rustc: Don't die when a crate id can't be inferred

The filestem of the desired output isn't necessarily a valid crate id, and
calling unwrap() will trigger an ICE in rustc. This tries a little harder to
infer a "valid crate id" from a crate, with an eventual fallback to a generic
crate id if alll else fails.

Closes #11107

src/librustc/back/link.rs

@@ -516,7 +516,10 @@ pub mod write {
 
 pub fn find_crate_id(attrs: &[ast::Attribute], out_filestem: &str) -> CrateId {
     match attr::find_crateid(attrs) {
-        None => from_str(out_filestem).unwrap(),
+        None => from_str(out_filestem).unwrap_or_else(|| {
+            let mut s = out_filestem.chars().filter(|c| c.is_XID_continue());
+            from_str(s.collect::<~str>()).or(from_str("rust-out")).unwrap()
+        }),
         Some(s) => s,
     }
 }

src/test/run-make/weird-output-filenames/Makefile

@@ -0,0 +1,9 @@
+-include ../tools.mk
+
+all:
+	$(RUSTC) foo.rs -o $(TMPDIR)/.foo
+	rm $(TMPDIR)/.foo
+	$(RUSTC) foo.rs -o $(TMPDIR)/.foo.bar
+	rm $(TMPDIR)/.foo.bar
+	$(RUSTC) foo.rs -o $(TMPDIR)/+foo+bar
+	rm $(TMPDIR)/+foo+bar

src/test/run-make/weird-output-filenames/foo.rs

@@ -0,0 +1,11 @@
+// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+fn main() {}