[dev.typeparams] go/types: add Named.SetTParams and Named.Orig methods

This is a port of CL 309832 to go/types, adjusted to not export the new
API and to amend TestSizeof.

Change-Id: I67efd3ba9b921c8431528eba1cd88ec1f41898bb
Reviewed-on: https://go-review.googlesource.com/c/go/+/324755
Trust: Robert Findley <rfindley@google.com>
Run-TryBot: Robert Findley <rfindley@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>

src/go/types/decl.go

@@ -333,7 +333,7 @@ func (check *Checker) validType(typ Type, path []Object) typeInfo {
 		switch t.info {
 		case unknown:
 			t.info = marked
-			t.info = check.validType(t.orig, append(path, t.obj)) // only types of current package added to path
+			t.info = check.validType(t.fromRHS, append(path, t.obj)) // only types of current package added to path
 		case marked:
 			// cycle detected
 			for i, tn := range path {
@@ -692,9 +692,8 @@ func (check *Checker) typeDecl(obj *TypeName, tdecl *ast.TypeSpec, def *Named) {
 	} else {
 		// defined type declaration
 
-		named := check.newNamed(obj, nil, nil)
+		named := check.newNamed(obj, nil, nil, nil, nil)
 		def.setUnderlying(named)
-		obj.typ = named // make sure recursive type declarations terminate
 
 		if tparams := typeparams.Get(tdecl); tparams != nil {
 			check.openScope(tdecl, "type parameters")
@@ -703,7 +702,7 @@ func (check *Checker) typeDecl(obj *TypeName, tdecl *ast.TypeSpec, def *Named) {
 		}
 
 		// determine underlying type of named
-		named.orig = check.definedType(tdecl.Type, named)
+		named.fromRHS = check.definedType(tdecl.Type, named)
 
 		// The underlying type of named may be itself a named type that is
 		// incomplete:
@@ -718,7 +717,7 @@ func (check *Checker) typeDecl(obj *TypeName, tdecl *ast.TypeSpec, def *Named) {
 		// and which has as its underlying type the named type B.
 		// Determine the (final, unnamed) underlying type by resolving
 		// any forward chain.
-		// TODO(gri) Investigate if we can just use named.origin here
+		// TODO(gri) Investigate if we can just use named.fromRHS here
 		//           and rely on lazy computation of the underlying type.
 		named.underlying = under(named)
 	}

src/go/types/sanitize.go

@@ -138,8 +138,8 @@ func (s sanitizer) typ(typ Type) Type {
 		if debug && t.check != nil {
 			panic("internal error: Named.check != nil")
 		}
-		if orig := s.typ(t.orig); orig != t.orig {
+		if orig := s.typ(t.fromRHS); orig != t.fromRHS {
-			t.orig = orig
+			t.fromRHS = orig
 		}
 		if under := s.typ(t.underlying); under != t.underlying {
 			t.underlying = under

src/go/types/sizeof_test.go

@@ -30,7 +30,7 @@ func TestSizeof(t *testing.T) {
 		{Interface{}, 60, 120},
 		{Map{}, 16, 32},
 		{Chan{}, 12, 24},
-		{Named{}, 64, 128},
+		{Named{}, 68, 136},
 		{_TypeParam{}, 28, 48},
 		{instance{}, 44, 88},
 		{bottom{}, 0, 0},

src/go/types/subst.go

@@ -396,8 +396,7 @@ func (subst *subster) typ(typ Type) Type {
 
 		// create a new named type and populate caches to avoid endless recursion
 		tname := NewTypeName(subst.pos, t.obj.pkg, t.obj.name, nil)
-		named := subst.check.newNamed(tname, t.underlying, t.methods) // method signatures are updated lazily
+		named := subst.check.newNamed(tname, t, t.underlying, t.tparams, t.methods) // method signatures are updated lazily
-		named.tparams = t.tparams                                     // new type is still parameterized
 		named.targs = newTargs
 		if subst.check != nil {
 			subst.check.typMap[h] = named
@@ -407,7 +406,7 @@ func (subst *subster) typ(typ Type) Type {
 		// do the substitution
 		dump(">>> subst %s with %s (new: %s)", t.underlying, subst.smap, newTargs)
 		named.underlying = subst.typOrNil(t.underlying)
-		named.orig = named.underlying // for cycle detection (Checker.validType)
+		named.fromRHS = named.underlying // for cycle detection (Checker.validType)
 
 		return named
 

src/go/types/type.go

@@ -642,12 +642,15 @@ func (c *Chan) Dir() ChanDir { return c.dir }
 // Elem returns the element type of channel c.
 func (c *Chan) Elem() Type { return c.elem }
 
+// TODO(rfindley) Clean up Named struct below; specifically the fromRHS field (can we use underlying?).
+
 // A Named represents a named (defined) type.
 type Named struct {
 	check      *Checker    // for Named.under implementation; nilled once under has been called
 	info       typeInfo    // for cycle detection
 	obj        *TypeName   // corresponding declared object
-	orig       Type        // type (on RHS of declaration) this *Named type is derived of (for cycle reporting)
+	orig       *Named      // original, uninstantiated type
+	fromRHS    Type        // type (on RHS of declaration) this *Named type is derived of (for cycle reporting)
 	underlying Type        // possibly a *Named during setup; never a *Named once set up completely
 	tparams    []*TypeName // type parameters, or nil
 	targs      []Type      // type arguments (after instantiation), or nil
@@ -661,11 +664,14 @@ func NewNamed(obj *TypeName, underlying Type, methods []*Func) *Named {
 	if _, ok := underlying.(*Named); ok {
 		panic("types.NewNamed: underlying type must not be *Named")
 	}
-	return (*Checker)(nil).newNamed(obj, underlying, methods)
+	return (*Checker)(nil).newNamed(obj, nil, underlying, nil, methods)
 }
 
-func (check *Checker) newNamed(obj *TypeName, underlying Type, methods []*Func) *Named {
+func (check *Checker) newNamed(obj *TypeName, orig *Named, underlying Type, tparams []*TypeName, methods []*Func) *Named {
-	typ := &Named{check: check, obj: obj, orig: underlying, underlying: underlying, methods: methods}
+	typ := &Named{check: check, obj: obj, orig: orig, fromRHS: underlying, underlying: underlying, tparams: tparams, methods: methods}
+	if typ.orig == nil {
+		typ.orig = typ
+	}
 	if obj.typ == nil {
 		obj.typ = typ
 	}
@@ -692,6 +698,10 @@ func (check *Checker) newNamed(obj *TypeName, underlying Type, methods []*Func)
 // Obj returns the type name for the named type t.
 func (t *Named) Obj() *TypeName { return t.obj }
 
+// _Orig returns the original generic type an instantiated type is derived from.
+// If t is not an instantiated type, the result is t.
+func (t *Named) _Orig() *Named { return t.orig }
+
 // TODO(gri) Come up with a better representation and API to distinguish
 //           between parameterized instantiated and non-instantiated types.
 
@@ -699,10 +709,13 @@ func (t *Named) Obj() *TypeName { return t.obj }
 // The result is non-nil for an (originally) parameterized type even if it is instantiated.
 func (t *Named) _TParams() []*TypeName { return t.tparams }
 
+// _SetTParams sets the type parameters of the named type t.
+func (t *Named) _SetTParams(tparams []*TypeName) { t.tparams = tparams }
+
 // _TArgs returns the type arguments after instantiation of the named type t, or nil if not instantiated.
 func (t *Named) _TArgs() []Type { return t.targs }
 
-// _SetTArgs sets the type arguments of Named.
+// SetTArgs sets the type arguments of the named type t.
 func (t *Named) _SetTArgs(args []Type) { t.targs = args }
 
 // NumMethods returns the number of explicit methods whose receiver is named type t.
@@ -741,9 +754,9 @@ func nextID() uint64 { return uint64(atomic.AddUint32(&lastID, 1)) }
 // A _TypeParam represents a type parameter type.
 type _TypeParam struct {
 	check *Checker  // for lazy type bound completion
-	id    uint64    // unique id
+	id    uint64    // unique id, for debugging only
 	obj   *TypeName // corresponding type name
-	index int       // parameter index
+	index int       // type parameter index in source order, starting at 0
 	bound Type      // *Named or *Interface; underlying type is always *Interface
 }