fastly-compute-rust-edition2024-fix

name	fastly-compute-rust-edition2024-fix
description	Fix Fastly Compute Rust build failures caused by edition2024 dependencies. Use when: (1) cargo build fails with "feature `edition2024` is required", (2) wit-bindgen or wasip2 crates fail to download/parse, (3) Fastly SDK pulls in incompatible transitive dependencies, (4) Build worked before but fails after dependency update. Solves by pinning wit-bindgen, wasip2, and related crates to pre-edition2024 versions.
author	Claude Code
version	1.0.0
date	"2026-01-20T00:00:00.000Z"

Fastly Compute Rust Edition2024 Dependency Fix

Problem

Fastly Compute Rust projects fail to build with errors about edition2024 being required, even when using stable Rust. The error appears when transitive dependencies (especially wit-bindgen 0.51+ and wasip2 1.0.2+) require Rust 1.87+ which isn't stable yet.

Context / Trigger Conditions

• Error: feature 'edition2024' is required
• Error: failed to parse manifest at .../wit-bindgen-0.51.0/Cargo.toml
• Error mentions "requires Rust 1.87.0" for wit-bindgen or wasip2
• Build previously worked but fails after running cargo update
• Using Fastly SDK (fastly crate) version 0.11.x

Solution

Pin the problematic transitive dependencies in your Cargo.toml:

[dependencies]
# Fastly Compute SDK - pin to specific version
fastly = "=0.11.12"

# Pin these to avoid edition2024 requirement
wit-bindgen = "=0.46.0"
wasip2 = "=1.0.1"

# Also pin these if you use k256 or crypto
k256 = { version = "=0.13.3", features = ["schnorr"] }
base64ct = "=1.6.0"

Also update rust-toolchain.toml to include both WASM targets:

[toolchain]
channel = "1.83.0"
targets = ["wasm32-wasi", "wasm32-wasip1"]

Then:

rm Cargo.lock
rustup target add wasm32-wasip1
cargo build --target wasm32-wasi

Verification

Build should complete without edition2024 errors:

cargo build --target wasm32-wasi 2>&1 | grep -i "edition2024"
# Should return nothing (no matches)

Example

Before fix (Cargo.toml):

[dependencies]
fastly = "0.11"  # Allows 0.11.x which pulls wit-bindgen 0.51+

After fix (Cargo.toml):

[dependencies]
fastly = "=0.11.12"
wit-bindgen = "=0.46.0"
wasip2 = "=1.0.1"

Notes

• The = prefix in version strings means "exactly this version"
• Fastly CLI 13.x switched from wasm32-wasi to wasm32-wasip1 target
• This is a temporary fix until Rust 1.87 becomes stable
• The warning about wasm32-wasi being renamed to wasm32-wasip1 is expected
• When Rust 1.87 is stable, these pins can be removed

References

• Fastly Compute Rust SDK: https://docs.fastly.com/products/compute
• Rust Edition 2024: https://doc.rust-lang.org/edition-guide/rust-2024/