Rename fail! to panic!

https://github.com/rust-lang/rfcs/pull/221

The current terminology of "task failure" often causes problems when
writing or speaking about code. You often want to talk about the
possibility of an operation that returns a Result "failing", but cannot
because of the ambiguity with task failure. Instead, you have to speak
of "the failing case" or "when the operation does not succeed" or other
circumlocutions.

Likewise, we use a "Failure" header in rustdoc to describe when
operations may fail the task, but it would often be helpful to separate
out a section describing the "Err-producing" case.

We have been steadily moving away from task failure and toward Result as
an error-handling mechanism, so we should optimize our terminology
accordingly: Result-producing functions should be easy to describe.

To update your code, rename any call to `fail!` to `panic!` instead.
Assuming you have not created your own macro named `panic!`, this
will work on UNIX based systems:

    grep -lZR 'fail!' . | xargs -0 -l sed -i -e 's/fail!/panic!/g'

You can of course also do this by hand.

[breaking-change]

3 files changed, 13 insertions, 11 deletions

diff --git a/src/libstd/rand/mod.rs b/src/libstd/rand/mod.rs
index 29eae0ced54..d1c655cb4d0 100644
--- a/src/libstd/rand/mod.rs
+++ b/src/libstd/rand/mod.rs
@@ -297,7 +297,7 @@ impl<'a> SeedableRng<&'a [uint]> for StdRng {
 pub fn weak_rng() -> XorShiftRng {
     match OsRng::new() {
         Ok(mut r) => r.gen(),
-        Err(e) => fail!("weak_rng: failed to create seeded RNG: {}", e)
+        Err(e) => panic!("weak_rng: failed to create seeded RNG: {}", e)
     }
 }
 
@@ -308,7 +308,7 @@ impl reseeding::Reseeder<StdRng> for TaskRngReseeder {
     fn reseed(&mut self, rng: &mut StdRng) {
         *rng = match StdRng::new() {
             Ok(r) => r,
-            Err(e) => fail!("could not reseed task_rng: {}", e)
+            Err(e) => panic!("could not reseed task_rng: {}", e)
         }
     }
 }
@@ -339,7 +339,7 @@ pub fn task_rng() -> TaskRng {
         None => {
             let r = match StdRng::new() {
                 Ok(r) => r,
-                Err(e) => fail!("could not initialize task_rng: {}", e)
+                Err(e) => panic!("could not initialize task_rng: {}", e)
             };
             let rng = reseeding::ReseedingRng::new(r,
                                                    TASK_RNG_RESEED_THRESHOLD,
@@ -445,7 +445,7 @@ mod test {
             // use this to get nicer error messages.
             for (i, &byte) in v.iter().enumerate() {
                 if byte == 0 {
-                    fail!("byte {} of {} is zero", i, n)
+                    panic!("byte {} of {} is zero", i, n)
                 }
             }
         }
@@ -472,14 +472,14 @@ mod test {
 
     #[test]
     #[should_fail]
-    fn test_gen_range_fail_int() {
+    fn test_gen_range_panic_int() {
         let mut r = task_rng();
         r.gen_range(5i, -2);
     }
 
     #[test]
     #[should_fail]
-    fn test_gen_range_fail_uint() {
+    fn test_gen_range_panic_uint() {
         let mut r = task_rng();
         r.gen_range(5u, 2u);
     }
diff --git a/src/libstd/rand/os.rs b/src/libstd/rand/os.rs
index 91308be21ed..424fd039fd4 100644
--- a/src/libstd/rand/os.rs
+++ b/src/libstd/rand/os.rs
@@ -120,7 +120,7 @@ mod imp {
                 SecRandomCopyBytes(kSecRandomDefault, v.len() as size_t, v.as_mut_ptr())
             };
             if ret == -1 {
-                fail!("couldn't generate random bytes: {}", os::last_os_error());
+                panic!("couldn't generate random bytes: {}", os::last_os_error());
             }
         }
     }
@@ -208,7 +208,7 @@ mod imp {
                                v.as_mut_ptr())
             };
             if ret == 0 {
-                fail!("couldn't generate random bytes: {}", os::last_os_error());
+                panic!("couldn't generate random bytes: {}", os::last_os_error());
             }
         }
     }
@@ -219,7 +219,7 @@ mod imp {
                 CryptReleaseContext(self.hcryptprov, 0)
             };
             if ret == 0 {
-                fail!("couldn't release context: {}", os::last_os_error());
+                panic!("couldn't release context: {}", os::last_os_error());
             }
         }
     }
diff --git a/src/libstd/rand/reader.rs b/src/libstd/rand/reader.rs
index 8ca1cec3e0a..4f220531237 100644
--- a/src/libstd/rand/reader.rs
+++ b/src/libstd/rand/reader.rs
@@ -18,7 +18,9 @@ use result::{Ok, Err};
 /// An RNG that reads random bytes straight from a `Reader`. This will
 /// work best with an infinite reader, but this is not required.
 ///
-/// It will fail if it there is insufficient data to fulfill a request.
+/// # Panics
+///
+/// It will panic if it there is insufficient data to fulfill a request.
 ///
 /// # Example
 ///
@@ -65,7 +67,7 @@ impl<R: Reader> Rng for ReaderRng<R> {
         if v.len() == 0 { return }
         match self.reader.read_at_least(v.len(), v) {
             Ok(_) => {}
-            Err(e) => fail!("ReaderRng.fill_bytes error: {}", e)
+            Err(e) => panic!("ReaderRng.fill_bytes error: {}", e)
         }
     }
 }