Distinguish argument from local variable

src/librustc/front/map/mod.rs

@@ -348,6 +348,27 @@ pub fn get_parent_node(&self, id: NodeId) -> NodeId {
         self.find_entry(id).and_then(|x| x.parent_node()).unwrap_or(id)
     }
 
+    /// Check if the node is an argument. An argument is a local variable whose
+    /// immediate parent is an item or a closure.
+    pub fn is_argument(&self, id: NodeId) -> bool {
+        match self.find(id) {
+            Some(NodeLocal(_)) => (),
+            _ => return false,
+        }
+        match self.find(self.get_parent_node(id)) {
+            Some(NodeItem(_)) |
+            Some(NodeTraitItem(_)) |
+            Some(NodeImplItem(_)) => true,
+            Some(NodeExpr(e)) => {
+                match e.node {
+                    ExprClosure(..) => true,
+                    _ => false,
+                }
+            }
+            _ => false,
+        }
+    }
+
     /// If there is some error when walking the parents (e.g., a node does not
     /// have a parent in the map or a node can't be found), then we return the
     /// last good node id we found. Note that reaching the crate root (id == 0),

src/librustc/middle/expr_use_visitor.rs

@@ -278,7 +278,7 @@ enum PassArgs {
 impl<'d,'t,'a,'tcx> ExprUseVisitor<'d,'t,'a,'tcx> {
     pub fn new(delegate: &'d mut (Delegate<'tcx>),
                typer: &'t infer::InferCtxt<'a, 'tcx>)
-               -> ExprUseVisitor<'d,'t,'a,'tcx> where 'tcx:'a
+               -> ExprUseVisitor<'d,'t,'a,'tcx> where 'tcx:'a+'d
     {
         let mc: mc::MemCategorizationContext<'t, 'a, 'tcx> =
             mc::MemCategorizationContext::new(typer);

src/librustc/middle/mem_categorization.rs

@@ -1463,11 +1463,10 @@ pub fn descriptive_string(&self, tcx: &ty::ctxt) -> String {
                 "non-lvalue".to_string()
             }
             cat_local(vid) => {
-                match tcx.map.find(vid) {
-                    Some(ast_map::NodeArg(_)) => {
-                        "argument".to_string()
-                    }
-                    _ => "local variable".to_string()
+                if tcx.map.is_argument(vid) {
+                    "argument".to_string()
+                } else {
+                    "local variable".to_string()
                 }
             }
             cat_deref(_, _, pk) => {

src/test/compile-fail/borrowck-argument.rs

@@ -0,0 +1,43 @@
+// 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.
+
+#[derive(Copy, Clone)]
+struct S;
+
+impl S {
+    fn mutate(&mut self) {
+    }
+}
+
+fn func(arg: S) {
+    arg.mutate(); //~ ERROR: cannot borrow immutable argument
+}
+
+impl S {
+    fn method(&self, arg: S) {
+        arg.mutate(); //~ ERROR: cannot borrow immutable argument
+    }
+}
+
+trait T {
+    fn default(&self, arg: S) {
+        arg.mutate(); //~ ERROR: cannot borrow immutable argument
+    }
+}
+
+impl T for S {}
+
+fn main() {
+    let s = S;
+    func(s);
+    s.method(s);
+    s.default(s);
+    (|arg: S| { arg.mutate() })(s); //~ ERROR: cannot borrow immutable argument
+}

src/test/compile-fail/borrowck-closures-unique.rs

@@ -43,7 +43,7 @@ fn d(x: &mut isize) {
 }
 
 fn e(x: &mut isize) {
-    let c1 = || x = panic!(); //~ ERROR closure cannot assign to immutable local variable
+    let c1 = || x = panic!(); //~ ERROR closure cannot assign to immutable argument
 }
 
 fn main() {

src/test/compile-fail/borrowck-unboxed-closures.rs

@@ -17,7 +17,7 @@ fn a<F:Fn(isize, isize) -> isize>(mut f: F) {
 }
 
 fn b<F:FnMut(isize, isize) -> isize>(f: F) {
-    f(1, 2);    //~ ERROR cannot borrow immutable local variable
+    f(1, 2);    //~ ERROR cannot borrow immutable argument
 }
 
 fn c<F:FnOnce(isize, isize) -> isize>(f: F) {