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]

2 files changed, 5 insertions, 5 deletions

diff --git a/src/libcore/fmt/float.rs b/src/libcore/fmt/float.rs
index 343ab7cfd28..79191c5a2b4 100644
--- a/src/libcore/fmt/float.rs
+++ b/src/libcore/fmt/float.rs
@@ -94,7 +94,7 @@ pub fn float_to_str_bytes_common<T: Primitive + Float, U>(
     assert!(2 <= radix && radix <= 36);
     match exp_format {
         ExpDec if radix >= DIGIT_E_RADIX       // decimal exponent 'e'
-          => fail!("float_to_str_bytes_common: radix {} incompatible with \
+          => panic!("float_to_str_bytes_common: radix {} incompatible with \
                     use of 'e' as decimal exponent", radix),
         _ => ()
     }
@@ -127,7 +127,7 @@ pub fn float_to_str_bytes_common<T: Primitive + Float, U>(
         ExpDec => {
             let (exp, exp_base) = match exp_format {
                 ExpDec => (num.abs().log10().floor(), cast::<f64, T>(10.0f64).unwrap()),
-                ExpNone => fail!("unreachable"),
+                ExpNone => panic!("unreachable"),
             };
 
             (num / exp_base.powf(exp), cast::<T, i32>(exp).unwrap())
@@ -299,7 +299,7 @@ pub fn float_to_str_bytes_common<T: Primitive + Float, U>(
             buf[end] = match exp_format {
                 ExpDec if exp_upper => 'E',
                 ExpDec if !exp_upper => 'e',
-                _ => fail!("unreachable"),
+                _ => panic!("unreachable"),
             } as u8;
             end += 1;
 
diff --git a/src/libcore/fmt/num.rs b/src/libcore/fmt/num.rs
index e57c4999483..22d8ba63b20 100644
--- a/src/libcore/fmt/num.rs
+++ b/src/libcore/fmt/num.rs
@@ -92,7 +92,7 @@ macro_rules! radix {
             fn digit(&self, x: u8) -> u8 {
                 match x {
                     $($x => $conv,)+
-                    x => fail!("number not in the range 0..{}: {}", self.base() - 1, x),
+                    x => panic!("number not in the range 0..{}: {}", self.base() - 1, x),
                 }
             }
         }
@@ -126,7 +126,7 @@ impl GenericRadix for Radix {
         match x {
             x @  0 ... 9 => b'0' + x,
             x if x < self.base() => b'a' + (x - 10),
-            x => fail!("number not in the range 0..{}: {}", self.base() - 1, x),
+            x => panic!("number not in the range 0..{}: {}", self.base() - 1, x),
         }
     }
 }