Add build script to check for nightly

The rustdoc_missing_doc_code_examples lint has been sending
warnings and causing CI issues due to being an unstable feature.

This change introduces a small build script that detects whether
the current toolchain is nightly and, if so, sets the config option
"nightly_features". This config option then sets the feature gate
for missing_doc_code_examples and turns on 'warn'.

It expands the existing code for parsing minor version
to parse the rest of the rust --version.

This change also introduces a toolchain test that uses
rust_version to double-check that the config option was enabled
IFF the nightly toolchain is being used.

color-spantrace/src/lib.rs

@@ -60,10 +60,14 @@
 //! [`tracing_error::SpanTrace`]: https://docs.rs/tracing-error/*/tracing_error/struct.SpanTrace.html
 //! [`color-backtrace`]: https://github.com/athre0z/color-backtrace
 #![doc(html_root_url = "https://docs.rs/color-spantrace/0.2.0")]
+#![cfg_attr(
+    nightly_features,
+    feature(rustdoc_missing_doc_code_examples),
+    warn(rustdoc::missing_doc_code_examples)
+)]
 #![warn(
     missing_debug_implementations,
     missing_docs,
-    rustdoc::missing_doc_code_examples,
     rust_2018_idioms,
     unreachable_pub,
     bad_style,

eyre/build.rs

@@ -1,4 +1,5 @@
 use std::env;
+use std::ffi::OsString;
 use std::fs;
 use std::path::Path;
 use std::process::{Command, ExitStatus};
@@ -55,16 +56,20 @@ fn main() {
         _ => {}
     }
 
-    let rustc = match rustc_minor_version() {
-        Some(rustc) => rustc,
+    let version = match rustc_version_info() {
+        Some(version) => version,
         None => return,
     };
 
-    if rustc < 52 {
+    if version.is_nightly {
+        println!("cargo:rustc-cfg=nightly_features");
+    }
+
+    if version.minor < 52 {
         println!("cargo:rustc-cfg=eyre_no_fmt_arguments_as_str");
     }
 
-    if rustc < 58 {
+    if version.minor < 58 {
         println!("cargo:rustc-cfg=eyre_no_fmt_args_capture");
     }
 }
@@ -86,13 +91,23 @@ fn compile_probe(probe: &str) -> Option<ExitStatus> {
         .ok()
 }
 
-fn rustc_minor_version() -> Option<u32> {
-    let rustc = env::var_os("RUSTC")?;
+struct VersionInfo {
+    minor: u32,
+    is_nightly: bool,
+}
+
+fn rustc_version_info() -> Option<VersionInfo> {
+    let rustc = env::var_os("RUSTC").unwrap_or_else(|| OsString::from("rustc"));
     let output = Command::new(rustc).arg("--version").output().ok()?;
     let version = str::from_utf8(&output.stdout).ok()?;
-    let mut pieces = version.split('.');
-    if pieces.next() != Some("rustc 1") {
+    let mut pieces = version.split(['.', ' ', '-']);
+    if pieces.next() != Some("rustc") {
         return None;
     }
-    pieces.next()?.parse().ok()
+    let _major: u32 = pieces.next()?.parse().ok()?;
+    let minor = pieces.next()?.parse().ok()?;
+    let _patch: u32 = pieces.next()?.parse().ok()?;
+    let is_nightly = pieces.next() == Some("nightly");
+    let version = VersionInfo { minor, is_nightly };
+    return Some(version);
 }

eyre/src/lib.rs

@@ -329,11 +329,17 @@
 //! [`color-spantrace`]: https://github.com/eyre-rs/color-spantrace
 //! [`color-backtrace`]: https://github.com/athre0z/color-backtrace
 #![doc(html_root_url = "https://docs.rs/eyre/0.6.8")]
+// #![cfg_attr(feature = "nightly",
+//             feature(rustdoc_missing_doc_code_examples),
+//             warn(rustdoc::missing_doc_code_examples))]
+#![cfg_attr(
+    nightly_features,
+    feature(rustdoc_missing_doc_code_examples),
+    warn(rustdoc::missing_doc_code_examples)
+)]
 #![warn(
     missing_debug_implementations,
     missing_docs,
-    // FIXME: this lint is currently nightly only
-    rustdoc::missing_doc_code_examples,
     unsafe_op_in_unsafe_fn,
     rust_2018_idioms,
     unreachable_pub,

eyre/tests/test_toolchain.rs

@@ -0,0 +1,17 @@
+#[rustversion::attr(not(nightly), ignore)]
+//#[cfg_attr(miri, ignore)]
+#[test]
+fn nightlytest() {
+    if !cfg!(nightly_features) {
+        panic!("nightly feature isn't set when the toolchain is nightly");
+    }
+}
+
+#[rustversion::attr(nightly, ignore)]
+//#[cfg_attr(miri, ignore)]
+#[test]
+fn stabletest() {
+    if cfg!(nightly_features) {
+        panic!("nightly feature is set when the toolchain isn't nightly");
+    }
+}