Allow crate users to opt out of some platform support

Cargo.toml

@@ -1,7 +1,7 @@
 [package]
 name = "iana-time-zone"
 description = "get the IANA time zone for the current system"
-version = "0.1.56"
+version = "0.2.0"
 authors = [
     "Andrew Straw <[email protected]>",
     "René Kijewski <[email protected]>",
@@ -15,27 +15,44 @@ readme = "README.md"
 edition = "2018"
 
 [features]
+default = ["platform-all"]
+# Allow users to opt out of platform support for platforms that require third
+# party dependencies. Disabling any of these platforms (i.e. with
+# `default-features = false`) will prevent the platform dependencies from
+# appearing in downstream applications' `Cargo.lock`.
+platform-all = [
+  "platform-android",
+  "platform-apple",
+  "platform-haiku",
+  "platform-wasm",
+  "platform-windows",
+]
+platform-android = ["android_system_properties"]
+platform-apple = ["core-foundation-sys"]
+platform-haiku = ["iana-time-zone-haiku"]
+platform-wasm = ["js-sys", "wasm-bindgen"]
+platform-windows = ["windows"]
 # When enabled, the library will succeed to compile for unknown target platforms, and return an `Err(GetTimezoneError::OsError)` at runtime.
 fallback = []
 
 [target.'cfg(target_os = "android")'.dependencies]
-android_system_properties = "0.1.5"
+android_system_properties = { version = "0.1.5", optional = true }
 
 [target.'cfg(any(target_os = "macos", target_os = "ios"))'.dependencies]
-core-foundation-sys = "0.8.3"
+core-foundation-sys = { version = "0.8.3", optional = true }
 
 [target.'cfg(target_os = "windows")'.dependencies]
-windows = { version = "0.48.0", features = [ "Globalization" ] }
+windows = { version = "0.48.0", features = [ "Globalization" ], optional = true }
 
 [target.'cfg(target_arch = "wasm32")'.dependencies]
-js-sys = "0.3.50"
-wasm-bindgen = "0.2.70"
+js-sys = { version = "0.3.50", optional = true }
+wasm-bindgen = { version = "0.2.70", optional = true }
 
 [target.'cfg(target_arch = "wasm32")'.dev-dependencies]
 wasm-bindgen-test = "0.3"
 
 [target.'cfg(target_os = "haiku")'.dependencies]
-iana-time-zone-haiku = { version = "0.1.1", path = "haiku" }
+iana-time-zone-haiku = { version = "0.1.1", path = "haiku", optional = true }
 
 [workspace]
 members = [".", "haiku"]

src/lib.rs

@@ -34,10 +34,23 @@
 mod ffi_utils;
 
 #[cfg_attr(target_os = "linux", path = "tz_linux.rs")]
-#[cfg_attr(target_os = "windows", path = "tz_windows.rs")]
-#[cfg_attr(any(target_os = "macos", target_os = "ios"), path = "tz_macos.rs")]
 #[cfg_attr(
-    all(target_arch = "wasm32", not(target_os = "wasi")),
+    all(feature = "platform-windows", target_os = "windows"),
+    path = "tz_windows.rs"
+)]
+#[cfg_attr(
+    all(
+        feature = "platform-apple",
+        any(target_os = "macos", target_os = "ios")
+    ),
+    path = "tz_macos.rs"
+)]
+#[cfg_attr(
+    all(
+        feature = "platform-wasm",
+        target_arch = "wasm32",
+        not(target_os = "wasi")
+    ),
     path = "tz_wasm32.rs"
 )]
 #[cfg_attr(
@@ -52,8 +65,14 @@ mod ffi_utils;
     any(target_os = "illumos", target_os = "solaris"),
     path = "tz_illumos.rs"
 )]
-#[cfg_attr(target_os = "android", path = "tz_android.rs")]
-#[cfg_attr(target_os = "haiku", path = "tz_haiku.rs")]
+#[cfg_attr(
+    all(feature = "platform-android", target_os = "android"),
+    path = "tz_android.rs"
+)]
+#[cfg_attr(
+    all(feature = "platform-haiku", target_os = "haiku"),
+    path = "tz_haiku.rs"
+)]
 mod platform;
 
 /// Error types

src/platform.rs

@@ -5,5 +5,8 @@ pub fn get_timezone_inner() -> std::result::Result<String, crate::GetTimezoneErr
 #[cfg(not(feature = "fallback"))]
 compile_error!(
     "iana-time-zone is currently implemented for Linux, Window, MacOS, FreeBSD, NetBSD, \
-    OpenBSD, Dragonfly, WebAssembly (browser), iOS, Illumos, Android, Solaris and Haiku.",
+    OpenBSD, Dragonfly, WebAssembly (browser), iOS, Illumos, Android, Solaris and Haiku. \
+    If you are seeing this error on a supported platform, ensure the platform support \
+    Cargo feature is enabled, e.g. platform-android, platform-apple, platform-haiku, \
+    platform-wasm, platform-windows, or platform-all.",
 );