Restore Time::try_from.

Cargo.toml

@@ -68,8 +68,12 @@ all-features = true
 name = "webpki"
 
 [features]
+# TODO: In the next release, make this non-default.
+default = ["std"]
 alloc = ["ring/alloc"]
 std = ["alloc"]
+# TODO: In the next release, remove this.
+trust_anchor_util = ["std"]
 
 [dependencies]
 ring = { version = "0.16.19", default-features = false }

src/time.rs

@@ -23,6 +23,13 @@
 pub struct Time(u64);
 
 impl Time {
+    /// Deprecated. Use `TryFrom::try_from`.
+    #[cfg(feature = "std")]
+    // Soft deprecation. #[deprecated(note = "Use TryFrom::try_from")]
+    pub fn try_from(time: std::time::SystemTime) -> Result<Self, ring::error::Unspecified> {
+        core::convert::TryFrom::try_from(time)
+    }
+
     /// Create a `webpki::Time` from a unix timestamp.
     ///
     /// It is usually better to use the less error-prone
@@ -37,7 +44,8 @@ impl Time {
 
 #[cfg(feature = "std")]
 impl core::convert::TryFrom<std::time::SystemTime> for Time {
-    type Error = std::time::SystemTimeError;
+    // TODO: In the next release, make this `std::time::SystemTimeError`.
+    type Error = ring::error::Unspecified;
 
     /// Create a `webpki::Time` from a `std::time::SystemTime`.
     ///
@@ -50,9 +58,9 @@ impl core::convert::TryFrom<std::time::SystemTime> for Time {
     /// # extern crate webpki;
     /// #
     /// #![cfg(feature = "std")]
-    /// use std::{convert::TryFrom, time::{SystemTime, SystemTimeError}};
+    /// use std::{convert::TryFrom, time::SystemTime};
     ///
-    /// # fn foo() -> Result<(), SystemTimeError> {
+    /// # fn foo() -> Result<(), ring::error::Unspecified> {
     /// let time = webpki::Time::try_from(SystemTime::now())?;
     /// # Ok(())
     /// # }
@@ -61,5 +69,6 @@ impl core::convert::TryFrom<std::time::SystemTime> for Time {
         value
             .duration_since(std::time::UNIX_EPOCH)
             .map(|d| Self::from_seconds_since_unix_epoch(d.as_secs()))
+            .map_err(|_| ring::error::Unspecified)
     }
 }