lang: core: deploy: Add a function to get the binary path

Useful for bootstrapping new machines.

examples/lang/binarypath.mcl

@@ -0,0 +1,5 @@
+import "deploy"
+
+print "debug" {
+	msg => deploy.binary_path(),
+}

lang/core/deploy/binary_func.go

@@ -0,0 +1,69 @@
+// 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 <https://www.gnu.org/licenses/>.
+//
+// Additional permission under GNU GPL version 3 section 7
+//
+// If you modify this program, or any covered work, by linking or combining it
+// with embedded mcl code and modules (and that the embedded mcl code and
+// modules which link with this program, contain a copy of their source code in
+// the authoritative form) containing parts covered by the terms of any other
+// license, the licensors of this program grant you additional permission to
+// convey the resulting work. Furthermore, the licensors of this program grant
+// the original author, James Shubin, additional permission to update this
+// additional permission if he deems it necessary to achieve the goals of this
+// additional permission.
+
+package coredeploy
+
+import (
+	"context"
+	"os"
+	"path/filepath"
+
+	"github.com/purpleidea/mgmt/lang/funcs/simple"
+	"github.com/purpleidea/mgmt/lang/types"
+)
+
+func init() {
+	simple.ModuleRegister(ModuleName, "binary_path", &simple.Scaffold{
+		T: types.NewType("func() str"),
+		F: BinaryPath,
+	})
+}
+
+// BinaryPath returns the path to the binary of this program. This is useful for
+// bootstrapping new machines when we want to get the path to copy it over from.
+func BinaryPath(ctx context.Context, input []types.Value) (types.Value, error) {
+	p1, err := os.Executable()
+	if err != nil {
+		return nil, err
+	}
+
+	p2, err := filepath.EvalSymlinks(p1)
+	if err != nil {
+		return nil, err
+	}
+
+	p3, err := filepath.Abs(p2)
+	if err != nil {
+		return nil, err
+	}
+
+	return &types.StrValue{
+		V: p3,
+	}, nil
+}