cmd/cgo: walk {FuncType,TypeSpec}.TypeParams fields

This CL updates the cgo tool to walk the TypeParams fields for
function types and type declarations, so that C.xxx identifiers can
appear within type parameter lists.

Fixes #52542.

Change-Id: Id02a88d529d50fe59b0a834f415c2575204ffd1f
Reviewed-on: https://go-review.googlesource.com/c/go/+/453977
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Auto-Submit: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

misc/cgo/test/test.go

@@ -2295,3 +2295,9 @@ func test45451(t *testing.T) {
 	_ = reflect.New(typ)
 	t.Errorf("reflect.New(%v) should have panicked", typ)
 }
+
+// issue 52542
+
+func func52542[T ~[]C.int]() {}
+
+type type52542[T ~*C.float] struct{}

src/cmd/cgo/ast.go

@@ -409,6 +409,9 @@ func (f *File) walk(x interface{}, context astContext, visit func(*File, interfa
 	case *ast.StructType:
 		f.walk(n.Fields, ctxField, visit)
 	case *ast.FuncType:
+		if tparams := funcTypeTypeParams(n); tparams != nil {
+			f.walk(tparams, ctxParam, visit)
+		}
 		f.walk(n.Params, ctxParam, visit)
 		if n.Results != nil {
 			f.walk(n.Results, ctxParam, visit)
@@ -496,6 +499,9 @@ func (f *File) walk(x interface{}, context astContext, visit func(*File, interfa
 			f.walk(n.Values, ctxExpr, visit)
 		}
 	case *ast.TypeSpec:
+		if tparams := typeSpecTypeParams(n); tparams != nil {
+			f.walk(tparams, ctxParam, visit)
+		}
 		f.walk(&n.Type, ctxType, visit)
 
 	case *ast.BadDecl:

src/cmd/cgo/ast_go1.go

@@ -7,6 +7,7 @@
 package main
 
 import (
+	"go/ast"
 	"go/token"
 )
 
@@ -14,3 +15,11 @@ func (f *File) walkUnexpected(x interface{}, context astContext, visit func(*Fil
 	error_(token.NoPos, "unexpected type %T in walk", x)
 	panic("unexpected type")
 }
+
+func funcTypeTypeParams(n *ast.FuncType) *ast.FieldList {
+	return nil
+}
+
+func typeSpecTypeParams(n *ast.TypeSpec) *ast.FieldList {
+	return nil
+}

src/cmd/cgo/ast_go118.go

@@ -22,3 +22,11 @@ func (f *File) walkUnexpected(x interface{}, context astContext, visit func(*Fil
 		f.walk(n.Indices, ctxExpr, visit)
 	}
 }
+
+func funcTypeTypeParams(n *ast.FuncType) *ast.FieldList {
+	return n.TypeParams
+}
+
+func typeSpecTypeParams(n *ast.TypeSpec) *ast.FieldList {
+	return n.TypeParams
+}