[dev.typeparams] go/ast: remove the typeparams build constraint

This CL removes the typeparams build constraint guarding changes to the
go/ast and go/types APIs. Notably it does not remove all indirection
added to hide the type parameter API: the go/internal/typeparams
package is not yet deleted, nor have go/parser or go/types been updated
to access type parameter data directly. This will be done in a follow-up
CL; the intent of this CL is to make it easier to support the new type
set syntax, and to experiment with different AST APIs.

Change-Id: I13ea0285752991b87b3aead1d1371e1f3f817b1a
Reviewed-on: https://go-review.googlesource.com/c/go/+/325689
Trust: Robert Findley <[email protected]>
Run-TryBot: Robert Findley <[email protected]>
TryBot-Result: Go Bot <[email protected]>
Reviewed-by: Robert Griesemer <[email protected]>

Author: findleyr

src/go/ast/ast.go

@@ -374,6 +374,13 @@ type (
 		Rparen   token.Pos // position of ")"
 	}
 
+	// A ListExpr node represents a list of expressions separated by commas.
+	// ListExpr nodes are used as index in IndexExpr nodes representing type
+	// or function instantiations with more than one type argument.
+	ListExpr struct {
+		ElemList []Expr
+	}
+
 	// A StarExpr node represents an expression of the form "*" Expression.
 	// Semantically it could be a unary "*" expression, or a pointer type.
 	//
@@ -440,6 +447,14 @@ type (
 
 	// Pointer types are represented via StarExpr nodes.
 
+	// A FuncType node represents a function type.
+	FuncType struct {
+		Func    token.Pos  // position of "func" keyword (token.NoPos if there is no "func")
+		TParams *FieldList // type parameters; or nil
+		Params  *FieldList // (incoming) parameters; non-nil
+		Results *FieldList // (outgoing) results; or nil
+	}
+
 	// An InterfaceType node represents an interface type.
 	InterfaceType struct {
 		Interface  token.Pos  // position of "interface" keyword
@@ -482,12 +497,18 @@ func (x *IndexExpr) Pos() token.Pos      { return x.X.Pos() }
 func (x *SliceExpr) Pos() token.Pos      { return x.X.Pos() }
 func (x *TypeAssertExpr) Pos() token.Pos { return x.X.Pos() }
 func (x *CallExpr) Pos() token.Pos       { return x.Fun.Pos() }
-func (x *StarExpr) Pos() token.Pos       { return x.Star }
-func (x *UnaryExpr) Pos() token.Pos      { return x.OpPos }
-func (x *BinaryExpr) Pos() token.Pos     { return x.X.Pos() }
-func (x *KeyValueExpr) Pos() token.Pos   { return x.Key.Pos() }
-func (x *ArrayType) Pos() token.Pos      { return x.Lbrack }
-func (x *StructType) Pos() token.Pos     { return x.Struct }
+func (x *ListExpr) Pos() token.Pos {
+	if len(x.ElemList) > 0 {
+		return x.ElemList[0].Pos()
+	}
+	return token.NoPos
+}
+func (x *StarExpr) Pos() token.Pos     { return x.Star }
+func (x *UnaryExpr) Pos() token.Pos    { return x.OpPos }
+func (x *BinaryExpr) Pos() token.Pos   { return x.X.Pos() }
+func (x *KeyValueExpr) Pos() token.Pos { return x.Key.Pos() }
+func (x *ArrayType) Pos() token.Pos    { return x.Lbrack }
+func (x *StructType) Pos() token.Pos   { return x.Struct }
 func (x *FuncType) Pos() token.Pos {
 	if x.Func.IsValid() || x.Params == nil { // see issue 3870
 		return x.Func
@@ -515,12 +536,18 @@ func (x *IndexExpr) End() token.Pos      { return x.Rbrack + 1 }
 func (x *SliceExpr) End() token.Pos      { return x.Rbrack + 1 }
 func (x *TypeAssertExpr) End() token.Pos { return x.Rparen + 1 }
 func (x *CallExpr) End() token.Pos       { return x.Rparen + 1 }
-func (x *StarExpr) End() token.Pos       { return x.X.End() }
-func (x *UnaryExpr) End() token.Pos      { return x.X.End() }
-func (x *BinaryExpr) End() token.Pos     { return x.Y.End() }
-func (x *KeyValueExpr) End() token.Pos   { return x.Value.End() }
-func (x *ArrayType) End() token.Pos      { return x.Elt.End() }
-func (x *StructType) End() token.Pos     { return x.Fields.End() }
+func (x *ListExpr) End() token.Pos {
+	if len(x.ElemList) > 0 {
+		return x.ElemList[len(x.ElemList)-1].End()
+	}
+	return token.NoPos
+}
+func (x *StarExpr) End() token.Pos     { return x.X.End() }
+func (x *UnaryExpr) End() token.Pos    { return x.X.End() }
+func (x *BinaryExpr) End() token.Pos   { return x.Y.End() }
+func (x *KeyValueExpr) End() token.Pos { return x.Value.End() }
+func (x *ArrayType) End() token.Pos    { return x.Elt.End() }
+func (x *StructType) End() token.Pos   { return x.Fields.End() }
 func (x *FuncType) End() token.Pos {
 	if x.Results != nil {
 		return x.Results.End()
@@ -546,6 +573,7 @@ func (*IndexExpr) exprNode()      {}
 func (*SliceExpr) exprNode()      {}
 func (*TypeAssertExpr) exprNode() {}
 func (*CallExpr) exprNode()       {}
+func (*ListExpr) exprNode()       {}
 func (*StarExpr) exprNode()       {}
 func (*UnaryExpr) exprNode()      {}
 func (*BinaryExpr) exprNode()     {}
@@ -892,6 +920,16 @@ type (
 		Values  []Expr        // initial values; or nil
 		Comment *CommentGroup // line comments; or nil
 	}
+
+	// A TypeSpec node represents a type declaration (TypeSpec production).
+	TypeSpec struct {
+		Doc     *CommentGroup // associated documentation; or nil
+		Name    *Ident        // type name
+		TParams *FieldList    // type parameters; or nil
+		Assign  token.Pos     // position of '=', if any
+		Type    Expr          // *Ident, *ParenExpr, *SelectorExpr, *StarExpr, or any of the *XxxTypes
+		Comment *CommentGroup // line comments; or nil
+	}
 )
 
 // Pos and End implementations for spec nodes.

src/go/ast/ast_notypeparams.go

@@ -4,6 +4,8 @@
 
 package ast
 
+import "fmt"
+
 // A Visitor's Visit method is invoked for each node encountered by Walk.
 // If the result visitor w is not nil, Walk visits each of the children
 // of node with the visitor w, followed by a call of w.Visit(nil).
@@ -136,6 +138,11 @@ func Walk(v Visitor, node Node) {
 		Walk(v, n.Fun)
 		walkExprList(v, n.Args)
 
+	case *ListExpr:
+		for _, elem := range n.ElemList {
+			Walk(v, elem)
+		}
+
 	case *StarExpr:
 		Walk(v, n.X)
 
@@ -161,7 +168,9 @@ func Walk(v Visitor, node Node) {
 		Walk(v, n.Fields)
 
 	case *FuncType:
-		walkFuncTypeParams(v, n)
+		if n.TParams != nil {
+			Walk(v, n.TParams)
+		}
 		if n.Params != nil {
 			Walk(v, n.Params)
 		}
@@ -316,7 +325,9 @@ func Walk(v Visitor, node Node) {
 			Walk(v, n.Doc)
 		}
 		Walk(v, n.Name)
-		walkTypeSpecParams(v, n)
+		if n.TParams != nil {
+			Walk(v, n.TParams)
+		}
 		Walk(v, n.Type)
 		if n.Comment != nil {
 			Walk(v, n.Comment)
@@ -363,7 +374,7 @@ func Walk(v Visitor, node Node) {
 		}
 
 	default:
-		walkOtherNodes(v, n)
+		panic(fmt.Sprintf("ast.Walk: unexpected node type %T", n))
 	}
 
 	v.Visit(nil)

src/go/ast/ast_typeparams.go

@@ -2,9 +2,6 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-//go:build typeparams
-// +build typeparams
-
 package typeparams
 
 import (