rustc 1.87.0 ICE compiling rusqlite 0.31.0 in Docker release build

Summary

I hit an internal compiler error from rustc 1.87.0 while building rusqlite 0.31.0 inside a Docker release build.

The crash happened repeatedly while compiling rusqlite with feature="bundled" and involved repeated panics in:

• compiler/rustc_trait_selection/src/traits/specialize/specialization_graph.rs:41:57
• compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs:563:83

The panic message was:

called `Option::unwrap()` on a `None` value

This was reported by rustc itself as:

error: the compiler unexpectedly panicked. this is a bug.

As of April 15, 2026, I can no longer reproduce this reliably from the same checkout with the same rust:1.87-slim tag, so this may be an unstable or dependency-resolution-sensitive ICE. I am filing it anyway because the original failure log is very detailed and points at compiler internals.

Reproducer

The failing build came from this Dockerfile:

FROM rust:1.87-slim AS builder
WORKDIR /app
RUN apt-get update && apt-get install -y pkg-config libssl-dev && rm -rf /var/lib/apt/lists/*
COPY Cargo.toml .
COPY src ./src
RUN cargo build --release

The crate under build depended on:

rusqlite = { version = "0.31", features = ["bundled"] }

The failure occurred during:

RUN cargo build --release

and the final error was:

error: could not compile `rusqlite` (lib)

One of the rustc invocations from the failing log was:

/usr/local/rustup/toolchains/1.87.0-x86_64-unknown-linux-gnu/bin/rustc --crate-name rusqlite --edition=2021 /usr/local/cargo/registry/src/index.crates.io-1949cf8c6b5b557f/rusqlite-0.31.0/src/lib.rs --error-format=json --json=diagnostic-rendered-ansi,artifacts,future-incompat --crate-type lib --emit=dep-info,metadata,link -C opt-level=3 -C embed-bitcode=no --cfg 'feature="bundled"' --cfg 'feature="modern_sqlite"' ... -C strip=debuginfo ...

Relevant resolved crates from the failure log included:

• rusqlite 0.31.0
• bitflags 2.11.1
• libsqlite3-sys 0.28.0
• hashlink 0.9.1
• smallvec 1.15.1

What I expected

cargo build --release should either compile successfully or produce a normal diagnostic from the crate graph. It should not ICE in trait selection.

What happened instead

rustc repeatedly panicked while compiling rusqlite, including query stacks like:

#0 [specialization_graph_of] building specialization graph of trait `core::ops::drop::Drop`
#1 [coherent_trait] coherence checking all impls of trait `core::ops::drop::Drop`

and:

#0 [evaluate_obligation] evaluating trait selection obligation `<i32 as core::ops::bit::BitXor>::Output == i32`
#1 [compare_impl_item] checking assoc item `<impl at /usr/local/cargo/registry/src/index.crates.io-1949cf8c6b5b557f/bitflags-2.11.1/src/public.rs:536:9: 536:47>::Bits` is compatible with trait definition

The repeated panic sites were:

thread 'rustc' panicked at compiler/rustc_trait_selection/src/traits/specialize/specialization_graph.rs:41:57:
called `Option::unwrap()` on a `None` value

and later:

thread 'rustc' panicked at compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs:563:83:
called `Option::unwrap()` on a `None` value

I saw many repeated query stacks for traits like:

• core::ops::drop::Drop
• core::marker::Copy
• core::clone::Clone
• core::fmt::Debug
• core::marker::Send
• core::cmp::Eq
• core::hash::Hash
• core::cmp::PartialEq
• core::cmp::PartialOrd
• core::cmp::Ord
• core::ops::bit::BitXor
• core::ops::bit::BitXorAssign
• core::ops::bit::BitAnd
• core::ops::bit::BitAndAssign
• core::ops::arith::Sub
• core::ops::arith::SubAssign
• core::ops::bit::Not
• core::marker::Sync
• core::error::Error
• core::ops::deref::Deref
• core::ops::deref::DerefMut
• core::convert::TryFrom

Version

From the failing output:

rustc 1.87.0 (17067e9ac 2025-05-09) running on x86_64-unknown-linux-gnu

I also confirmed on April 15, 2026 that rust:1.87-slim currently reports:

rustc 1.87.0 (17067e9ac 2025-05-09)
host: x86_64-unknown-linux-gnu
LLVM version: 20.1.1

Additional context

• The build was happening in Docker, not in a local interactive shell.
• The builder stage used rust:1.87-slim.
• The original failure log was very large because the compiler panicked repeatedly across many trait queries before the build stopped.
• On April 15, 2026, docker build -q -f products/signal-hive/backend/Dockerfile products/signal-hive/backend succeeded for me from the same checkout, so I do not currently have a stable minimized reproducer.

Start with the Dockerfile and run cargo build --release using rust:1.87-slim and the listed rusqlite dependency versions. Then inspect the reported panic locations in compiler/rustc_trait_selection/src/traits/specialize/specialization_graph.rs and compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs. Done means establishing a stable reproducer or documenting why the ICE cannot be reproduced from the supplied inputs.