consider mtime for generated files (#1153)

* consider mtime for generated files

* deterministic test mtime

Author: mbostock

src/dataloader.ts

@@ -1,3 +1,4 @@
+import {createHash} from "node:crypto";
 import {type WriteStream, createReadStream, existsSync, statSync} from "node:fs";
 import {mkdir, open, readFile, rename, unlink} from "node:fs/promises";
 import {dirname, extname, join, relative} from "node:path/posix";
@@ -7,7 +8,7 @@ import JSZip from "jszip";
 import {extract} from "tar-stream";
 import {maybeStat, prepareOutput} from "./files.js";
 import {FileWatchers} from "./fileWatchers.js";
-import {getFileHash, getFileInfo} from "./javascript/module.js";
+import {getFileInfo} from "./javascript/module.js";
 import type {Logger, Writer} from "./logger.js";
 import {cyan, faint, green, red, yellow} from "./tty.js";
 
@@ -155,8 +156,19 @@ export class LoaderResolver {
     return path;
   }
 
+  /**
+   * Returns the hash of the file with the given name within the source root, or
+   * if the name refers to a file generated by a data loader, the hash of the
+   * corresponding data loader source and its modification time. The latter
+   * ensures that if the data loader is “touched” (even without changing its
+   * contents) that the data loader will be re-run.
+   */
   getSourceFileHash(name: string): string {
-    return getFileHash(this.root, this.getSourceFilePath(name));
+    const path = this.getSourceFilePath(name);
+    const info = getFileInfo(this.root, path);
+    if (!info) return createHash("sha256").digest("hex");
+    const {hash} = info;
+    return path === name ? hash : createHash("sha256").update(hash).update(String(info.mtimeMs)).digest("hex");
   }
 
   getSourceLastModified(name: string): number | undefined {

test/dataloaders-test.ts

@@ -100,13 +100,16 @@ describe("LoaderResolver.find(path, {useStale: true})", () => {
 });
 
 describe("LoaderResolver.getSourceFileHash(path)", () => {
+  const time = new Date(Date.UTC(2023, 11, 1));
   it("returns the content hash for the specified file’s data loader", async () => {
+    await utimes("test/input/build/archives.posix/dynamic.zip.sh", time, time);
+    await utimes("test/input/build/archives.posix/static.zip", time, time);
     const loaders = new LoaderResolver({root: "test/input/build/archives.posix"});
     assert.strictEqual(loaders.getSourceFileHash("dynamic.zip.sh"), "516cec2431ce8f1181a7a2a161db8bdfcaea132d3b2c37f863ea6f05d64d1d10"); // prettier-ignore
-    assert.strictEqual(loaders.getSourceFileHash("dynamic.zip"), "516cec2431ce8f1181a7a2a161db8bdfcaea132d3b2c37f863ea6f05d64d1d10"); // prettier-ignore
-    assert.strictEqual(loaders.getSourceFileHash("dynamic/file.txt"), "516cec2431ce8f1181a7a2a161db8bdfcaea132d3b2c37f863ea6f05d64d1d10"); // prettier-ignore
+    assert.strictEqual(loaders.getSourceFileHash("dynamic.zip"), "64acd011e27907a2594fda3272bfc951e75db4c80495ce41e84ced61383bbb60"); // prettier-ignore
+    assert.strictEqual(loaders.getSourceFileHash("dynamic/file.txt"), "64acd011e27907a2594fda3272bfc951e75db4c80495ce41e84ced61383bbb60"); // prettier-ignore
     assert.strictEqual(loaders.getSourceFileHash("static.zip"), "e6afff224da77b900cfe3ab8789f2283883300e1497548c30af66dfe4c29b429"); // prettier-ignore
-    assert.strictEqual(loaders.getSourceFileHash("static/file.txt"), "e6afff224da77b900cfe3ab8789f2283883300e1497548c30af66dfe4c29b429"); // prettier-ignore
+    assert.strictEqual(loaders.getSourceFileHash("static/file.txt"), "76ac155a1184b392ed40fb79eff680d5bf57e8afd9a494b1066f26dfd1e4c5e6"); // prettier-ignore
   });
   it("returns the empty hash if the specified file does not exist", async () => {
     const loaders = new LoaderResolver({root: "test/input/build/files"});