---

yaml
---
r: 136829
b: refs/heads/dist-snap
c: 2f15dcd
h: refs/heads/master
i:
  136827: 9edbc2a
v: v3

Author: bors

[refs]

@@ -6,7 +6,7 @@ refs/heads/try: 189b7332968972f34cdbbbd9b62d97ababf53059
 refs/tags/release-0.1: 1f5c5126e96c79d22cb7862f75304136e204f105
 refs/heads/ndm: f3868061cd7988080c30d6d5bf352a5a5fe2460b
 refs/heads/try2: 147ecfdd8221e4a4d4e090486829a06da1e0ca3c
-refs/heads/dist-snap: 416144b8279fbffceacea6d0fd90e0fd1f8ce53d
+refs/heads/dist-snap: 2f15dcd4d3865f9cc466637027eb02d5607b2bb7
 refs/tags/release-0.2: c870d2dffb391e14efb05aa27898f1f6333a9596
 refs/tags/release-0.3: b5f0d0f648d9a6153664837026ba1be43d3e2503
 refs/heads/try3: 9387340aab40a73e8424c48fd42f0c521a4875c0

branches/dist-snap/src/doc/reference.md

@@ -2441,6 +2441,8 @@ The currently implemented features of the reference compiler are:
 * `default_type_params` - Allows use of default type parameters. The future of
                           this feature is uncertain.
 
+* `if_let` - Allows use of the `if let` syntax.
+
 * `intrinsics` - Allows use of the "rust-intrinsics" ABI. Compiler intrinsics
                  are inherently unstable and no promise about them is made.
 
@@ -3229,7 +3231,7 @@ for i in range(0u, 256) {
 if_expr : "if" no_struct_literal_expr '{' block '}'
           else_tail ? ;
 
-else_tail : "else" [ if_expr
+else_tail : "else" [ if_expr | if_let_expr
                    | '{' block '}' ] ;
 ```
 
@@ -3434,6 +3436,19 @@ let message = match maybe_digit {
 };
 ```
 
+### If let expressions
+
+```{.ebnf .gram}
+if_let_expr : "if" "let" pat '=' expr '{' block '}'
+               else_tail ? ;
+else_tail : "else" [ if_expr | if_let_expr | '{' block '}' ] ;
+```
+
+An `if let` expression is semantically identical to an `if` expression but in place
+of a condition expression it expects a refutable let statement. If the value of the
+expression on the right hand side of the let statement matches the pattern, the corresponding
+block will execute, otherwise flow proceeds to the first `else` block that follows.
+
 ### Return expressions
 
 ```{.ebnf .gram}

branches/dist-snap/src/etc/emacs/rust-mode-tests.el

@@ -623,7 +623,7 @@ Convert the line-column information from that list into a buffer position value.
       (move-to-column column)
       (point))))
 
-;;; TODO: Maybe add an ERT explainer function (something that shows the
+;;; FIXME: Maybe add an ERT explainer function (something that shows the
 ;;; surrounding code of the final point, not just the position).
 (defun rust-test-motion (source-code init-pos final-pos manip-func &optional &rest args)
   "Test that MANIP-FUNC moves point from INIT-POS to FINAL-POS.

branches/dist-snap/src/etc/kate/rust.xml

@@ -1,7 +1,7 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <!DOCTYPE language SYSTEM "language.dtd"
 [
-	<!-- TODO: Kate's regex engine has very limited support for
+	<!-- FIXME: Kate's regex engine has very limited support for
 	predefined char classes, so making rustIdent consistent with actual
 	Rust identifiers will be a bit difficult -->
 	<!ENTITY rustIdent "[a-zA-Z_][a-zA-Z_0-9]*">

branches/dist-snap/src/etc/vim/syntax/rust.vim

@@ -216,7 +216,7 @@ syn keyword rustTodo contained TODO FIXME XXX NB NOTE
 
 " Folding rules {{{2
 " Trivial folding rules to begin with.
-" TODO: use the AST to make really good folding
+" FIXME: use the AST to make really good folding
 syn region rustFoldBraces start="{" end="}" transparent fold
 
 " Default highlighting {{{1

branches/dist-snap/src/librustc/diagnostics.rs

@@ -151,5 +151,6 @@ register_diagnostics!(
     E0157,
     E0158,
     E0159,
-    E0161
+    E0161,
+    E0162
 )

branches/dist-snap/src/librustc/lint/builtin.rs

@@ -593,6 +593,7 @@ impl LintPass for UnusedAttribute {
             "static_assert",
             "thread_local",
             "no_debug",
+            "unsafe_no_drop_flag",
 
             // used in resolve
             "prelude_import",
@@ -1091,7 +1092,10 @@ impl LintPass for UnnecessaryParens {
         let (value, msg, struct_lit_needs_parens) = match e.node {
             ast::ExprIf(ref cond, _, _) => (cond, "`if` condition", true),
             ast::ExprWhile(ref cond, _, _) => (cond, "`while` condition", true),
-            ast::ExprMatch(ref head, _) => (head, "`match` head expression", true),
+            ast::ExprMatch(ref head, _, source) => match source {
+                ast::MatchNormal => (head, "`match` head expression", true),
+                ast::MatchIfLetDesugar => (head, "`if let` head expression", true)
+            },
             ast::ExprRet(Some(ref value)) => (value, "`return` value", false),
             ast::ExprAssign(_, ref value) => (value, "assigned value", false),
             ast::ExprAssignOp(_, _, ref value) => (value, "assigned value", false),
@@ -1241,7 +1245,7 @@ impl LintPass for UnusedMut {
 
     fn check_expr(&mut self, cx: &Context, e: &ast::Expr) {
         match e.node {
-            ast::ExprMatch(_, ref arms) => {
+            ast::ExprMatch(_, ref arms, _) => {
                 for a in arms.iter() {
                     self.check_unused_mut_pat(cx, a.pats.as_slice())
                 }

branches/dist-snap/src/librustc/metadata/common.rs

@@ -214,6 +214,8 @@ pub static tag_reachable_extern_fn_id: uint = 0x91;
 
 pub static tag_items_data_item_stability: uint = 0x92;
 
+pub static tag_items_data_item_repr: uint = 0x93;
+
 #[deriving(Clone, Show)]
 pub struct LinkMeta {
     pub crate_name: String,

branches/dist-snap/src/librustc/metadata/csearch.rs

@@ -350,6 +350,12 @@ pub fn get_stability(cstore: &cstore::CStore,
     decoder::get_stability(&*cdata, def.node)
 }
 
+pub fn get_repr_attrs(cstore: &cstore::CStore, def: ast::DefId)
+                      -> Vec<attr::ReprAttr> {
+    let cdata = cstore.get_crate_data(def.krate);
+    decoder::get_repr_attrs(&*cdata, def.node)
+}
+
 pub fn is_associated_type(cstore: &cstore::CStore, def: ast::DefId) -> bool {
     let cdata = cstore.get_crate_data(def.krate);
     decoder::is_associated_type(&*cdata, def.node)

branches/dist-snap/src/librustc/metadata/decoder.rs

@@ -384,6 +384,17 @@ pub fn get_stability(cdata: Cmd, id: ast::NodeId) -> Option<attr::Stability> {
     })
 }
 
+pub fn get_repr_attrs(cdata: Cmd, id: ast::NodeId) -> Vec<attr::ReprAttr> {
+    let item = lookup_item(id, cdata.data());
+    match reader::maybe_get_doc(item, tag_items_data_item_repr).map(|doc| {
+        let mut decoder = reader::Decoder::new(doc);
+        Decodable::decode(&mut decoder).unwrap()
+    }) {
+        Some(attrs) => attrs,
+        None => Vec::new(),
+    }
+}
+
 pub fn get_impl_trait(cdata: Cmd,
                       id: ast::NodeId,
                       tcx: &ty::ctxt) -> Option<Rc<ty::TraitRef>>

branches/dist-snap/src/librustc/metadata/encoder.rs

@@ -332,6 +332,7 @@ fn encode_enum_variant_info(ecx: &EncodeContext,
         encode_parent_item(rbml_w, local_def(id));
         encode_visibility(rbml_w, variant.node.vis);
         encode_attributes(rbml_w, variant.node.attrs.as_slice());
+        encode_repr_attrs(rbml_w, ecx, variant.node.attrs.as_slice());
 
         let stab = stability::lookup(ecx.tcx, ast_util::local_def(variant.node.id));
         encode_stability(rbml_w, stab);
@@ -948,6 +949,19 @@ fn encode_method_argument_names(rbml_w: &mut Encoder,
     rbml_w.end_tag();
 }
 
+fn encode_repr_attrs(rbml_w: &mut Encoder,
+                     ecx: &EncodeContext,
+                     attrs: &[Attribute]) {
+    let mut repr_attrs = Vec::new();
+    for attr in attrs.iter() {
+        repr_attrs.extend(attr::find_repr_attrs(ecx.tcx.sess.diagnostic(),
+                                                attr).into_iter());
+    }
+    rbml_w.start_tag(tag_items_data_item_repr);
+    repr_attrs.encode(rbml_w);
+    rbml_w.end_tag();
+}
+
 fn encode_inlined_item(ecx: &EncodeContext,
                        rbml_w: &mut Encoder,
                        ii: InlinedItemRef) {
@@ -1137,6 +1151,7 @@ fn encode_info_for_item(ecx: &EncodeContext,
         encode_bounds_and_type(rbml_w, ecx, &lookup_item_type(tcx, def_id));
         encode_name(rbml_w, item.ident.name);
         encode_attributes(rbml_w, item.attrs.as_slice());
+        encode_repr_attrs(rbml_w, ecx, item.attrs.as_slice());
         for v in (*enum_definition).variants.iter() {
             encode_variant_id(rbml_w, local_def(v.node.id));
         }
@@ -1183,6 +1198,7 @@ fn encode_info_for_item(ecx: &EncodeContext,
         encode_path(rbml_w, path.clone());
         encode_stability(rbml_w, stab);
         encode_visibility(rbml_w, vis);
+        encode_repr_attrs(rbml_w, ecx, item.attrs.as_slice());
 
         /* Encode def_ids for each field and method
          for methods, write all the stuff get_trait_method

branches/dist-snap/src/librustc/middle/cfg/construct.rs

@@ -222,6 +222,10 @@ impl<'a, 'tcx> CFGBuilder<'a, 'tcx> {
                 self.add_node(expr.id, [then_exit, else_exit])           // 4, 5
             }
 
+            ast::ExprIfLet(..) => {
+                self.tcx.sess.span_bug(expr.span, "non-desugared ExprIfLet");
+            }
+
             ast::ExprWhile(ref cond, ref body, _) => {
                 //
                 //         [pred]
@@ -322,7 +326,7 @@ impl<'a, 'tcx> CFGBuilder<'a, 'tcx> {
                 expr_exit
             }
 
-            ast::ExprMatch(ref discr, ref arms) => {
+            ast::ExprMatch(ref discr, ref arms, _) => {
                 //
                 //     [pred]
                 //       |

branches/dist-snap/src/librustc/middle/check_match.rs

@@ -147,7 +147,7 @@ pub fn check_crate(tcx: &ty::ctxt) {
 fn check_expr(cx: &mut MatchCheckCtxt, ex: &Expr) {
     visit::walk_expr(cx, ex);
     match ex.node {
-        ExprMatch(ref scrut, ref arms) => {
+        ExprMatch(ref scrut, ref arms, source) => {
             // First, check legality of move bindings.
             for arm in arms.iter() {
                 check_legality_of_move_bindings(cx,
@@ -184,7 +184,7 @@ fn check_expr(cx: &mut MatchCheckCtxt, ex: &Expr) {
             }
 
             // Fourth, check for unreachable arms.
-            check_arms(cx, inlined_arms.as_slice());
+            check_arms(cx, inlined_arms.as_slice(), source);
 
             // Finally, check if the whole match expression is exhaustive.
             // Check for empty enum, because is_useful only works on inhabited types.
@@ -252,13 +252,31 @@ fn check_for_static_nan(cx: &MatchCheckCtxt, pats: &[P<Pat>]) {
 }
 
 // Check for unreachable patterns
-fn check_arms(cx: &MatchCheckCtxt, arms: &[(Vec<P<Pat>>, Option<&Expr>)]) {
+fn check_arms(cx: &MatchCheckCtxt, arms: &[(Vec<P<Pat>>, Option<&Expr>)], source: MatchSource) {
     let mut seen = Matrix(vec![]);
+    let mut printed_if_let_err = false;
     for &(ref pats, guard) in arms.iter() {
         for pat in pats.iter() {
             let v = vec![&**pat];
+
             match is_useful(cx, &seen, v.as_slice(), LeaveOutWitness) {
-                NotUseful => span_err!(cx.tcx.sess, pat.span, E0001, "unreachable pattern"),
+                NotUseful => {
+                    if source == MatchIfLetDesugar {
+                        if printed_if_let_err {
+                            // we already printed an irrefutable if-let pattern error.
+                            // We don't want two, that's just confusing.
+                        } else {
+                            // find the first arm pattern so we can use its span
+                            let &(ref first_arm_pats, _) = &arms[0];
+                            let first_pat = first_arm_pats.get(0);
+                            let span = first_pat.span;
+                            span_err!(cx.tcx.sess, span, E0162, "irrefutable if-let pattern");
+                            printed_if_let_err = true;
+                        }
+                    } else {
+                        span_err!(cx.tcx.sess, pat.span, E0001, "unreachable pattern");
+                    }
+                }
                 Useful => (),
                 UsefulWithWitness(_) => unreachable!()
             }

branches/dist-snap/src/librustc/middle/expr_use_visitor.rs

@@ -374,7 +374,11 @@ impl<'d,'t,'tcx,TYPER:mc::Typer<'tcx>> ExprUseVisitor<'d,'t,TYPER> {
                 }
             }
 
-            ast::ExprMatch(ref discr, ref arms) => {
+            ast::ExprIfLet(..) => {
+                self.tcx().sess.span_bug(expr.span, "non-desugared ExprIfLet");
+            }
+
+            ast::ExprMatch(ref discr, ref arms, _) => {
                 let discr_cmt = return_if_err!(self.mc.cat_expr(&**discr));
                 self.borrow_expr(&**discr, ty::ReEmpty, ty::ImmBorrow, MatchDiscriminant);
 

branches/dist-snap/src/librustc/middle/liveness.rs

@@ -481,6 +481,9 @@ fn visit_expr(ir: &mut IrMaps, expr: &Expr) {
         ir.add_live_node_for_node(expr.id, ExprNode(expr.span));
         visit::walk_expr(ir, expr);
       }
+      ExprIfLet(..) => {
+          ir.tcx.sess.span_bug(expr.span, "non-desugared ExprIfLet");
+      }
       ExprForLoop(ref pat, _, _, _) => {
         pat_util::pat_bindings(&ir.tcx.def_map, &**pat, |bm, p_id, sp, path1| {
             debug!("adding local variable {} from for loop with bm {:?}",
@@ -1011,6 +1014,10 @@ impl<'a, 'tcx> Liveness<'a, 'tcx> {
             self.propagate_through_expr(&**cond, ln)
           }
 
+          ExprIfLet(..) => {
+              self.ir.tcx.sess.span_bug(expr.span, "non-desugared ExprIfLet");
+          }
+
           ExprWhile(ref cond, ref blk, _) => {
             self.propagate_through_loop(expr, WhileLoop(&**cond), &**blk, succ)
           }
@@ -1026,7 +1033,7 @@ impl<'a, 'tcx> Liveness<'a, 'tcx> {
             self.propagate_through_loop(expr, LoopLoop, &**blk, succ)
           }
 
-          ExprMatch(ref e, ref arms) => {
+          ExprMatch(ref e, ref arms, _) => {
             //
             //      (e)
             //       |
@@ -1470,6 +1477,9 @@ fn check_expr(this: &mut Liveness, expr: &Expr) {
       ExprPath(..) | ExprBox(..) => {
         visit::walk_expr(this, expr);
       }
+      ExprIfLet(..) => {
+        this.ir.tcx.sess.span_bug(expr.span, "non-desugared ExprIfLet");
+      }
     }
 }
 

branches/dist-snap/src/librustc/middle/mem_categorization.rs

@@ -505,6 +505,10 @@ impl<'t,'tcx,TYPER:Typer<'tcx>> MemCategorizationContext<'t,TYPER> {
           ast::ExprForLoop(..) => {
             Ok(self.cat_rvalue_node(expr.id(), expr.span(), expr_ty))
           }
+
+          ast::ExprIfLet(..) => {
+            self.tcx().sess.span_bug(expr.span, "non-desugared ExprIfLet");
+          }
         }
     }
 

branches/dist-snap/src/librustc/middle/trans/debuginfo.rs

@@ -3576,6 +3576,11 @@ fn populate_scope_map(cx: &CrateContext,
                 }
             }
 
+            ast::ExprIfLet(..) => {
+                cx.sess().span_bug(exp.span, "debuginfo::populate_scope_map() - \
+                                              Found unexpanded if-let.");
+            }
+
             ast::ExprWhile(ref cond_exp, ref loop_body, _) => {
                 walk_expr(cx, &**cond_exp, scope_stack, scope_map);
 
@@ -3654,7 +3659,7 @@ fn populate_scope_map(cx: &CrateContext,
                 }
             }
 
-            ast::ExprMatch(ref discriminant_exp, ref arms) => {
+            ast::ExprMatch(ref discriminant_exp, ref arms, _) => {
                 walk_expr(cx, &**discriminant_exp, scope_stack, scope_map);
 
                 // For each arm we have to first walk the pattern as these might

branches/dist-snap/src/librustc/middle/trans/expr.rs

@@ -1013,7 +1013,7 @@ fn trans_rvalue_dps_unadjusted<'blk, 'tcx>(bcx: Block<'blk, 'tcx>,
         ast::ExprIf(ref cond, ref thn, ref els) => {
             controlflow::trans_if(bcx, expr.id, &**cond, &**thn, els.as_ref().map(|e| &**e), dest)
         }
-        ast::ExprMatch(ref discr, ref arms) => {
+        ast::ExprMatch(ref discr, ref arms, _) => {
             _match::trans_match(bcx, expr, &**discr, arms.as_slice(), dest)
         }
         ast::ExprBlock(ref blk) => {