cmd/compile: get instantiated generic types working with interfaces

Get instantiatiated generic types working with interfaces, including
typechecking assignments to interfaces and instantiating all the methods
properly. To get it all working, this change includes:

 - Add support for substituting in interfaces in subster.typ()

 - Fill in the info for the methods for all instantiated generic types,
   so those methods will be available for later typechecking (by the old
   typechecker) when assigning an instantiated generic type to an
   interface. We also want those methods available so we have the list
   when we want to instantiate all methods of an instantiated type. We
   have both for instantiated types encountered during the initial noder
   phase, and for instantiated types created during stenciling of a
   function/method.

 - When we first create a fully-instantiated generic type (whether
   during initial noder2 pass or while instantiating a method/function),
   add it to a list so that all of its methods will also be
   instantiated. This is needed so that an instantiated type can be
   assigned to an interface.

 - Properly substitute type names in the names of instantiated methods.

 - New accessor methods for types.Type.RParam.

 - To deal with generic types which are empty structs (or just don't use
   their type params anywhere), we want to set HasTParam if a named type
   has any type params that are not fully instantiated, even if the
   type param is not used in the type.

 - In subst.typ() and elsewhere, always set sym.Def for a new forwarding
   type we are creating, so we always create a single unique type for
   each generic type instantiation. This handles recursion within a
   type, and also recursive relationships across many types or methods.
   We remove the seen[] hashtable, which was serving the same purpose,
   but for subst.typ() only. We now handle all kinds of recursive types.

 - We don't seem to need to force types.CheckSize() on
   created/substituted generic types anymore, so commented out for now.

 - Add an RParams accessor to types2.Signature, and also a new
   exported types2.AsSignature() function.

Change-Id: If6c5dd98427b20bfe9de3379cc16f83df9c9b632
Reviewed-on: https://go-review.googlesource.com/c/go/+/298449
Run-TryBot: Dan Scales <danscales@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Trust: Dan Scales <danscales@google.com>
Reviewed-by: Robert Griesemer <gri@golang.org>

1 files changed, 8 insertions, 2 deletions

diff --git a/src/cmd/compile/internal/noder/decl.go b/src/cmd/compile/internal/noder/decl.go
index a1596be4a4..f0cdcbfc2e 100644
--- a/src/cmd/compile/internal/noder/decl.go
+++ b/src/cmd/compile/internal/noder/decl.go
@@ -134,14 +134,14 @@ func (g *irgen) typeDecl(out *ir.Nodes, decl *syntax.TypeDecl) {
 	}
 
 	// We need to use g.typeExpr(decl.Type) here to ensure that for
-	// chained, defined-type declarations like
+	// chained, defined-type declarations like:
 	//
 	//	type T U
 	//
 	//	//go:notinheap
 	//	type U struct { … }
 	//
-	// that we mark both T and U as NotInHeap. If we instead used just
+	// we mark both T and U as NotInHeap. If we instead used just
 	// g.typ(otyp.Underlying()), then we'd instead set T's underlying
 	// type directly to the struct type (which is not marked NotInHeap)
 	// and fail to mark T as NotInHeap.
@@ -154,6 +154,12 @@ func (g *irgen) typeDecl(out *ir.Nodes, decl *syntax.TypeDecl) {
 	// [mdempsky: Subtleties like these are why I always vehemently
 	// object to new type pragmas.]
 	ntyp.SetUnderlying(g.typeExpr(decl.Type))
+	if len(decl.TParamList) > 0 {
+		// Set HasTParam if there are any tparams, even if no tparams are
+		// used in the type itself (e.g., if it is an empty struct, or no
+		// fields in the struct use the tparam).
+		ntyp.SetHasTParam(true)
+	}
 	types.ResumeCheckSize()
 
 	if otyp, ok := otyp.(*types2.Named); ok && otyp.NumMethods() != 0 {