{"record":{"id":"5eed52d794054167","repo":"denoland/deno","slug":"failed-to-initialize-jsruntime-for-snapshotting","errorCode":null,"errorMessage":"Failed to initialize JsRuntime for snapshotting: {:?}","messagePattern":"Failed to initialize JsRuntime for snapshotting: (.+?)","errorType":"panic","errorClass":null,"httpStatus":null,"severity":"critical","filePath":"libs/core/runtime/jsruntime.rs","lineNumber":2879,"sourceCode":"    )\n  };\n\n  let scope = &mut v8::ContextScope::new(scope, context);\n\n  let global = context.global(scope);\n  for middleware in global_object_middlewares {\n    middleware(scope, global);\n  }\n  context\n}\n\nimpl JsRuntimeForSnapshot {\n  /// Create a new runtime, panicking if the process fails.\n  pub fn new(options: RuntimeOptions) -> JsRuntimeForSnapshot {\n    match Self::try_new(options) {\n      Ok(runtime) => runtime,\n      Err(err) => {\n        panic!(\"Failed to initialize JsRuntime for snapshotting: {:?}\", err);\n      }\n    }\n  }\n\n  /// Try to create a new runtime, returning an error if the process fails.\n  pub fn try_new(\n    mut options: RuntimeOptions,\n  ) -> Result<JsRuntimeForSnapshot, CoreError> {\n    setup::init_v8(\n      options.v8_platform.take(),\n      true,\n      options.unsafe_expose_natives_and_gc(),\n    );\n\n    let runtime = JsRuntime::new_inner(options, true)?;\n    Ok(JsRuntimeForSnapshot(runtime))\n  }\n","sourceCodeStart":2861,"sourceCodeEnd":2897,"githubUrl":"https://github.com/denoland/deno/blob/336da420f4343cbb1dcbd5eed9d075ff555ed6ee/libs/core/runtime/jsruntime.rs#L2861-L2897","documentation":"JsRuntimeForSnapshot::new is the panicking constructor used when generating snapshots (the create_snapshot / build.rs path): like JsRuntime::new it delegates to try_new and panics with the debug-formatted error if runtime construction for snapshotting fails. Because this variant deserializes an existing startup_snapshot and prepares the isolate for a new snapshot, typical failures are an incompatible base snapshot or extension init errors. The try_new twin returns Result instead of panicking.","triggerScenarios":"Running create_snapshot (usually from build.rs) with a startup_snapshot base built by a different deno_core version; snapshot-generation extension list differing from the base snapshot's layout; extension init JS throwing during the snapshot build; CI environments where the snapshot artifact is stale relative to the source tree.","commonSituations":"cargo build picking up a cached/stale snapshot file after a deno_core bump; build.rs not emitting cargo:rerun-if-changed for extension changes, so the snapshot-for-snapshotting runtime is built against an outdated base.","solutions":["Use JsRuntimeForSnapshot::try_new in custom snapshot tooling to surface the CoreError instead of a panic","Regenerate the base startup snapshot with the current deno_core before building the derived snapshot","Ensure build.rs prints rerun-if-changed lines (create_snapshot returns them) so cargo rebuilds the snapshot when inputs change","Keep the extension vector identical between base snapshot creation and the snapshotting runtime"],"exampleFix":"// before\nlet rt = JsRuntimeForSnapshot::new(options); // panics inside build.rs\n\n// after\nlet rt = JsRuntimeForSnapshot::try_new(options)\n  .expect(\"snapshot runtime init\"); // or propagate the CoreError","handlingStrategy":"try-catch","validationCode":"// In build.rs-adjacent tooling: sanity-check the base snapshot boots for-snapshot\n// before the real run.\nif JsRuntimeForSnapshot::try_new(base_options).is_err() {\n  panic!(\"base startup snapshot is incompatible; regenerate it first\");\n}","typeGuard":null,"tryCatchPattern":"let rt = match JsRuntimeForSnapshot::try_new(options) {\n  Ok(rt) => rt,\n  Err(err) => {\n    eprintln!(\"snapshot runtime init failed: {err:?}\");\n    std::process::exit(1);\n  }\n};","preventionTips":["Print create_snapshot's returned files as cargo:rerun-if-changed so snapshots rebuild on input changes","Regenerate base snapshots whenever deno_core or extensions change","Fail the build loudly on stale snapshot artifacts instead of producing them later"],"tags":["deno-core","snapshot","build-rs","runtime-init","panic"],"backgroundTag":"runtime-initialization-failed","analyzedSha":"336da420f4343cbb1dcbd5eed9d075ff555ed6ee","analyzedAt":"2026-08-20T13:07:44.778Z","contentChangedAt":"2026-08-20T13:07:44.778Z","schemaVersion":2},"datasetVersion":"2026-09-14T05:17:10.506Z"}