Merge rust-bitcoin/rust-bitcoin#1269: Hex fixups

6b96050d1f Document `cfg` (Martin Habovstiak)
6fc4860813 Activate `rust_v_1_46` when on high-enough rustc (Martin Habovstiak)

Pull request description:

  This fixes minor mistakes that I made in previous PR.

ACKs for top commit:
  apoelstra:
    ACK 6b96050d1f
  tcharding:
    tACK 6b96050d1f

Tree-SHA512: a926d1b642058538c3a61760593c387a9316050d7468c3eefd18c7a6c1109e736032ac49704b16f418dc0649fe110d48e188cb6b267f002ac60803f0f5a9fedb

internals/build.rs

@@ -0,0 +1,34 @@
+fn main() {
+    let rustc = std::env::var_os("RUSTC");
+    let rustc = rustc.as_ref().map(std::path::Path::new).unwrap_or_else(|| "rustc".as_ref());
+    let output = std::process::Command::new(rustc)
+        .arg("--version")
+        .output()
+        .unwrap_or_else(|error| panic!("Failed to run `{:?} --version`: {:?}", rustc, error));
+    assert!(output.status.success(), "{:?} -- version returned non-zero exit code", rustc);
+    let stdout = String::from_utf8(output.stdout).expect("rustc produced non-UTF-8 output");
+    let version_prefix = "rustc ";
+    if !stdout.starts_with(version_prefix) {
+        panic!("unexpected rustc output: {}", stdout);
+    }
+
+    let version = &stdout[version_prefix.len()..];
+    let end = version.find(&[' ', '-'] as &[_]).unwrap_or(version.len());
+    let version = &version[..end];
+    let mut version_components = version.split('.');
+    let major = version_components.next().unwrap();
+    assert_eq!(major, "1", "Unexpected Rust major version");
+    let minor = version_components
+        .next()
+        .unwrap_or("0")
+        .parse::<u64>()
+        .expect("invalid Rust minor version");
+
+    // print cfg for all interesting versions less than or equal to minor
+    // 46 adds `track_caller`
+    for version in &[46] {
+        if *version <= minor {
+            println!("cargo:rustc-cfg=rust_v_1_{}", version);
+        }
+    }
+}

internals/src/hex/display.rs

@@ -45,6 +45,7 @@ pub trait DisplayHex: Copy + sealed::IsRef {
     ///
     /// This may be faster than `.display_hex().to_string()` because it uses `reserve_suggestion`.
     #[cfg(feature = "alloc")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "alloc")))]
     fn to_lower_hex_string(self) -> String {
         self.to_hex_string(Case::Lower)
     }
@@ -55,6 +56,7 @@ pub trait DisplayHex: Copy + sealed::IsRef {
     ///
     /// This may be faster than `.display_hex().to_string()` because it uses `reserve_suggestion`.
     #[cfg(feature = "alloc")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "alloc")))]
     fn to_upper_hex_string(self) -> String {
         self.to_hex_string(Case::Upper)
     }
@@ -63,6 +65,7 @@ pub trait DisplayHex: Copy + sealed::IsRef {
     ///
     /// This may be faster than `.display_hex().to_string()` because it uses `reserve_suggestion`.
     #[cfg(feature = "alloc")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "alloc")))]
     fn to_hex_string(self, case: Case) -> String {
         let mut string = String::new();
         self.append_hex_to_string(case, &mut string);
@@ -74,6 +77,7 @@ pub trait DisplayHex: Copy + sealed::IsRef {
     /// This may be faster than `write!(string, "{}", self.display_hex())` because it uses
     /// `reserve_sugggestion`.
     #[cfg(feature = "alloc")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "alloc")))]
     fn append_hex_to_string(self, case: Case, string: &mut String) {
         use fmt::Write;