lang: Unnested the core package from the functions dir

The core package could contain non-functions, so we might as well move
it upwards.

lang/core/sys/hostname_fact.go

@@ -0,0 +1,80 @@
+// Mgmt
+// Copyright (C) 2013-2024+ James Shubin and the project contributors
+// Written by James Shubin <james@shubin.ca> and the project contributors
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package coresys
+
+import (
+	"context"
+
+	"github.com/purpleidea/mgmt/lang/funcs/facts"
+	"github.com/purpleidea/mgmt/lang/types"
+)
+
+const (
+	// HostnameFuncName is the name this fact is registered as. It's still a
+	// Func Name because this is the name space the fact is actually using.
+	HostnameFuncName = "hostname"
+)
+
+func init() {
+	facts.ModuleRegister(ModuleName, HostnameFuncName, func() facts.Fact { return &HostnameFact{} }) // must register the fact and name
+}
+
+// HostnameFact is a function that returns the hostname.
+// TODO: support hostnames that change in the future.
+type HostnameFact struct {
+	init *facts.Init
+}
+
+// String returns a simple name for this fact. This is needed so this struct can
+// satisfy the pgraph.Vertex interface.
+func (obj *HostnameFact) String() string {
+	return HostnameFuncName
+}
+
+// Validate makes sure we've built our struct properly. It is usually unused for
+// normal facts that users can use directly.
+//func (obj *HostnameFact) Validate() error {
+//	return nil
+//}
+
+// Info returns some static info about itself.
+func (obj *HostnameFact) Info() *facts.Info {
+	return &facts.Info{
+		Output: types.NewType("str"),
+	}
+}
+
+// Init runs some startup code for this fact.
+func (obj *HostnameFact) Init(init *facts.Init) error {
+	obj.init = init
+	return nil
+}
+
+// Stream returns the single value that this fact has, and then closes.
+func (obj *HostnameFact) Stream(ctx context.Context) error {
+	select {
+	case obj.init.Output <- &types.StrValue{
+		V: obj.init.Hostname,
+	}:
+		// pass
+	case <-ctx.Done():
+		return nil
+	}
+	close(obj.init.Output) // signal that we're done sending
+	return nil
+}