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, 7 insertions, 7 deletions

diff --git a/src/libsyntax/parse/lexer/comments.rs b/src/libsyntax/parse/lexer/comments.rs
index 3814ecfbe5b..5a7679570bf 100644
--- a/src/libsyntax/parse/lexer/comments.rs
+++ b/src/libsyntax/parse/lexer/comments.rs
@@ -142,7 +142,7 @@ pub fn strip_doc_comment_decoration(comment: &str) -> String {
         return lines.connect("\n");
     }
 
-    fail!("not a doc-comment: {}", comment);
+    panic!("not a doc-comment: {}", comment);
 }
 
 fn push_blank_line_comment(rdr: &StringReader, comments: &mut Vec<Comment>) {
@@ -322,7 +322,7 @@ fn consume_comment(rdr: &mut StringReader,
         read_block_comment(rdr, code_to_the_left, comments);
     } else if rdr.curr_is('#') && rdr.nextch_is('!') {
         read_shebang_comment(rdr, code_to_the_left, comments);
-    } else { fail!(); }
+    } else { panic!(); }
     debug!("<<< consume comment");
 }
 
diff --git a/src/libsyntax/parse/lexer/mod.rs b/src/libsyntax/parse/lexer/mod.rs
index b439353ad95..3a6cf610b4f 100644
--- a/src/libsyntax/parse/lexer/mod.rs
+++ b/src/libsyntax/parse/lexer/mod.rs
@@ -555,8 +555,8 @@ impl<'a> StringReader<'a> {
                                                whence: &str) {
             match r.curr {
                 Some(r_c) if r_c == c => r.bump(),
-                Some(r_c) => fail!("expected {}, hit {}, {}", described_c, r_c, whence),
-                None      => fail!("expected {}, hit EOF, {}", described_c, whence),
+                Some(r_c) => panic!("expected {}, hit {}, {}", described_c, r_c, whence),
+                None      => panic!("expected {}, hit EOF, {}", described_c, whence),
             }
         }
 
@@ -577,7 +577,7 @@ impl<'a> StringReader<'a> {
         self.scan_digits(base);
         let encoded_name : u32 = self.with_str_from(start_bpos, |s| {
             num::from_str_radix(s, 10).unwrap_or_else(|| {
-                fail!("expected digits representing a name, got `{}`, {}, range [{},{}]",
+                panic!("expected digits representing a name, got `{}`, {}, range [{},{}]",
                       s, whence, start_bpos, self.last_pos);
             })
         });
@@ -595,7 +595,7 @@ impl<'a> StringReader<'a> {
         self.scan_digits(base);
         let encoded_ctxt : ast::SyntaxContext = self.with_str_from(start_bpos, |s| {
             num::from_str_radix(s, 10).unwrap_or_else(|| {
-                fail!("expected digits representing a ctxt, got `{}`, {}", s, whence);
+                panic!("expected digits representing a ctxt, got `{}`, {}", s, whence);
             })
         });
 
@@ -1542,7 +1542,7 @@ mod test {
         let mut lexer = setup(&sh, "/* /* */ */'a'".to_string());
         match lexer.next_token().tok {
             token::Comment => { },
-            _ => fail!("expected a comment!")
+            _ => panic!("expected a comment!")
         }
         assert_eq!(lexer.next_token().tok, token::LitChar(token::intern("a")));
     }