Constrain operands to outlive the operation. Fixes #21422.

Author: nikomatsakis

src/librustc/middle/infer/error_reporting.rs

@@ -675,6 +675,17 @@ impl<'a, 'tcx> ErrorReporting<'tcx> for InferCtxt<'a, 'tcx> {
                     sup,
                     "");
             }
+            infer::Operand(span) => {
+                self.tcx.sess.span_err(
+                    span,
+                    "lifetime of operand does not outlive \
+                     the operation");
+                note_and_explain_region(
+                    self.tcx,
+                    "the operand is only valid for ",
+                    sup,
+                    "");
+            }
             infer::AddrOf(span) => {
                 self.tcx.sess.span_err(
                     span,
@@ -1593,6 +1604,11 @@ impl<'a, 'tcx> ErrorReportingHelpers<'tcx> for InferCtxt<'a, 'tcx> {
                     span,
                     "...so that return value is valid for the call");
             }
+            infer::Operand(span) => {
+                self.tcx.sess.span_err(
+                    span,
+                    "...so that operand is valid for operation");
+            }
             infer::AddrOf(span) => {
                 self.tcx.sess.span_note(
                     span,

src/librustc/middle/infer/mod.rs

@@ -210,6 +210,9 @@ pub enum SubregionOrigin<'tcx> {
     // Region in return type of invoked fn must enclose call
     CallReturn(Span),
 
+    // Operands must be in scope
+    Operand(Span),
+
     // Region resulting from a `&` expr must enclose the `&` expr
     AddrOf(Span),
 
@@ -1195,6 +1198,7 @@ impl<'tcx> SubregionOrigin<'tcx> {
             CallRcvr(a) => a,
             CallArg(a) => a,
             CallReturn(a) => a,
+            Operand(a) => a,
             AddrOf(a) => a,
             AutoBorrow(a) => a,
             SafeDestructor(a) => a,
@@ -1258,6 +1262,7 @@ impl<'tcx> Repr<'tcx> for SubregionOrigin<'tcx> {
             CallRcvr(a) => format!("CallRcvr({})", a.repr(tcx)),
             CallArg(a) => format!("CallArg({})", a.repr(tcx)),
             CallReturn(a) => format!("CallReturn({})", a.repr(tcx)),
+            Operand(a) => format!("Operand({})", a.repr(tcx)),
             AddrOf(a) => format!("AddrOf({})", a.repr(tcx)),
             AutoBorrow(a) => format!("AutoBorrow({})", a.repr(tcx)),
             SafeDestructor(a) => format!("SafeDestructor({})", a.repr(tcx)),

src/librustc_typeck/check/regionck.rs

@@ -610,6 +610,20 @@ fn visit_expr(rcx: &mut Rcx, expr: &ast::Expr) {
             visit::walk_expr(rcx, expr);
         }
 
+        ast::ExprBinary(_, ref lhs, ref rhs) => {
+            // If you do `x OP y`, then the types of `x` and `y` must
+            // outlive the operation you are performing.
+            let lhs_ty = rcx.resolve_expr_type_adjusted(&**lhs);
+            let rhs_ty = rcx.resolve_expr_type_adjusted(&**rhs);
+            for &ty in [lhs_ty, rhs_ty].iter() {
+                type_must_outlive(rcx,
+                                  infer::Operand(expr.span),
+                                  ty,
+                                  ty::ReScope(CodeExtent::from_node_id(expr.id)));
+            }
+            visit::walk_expr(rcx, expr);
+        }
+
         ast::ExprUnary(op, ref lhs) if has_method_map => {
             let implicitly_ref_args = !ast_util::is_by_value_unop(op);
 

src/test/run-pass/regions-issue-21422.rs

@@ -0,0 +1,25 @@
+// 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.
+
+// Regression test for issue #21422, which was related to failing to
+// add inference constraints that the operands of a binary operator
+// should outlive the binary operation itself.
+
+pub struct P<'a> {
+    _ptr: *const &'a u8,
+}
+
+impl <'a> PartialEq for P<'a> {
+    fn eq(&self, other: &P<'a>) -> bool {
+        (self as *const _) == (other as *const _)
+    }
+}
+
+fn main() {}