Support iOS, don't compile error if unsupported

Cf. baoyachi/shadow-rs#107 (comment)

Cargo.toml

@@ -10,7 +10,7 @@ categories = ["date-and-time", "internationalization", "os"]
 readme = "README.md"
 edition = "2018"
 
-[target.'cfg(target_os = "macos")'.dependencies]
+[target.'cfg(any(target_os = "macos", target_os = "ios"))'.dependencies]
 core-foundation = "0.9"
 
 [target.'cfg(target_os = "windows")'.dependencies]

src/lib.rs

@@ -20,7 +20,7 @@
 
 #[cfg_attr(target_os = "linux", path = "tz_linux.rs")]
 #[cfg_attr(target_os = "windows", path = "tz_windows.rs")]
-#[cfg_attr(target_os = "macos", path = "tz_macos.rs")]
+#[cfg_attr(any(target_os = "macos", target_os = "ios"), path = "tz_macos.rs")]
 #[cfg_attr(
     all(target_arch = "wasm32", not(target_os = "wasi")),
     path = "tz_wasm32.rs"
@@ -44,20 +44,22 @@ pub enum GetTimezoneError {
     IoError(std::io::Error),
     /// Platform-specific error from the operating system
     OsError,
+    /// Unsupported target OS
+    Unsupported,
 }
 
 impl std::error::Error for GetTimezoneError {}
 
 impl std::fmt::Display for GetTimezoneError {
     fn fmt(&self, f: &mut std::fmt::Formatter) -> Result<(), std::fmt::Error> {
-        use GetTimezoneError::*;
-        let descr = match self {
-            FailedParsingString => "GetTimezoneError::FailedParsingString",
-            IoError(_) => "GetTimezoneError::IoError(_)",
-            OsError => "OsError",
-        };
-
-        write!(f, "{}", descr)
+        f.write_str(match self {
+            Self::FailedParsingString => "GetTimezoneError::FailedParsingString",
+            Self::IoError(err) => return err.fmt(f),
+            Self::OsError => "OsError",
+            Self::Unsupported => {
+                "Unsupported operating system, please file a bug report to iana-time-zone"
+            }
+        })
     }
 }
 
@@ -71,6 +73,7 @@ impl std::convert::From<std::io::Error> for GetTimezoneError {
 ///
 /// See the module-level documentatation for a usage example and more details
 /// about this function.
+#[inline]
 pub fn get_timezone() -> std::result::Result<String, crate::GetTimezoneError> {
     platform::get_timezone_inner()
 }

src/platform.rs

@@ -1,8 +1,3 @@
 pub fn get_timezone_inner() -> std::result::Result<String, crate::GetTimezoneError> {
-    Err(crate::GetTimezoneError::FailedParsingString)
+    Err(crate::GetTimezoneError::Unsupported)
 }
-
-compile_error!(
-    "iana-time-zone is currently implemented for Linux, Window, MacOS, FreeBSD, NetBSD, \
-    OpenBSD, Dragonfly, and WebAssembly (browser).",
-);