Auto merge of #23489 - michaelwoerister:span-artihmetic-overflow-bug, r=alexcrichton

This should solve issues #23115, #23469, and #23407.

As the title says, this is just a workaround. The underlying problem is that macro expansion can produce invalid spans. I've opened issue #23480 so we don't forget about that.

src/librustc/middle/astencode.rs

@@ -235,12 +235,27 @@ impl<'a, 'b, 'tcx> DecodeContext<'a, 'b, 'tcx> {
     pub fn tr_span(&self, span: Span) -> Span {
         let imported_filemaps = &self.cdata.codemap_import_info[..];
 
+        let span = if span.lo > span.hi {
+            // Currently macro expansion sometimes produces invalid Span values
+            // where lo > hi. In order not to crash the compiler when trying to
+            // translate these values, let's transform them into something we
+            // can handle (and which will produce useful debug locations at
+            // least some of the time).
+            // This workaround is only necessary as long as macro expansion is
+            // not fixed. FIXME(#23480)
+            codemap::mk_sp(span.lo, span.lo)
+        } else {
+            span
+        };
+
         let filemap_index = {
             // Optimize for the case that most spans within a translated item
             // originate from the same filemap.
             let last_filemap_index = self.last_filemap_index.get();
 
             if span.lo >= imported_filemaps[last_filemap_index].original_start_pos &&
+               span.lo <= imported_filemaps[last_filemap_index].original_end_pos &&
+               span.hi >= imported_filemaps[last_filemap_index].original_start_pos &&
                span.hi <= imported_filemaps[last_filemap_index].original_end_pos {
                 last_filemap_index
             } else {

src/test/auxiliary/crate_with_invalid_spans.rs

@@ -0,0 +1,30 @@
+// Copyright 2015 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.
+
+#![crate_type = "rlib"]
+// no-prefer-dynamic
+
+// compile-flags: -g
+
+#[macro_use]
+mod crate_with_invalid_spans_macros;
+
+pub fn exported_generic<T>(x: T, y: u32) -> (T, u32) {
+    // Using the add1 macro will produce an invalid span, because the `y` passed
+    // to the macro will have a span from this file, but the rest of the code
+    // generated from the macro will have spans from the macro-defining file.
+    // The AST node for the (1 + y) expression generated by the macro will then
+    // take it's `lo` span bound from the `1` literal in the macro-defining file
+    // and it's `hi` bound from `y` in this file, which should be lower than the
+    // `lo` and even lower than the lower bound of the FileMap it is supposedly
+    // contained in because the FileMap for this file was allocated earlier than
+    // the FileMap of the macro-defining file.
+    return (x, add1!(y));
+}

src/test/auxiliary/crate_with_invalid_spans_macros.rs

@@ -0,0 +1,17 @@
+// Copyright 2015 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.
+
+macro_rules! add1 {
+    ($e:expr) => ({
+        let a = 1 + $e;
+        let b = $e + 1;
+        a + b - 1
+    })
+}

src/test/run-pass/import-crate-with-invalid-spans.rs

@@ -0,0 +1,20 @@
+// Copyright 2015 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.
+
+// aux-build:crate_with_invalid_spans.rs
+
+extern crate crate_with_invalid_spans;
+
+fn main() {
+    // The AST of `exported_generic` stored in crate_with_invalid_spans's
+    // metadata should contain an invalid span where span.lo > span.hi.
+    // Let's make sure the compiler doesn't crash when encountering this.
+    let _ = crate_with_invalid_spans::exported_generic(32u32, 7u32);
+}