Specify default-features = false for proc-macro related ctates

ci/travis/setup.sh

@@ -4,7 +4,8 @@ set -e
 
 ### Setup Rust toolchain #######################################################
 
-curl https://sh.rustup.rs -sSf | sh -s -- -y --default-toolchain=$TRAVIS_RUST_VERSION
+# Use profile=minimal here to skip installing clippy
+curl https://sh.rustup.rs -sSf | sh -s -- --default-toolchain=$TRAVIS_RUST_VERSION --profile=minimal -y
 export PATH=$PATH:$HOME/.cargo/bin
 if [ "$TRAVIS_JOB_NAME" = "Minimum nightly" ]; then
     rustup component add clippy

pyo3-derive-backend/Cargo.toml

@@ -10,7 +10,14 @@ categories = ["api-bindings", "development-tools::ffi"]
 license = "Apache-2.0"
 edition = "2018"
 
+# Note: we use default-features = false for proc-macro related crates
+# not to depend on proc-macro itself.
+# See https://github.com/PyO3/pyo3/pull/810 for more.
 [dependencies]
-quote = "1"
-proc-macro2 = "1"
-syn = { version = "1", features = ["full", "extra-traits"] }
+quote = { version = "1", default-features = false }
+proc-macro2 = { version = "1", default-features = false }
+
+[dependencies.syn]
+version = "1"
+default-features = false
+features = ["derive", "parsing", "printing", "clone-impls", "full", "extra-traits"]

pyo3cls/Cargo.toml

@@ -15,6 +15,5 @@ proc-macro = true
 
 [dependencies]
 quote = "1"
-proc-macro2 = "1"
 syn = { version = "1", features = ["full", "extra-traits"] }
 pyo3-derive-backend = { path = "../pyo3-derive-backend", version = "=0.9.0-alpha.1" }