Do not display UnpinStruct in the document by default

pin-project-internal/Cargo.toml

@@ -35,6 +35,3 @@ lazy_static = { version = "1.3", optional = true }
 
 [dev-dependencies]
 pin-project = { version = "0.4.0-alpha.8", path = ".." }
-
-[build-dependencies]
-rustc_version = "0.2.3"

pin-project-internal/build.rs

@@ -1,37 +1,20 @@
-// Based on https://stackoverflow.com/a/49250753/1290530
-
 use std::env;
 
-use rustc_version::{version_meta, Channel};
-
 fn main() {
-    // Set cfg flags depending on release channel
-    match version_meta().unwrap().channel {
-        // Enable our feature on nightly, or when using a
-        // locally build rustc.
-        //
-        // This is intended to avoid the issue that cannot know the actual
-        // trait implementation bounds of the `Unpin` implementation from the
-        // document of generated code.
-        // See [taiki-e/pin-project#53] and [rust-lang/rust#63281] for more details.
-        //
-        // [taiki-e/pin-project#53]: https://github.com/taiki-e/pin-project/pull/53#issuecomment-525906867
-        // [rust-lang/rust#63281]: https://github.com/rust-lang/rust/issues/63281
-        //
-        // You can opt-out of this in one of the followg ways:
-        // * Use `--cfg pin_project_stable_docs` in RUSTFLAGS.
-        //   ```toml
-        //   # in Cargo.toml
-        //   [package.metadata.docs.rs]
-        //   rustdoc-args = ["--cfg", "pin_project_stable_docs"]
-        //   ```
-        // * Use `-Zallow-features` in RUSTFLAGS to disallow unstable features.
-        Channel::Nightly | Channel::Dev
-            if feature_allowed("proc_macro_def_site") && !cfg!(pin_project_stable_docs) =>
-        {
-            println!("cargo:rustc-cfg=proc_macro_def_site");
-        }
-        _ => {}
+    // While this crate supports stable Rust, it currently requires
+    // nightly Rust in order for rustdoc to correctly document auto-generated
+    // `Unpin` impls. This does not affect the runtime functionality of this crate,
+    // nor does it affect the safety of the api provided by this crate.
+    //
+    // This is disabled by default and can be enabled using
+    // `--cfg pin_project_show_unpin_struct` in RUSTFLAGS.
+    //
+    // Refs:
+    // * https://github.com/taiki-e/pin-project/pull/53#issuecomment-525906867
+    // * https://github.com/taiki-e/pin-project/pull/70
+    // * https://github.com/rust-lang/rust/issues/63281
+    if cfg!(pin_project_show_unpin_struct) && feature_allowed("proc_macro_def_site") {
+        println!("cargo:rustc-cfg=proc_macro_def_site");
     }
 }
 

pin-project-internal/src/pin_project/mod.rs

@@ -192,7 +192,6 @@ impl Context {
                 {
                     proc_macro::Span::def_site().into()
                 }
-
                 #[cfg(not(proc_macro_def_site))]
                 {
                     Span::call_site()

src/lib.rs

@@ -6,12 +6,6 @@
 //! * [`pinned_drop`] - An attribute for annotating a function that implements `Drop`.
 //! * [`project`] - An attribute to support pattern matching.
 //!
-//! NOTE: While this crate supports stable Rust, it currently requires
-//! nightly Rust in order for rustdoc to correctly document auto-generated
-//! `Unpin` impls. This does not affect the runtime functionality of this crate,
-//! nor does it affect the safety of the api provided by this crate.
-//!
-//!
 //! ## Examples
 //!
 //! [`pin_project`] attribute creates a projection struct covering all the fields.