringify = require("json-stable-stringify-without-jsonify");
 const pkg = require("../../package.json");
 const hash = require("./hash");
 
+const debug = require("debug")("eslint:lint-result-cache");
+
 //-----------------------------------------------------------------------------
 // Helpers
 //-----------------------------------------------------------------------------
 
 const configHashCache = new WeakMap();
 const nodeVersion = process && process.version;
 
+const validCacheStrategies = ["metadata", "content"];
+const invalidCacheStrategyErrorMessage = `Cache strategy must be one of: ${validCacheStrategies
+    .map(strategy => `"${strategy}"`)
+    .join(", ")}`;
+
+/**
+ * Tests whether a provided cacheStrategy is valid
+ * @param {Object} configHelper The config helper for retrieving configuration information
+ * @returns {boolean} true if `configHelper.options.cacheStrategy` is one of `validCacheStrategies`; false otherwise
+ */
+function isValidCacheStrategy(configHelper) {
+    return (
+        validCacheStrategies.indexOf(configHelper.options.cacheStrategy) !== -1
+    );
+}
+
 /**
  * Calculates the hash of the config
  * @param {ConfigArray} config The config.
@@ -50,11 +68,32 @@ class LintResultCache {
      * Creates a new LintResultCache instance.
      * @param {string} cacheFileLocation The cache file location.
      *   configuration lookup by file path).
+     * @param {Object} configHelper The configuration helper (used for
+     *   configuration lookup by file path).
      */
-    constructor(cacheFileLocation) {
+    constructor(cacheFileLocation, configHelper) {
         assert(cacheFileLocation, "Cache file location is required");
-
-        this.fileEntryCache = fileEntryCache.create(cacheFileLocation);
+        assert(configHelper, "Config helper is required");
+        assert(
+            isValidCacheStrategy(configHelper),
+            invalidCacheStrategyErrorMessage
+        );
+
+        debug(`Caching results to ${cacheFileLocation}`);
+
+        const useChecksum = configHelper.options.cacheStrategy === "content";
+
+        debug(
+            `Using "${configHelper.options.cacheStrategy}" strategy to detect changes`
+        );
+
+        this.fileEntryCache = fileEntryCache.create(
+            cacheFileLocation,
+            null,
+            useChecksum
+        );
+        this.cacheFileLocation = cacheFileLocation;
+        this.configHelper = configHelper || { options: {} };
     }
 
     /**
@@ -76,17 +115,28 @@ class LintResultCache {
          *    was previously linted
          * If any of these are not true, we will not reuse the lint results.
          */
-
         const fileDescriptor = this.fileEntryCache.getFileDescriptor(filePath);
         const hashOfConfig = hashOfConfigFor(config);
-        const changed = fileDescriptor.changed || fileDescriptor.meta.hashOfConfig !== hashOfConfig;
+        const changed =
+            fileDescriptor.changed ||
+            fileDescriptor.meta.hashOfConfig !== hashOfConfig;
+
+        if (fileDescriptor.notFound) {
+            debug(`Cached result not found: ${filePath}`);
+            return null;
+        }
 
-        if (fileDescriptor.notFound || changed) {
+        if (changed) {
+            debug(`Cached result changed: ${filePath}`);
             return null;
         }
 
         // If source is present but null, need to reread the file from the filesystem.
-        if (fileDescriptor.meta.results && fileDescriptor.meta.results.source === null) {
+        if (
+            fileDescriptor.meta.results &&
+            fileDescriptor.meta.results.source === null
+        ) {
+            debug(`Rereading cached result source from filesystem: ${filePath}`);
             fileDescriptor.meta.results.source = fs.readFileSync(filePath, "utf-8");
         }
 
@@ -112,6 +162,7 @@ class LintResultCache {
         const fileDescriptor = this.fileEntryCache.getFileDescriptor(filePath);
 
         if (fileDescriptor && !fileDescriptor.notFound) {
+            debug(`Updating cached result: ${filePath}`);
 
             // Serialize the result, except that we want to remove the file source if present.
             const resultToSerialize = Object.assign({}, result);
@@ -135,6 +186,7 @@ class LintResultCache {
      * @returns {void}
      */
     reconcile() {
+        debug(`Persisting cached results: ${this.cacheFileLocation}`);
         this.fileEntryCache.reconcile();
     }
 }

lib/cli.js

@@ -62,6 +62,7 @@ function translateOptions({
     cache,
     cacheFile,
     cacheLocation,
+    cacheStrategy,
     config,
     env,
     errorOnUnmatchedPattern,
@@ -88,6 +89,7 @@ function translateOptions({
         allowInlineConfig: inlineConfig,
         cache,
         cacheLocation: cacheLocation || cacheFile,
+        cacheStrategy,
         errorOnUnmatchedPattern,
         extensions: ext,
         fix: (fix || fixDryRun) && (quiet ? quietFixPredicate : true),

lib/eslint/eslint.js

@@ -43,6 +43,7 @@ const { version } = require("../../package.json");
  * @property {ConfigData} [baseConfig] Base config object, extended by all configs used with this instance
  * @property {boolean} [cache] Enable result caching.
  * @property {string} [cacheLocation] The cache file to use instead of .eslintcache.
+ * @property {"metadata" | "content"} [cacheStrategy] The strategy used to detect changed files.
  * @property {string} [cwd] The value to use for the current working directory.
  * @property {boolean} [errorOnUnmatchedPattern] If `false` then `ESLint#lintFiles()` doesn't throw even if no target files found. Defaults to `true`.
  * @property {string[]} [extensions] An array of file extensions to check.
@@ -157,6 +158,7 @@ function processOptions({
     baseConfig = null,
     cache = false,
     cacheLocation = ".eslintcache",
+    cacheStrategy = "metadata",
     cwd = process.cwd(),
     errorOnUnmatchedPattern = true,
     extensions = null, // ← should be null by default because if it's an array then it suppresses RFC20 feature.
@@ -216,6 +218,12 @@ function processOptions({
     if (!isNonEmptyString(cacheLocation)) {
         errors.push("'cacheLocation' must be a non-empty string.");
     }
+    if (
+        cacheStrategy !== "metadata" &&
+        cacheStrategy !== "content"
+    ) {
+        errors.push("'cacheStrategy' must be any of \"metadata\", \"content\".");
+    }
     if (!isNonEmptyString(cwd) || !path.isAbsolute(cwd)) {
         errors.push("'cwd' must be an absolute path.");
     }

lib/options.js

@@ -214,6 +214,14 @@ module.exports = optionator({
             type: "path::String",
             description: "Path to the cache file or directory"
         },
+        {
+            option: "cache-strategy",
+            dependsOn: ["cache"],
+            type: "String",
+            default: "metadata",
+            enum: ["metadata", "content"],
+            description: "Strategy to use for detecting changed files in the cache"
+        },
         {
             heading: "Miscellaneous"
         },

tests/lib/cli-engine/cli-engine.js

@@ -2702,6 +2702,127 @@ describe("CLIEngine", () => {
                     assert.deepStrictEqual(result, cachedResult, "result is the same with or without cache");
                 });
             });
+
+            describe("cacheStrategy", () => {
+                it("should detect changes using a file's modification time when set to 'metadata'", () => {
+                    const cacheFile = getFixturePath(".eslintcache");
+                    const badFile = getFixturePath("cache/src", "fail-file.js");
+                    const goodFile = getFixturePath("cache/src", "test-file.js");
+
+                    doDelete(cacheFile);
+
+                    engine = new CLIEngine({
+                        cwd: path.join(fixtureDir, ".."),
+                        useEslintrc: false,
+
+                        // specifying cache true the cache will be created
+                        cache: true,
+                        cacheFile,
+                        cacheStrategy: "metadata",
+                        rules: {
+                            "no-console": 0,
+                            "no-unused-vars": 2
+                        },
+                        extensions: ["js"]
+                    });
+
+                    engine.executeOnFiles([badFile, goodFile]);
+
+                    let fileCache = fCache.createFromFile(cacheFile, false);
+                    const entries = fileCache.normalizeEntries([badFile, goodFile]);
+
+                    entries.forEach(entry => {
+                        assert.isFalse(entry.changed, `the entry for ${entry.key} is initially unchanged`);
+                    });
+
+                    // this should result in a changed entry
+                    shell.touch(goodFile);
+                    fileCache = fCache.createFromFile(cacheFile, false);
+                    assert.isFalse(fileCache.getFileDescriptor(badFile).changed, `the entry for ${badFile} is unchanged`);
+                    assert.isTrue(fileCache.getFileDescriptor(goodFile).changed, `the entry for ${goodFile} is changed`);
+                });
+
+                it("should not detect changes using a file's modification time when set to 'content'", () => {
+                    const cacheFile = getFixturePath(".eslintcache");
+                    const badFile = getFixturePath("cache/src", "fail-file.js");
+                    const goodFile = getFixturePath("cache/src", "test-file.js");
+
+                    doDelete(cacheFile);
+
+                    engine = new CLIEngine({
+                        cwd: path.join(fixtureDir, ".."),
+                        useEslintrc: false,
+
+                        // specifying cache true the cache will be created
+                        cache: true,
+                        cacheFile,
+                        cacheStrategy: "content",
+                        rules: {
+                            "no-console": 0,
+                            "no-unused-vars": 2
+                        },
+                        extensions: ["js"]
+                    });
+
+                    engine.executeOnFiles([badFile, goodFile]);
+
+                    let fileCache = fCache.createFromFile(cacheFile, true);
+                    let entries = fileCache.normalizeEntries([badFile, goodFile]);
+
+                    entries.forEach(entry => {
+                        assert.isFalse(entry.changed, `the entry for ${entry.key} is initially unchanged`);
+                    });
+
+                    // this should NOT result in a changed entry
+                    shell.touch(goodFile);
+                    fileCache = fCache.createFromFile(cacheFile, true);
+                    entries = fileCache.normalizeEntries([badFile, goodFile]);
+                    entries.forEach(entry => {
+                        assert.isFalse(entry.changed, `the entry for ${entry.key} remains unchanged`);
+                    });
+                });
+
+                it("should detect changes using a file's contents when set to 'content'", () => {
+                    const cacheFile = getFixturePath(".eslintcache");
+                    const badFile = getFixturePath("cache/src", "fail-file.js");
+                    const goodFile = getFixturePath("cache/src", "test-file.js");
+                    const goodFileCopy = path.resolve(`${path.dirname(goodFile)}`, "test-file-copy.js");
+
+                    shell.cp(goodFile, goodFileCopy);
+
+                    doDelete(cacheFile);
+
+                    engine = new CLIEngine({
+                        cwd: path.join(fixtureDir, ".."),
+                        useEslintrc: false,
+
+                        // specifying cache true the cache will be created
+                        cache: true,
+                        cacheFile,
+                        cacheStrategy: "content",
+                        rules: {
+                            "no-console": 0,
+                            "no-unused-vars": 2
+                        },
+                        extensions: ["js"]
+                    });
+
+                    engine.executeOnFiles([badFile, goodFileCopy]);
+
+                    let fileCache = fCache.createFromFile(cacheFile, true);
+                    const entries = fileCache.normalizeEntries([badFile, goodFileCopy]);
+
+                    entries.forEach(entry => {
+                        assert.isFalse(entry.changed, `the entry for ${entry.key} is initially unchanged`);
+                    });
+
+                    // this should result in a changed entry
+                    shell.sed("-i", "abc", "xzy", goodFileCopy);
+                    fileCache = fCache.createFromFile(cacheFile, true);
+                    assert.isFalse(fileCache.getFileDescriptor(badFile).changed, `the entry for ${badFile} is unchanged`);
+                    assert.isTrue(fileCache.getFileDescriptor(goodFileCopy).changed, `the entry for ${goodFileCopy} is changed`);
+                });
+            });
         });
 
         describe("processors", () => {