Remove Utc::now() and Local::now() on unsupported platforms

src/datetime/mod.rs

@@ -874,11 +874,16 @@ impl DateTime<Utc> {
         feature = "std",
         all(
             feature = "now",
-            not(all(
-                target_arch = "wasm32",
-                feature = "wasmbind",
-                not(any(target_os = "emscripten", target_os = "wasi"))
-            ))
+            any(
+                unix,
+                windows,
+                target_os = "solid_asp3",
+                target_os = "hermit",
+                target_os = "wasi",
+                target_os = "xous",
+                all(target_vendor = "fortanix", target_env = "sgx"),
+                target_os = "teeos",
+            )
         )
     ))]
     pub(crate) fn try_from_system_time(t: std::time::SystemTime) -> Result<DateTime<Utc>, Error> {

src/offset/local/mod.rs

@@ -11,7 +11,7 @@ use rkyv::{Archive, Deserialize, Serialize};
 
 use super::fixed::FixedOffset;
 use super::{MappedLocalTime, TimeZone};
-use crate::{DateTime, NaiveDateTime, Utc};
+use crate::NaiveDateTime;
 
 #[cfg(unix)]
 #[path = "unix.rs"]
@@ -120,8 +120,8 @@ impl Local {
     /// Returns a `DateTime<Local>` which corresponds to the current date, time and offset from
     /// UTC.
     ///
-    /// See also the similar [`Utc::now()`] which returns `DateTime<Utc>`, i.e. without the local
-    /// offset.
+    /// See also the similar [`Utc::now()`](crate::Utc::now) which returns `DateTime<Utc>`, i.e.
+    /// without the local offset.
     ///
     /// # Example
     ///
@@ -144,8 +144,19 @@ impl Local {
     /// let offset = FixedOffset::east(5 * 60 * 60).unwrap();
     /// let now_with_offset = Local::now().with_timezone(&offset);
     /// ```
-    pub fn now() -> DateTime<Local> {
-        Utc::now().with_timezone(&Local)
+    #[cfg(any(
+        unix,
+        windows,
+        target_os = "solid_asp3",
+        target_os = "hermit",
+        target_os = "wasi",
+        target_os = "xous",
+        all(target_vendor = "fortanix", target_env = "sgx"),
+        target_os = "teeos",
+        all(target_arch = "wasm32", feature = "wasmbind")
+    ))]
+    pub fn now() -> crate::DateTime<Local> {
+        crate::Utc::now().with_timezone(&Local)
     }
 }
 

src/offset/utc.rs

@@ -4,23 +4,12 @@
 //! The UTC (Coordinated Universal Time) time zone.
 
 use core::fmt;
-#[cfg(all(
-    feature = "now",
-    not(all(
-        target_arch = "wasm32",
-        feature = "wasmbind",
-        not(any(target_os = "emscripten", target_os = "wasi"))
-    ))
-))]
-use std::time::SystemTime;
 
 #[cfg(any(feature = "rkyv-16", feature = "rkyv-32", feature = "rkyv-64"))]
 use rkyv::{Archive, Deserialize, Serialize};
 
 use super::{FixedOffset, MappedLocalTime, Offset, TimeZone};
 use crate::naive::NaiveDateTime;
-#[cfg(feature = "now")]
-use crate::DateTime;
 #[cfg(all(feature = "now", doc))]
 use crate::OutOfRange;
 
@@ -82,14 +71,25 @@ impl Utc {
     /// Panics if the system clock is set to a time in the extremely distant past or future, such
     /// that it is out of the range representable by `DateTime<Utc>`. It is assumed that this
     /// crate will no longer be in use by that time.
-    #[cfg(not(all(
-        target_arch = "wasm32",
-        feature = "wasmbind",
-        not(any(target_os = "emscripten", target_os = "wasi"))
-    )))]
+    // Covers the platforms with `SystemTime::time()` supported by the Rust Standard Library as of
+    // Rust 1.78. See:
+    //   https://github.com/rust-lang/rust/blob/5e9bed7b1e1524936001b37b6ecbf406179d8ebe/library/std/src/sys/pal/mod.rs
+    // Note that some platforms listed in the PAL table do not support `SystemTime::time()` (e.g.,
+    // `zkvm` and `wasm`). When updating this configuration, also be sure to update `Local::now()`
+    // and `DateTime::try_from_system_time()`.
+    #[cfg(any(
+        unix,
+        windows,
+        target_os = "solid_asp3",
+        target_os = "hermit",
+        target_os = "wasi",
+        target_os = "xous",
+        all(target_vendor = "fortanix", target_env = "sgx"),
+        target_os = "teeos",
+    ))]
     #[must_use]
-    pub fn now() -> DateTime<Utc> {
-        DateTime::try_from_system_time(SystemTime::now()).expect(
+    pub fn now() -> crate::DateTime<Utc> {
+        crate::DateTime::try_from_system_time(std::time::SystemTime::now()).expect(
             "system clock is set to a time extremely far into the past or future; cannot convert",
         )
     }
@@ -101,9 +101,9 @@ impl Utc {
         not(any(target_os = "emscripten", target_os = "wasi"))
     ))]
     #[must_use]
-    pub fn now() -> DateTime<Utc> {
+    pub fn now() -> crate::DateTime<Utc> {
         let now = js_sys::Date::new_0();
-        DateTime::<Utc>::from(now)
+        crate::DateTime::<Utc>::from(now)
     }
 }