From be88be6e7a24cfa888b3fd5c81b8a51a70240d9f Mon Sep 17 00:00:00 2001
From: Robert Griesemer <gri@golang.org>
Date: Thu, 18 Jul 2019 21:29:24 -0700
Subject: [PATCH] go/types: steps towards type-checking of methods with
 parameterized receivers

Change-Id: I80b4d4c248cb5e29933366322cca1d76c3ed5e23
---
 src/go/types/decl.go          | 12 +++++++++++-
 src/go/types/object.go        |  3 +++
 src/go/types/testdata/tmp.go2 | 17 +++++++----------
 src/go/types/type.go          |  5 +++--
 src/go/types/typexpr.go       | 14 +++-----------
 5 files changed, 27 insertions(+), 24 deletions(-)

diff --git a/src/go/types/decl.go b/src/go/types/decl.go
index 70f36d826e..d2361e1842 100644
--- a/src/go/types/decl.go
+++ b/src/go/types/decl.go
@@ -659,10 +659,20 @@ func (check *Checker) funcDecl(obj *Func, decl *declInfo) {
 	// func declarations cannot use iota
 	assert(check.iota == nil)
 
+	if obj.IsParameterized() {
+		assert(obj.scope != nil)
+		check.scope = obj.scope // push type parameter scope
+	}
+
 	sig := new(Signature)
 	obj.typ = sig // guard against cycles
 	fdecl := decl.fdecl
-	check.funcType(sig, fdecl.Recv, obj.scope, obj.tparams, fdecl.Type)
+	check.funcType(sig, fdecl.Recv, fdecl.Type)
+	sig.tparams = obj.tparams
+
+	if obj.IsParameterized() {
+		check.closeScope()
+	}
 
 	// function body must be type-checked after global declarations
 	// (functions implemented elsewhere have no body)
diff --git a/src/go/types/object.go b/src/go/types/object.go
index f0db9fbaad..30db273935 100644
--- a/src/go/types/object.go
+++ b/src/go/types/object.go
@@ -338,6 +338,9 @@ func (obj *Func) FullName() string {
 // Scope returns the scope of the function's body block.
 func (obj *Func) Scope() *Scope { return obj.typ.(*Signature).scope }
 
+// IsParameterized reports whether obj is a parameterized function.
+func (obj *Func) IsParameterized() bool { return len(obj.tparams) > 0 }
+
 func (*Func) isDependency() {} // a function may be a dependency of an initialization expression
 
 // A Label represents a declared label.
diff --git a/src/go/types/testdata/tmp.go2 b/src/go/types/testdata/tmp.go2
index 7c694dd9b0..f43cdc68c6 100644
--- a/src/go/types/testdata/tmp.go2
+++ b/src/go/types/testdata/tmp.go2
@@ -6,14 +6,11 @@ package p
 
 type List(type E) []E
 
-func f(type P) (x P) List(P) {
-	return List(P){x}
+/*
+func (l List(E)) First() E {
+        if len(l) == 0 {
+                panic("no first")
+        }
+        return l[0]
 }
-
-var (
-	_ []int = f(0)
-	_ []float32 = f(float32)(10)
-	_ [](List(int)) = f(List(int){})
-        _ List(List(int)) = [](List(int)){}
-        _ = [](List(int)){}
-)
+*/
\ No newline at end of file
diff --git a/src/go/types/type.go b/src/go/types/type.go
index 43570a0a18..fb9e74c8a4 100644
--- a/src/go/types/type.go
+++ b/src/go/types/type.go
@@ -199,8 +199,9 @@ type Signature struct {
 	// and store it in the Func Object) because when type-checking a function
 	// literal we call the general type checker which returns a general Type.
 	// We then unpack the *Signature and use the scope for the literal body.
-	scope    *Scope      // function scope, present for package-local signatures
-	recv     *Var        // nil if not a method
+	scope *Scope // function scope, present for package-local signatures
+	recv  *Var   // nil if not a method
+	// TODO(gri) do we need to keep tparams in the signature?
 	tparams  []*TypeName // type parameters from left to right; or nil
 	params   *Tuple      // (incoming) parameters from left to right; or nil
 	results  *Tuple      // (outgoing) results from left to right; or nil
diff --git a/src/go/types/typexpr.go b/src/go/types/typexpr.go
index 320390fd2d..15f342d3c4 100644
--- a/src/go/types/typexpr.go
+++ b/src/go/types/typexpr.go
@@ -157,15 +157,8 @@ func (check *Checker) instantiatedType(e ast.Expr) Type {
 }
 
 // funcType type-checks a function or method type.
-func (check *Checker) funcType(sig *Signature, recvPar *ast.FieldList, scope *Scope, tparams []*TypeName, ftyp *ast.FuncType) {
-	// type parameters are in a scope enclosing the function scope
-	if tparams != nil {
-		check.scope = scope
-		// TODO(gri) push/pop both (type parameter and function) scopes
-		// defer check.closeScope()
-	}
-
-	scope = NewScope(check.scope, token.NoPos, token.NoPos, "function")
+func (check *Checker) funcType(sig *Signature, recvPar *ast.FieldList, ftyp *ast.FuncType) {
+	scope := NewScope(check.scope, token.NoPos, token.NoPos, "function")
 	// TODO(gri) should we close this scope?
 	scope.isFunc = true
 	check.recordScope(ftyp, scope)
@@ -224,7 +217,6 @@ func (check *Checker) funcType(sig *Signature, recvPar *ast.FieldList, scope *Sc
 	}
 
 	sig.scope = scope
-	sig.tparams = tparams
 	sig.params = NewTuple(params...)
 	sig.results = NewTuple(results...)
 	sig.variadic = variadic
@@ -319,7 +311,7 @@ func (check *Checker) typInternal(e ast.Expr, def *Named) Type {
 	case *ast.FuncType:
 		typ := new(Signature)
 		def.setUnderlying(typ)
-		check.funcType(typ, nil, nil, nil, e)
+		check.funcType(typ, nil, e)
 		return typ
 
 	case *ast.InterfaceType: