@@ -67,6 +67,7 @@ pub enum CandidateSimilarity {
6767pub struct ImplCandidate < ' tcx > {
6868 pub trait_ref : ty:: TraitRef < ' tcx > ,
6969 pub similarity : CandidateSimilarity ,
70+ impl_def_id : DefId ,
7071}
7172
7273enum GetSafeTransmuteErrorAndReason {
@@ -1331,6 +1332,7 @@ trait InferCtxtPrivExt<'tcx> {
13311332 body_def_id : LocalDefId ,
13321333 err : & mut Diagnostic ,
13331334 other : bool ,
1335+ param_env : ty:: ParamEnv < ' tcx > ,
13341336 ) -> bool ;
13351337
13361338 fn report_similar_impl_candidates_for_root_obligation (
@@ -1918,8 +1920,9 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
19181920
19191921 let imp = self . tcx . impl_trait_ref ( def_id) . unwrap ( ) . skip_binder ( ) ;
19201922
1921- self . fuzzy_match_tys ( trait_pred. skip_binder ( ) . self_ty ( ) , imp. self_ty ( ) , false )
1922- . map ( |similarity| ImplCandidate { trait_ref : imp, similarity } )
1923+ self . fuzzy_match_tys ( trait_pred. skip_binder ( ) . self_ty ( ) , imp. self_ty ( ) , false ) . map (
1924+ |similarity| ImplCandidate { trait_ref : imp, similarity, impl_def_id : def_id } ,
1925+ )
19231926 } )
19241927 . collect ( ) ;
19251928 if candidates. iter ( ) . any ( |c| matches ! ( c. similarity, CandidateSimilarity :: Exact { .. } ) ) {
@@ -1938,7 +1941,71 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
19381941 body_def_id : LocalDefId ,
19391942 err : & mut Diagnostic ,
19401943 other : bool ,
1944+ param_env : ty:: ParamEnv < ' tcx > ,
19411945 ) -> bool {
1946+ if let [ single] = & impl_candidates {
1947+ if self . probe ( |_| {
1948+ let ocx = ObligationCtxt :: new ( self ) ;
1949+ let obligation_trait_ref = self . instantiate_binder_with_placeholders ( trait_ref) ;
1950+ let impl_args = self . fresh_args_for_item ( DUMMY_SP , single. impl_def_id ) ;
1951+ let impl_trait_ref = ocx. normalize (
1952+ & ObligationCause :: dummy ( ) ,
1953+ param_env,
1954+ ty:: EarlyBinder :: bind ( single. trait_ref ) . instantiate ( self . tcx , impl_args) ,
1955+ ) ;
1956+
1957+ ocx. register_obligations (
1958+ self . tcx
1959+ . predicates_of ( single. impl_def_id )
1960+ . instantiate ( self . tcx , impl_args)
1961+ . into_iter ( )
1962+ . map ( |( clause, _) | {
1963+ Obligation :: new ( self . tcx , ObligationCause :: dummy ( ) , param_env, clause)
1964+ } ) ,
1965+ ) ;
1966+ if !ocx. select_where_possible ( ) . is_empty ( ) {
1967+ return false ;
1968+ }
1969+
1970+ let mut terrs = vec ! [ ] ;
1971+ for ( obligation_arg, impl_arg) in
1972+ std:: iter:: zip ( obligation_trait_ref. args , impl_trait_ref. args )
1973+ {
1974+ if let Err ( terr) =
1975+ ocx. eq ( & ObligationCause :: dummy ( ) , param_env, obligation_arg, impl_arg)
1976+ {
1977+ terrs. push ( terr) ;
1978+ }
1979+ if !ocx. select_where_possible ( ) . is_empty ( ) {
1980+ return false ;
1981+ }
1982+ }
1983+
1984+ // Literally nothing unified, just give up.
1985+ if terrs. len ( ) == impl_trait_ref. args . len ( ) {
1986+ return false ;
1987+ }
1988+
1989+ let cand =
1990+ self . resolve_vars_if_possible ( impl_trait_ref) . fold_with ( & mut BottomUpFolder {
1991+ tcx : self . tcx ,
1992+ ty_op : |ty| ty,
1993+ lt_op : |lt| lt,
1994+ ct_op : |ct| ct. normalize ( self . tcx , ty:: ParamEnv :: empty ( ) ) ,
1995+ } ) ;
1996+ err. highlighted_help ( vec ! [
1997+ ( format!( "the trait `{}` " , cand. print_only_trait_path( ) ) , Style :: NoStyle ) ,
1998+ ( "is" . to_string( ) , Style :: Highlight ) ,
1999+ ( " implemented for `" . to_string( ) , Style :: NoStyle ) ,
2000+ ( cand. self_ty( ) . to_string( ) , Style :: Highlight ) ,
2001+ ( "`" . to_string( ) , Style :: NoStyle ) ,
2002+ ] ) ;
2003+ true
2004+ } ) {
2005+ return true ;
2006+ }
2007+ }
2008+
19422009 let other = if other { "other " } else { "" } ;
19432010 let report = |candidates : Vec < TraitRef < ' tcx > > , err : & mut Diagnostic | {
19442011 if candidates. is_empty ( ) {
@@ -2062,9 +2129,11 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
20622129 } )
20632130 . collect ( ) ;
20642131 impl_candidates. sort_by_key ( |cand| ( cand. similarity , cand. trait_ref ) ) ;
2132+ let mut impl_candidates: Vec < _ > =
2133+ impl_candidates. into_iter ( ) . map ( |cand| cand. trait_ref ) . collect ( ) ;
20652134 impl_candidates. dedup ( ) ;
20662135
2067- report ( impl_candidates. into_iter ( ) . map ( |cand| cand . trait_ref ) . collect ( ) , err)
2136+ report ( impl_candidates, err)
20682137 }
20692138
20702139 fn report_similar_impl_candidates_for_root_obligation (
@@ -2108,6 +2177,7 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
21082177 body_def_id,
21092178 err,
21102179 true ,
2180+ obligation. param_env ,
21112181 ) ;
21122182 }
21132183 }
@@ -2316,6 +2386,7 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
23162386 obligation. cause . body_id ,
23172387 & mut err,
23182388 false ,
2389+ obligation. param_env ,
23192390 ) ;
23202391 }
23212392 }
@@ -3051,6 +3122,7 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
30513122 body_def_id,
30523123 err,
30533124 true ,
3125+ obligation. param_env ,
30543126 ) {
30553127 self . report_similar_impl_candidates_for_root_obligation (
30563128 & obligation,
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