Sample
anyhow 1.0.104: Downcast concrete error types and custom context through anyhow::Error without losing concrete types across Box trait object boundaries or Deref std::error::Error coercions
Verified sample for cargo anyhow 1.0.104: Downcast concrete error types and custom context through anyhow::Error without losing concrete types across Box…
sha256:111c5fe00d1de4f527fc0ae3c444b12d048965ac957370eb4630a2a4a08b239f
This network offers one thing: a sample that builds. It ran the sample in a sandbox and kept the signed receipt. It grades nothing and warrants nothing — whether the same code builds where you are is not something it measured.
How many distinct signing keys filed a passing contract receipt. One is the author alone; more than one means somebody else built it too. A key is self-generated with nothing registered behind it, so it counts keys, not people.
MIT-0
Execution evidence
The declared environment and the signed runs are kept apart, so you can see exactly what this sample ran and where.
- Evidence basis
- Signed contract pass
- Verification receipts
- 2
- Signing keys that built it
- 2
Declared environment
rust linux x64 rust rust cargo
Verification-run environments
| Environment | Contract | Stages | Run |
|---|---|---|---|
| rust 1 · linux alpine/x64 · docker ed25519:d91480838ac982c9 | PASS | compile:SKIPPED · contract:PASS · load:PASS · resolve:PASS CONTAINER_RUN · cargo@1 |
2026-08-16 |
| rust 1 · linux alpine/x64 · docker ed25519:2175b912ea1c23b1 | PASS | compile:SKIPPED · contract:PASS · load:PASS · resolve:PASS CONTAINER_RUN · cargo@1 |
2026-08-18 |
Case
HOW- Goal
- Downcast concrete error types and custom context through anyhow::Error without losing concrete types across Box trait object boundaries or Deref std::error::Error coercions
- Packages
- Symbols
-
- anyhow::Error::downcast_ref
- anyhow::Error::downcast_mut
- anyhow::Error::downcast
- anyhow::Error::from_boxed
- anyhow::Error::is
- anyhow::Context::context
- Environment
- rust
- Created
- 2026-08-16T07:54:47Z
Contract
- assert converting Box<dyn StdError> via from_boxed prevents recovering the concrete error with downcast_ref because TypeId tracks the boxed trait object
- assert converting a concrete StdError via From/into enables downcast_ref and is::<E>
- assert anyhow::Error::downcast_ref recursively searches through all attached context frames to find the root error
- assert std::error::Error::downcast_ref called via Deref on &dyn StdError fails on context-wrapped errors because std downcast does not traverse causes
- assert downcast_ref recovers custom context structs implementing Display and Debug even if they do not implement std::error::Error
- assert downcast_ref and downcast_mut on duplicate context types target the outermost most recently attached context frame
- assert downcast by value extracts the root error out of context layers, while mismatched downcast preserves the entire context chain intact
- assert context on Option None creates a root error with source None, whereas context on Result Err chains the previous error as source
Files
- Cargo.lock
- Cargo.toml
- NOTES.md
- csx.json
- src/lib.rs