Address review feedback

Author: josephlr

src/error.rs

@@ -20,6 +20,11 @@ use core::num::NonZeroU32;
 pub struct Error(NonZeroU32);
 
 impl Error {
+    #[deprecated(since = "0.1.7")]
+    pub const UNKNOWN: Error = UNSUPPORTED;
+    #[deprecated(since = "0.1.7")]
+    pub const UNAVAILABLE: Error = UNSUPPORTED;
+
     /// Codes below this point represent OS Errors (i.e. positive i32 values).
     /// Codes at or above this point, but below [`Error::CUSTOM_START`] are
     /// reserved for use by the `rand` and `getrandom` crates.
@@ -111,25 +116,31 @@ impl From<NonZeroU32> for Error {
     }
 }
 
-/// Internal Error constants
-pub(crate) const UNSUPPORTED: Error = internal_error(0);
-pub(crate) const UNKNOWN_IO_ERROR: Error = internal_error(1);
-pub(crate) const SEC_RANDOM_FAILED: Error = internal_error(2);
-pub(crate) const RTL_GEN_RANDOM_FAILED: Error = internal_error(3);
-pub(crate) const FAILED_RDRAND: Error = internal_error(4);
-pub(crate) const NO_RDRAND: Error = internal_error(5);
-pub(crate) const BINDGEN_CRYPTO_UNDEF: Error = internal_error(6);
-pub(crate) const BINDGEN_GRV_UNDEF: Error = internal_error(7);
-pub(crate) const STDWEB_NO_RNG: Error = internal_error(8);
-pub(crate) const STDWEB_RNG_FAILED: Error = internal_error(9);
-
-const fn internal_error(n: u16) -> Error {
-    Error(unsafe { NonZeroU32::new_unchecked(Error::INTERNAL_START + n as u32) })
+// TODO: Convert to a function when min_version >= 1.33
+macro_rules! internal_error {
+    ($code:expr) => {{
+        let n: u16 = $code;
+        Error(unsafe { NonZeroU32::new_unchecked(Error::INTERNAL_START + n as u32) })
+    }};
 }
 
+/// Internal Error constants
+pub(crate) const UNSUPPORTED: Error = internal_error!(0);
+pub(crate) const ERRNO_NOT_POSITIVE: Error = internal_error!(1);
+pub(crate) const UNKNOWN_IO_ERROR: Error = internal_error!(2);
+pub(crate) const SEC_RANDOM_FAILED: Error = internal_error!(3);
+pub(crate) const RTL_GEN_RANDOM_FAILED: Error = internal_error!(4);
+pub(crate) const FAILED_RDRAND: Error = internal_error!(5);
+pub(crate) const NO_RDRAND: Error = internal_error!(6);
+pub(crate) const BINDGEN_CRYPTO_UNDEF: Error = internal_error!(7);
+pub(crate) const BINDGEN_GRV_UNDEF: Error = internal_error!(8);
+pub(crate) const STDWEB_NO_RNG: Error = internal_error!(9);
+pub(crate) const STDWEB_RNG_FAILED: Error = internal_error!(10);
+
 fn internal_desc(error: Error) -> Option<&'static str> {
     match error {
         UNSUPPORTED => Some("getrandom: this target is not supported"),
+        ERRNO_NOT_POSITIVE => Some("errno: did not return a positive value"),
         UNKNOWN_IO_ERROR => Some("Unknown std::io::Error"),
         SEC_RANDOM_FAILED => Some("SecRandomCopyBytes: call failed"),
         RTL_GEN_RANDOM_FAILED => Some("RtlGenRandom: call failed"),

src/util_libc.rs

@@ -5,6 +5,7 @@
 // <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
+use crate::error::ERRNO_NOT_POSITIVE;
 use crate::util::LazyUsize;
 use crate::Error;
 use core::num::NonZeroU32;
@@ -25,7 +26,12 @@ cfg_if! {
 }
 
 pub fn last_os_error() -> Error {
-    Error::from(NonZeroU32::new(unsafe { *errno_location() } as u32).unwrap())
+    let errno = unsafe { *errno_location() };
+    if errno > 0 {
+        Error::from(NonZeroU32::new(errno as u32).unwrap())
+    } else {
+        ERRNO_NOT_POSITIVE
+    }
 }
 
 // Fill a buffer by repeatedly invoking a system call. The `sys_fill` function: