skip TryFrom doc test if TryFrom not supported by rustc

build.rs

@@ -28,7 +28,8 @@ fn main() {
         out_dir: PathBuf::from(cargo_env("OUT_DIR")),
         rustc: cargo_env("RUSTC"),
     };
-    // env.check_feature(...);
+    // TryFrom is needed for some doc tests
+    env.check_feature("try_from", Optional(true), TRY_TRY_FROM, None);
 }
 
 #[derive(PartialEq)]
@@ -130,3 +131,10 @@ fn create_file_or_panic(filename: &Path, contents: &str) {
     file.write_all(contents.as_bytes())
         .unwrap_or_else(|_| panic!("Unable to write to file: {:?}", filename));
 }
+
+const TRY_TRY_FROM: &str = r#"// try_try_from.rs
+use std::convert::TryFrom;
+fn main() {
+    let _ = i8::try_from(1u64);
+}
+"#;

src/traits.rs

@@ -164,6 +164,7 @@ depending on the crate’s [optional features].
 /// is [`u8`] or [`i8`].)
 ///
 /// ```rust
+/// # #[cfg(try_from)] {
 /// use fixed::{traits::Fixed, types::I12F4};
 /// use std::convert::TryFrom;
 ///
@@ -177,6 +178,7 @@ depending on the crate’s [optional features].
 ///
 /// let val = checked_add_times_500(I12F4::from_float(0.25), Fixed::from_float(1.5));
 /// assert_eq!(val, Some(Fixed::from_float(750.25)));
+/// # }
 /// ```
 ///
 /// [`None`]: https://doc.rust-lang.org/nightly/std/option/enum.Option.html#variant.None