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, 4 insertions, 4 deletions

diff --git a/src/libsyntax/print/pp.rs b/src/libsyntax/print/pp.rs
index 65efd4f0042..57c72ca77c6 100644
--- a/src/libsyntax/print/pp.rs
+++ b/src/libsyntax/print/pp.rs
@@ -600,7 +600,7 @@ impl Printer {
           }
           Eof => {
             // Eof should never get here.
-            fail!();
+            panic!();
           }
         }
     }
diff --git a/src/libsyntax/print/pprust.rs b/src/libsyntax/print/pprust.rs
index a52987f5bd1..d347d0199a7 100644
--- a/src/libsyntax/print/pprust.rs
+++ b/src/libsyntax/print/pprust.rs
@@ -1072,7 +1072,7 @@ impl<'a> State<'a> {
                     Inconsistent, struct_def.fields.as_slice(),
                     |s, field| {
                         match field.node.kind {
-                            ast::NamedField(..) => fail!("unexpected named field"),
+                            ast::NamedField(..) => panic!("unexpected named field"),
                             ast::UnnamedField(vis) => {
                                 try!(s.print_visibility(vis));
                                 try!(s.maybe_print_comment(field.span.lo));
@@ -1093,7 +1093,7 @@ impl<'a> State<'a> {
 
             for field in struct_def.fields.iter() {
                 match field.node.kind {
-                    ast::UnnamedField(..) => fail!("unexpected unnamed field"),
+                    ast::UnnamedField(..) => panic!("unexpected unnamed field"),
                     ast::NamedField(ident, visibility) => {
                         try!(self.hardbreak_if_not_bol());
                         try!(self.maybe_print_comment(field.span.lo));
@@ -1440,7 +1440,7 @@ impl<'a> State<'a> {
                     }
                     // BLEAH, constraints would be great here
                     _ => {
-                        fail!("print_if saw if with weird alternative");
+                        panic!("print_if saw if with weird alternative");
                     }
                 }
             }