@@ -20,6 +20,7 @@ pub use self::Variance::*;
2020pub use self :: AutoAdjustment :: * ;
2121pub use self :: Representability :: * ;
2222pub use self :: AutoRef :: * ;
23+ pub use self :: ExprKind :: * ;
2324pub use self :: DtorKind :: * ;
2425pub use self :: ExplicitSelfCategory :: * ;
2526pub use self :: FnOutput :: * ;
@@ -86,7 +87,7 @@ use syntax::abi;
8687use syntax:: ast:: { CrateNum , DefId , ItemImpl , ItemTrait , LOCAL_CRATE } ;
8788use syntax:: ast:: { MutImmutable , MutMutable , Name , NamedField , NodeId } ;
8889use syntax:: ast:: { StmtExpr , StmtSemi , StructField , UnnamedField , Visibility } ;
89- use syntax:: ast_util:: { self , is_local, local_def} ;
90+ use syntax:: ast_util:: { self , is_local, lit_is_str , local_def} ;
9091use syntax:: attr:: { self , AttrMetaMethods , SignedInt , UnsignedInt } ;
9192use syntax:: codemap:: Span ;
9293use syntax:: parse:: token:: { self , InternedString , special_idents} ;
@@ -5105,35 +5106,104 @@ pub fn resolve_expr(tcx: &ctxt, expr: &ast::Expr) -> def::Def {
51055106 }
51065107}
51075108
5108- pub fn expr_is_lval ( tcx : & ctxt , expr : & ast:: Expr ) -> bool {
5109- match expr. node {
5109+ pub fn expr_is_lval ( tcx : & ctxt , e : & ast:: Expr ) -> bool {
5110+ match expr_kind ( tcx, e) {
5111+ LvalueExpr => true ,
5112+ RvalueDpsExpr | RvalueDatumExpr | RvalueStmtExpr => false
5113+ }
5114+ }
5115+
5116+ /// We categorize expressions into three kinds. The distinction between
5117+ /// lvalue/rvalue is fundamental to the language. The distinction between the
5118+ /// two kinds of rvalues is an artifact of trans which reflects how we will
5119+ /// generate code for that kind of expression. See trans/expr.rs for more
5120+ /// information.
5121+ #[ derive( Copy , Clone ) ]
5122+ pub enum ExprKind {
5123+ LvalueExpr ,
5124+ RvalueDpsExpr ,
5125+ RvalueDatumExpr ,
5126+ RvalueStmtExpr
5127+ }
5128+
5129+ pub fn expr_kind ( tcx : & ctxt , expr : & ast:: Expr ) -> ExprKind {
5130+ if tcx. method_map . borrow ( ) . contains_key ( & MethodCall :: expr ( expr. id ) ) {
5131+ // Overloaded operations are generally calls, and hence they are
5132+ // generated via DPS, but there are a few exceptions:
5133+ return match expr. node {
5134+ // `a += b` has a unit result.
5135+ ast:: ExprAssignOp ( ..) => RvalueStmtExpr ,
5136+
5137+ // the deref method invoked for `*a` always yields an `&T`
5138+ ast:: ExprUnary ( ast:: UnDeref , _) => LvalueExpr ,
5139+
5140+ // the index method invoked for `a[i]` always yields an `&T`
5141+ ast:: ExprIndex ( ..) => LvalueExpr ,
5142+
5143+ // in the general case, result could be any type, use DPS
5144+ _ => RvalueDpsExpr
5145+ } ;
5146+ }
5147+
5148+ match expr. node {
51105149 ast:: ExprPath ( ..) => {
5111- // We can't use resolve_expr here, as this needs to run on broken
5112- // programs. We don't need to through - associated items are all
5113- // rvalues.
5114- match tcx. def_map . borrow ( ) . get ( & expr. id ) {
5115- Some ( & def:: PathResolution {
5116- base_def : def:: DefStatic ( ..) , ..
5117- } ) | Some ( & def:: PathResolution {
5118- base_def : def:: DefUpvar ( ..) , ..
5119- } ) | Some ( & def:: PathResolution {
5120- base_def : def:: DefLocal ( ..) , ..
5121- } ) => {
5122- true
5150+ match resolve_expr ( tcx, expr) {
5151+ def:: DefVariant ( tid, vid, _) => {
5152+ let variant_info = enum_variant_with_id ( tcx, tid, vid) ;
5153+ if !variant_info. args . is_empty ( ) {
5154+ // N-ary variant.
5155+ RvalueDatumExpr
5156+ } else {
5157+ // Nullary variant.
5158+ RvalueDpsExpr
5159+ }
51235160 }
51245161
5125- Some ( ..) => false ,
5162+ def:: DefStruct ( _) => {
5163+ match tcx. node_types . borrow ( ) . get ( & expr. id ) {
5164+ Some ( ty) => match ty. sty {
5165+ TyBareFn ( ..) => RvalueDatumExpr ,
5166+ _ => RvalueDpsExpr
5167+ } ,
5168+ // See ExprCast below for why types might be missing.
5169+ None => RvalueDatumExpr
5170+ }
5171+ }
51265172
5127- None => tcx. sess . span_bug ( expr. span , & format ! (
5128- "no def for path {}" , expr. id) )
5173+ // Special case: A unit like struct's constructor must be called without () at the
5174+ // end (like `UnitStruct`) which means this is an ExprPath to a DefFn. But in case
5175+ // of unit structs this is should not be interpreted as function pointer but as
5176+ // call to the constructor.
5177+ def:: DefFn ( _, true ) => RvalueDpsExpr ,
5178+
5179+ // Fn pointers are just scalar values.
5180+ def:: DefFn ( ..) | def:: DefMethod ( ..) => RvalueDatumExpr ,
5181+
5182+ // Note: there is actually a good case to be made that
5183+ // DefArg's, particularly those of immediate type, ought to
5184+ // considered rvalues.
5185+ def:: DefStatic ( ..) |
5186+ def:: DefUpvar ( ..) |
5187+ def:: DefLocal ( ..) => LvalueExpr ,
5188+
5189+ def:: DefConst ( ..) |
5190+ def:: DefAssociatedConst ( ..) => RvalueDatumExpr ,
5191+
5192+ def => {
5193+ tcx. sess . span_bug (
5194+ expr. span ,
5195+ & format ! ( "uncategorized def for expr {}: {:?}" ,
5196+ expr. id,
5197+ def) ) ;
5198+ }
51295199 }
51305200 }
51315201
51325202 ast:: ExprUnary ( ast:: UnDeref , _) |
51335203 ast:: ExprField ( ..) |
51345204 ast:: ExprTupField ( ..) |
51355205 ast:: ExprIndex ( ..) => {
5136- true
5206+ LvalueExpr
51375207 }
51385208
51395209 ast:: ExprCall ( ..) |
@@ -5146,29 +5216,60 @@ pub fn expr_is_lval(tcx: &ctxt, expr: &ast::Expr) -> bool {
51465216 ast:: ExprClosure ( ..) |
51475217 ast:: ExprBlock ( ..) |
51485218 ast:: ExprRepeat ( ..) |
5149- ast:: ExprVec ( ..) |
5219+ ast:: ExprVec ( ..) => {
5220+ RvalueDpsExpr
5221+ }
5222+
5223+ ast:: ExprIfLet ( ..) => {
5224+ tcx. sess . span_bug ( expr. span , "non-desugared ExprIfLet" ) ;
5225+ }
5226+ ast:: ExprWhileLet ( ..) => {
5227+ tcx. sess . span_bug ( expr. span , "non-desugared ExprWhileLet" ) ;
5228+ }
5229+
5230+ ast:: ExprForLoop ( ..) => {
5231+ tcx. sess . span_bug ( expr. span , "non-desugared ExprForLoop" ) ;
5232+ }
5233+
5234+ ast:: ExprLit ( ref lit) if lit_is_str ( & * * lit) => {
5235+ RvalueDpsExpr
5236+ }
5237+
51505238 ast:: ExprBreak ( ..) |
51515239 ast:: ExprAgain ( ..) |
51525240 ast:: ExprRet ( ..) |
51535241 ast:: ExprWhile ( ..) |
51545242 ast:: ExprLoop ( ..) |
51555243 ast:: ExprAssign ( ..) |
51565244 ast:: ExprInlineAsm ( ..) |
5157- ast:: ExprAssignOp ( ..) |
5158- ast:: ExprLit ( _) |
5245+ ast:: ExprAssignOp ( ..) => {
5246+ RvalueStmtExpr
5247+ }
5248+
5249+ ast:: ExprLit ( _) | // Note: LitStr is carved out above
51595250 ast:: ExprUnary ( ..) |
5160- ast:: ExprBox ( .. ) |
5251+ ast:: ExprBox ( None , _ ) |
51615252 ast:: ExprAddrOf ( ..) |
51625253 ast:: ExprBinary ( ..) |
51635254 ast:: ExprCast ( ..) => {
5164- false
5255+ RvalueDatumExpr
5256+ }
5257+
5258+ ast:: ExprBox ( Some ( ref place) , _) => {
5259+ // Special case `Box<T>` for now:
5260+ let def_id = match tcx. def_map . borrow ( ) . get ( & place. id ) {
5261+ Some ( def) => def. def_id ( ) ,
5262+ None => panic ! ( "no def for place" ) ,
5263+ } ;
5264+ if tcx. lang_items . exchange_heap ( ) == Some ( def_id) {
5265+ RvalueDatumExpr
5266+ } else {
5267+ RvalueDpsExpr
5268+ }
51655269 }
51665270
5167- ast:: ExprParen ( ref e) => expr_is_lval ( tcx, e) ,
5271+ ast:: ExprParen ( ref e) => expr_kind ( tcx, & * * e) ,
51685272
5169- ast:: ExprIfLet ( ..) |
5170- ast:: ExprWhileLet ( ..) |
5171- ast:: ExprForLoop ( ..) |
51725273 ast:: ExprMac ( ..) => {
51735274 tcx. sess . span_bug (
51745275 expr. span ,
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