Improve error messages on panic

src/lib.rs

@@ -941,7 +941,7 @@ thread_local!(
         const THREAD_RNG_RESEED_THRESHOLD: u64 = 32_768;
         let mut entropy_source = EntropyRng::new();
         let r = StdRng::from_rng(&mut entropy_source)
-            .expect("could not initialize thread_rng");
+            .unwrap_or_else(|err| panic!("could not initialize thread_rng: {}", err));
         let rng = ReseedingRng::new(r,
                                     THREAD_RNG_RESEED_THRESHOLD,
                                     entropy_source);
@@ -1031,7 +1031,8 @@ impl Rng for EntropyRng {
     }
 
     fn fill_bytes(&mut self, dest: &mut [u8]) {
-        self.try_fill_bytes(dest).unwrap();
+        self.try_fill_bytes(dest).unwrap_or_else(|err|
+            panic!("all entropy sources failed; first error: {}", err))
     }
 
     fn try_fill_bytes(&mut self, dest: &mut [u8]) -> Result<(), Error> {
@@ -1170,10 +1171,10 @@ mod test {
     use impls;
     #[cfg(feature="std")]
     use super::{random, thread_rng};
-    use super::{Rng, SeedableRng, StdRng};
+    use super::{Rng, SeedableRng, StdRng, EntropyRng};
     #[cfg(feature="alloc")]
     use alloc::boxed::Box;
-
+    
     pub struct TestRng<R> { inner: R }
 
     impl<R: Rng> Rng for TestRng<R> {
@@ -1216,6 +1217,12 @@ mod test {
         }
     }
 
+    #[test]
+    fn test_entropy() {
+        let mut rng = EntropyRng::new();
+        rng.next_u32();
+    }
+
     #[test]
     fn test_fill_bytes_default() {
         let mut r = ConstRng { i: 0x11_22_33_44_55_66_77_88 };

src/reseeding.rs

@@ -45,7 +45,8 @@ impl<R: Rng+SeedableRng, Rsdr: Rng> ReseedingRng<R, Rsdr> {
     /// generated exceed the threshold.
     pub fn reseed_if_necessary(&mut self) {
         if self.bytes_generated >= self.generation_threshold {
-            R::from_rng(&mut self.reseeder).map(|result| self.rng = result).unwrap();
+            R::from_rng(&mut self.reseeder).map(|result| self.rng = result)
+                .unwrap_or_else(|err| panic!("reseeding failed: {}", err));
             self.bytes_generated = 0;
         }
     }