Do not overwrite input file if it has no extension

Check wether the source file has the same path as the executable to be
generated and fail early if it would overwrite the source file with the
executable.

```bash
% echo 'fn main(){}' > file && ./rustc file
error: the input file "file" would be overwritten by the generated executable
error: aborting due to previous error

% echo 'fn main(){}' > file.rs && ./rustc file.rs -o file.rs
error: the input file "file.rs" would be overwritten by the generated executable
error: aborting due to previous error
```

src/librustc/session/config.rs

@@ -399,6 +399,33 @@ impl OutputFilenames {
     pub fn filestem(&self) -> String {
         format!("{}{}", self.out_filestem, self.extra)
     }
+
+    pub fn is_path_used(&self, path: &PathBuf) -> bool {
+        fn eq(p1: &PathBuf, p2: &PathBuf) -> bool {
+            let p1 = match p1.canonicalize() {
+                Ok(p) => Some(p),
+                _ => None,
+            };
+            let p2 = match p2.canonicalize() {
+                Ok(p) => Some(p),
+                _ => None,
+            };
+            p1 == p2
+        }
+
+        match self.single_output_file {
+            Some(ref p) => eq(&p, path),
+            None => {
+                for k in self.outputs.keys() {
+                    let opath: PathBuf = self.path(k.to_owned());
+                    if eq(&opath, path) {
+                        return true;
+                    }
+                }
+                false
+            }
+        }
+    }
 }
 
 pub fn host_triple() -> &'static str {
@@ -455,6 +482,12 @@ impl Options {
         self.incremental.is_none() ||
         self.cg.codegen_units == 1
     }
+
+    /// True if there will be an output file generated
+    pub fn will_create_output_file(&self) -> bool {
+        !self.debugging_opts.parse_only ||  // we will generate an output file and
+            self.debugging_opts.ls          // we're not just querying an existing file
+    }
 }
 
 // The type of entry function, so

src/librustc_driver/lib.rs

@@ -210,10 +210,26 @@ pub fn run_compiler_with_file_loader<'a, L>(args: &[String],
     let codemap = Rc::new(CodeMap::with_file_loader(loader));
     let sess = session::build_session_with_codemap(sopts,
                                                    &dep_graph,
-                                                   input_file_path,
+                                                   input_file_path.clone(),
                                                    descriptions,
                                                    cstore.clone(),
                                                    codemap);
+
+    match input_file_path {
+        Some(ifile) => {
+            // This isn't used later in the compilation process, it's only used to check for
+            // overwrites of the source file.
+            if driver::build_output_filenames(&input, &odir, &ofile, &[], &sess)
+                .is_path_used(&ifile) && !sess.opts.will_create_output_file() {
+                sess.err(&format!(
+                    "the input file \"{}\" would be overwritten by the generated executable",
+                    ifile.display()));
+                return (Err(1), Some(sess));
+            }
+        },
+        None => (),
+    }
+
     rustc_lint::register_builtins(&mut sess.lint_store.borrow_mut(), Some(&sess));
     let mut cfg = config::build_configuration(&sess, cfg);
     target_features::add_configuration(&mut cfg, &sess);

src/test/run-make/output-filename-overwrites-input/Makefile

@@ -0,0 +1,10 @@
+-include ../tools.mk
+
+all:
+	cp foo.rs $(TMPDIR)/foo
+	$(RUSTC) $(TMPDIR)/foo 2>&1 \
+		| grep "the input file \".*foo\" would be overwritten by the generated executable"
+	$(RUSTC) foo.rs 2>&1 && $(RUSTC) -Z ls $(TMPDIR)/foo 2>&1
+	cp foo.rs $(TMPDIR)/foo.rs
+	$(RUSTC) $(TMPDIR)/foo.rs -o $(TMPDIR)/foo.rs 2>&1 \
+		| grep "the input file \".*foo.rs\" would be overwritten by the generated executable"

src/test/run-make/output-filename-overwrites-input/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() {}

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

@@ -7,8 +7,8 @@ all:
 	cp foo.rs $(TMPDIR)/.foo.bar
 	$(RUSTC) $(TMPDIR)/.foo.bar 2>&1 \
 		| grep "invalid character.*in crate name:"
-	cp foo.rs $(TMPDIR)/+foo+bar
-	$(RUSTC) $(TMPDIR)/+foo+bar 2>&1 \
+	cp foo.rs $(TMPDIR)/+foo+bar.rs
+	$(RUSTC) $(TMPDIR)/+foo+bar.rs 2>&1 \
 		| grep "invalid character.*in crate name:"
 	cp foo.rs $(TMPDIR)/-foo.rs
 	$(RUSTC) $(TMPDIR)/-foo.rs 2>&1 \