@@ -4,6 +4,7 @@ use crate::ids::Vector;
44use derive_generic_visitor:: * ;
55use std:: collections:: HashSet ;
66use std:: convert:: Infallible ;
7+ use std:: fmt:: Debug ;
78use std:: iter:: Iterator ;
89use std:: mem;
910use std:: ops:: Index ;
@@ -128,6 +129,27 @@ impl<T> RegionBinder<T> {
128129 skip_binder : x. move_under_binder ( ) ,
129130 }
130131 }
132+
133+ pub fn map_ref < U > ( & self , f : impl FnOnce ( & T ) -> U ) -> RegionBinder < U > {
134+ RegionBinder {
135+ regions : self . regions . clone ( ) ,
136+ skip_binder : f ( & self . skip_binder ) ,
137+ }
138+ }
139+
140+ /// Substitute the bound variables with erased lifetimes.
141+ pub fn erase ( self ) -> T
142+ where
143+ T : AstVisitable ,
144+ {
145+ let mut val = self . skip_binder ;
146+ let args = GenericArgs {
147+ regions : self . regions . map_ref_indexed ( |_, _| Region :: Erased ) ,
148+ ..GenericArgs :: empty ( GenericsSource :: Builtin )
149+ } ;
150+ val. drive_mut ( & mut SubstVisitor :: new ( & args) ) ;
151+ val
152+ }
131153}
132154
133155impl GenericArgs {
@@ -268,6 +290,88 @@ impl IntegerTy {
268290 }
269291}
270292
293+ /// A value of type `T` bound by the generic parameters of item
294+ /// `item`. Used when dealing with multiple items at a time, to
295+ /// ensure we don't mix up generics.
296+ ///
297+ /// To get the value, use `under_binder_of` or `subst_for`.
298+ #[ derive( Debug , Clone , Copy ) ]
299+ pub struct ItemBinder < ItemId , T > {
300+ pub item_id : ItemId ,
301+ val : T ,
302+ }
303+
304+ impl < ItemId , T > ItemBinder < ItemId , T >
305+ where
306+ ItemId : Debug + Copy + PartialEq ,
307+ {
308+ pub fn new ( item_id : ItemId , val : T ) -> Self {
309+ Self { item_id, val }
310+ }
311+
312+ pub fn as_ref ( & self ) -> ItemBinder < ItemId , & T > {
313+ ItemBinder {
314+ item_id : self . item_id ,
315+ val : & self . val ,
316+ }
317+ }
318+
319+ pub fn map_bound < U > ( self , f : impl FnOnce ( T ) -> U ) -> ItemBinder < ItemId , U > {
320+ ItemBinder {
321+ item_id : self . item_id ,
322+ val : f ( self . val ) ,
323+ }
324+ }
325+
326+ fn assert_item_id ( & self , item_id : ItemId ) {
327+ assert_eq ! (
328+ self . item_id, item_id,
329+ "Trying to use item bound for {:?} as if it belonged to {:?}" ,
330+ self . item_id, item_id
331+ ) ;
332+ }
333+
334+ /// Assert that the value is bound for item `item_id`, and returns it. This is used when we
335+ /// plan to store the returned value inside that item.
336+ pub fn under_binder_of ( self , item_id : ItemId ) -> T {
337+ self . assert_item_id ( item_id) ;
338+ self . val
339+ }
340+
341+ /// Given generic args for `item_id`, assert that the value is bound for `item_id` and
342+ /// substitute it with the provided generic arguments. Because the arguments are bound in the
343+ /// context of another item, so it the resulting substituted value.
344+ pub fn substitute < OtherItem : Debug + Copy + PartialEq > (
345+ self ,
346+ args : ItemBinder < OtherItem , & GenericArgs > ,
347+ ) -> ItemBinder < OtherItem , T >
348+ where
349+ ItemId : Into < AnyTransId > ,
350+ T : TyVisitable ,
351+ {
352+ args. map_bound ( |args| {
353+ assert_eq ! (
354+ args. target,
355+ GenericsSource :: item( self . item_id) ,
356+ "These `GenericArgs` are meant for {:?} but were used on {:?}" ,
357+ args. target,
358+ self . item_id
359+ ) ;
360+ self . val . substitute ( args)
361+ } )
362+ }
363+ }
364+
365+ /// Dummy item identifier that represents the current item when not ambiguous.
366+ #[ derive( Debug , Clone , Copy , PartialEq , Eq ) ]
367+ pub struct CurrentItem ;
368+
369+ impl < T > ItemBinder < CurrentItem , T > {
370+ pub fn under_current_binder ( self ) -> T {
371+ self . val
372+ }
373+ }
374+
271375impl Ty {
272376 /// Return true if it is actually unit (i.e.: 0-tuple)
273377pub fn is_unit ( & self ) -> bool {
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