go/internal/typeparams: remove typeparams.{Get,Set} (cleanup)

These helper functions are no longer necessary, now that type parameters
are enabled; we can access type parameters directly.

When considering the existence or non-existence of type parameters, we
can either check whether node.TParams != nil, or whether
node.TParams.NumFields() > 0. The heuristic I'm using for deciding
between these checks is as follows:
 - For data access, just check node.TParams != nil.
 - For producing errors if type parameters exist, check NumFields() > 0.

Change-Id: I6597536898e975564e9e8bf6a3a91bc798e0f110
Reviewed-on: https://go-review.googlesource.com/c/go/+/346549
Trust: Robert Findley <rfindley@google.com>
Run-TryBot: Robert Findley <rfindley@google.com>
Reviewed-by: Robert Griesemer <gri@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>

src/go/internal/typeparams/typeparams.go

@@ -5,7 +5,6 @@
 package typeparams
 
 import (
-	"fmt"
 	"go/ast"
 	"go/token"
 )
@@ -54,25 +53,3 @@ func UnpackIndexExpr(n ast.Node) *IndexExpr {
 	}
 	return nil
 }
-
-func Get(n ast.Node) *ast.FieldList {
-	switch n := n.(type) {
-	case *ast.TypeSpec:
-		return n.TParams
-	case *ast.FuncType:
-		return n.TParams
-	default:
-		panic(fmt.Sprintf("node type %T has no type parameters", n))
-	}
-}
-
-func Set(n ast.Node, params *ast.FieldList) {
-	switch n := n.(type) {
-	case *ast.TypeSpec:
-		n.TParams = params
-	case *ast.FuncType:
-		n.TParams = params
-	default:
-		panic(fmt.Sprintf("node type %T has no type parameters", n))
-	}
-}

src/go/parser/parser.go

@@ -972,8 +972,12 @@ func (p *parser) parseMethodSpec() *ast.Field {
 				_, params := p.parseParameters(false)
 				results := p.parseResult()
 				idents = []*ast.Ident{ident}
-				typ = &ast.FuncType{Func: token.NoPos, Params: params, Results: results}
-				typeparams.Set(typ, tparams)
+				typ = &ast.FuncType{
+					Func:    token.NoPos,
+					TParams: tparams,
+					Params:  params,
+					Results: results,
+				}
 			} else {
 				// embedded instantiated type
 				// TODO(rfindley) should resolve all identifiers in x.
@@ -2505,7 +2509,7 @@ func (p *parser) parseValueSpec(doc *ast.CommentGroup, _ token.Pos, keyword toke
 func (p *parser) parseGenericType(spec *ast.TypeSpec, openPos token.Pos, name0 *ast.Ident, closeTok token.Token) {
 	list := p.parseParameterList(name0, closeTok, p.parseParamDecl, true)
 	closePos := p.expect(closeTok)
-	typeparams.Set(spec, &ast.FieldList{Opening: openPos, List: list, Closing: closePos})
+	spec.TParams = &ast.FieldList{Opening: openPos, List: list, Closing: closePos}
 	// Type alias cannot have type parameters. Accept them for robustness but complain.
 	if p.tok == token.ASSIGN {
 		p.error(p.pos, "generic type cannot be alias")
@@ -2636,12 +2640,12 @@ func (p *parser) parseFuncDecl() *ast.FuncDecl {
 		Name: ident,
 		Type: &ast.FuncType{
 			Func:    pos,
+			TParams: tparams,
 			Params:  params,
 			Results: results,
 		},
 		Body: body,
 	}
-	typeparams.Set(decl.Type, tparams)
 	return decl
 }
 

src/go/parser/resolver.go

@@ -7,7 +7,6 @@ package parser
 import (
 	"fmt"
 	"go/ast"
-	"go/internal/typeparams"
 	"go/token"
 )
 
@@ -455,10 +454,10 @@ func (r *resolver) Visit(node ast.Node) ast.Visitor {
 				// at the identifier in the TypeSpec and ends at the end of the innermost
 				// containing block.
 				r.declare(spec, nil, r.topScope, ast.Typ, spec.Name)
-				if tparams := typeparams.Get(spec); tparams != nil {
+				if spec.TParams != nil {
 					r.openScope(spec.Pos())
 					defer r.closeScope()
-					r.walkTParams(tparams)
+					r.walkTParams(spec.TParams)
 				}
 				ast.Walk(r, spec.Type)
 			}
@@ -474,8 +473,8 @@ func (r *resolver) Visit(node ast.Node) ast.Visitor {
 
 		// Type parameters are walked normally: they can reference each other, and
 		// can be referenced by normal parameters.
-		if tparams := typeparams.Get(n.Type); tparams != nil {
-			r.walkTParams(tparams)
+		if n.Type.TParams != nil {
+			r.walkTParams(n.Type.TParams)
 			// TODO(rFindley): need to address receiver type parameters.
 		}
 
@@ -539,9 +538,6 @@ func (r *resolver) walkFieldList(list *ast.FieldList, kind ast.ObjKind) {
 // that they may be resolved in the constraint expressions held in the field
 // Type.
 func (r *resolver) walkTParams(list *ast.FieldList) {
-	if list == nil {
-		return
-	}
 	r.declareList(list, ast.Typ)
 	r.resolveList(list)
 }

src/go/printer/nodes.go

@@ -11,7 +11,6 @@ package printer
 import (
 	"bytes"
 	"go/ast"
-	"go/internal/typeparams"
 	"go/token"
 	"math"
 	"strconv"
@@ -383,8 +382,8 @@ func (p *printer) parameters(fields *ast.FieldList, isTypeParam bool) {
 }
 
 func (p *printer) signature(sig *ast.FuncType) {
-	if tparams := typeparams.Get(sig); tparams != nil {
-		p.parameters(tparams, true)
+	if sig.TParams != nil {
+		p.parameters(sig.TParams, true)
 	}
 	if sig.Params != nil {
 		p.parameters(sig.Params, false)
@@ -1633,8 +1632,8 @@ func (p *printer) spec(spec ast.Spec, n int, doIndent bool) {
 	case *ast.TypeSpec:
 		p.setComment(s.Doc)
 		p.expr(s.Name)
-		if tparams := typeparams.Get(s); tparams != nil {
-			p.parameters(tparams, true)
+		if s.TParams != nil {
+			p.parameters(s.TParams, true)
 		}
 		if n == 1 {
 			p.print(blank)

src/go/types/decl.go

@@ -8,7 +8,6 @@ import (
 	"fmt"
 	"go/ast"
 	"go/constant"
-	"go/internal/typeparams"
 	"go/token"
 )
 
@@ -590,7 +589,7 @@ func (check *Checker) typeDecl(obj *TypeName, tdecl *ast.TypeSpec, def *Named) {
 	})
 
 	alias := tdecl.Assign.IsValid()
-	if alias && typeparams.Get(tdecl) != nil {
+	if alias && tdecl.TParams.NumFields() != 0 {
 		// The parser will ensure this but we may still get an invalid AST.
 		// Complain and continue as regular type definition.
 		check.error(atPos(tdecl.Assign), 0, "generic type cannot be alias")
@@ -613,10 +612,10 @@ func (check *Checker) typeDecl(obj *TypeName, tdecl *ast.TypeSpec, def *Named) {
 	named := check.newNamed(obj, nil, nil, nil, nil)
 	def.setUnderlying(named)
 
-	if tparams := typeparams.Get(tdecl); tparams != nil {
+	if tdecl.TParams != nil {
 		check.openScope(tdecl, "type parameters")
 		defer check.closeScope()
-		named.tparams = check.collectTypeParams(tparams)
+		named.tparams = check.collectTypeParams(tdecl.TParams)
 	}
 
 	// determine underlying type of named

src/go/types/interface.go

@@ -6,7 +6,6 @@ package types
 
 import (
 	"go/ast"
-	"go/internal/typeparams"
 	"go/token"
 )
 
@@ -195,8 +194,8 @@ func (check *Checker) interfaceType(ityp *Interface, iface *ast.InterfaceType, d
 		// a receiver specification.)
 		if sig.tparams != nil {
 			var at positioner = f.Type
-			if tparams := typeparams.Get(f.Type); tparams != nil {
-				at = tparams
+			if ftyp, _ := f.Type.(*ast.FuncType); ftyp != nil && ftyp.TParams != nil {
+				at = ftyp.TParams
 			}
 			check.errorf(at, _Todo, "methods cannot have type parameters")
 		}

src/go/types/signature.go

@@ -156,13 +156,13 @@ func (check *Checker) funcType(sig *Signature, recvPar *ast.FieldList, ftyp *ast
 		}
 	}
 
-	if tparams := typeparams.Get(ftyp); tparams != nil {
-		sig.tparams = check.collectTypeParams(tparams)
+	if ftyp.TParams != nil {
+		sig.tparams = check.collectTypeParams(ftyp.TParams)
 		// Always type-check method type parameters but complain that they are not allowed.
 		// (A separate check is needed when type-checking interface method signatures because
 		// they don't have a receiver specification.)
 		if recvPar != nil {
-			check.errorf(tparams, _Todo, "methods cannot have type parameters")
+			check.errorf(ftyp.TParams, _Todo, "methods cannot have type parameters")
 		}
 	}