cmd/compile: document parsing decision for imported interfaces

Fixes #13245.

Change-Id: I87be63cc7b27f70ca2f9fb6bc9908b9061fe3d9d
Reviewed-on: https://go-review.googlesource.com/17203
Reviewed-by: Chris Manghane <cmang@golang.org>

diff --git a/src/cmd/compile/internal/gc/parser.go b/src/cmd/compile/internal/gc/parser.go
index 37b244cdc4308cfcf65420cc785a485a39306b37..3da648a15180fdb921ea04a44ecdb22d5cf62ed1 100644 (file)
--- a/src/cmd/compile/internal/gc/parser.go
+++ b/src/cmd/compile/internal/gc/parser.go
@@ -3279,24 +3279,32 @@ func (p *parser) hidden_interfacedcl() *Node {
                defer p.trace("hidden_interfacedcl")()
        }
 
-       // TODO(gri) possible conflict here: both cases may start with '@' per grammar
-       // (issue 13245).
+       // The original (now defunct) grammar in go.y accepted both a method
+       // or an (embedded) type:
+       //
+       // hidden_interfacedcl:
+       //      sym '(' ohidden_funarg_list ')' ohidden_funres
+       //      {
+       //              $$ = Nod(ODCLFIELD, newname($1), typenod(functype(fakethis(), $3, $5)));
+       //      }
+       // |    hidden_type
+       //      {
+       //              $$ = Nod(ODCLFIELD, nil, typenod($1));
+       //      }
+       //
+       // But the current textual export code only exports (inlined) methods,
+       // even if the methods came from embedded interfaces. Furthermore, in
+       // the original grammar, hidden_type may also start with a sym (LNAME
+       // or '@'), complicating matters further. Since we never have embedded
+       // types, only parse methods here.
 
-       switch p.tok {
-       case LNAME, '@', '?':
-               s1 := p.sym()
-               p.want('(')
-               s3 := p.ohidden_funarg_list()
-               p.want(')')
-               s5 := p.ohidden_funres()
-
-               return Nod(ODCLFIELD, newname(s1), typenod(functype(fakethis(), s3, s5)))
-
-       default:
-               s1 := p.hidden_type()
+       s1 := p.sym()
+       p.want('(')
+       s3 := p.ohidden_funarg_list()
+       p.want(')')
+       s5 := p.ohidden_funres()
 
-               return Nod(ODCLFIELD, nil, typenod(s1))
-       }
+       return Nod(ODCLFIELD, newname(s1), typenod(functype(fakethis(), s3, s5)))
 }
 
 func (p *parser) ohidden_funres() *NodeList {