From 50b7c806ce664754263101f9053e7227f13f4f72 Mon Sep 17 00:00:00 2001 From: Chris Tate Date: Sat, 24 Oct 2026 12:52:54 -0500 Subject: [PATCH] Check unchanged frontend inputs by file identity before hashing them A warm native build validates its frontend cache entry by reading and SHA-256 hashing every source and declaration file the frontend read. A tracked read now also records the file's identity (device, inode, size, modification and change time) when the identity is the same before and after the read and the file had been unchanged for two seconds. A later check accepts a file whose identity is unchanged without reading it, and hashes it otherwise. A write always gives a file a newer change time, which tools cannot set back, so an unchanged identity means the content hashed with it. The equivalent-edit check uses the same identity for the unchanged sources. --- .../src/frontend/input-tracker.test.ts | 46 +++++++++++++++ .../compiler/src/frontend/input-tracker.ts | 56 +++++++++++++++++-- 2 files changed, 97 insertions(+), 5 deletions(-) diff --git a/packages/compiler/src/frontend/input-tracker.test.ts b/packages/compiler/src/frontend/input-tracker.test.ts index b4f3957f5..d6f9a91b7 100644 --- a/packages/compiler/src/frontend/input-tracker.test.ts +++ b/packages/compiler/src/frontend/input-tracker.test.ts @@ -270,3 +270,49 @@ test("synchronous tracking restores parents after throws and propagates unstable trackedFileExists(join(dir, "outside.ts")); expect(parent.snapshot()).toEqual(before); }); + +test("a settled file is checked by its identity, and any write invalidates it", async () => { + const dir = await mkdtemp(join(tmpdir(), "scriptc-inputs-")); + scratch.push(dir); + const source = join(dir, "entry.ts"); + await writeFile(source, "export const answer = 1;\n"); + const written = fs.statSync(source); + // The file was last changed long enough before the read. + vi.useFakeTimers({ toFake: ["Date"] }); + vi.setSystemTime(Date.now() + 5000); + const tracker = new FrontendInputTracker(); + try { + tracker.run(() => trackedReadFile(source)); + } finally { + vi.useRealTimers(); + } + const snapshot = tracker.snapshot(); + const probe = snapshot.probes.find((entry) => entry.op === "file"); + expect(probe?.op === "file" && probe.identity !== undefined).toBe(true); + expect(validFrontendInputSnapshot(snapshot)).toBe(true); + const reads = vi.mocked(fs.readFileSync); + reads.mockClear(); + expect(frontendInputsStillMatch(snapshot)).toBe(true); + expect(reads.mock.calls.filter(([path]) => path === source)).toHaveLength(0); + // A same-size rewrite that restores the modification time still changes + // the change time. + await writeFile(source, "export const answer = 2;\n"); + fs.utimesSync(source, written.atime, written.mtime); + expect(frontendInputsStillMatch(snapshot)).toBe(false); +}); + +test("a file changed shortly before the read is hashed on every check", async () => { + const dir = await mkdtemp(join(tmpdir(), "scriptc-inputs-")); + scratch.push(dir); + const source = join(dir, "entry.ts"); + await writeFile(source, "export const answer = 1;\n"); + const tracker = new FrontendInputTracker(); + tracker.run(() => trackedReadFile(source)); + const snapshot = tracker.snapshot(); + const probe = snapshot.probes.find((entry) => entry.op === "file"); + expect(probe?.op === "file" && probe.identity).toBeUndefined(); + const reads = vi.mocked(fs.readFileSync); + reads.mockClear(); + expect(frontendInputsStillMatch(snapshot)).toBe(true); + expect(reads.mock.calls.filter(([path]) => path === source)).toHaveLength(1); +}); diff --git a/packages/compiler/src/frontend/input-tracker.ts b/packages/compiler/src/frontend/input-tracker.ts index d27ab6285..c23a87313 100644 --- a/packages/compiler/src/frontend/input-tracker.ts +++ b/packages/compiler/src/frontend/input-tracker.ts @@ -12,7 +12,8 @@ import { observeSourceText } from "./ts7/ast-node.js"; * behind an old resolution answer. */ export type FrontendInputProbe = - | { op: "file"; path: string; digest: string } + /** `identity` (fileIdentity) lets a later check skip hashing the file. */ + | { op: "file"; path: string; digest: string; identity?: string } | { op: "read-error"; path: string } | { op: "kind"; path: string; kind: "file" | "directory" | "other" | "missing" } | { op: "entries"; path: string; files: string[]; directories: string[] } @@ -53,6 +54,36 @@ function frontendSourceDigest(text: string): string { return createHash("sha256").update(text).digest("hex"); } +/** How long a file must have been unchanged before a read for its identity + * to stand for its content: a later write then gets a newer change time + * even on file systems whose timestamps tick once a second or every two. */ +const IDENTITY_SETTLE_MS = 2000; + +/** The device, inode, size, modification time and change time of `path`. A + * write changes the change time, which no tool can set back, so an equal + * identity means the content is the one hashed with it. */ +function fileIdentity(path: string): string | null { + try { + const info = statSync(path); + return `${info.dev}:${info.ino}:${info.size}:${info.mtimeMs}:${info.ctimeMs}`; + } catch { + return null; + } +} + +/** The text of `path` with its identity when the identity was the same before + * and after the read and the file had been unchanged for IDENTITY_SETTLE_MS. */ +function readWithIdentity(path: string): { text: string; identity: string | null } { + const readAt = Date.now(); + const before = statSync(path); + const text = readFileSync(path, "utf8"); + const after = fileIdentity(path); + const identity = `${before.dev}:${before.ino}:${before.size}:${before.mtimeMs}:${before.ctimeMs}`; + const settled = + before.mtimeMs <= readAt - IDENTITY_SETTLE_MS && before.ctimeMs <= readAt - IDENTITY_SETTLE_MS; + return { text, identity: settled && after === identity ? identity : null }; +} + function pathKind(path: string): Extract["kind"] { try { const info = statSync(path); @@ -199,8 +230,11 @@ export function trackedReadFile(path: string): string | null { const virtual = virtualSources.get(path); if (virtual !== undefined) return virtual; try { - const text = readFileSync(path, "utf8"); - record({ op: "file", path, digest: frontendSourceDigest(text) }); + const { text, identity } = readWithIdentity(path); + const digest = frontendSourceDigest(text); + record( + identity === null ? { op: "file", path, digest } : { op: "file", path, digest, identity }, + ); return text; } catch { record({ op: "read-error", path }); @@ -337,6 +371,9 @@ export function frontendInputsStillMatch( } switch (probe.op) { case "file": { + // An unchanged identity stands for the content hashed with it. + if (probe.identity !== undefined && fileIdentity(probe.path) === probe.identity) + return true; try { return frontendSourceDigest(readFileSync(probe.path, "utf8")) === probe.digest; } catch { @@ -443,6 +480,11 @@ export function frontendInputsSemanticallyMatch( probes.push(probe); continue; } + if (probe.identity !== undefined && fileIdentity(probe.path) === probe.identity) { + currentSources.set(probe.path, previous); + probes.push(probe); + continue; + } let current: string; try { current = readFileSync(probe.path, "utf8"); @@ -460,7 +502,7 @@ export function frontendInputsSemanticallyMatch( if (rawText.has(probe.path) || !isSemanticEquivalent(probe.path, previous, current)) return null; changed.push({ path: probe.path, previous, current }); - probes.push({ ...probe, digest: currentDigest }); + probes.push({ op: "file", path: probe.path, digest: currentDigest }); } const adjusted: FrontendInputSnapshot = { ...snapshot, probes }; if (!frontendInputsStillMatch(adjusted, exclusions)) return null; @@ -488,7 +530,11 @@ export function validFrontendInputSnapshot(snapshot: unknown): snapshot is Front if (typeof value.path !== "string" || typeof value.op !== "string") return false; switch (value.op) { case "file": - return typeof value.digest === "string" && /^[0-9a-f]{64}$/.test(value.digest); + return ( + typeof value.digest === "string" && + /^[0-9a-f]{64}$/.test(value.digest) && + (value.identity === undefined || typeof value.identity === "string") + ); case "read-error": return true; case "kind":