Specify minimum version for syn dependency With only an upper bound for the versioned dependency on syn, cargo can, and sometimes will, use a version <1.0 of syn. Example: [dependencies] memoize = "0.1.7" parse-display = "0.4.0" $ cargo tree [...] ├── memoize v0.1.7 │ └── syn v0.15.44 [...] └── parse-display v0.5.1 [...] ├── parse-display-derive v0.5.1 │ └── syn v1.0.73 (*) [...] To fix this, also specify a lower bound.

on: [push]

name: CI

jobs:
  build_and_test:
    name: Rust project
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v2
      - uses: actions-rs/toolchain@v1
        with:
          toolchain: stable
      - uses: actions-rs/cargo@v1
        with:
          command: test
          args: --features full