What causes "no encoded ident for item" in rust-lang/rust?

Run `cargo clean` then rebuild from scratch to eliminate stale/inconsistent metadata.

no encoded ident for item

Error message

no encoded ident for item

What it means

Fires in the rmeta decoder when `item_ident()` (decoder.rs:1058) calls `opt_item_name` and the item name table has no entry for the given `DefIndex`. The decoder assumes every definition it is asked to name has an encoded identifier; a missing entry means the serialized metadata is internally inconsistent with the query that requested the ident. This is an internal-compiler-error class panic, almost always a symptom of artifact corruption or a rustc bug rather than user-code error.

Source

Thrown at compiler/rustc_metadata/src/rmeta/decoder.rs:1058

    fn item_name(&self, item_index: DefIndex) -> Symbol {
        self.opt_item_name(item_index).expect("no encoded ident for item")
    }

    fn opt_item_ident(&self, tcx: TyCtxt<'_>, item_index: DefIndex) -> Option<Ident> {
        let name = self.opt_item_name(item_index)?;
        let span = self
            .root
            .tables
            .def_ident_span
            .get(self, item_index)
            .unwrap_or_else(|| self.missing("def_ident_span", item_index))
            .decode((self, tcx));
        Some(Ident::new(name, span))
    }

    fn item_ident(&self, tcx: TyCtxt<'_>, item_index: DefIndex) -> Ident {
        self.opt_item_ident(tcx, item_index).expect("no encoded ident for item")
    }

    #[inline]
    pub(super) fn map_encoded_cnum_to_current(&self, cnum: CrateNum) -> CrateNum {
        if cnum == LOCAL_CRATE { self.cnum } else { self.cnum_map[cnum] }
    }

    fn def_kind(&self, item_id: DefIndex) -> DefKind {
        self.root
            .tables
            .def_kind
            .get(self, item_id)
            .unwrap_or_else(|| self.missing("def_kind", item_id))
    }

    fn get_span(&self, tcx: TyCtxt<'_>, index: DefIndex) -> Span {
        self.root
            .tables

View on GitHub (pinned to 7088e4b63a)

Solutions

Run `cargo clean` then rebuild from scratch to eliminate stale/inconsistent metadata.
Verify every crate in the graph is built with the same `rustc --version` (run `rustup show` and check `Cargo.lock` toolchain pinning); reinstall the toolchain if it is partial.
Delete the offending dependency's artifact cache (`rm -rf target/debug/deps/<crate>*`) so it is re-fetched/recompiled.
If the panic reproduces on a clean build with a single toolchain, minimize it (`cargo bugreport` / `rustc -Z tiny-annotation` / `cargo-minimize`) and file an ICE against rustc with the backtrace.

Defensive patterns

Strategy: retry

Validate before calling

# Run before building to ensure a consistent metadata baseline
rustc --version --verbose   # confirm toolchain
find target -name '*.rmeta' -newer Cargo.lock -delete 2>/dev/null || true
cargo clean  # nuclear option: guarantees fresh metadata

Try / catch

# When driving rustc as a subprocess, treat its non-zero/ICE exit as retryable:
if cargo build; then
  echo ok
else
  rc=$?
  if cargo build 2>&1 | grep -q 'no encoded ident for item'; then
    cargo clean && cargo build   # one retry after cleaning metadata
  fi
  exit $rc
fi

Prevention

Never reuse a `target/` directory across different rustc versions; `cargo clean` after every toolchain change.
Pin the toolchain (`rust-toolchain.toml`) in CI and locally so the whole graph shares one compiler.
Avoid interrupting builds mid-link; a half-written rlib triggers decoder panics later.
In CI, start from a clean `target/` when the toolchain image changes.

When it happens

Trigger: Decoding a `DefIndex` whose name was never encoded (e.g. an anonymous/synthetic definition queried through a path that expects a named item), or reading an `.rlib`/rmeta produced by a different rustc version whose encoding schema changed. Also seen when incremental-compilation caches reference a definition that was pruned or renumbered after a stale `target/` directory is reused.

Common situations: Switching toolchains (stable <-> nightly, or a rustup update) without `cargo clean`; reusing a `target/` dir across commits that changed the dependency graph; a dependency recompiled with a patched rustc whose rmeta layout differs; corrupted download of an `.rlib`.

Related errors

AI-assisted analysis of rust-lang/rust@7088e4b63a (2026-08-10). Data as JSON: /api/errors/b9905cd7754cb0db. Report an issue: GitHub.