lang: core: local: Add a new vardir function

This gives us a function to return a created vardir folder. It is not
locally namespaced, and a future function will have to namespace one to
each scope.

examples/lang/vardir.mcl

@@ -0,0 +1,6 @@
+import "fmt"
+import "local"
+
+print "debug" {
+	msg => local.vardir("foo1/"),
+}

lang/core/core.go

@@ -45,6 +45,7 @@ import (
 	_ "github.com/purpleidea/mgmt/lang/core/fmt"
 	_ "github.com/purpleidea/mgmt/lang/core/iter"
 	_ "github.com/purpleidea/mgmt/lang/core/list"
+	_ "github.com/purpleidea/mgmt/lang/core/local"
 	_ "github.com/purpleidea/mgmt/lang/core/map"
 	_ "github.com/purpleidea/mgmt/lang/core/math"
 	_ "github.com/purpleidea/mgmt/lang/core/net"

lang/core/local/local.go

@@ -0,0 +1,35 @@
+// Mgmt
+// Copyright (C) 2013-2024+ James Shubin and the project contributors
+// Written by James Shubin <[email protected]> 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 corelocal
+
+const (
+	// ModuleName is the prefix given to all the functions in this module.
+	ModuleName = "local"
+)

lang/core/local/vardir_func.go

@@ -0,0 +1,184 @@
+// Mgmt
+// Copyright (C) 2013-2024+ James Shubin and the project contributors
+// Written by James Shubin <[email protected]> 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 corelocal
+
+import (
+	"context"
+	"fmt"
+	"path"
+	"strings"
+
+	"github.com/purpleidea/mgmt/lang/funcs"
+	"github.com/purpleidea/mgmt/lang/interfaces"
+	"github.com/purpleidea/mgmt/lang/types"
+)
+
+const (
+	// VarDirFunctionsPrefix is the prefix we prepend to any VarDir path
+	// request, so that if the local.VarDir API is used elsewhere, it
+	// doesn't conflict with what we're doing here.
+	VarDirFunctionsPrefix = "functions/"
+
+	// VarDirFuncName is the name this function is registered as.
+	VarDirFuncName = "vardir"
+
+	// arg names...
+	absPathArgNamePath = "path"
+)
+
+func init() {
+	// TODO: Add a function named UniqVarDir which returns a path within a
+	// private namespace that is unique to the caller of the function. IOW,
+	// we probably want to prepend the obj.data.Base path onto the path
+	// before we call local.VarDir().
+	funcs.ModuleRegister(ModuleName, VarDirFuncName, func() interfaces.Func { return &VarDirFunc{} }) // must register the func and name
+}
+
+// VarDirFunc is a function that returns the absolute, full path in the deploy
+// from an input path that is relative to the calling file. If you pass it an
+// empty string, you'll just get the absolute deploy directory path that you're
+// in.
+type VarDirFunc struct {
+	init *interfaces.Init
+	data *interfaces.FuncData
+	last types.Value // last value received to use for diff
+
+	path *string // the active path
+}
+
+// String returns a simple name for this function. This is needed so this struct
+// can satisfy the pgraph.Vertex interface.
+func (obj *VarDirFunc) String() string {
+	return VarDirFuncName
+}
+
+// SetData is used by the language to pass our function some code-level context.
+func (obj *VarDirFunc) SetData(data *interfaces.FuncData) {
+	obj.data = data
+}
+
+// ArgGen returns the Nth arg name for this function.
+func (obj *VarDirFunc) ArgGen(index int) (string, error) {
+	seq := []string{absPathArgNamePath}
+	if l := len(seq); index >= l {
+		return "", fmt.Errorf("index %d exceeds arg length of %d", index, l)
+	}
+	return seq[index], nil
+}
+
+// Validate makes sure we've built our struct properly. It is usually unused for
+// normal functions that users can use directly.
+func (obj *VarDirFunc) Validate() error {
+	return nil
+}
+
+// Info returns some static info about itself.
+func (obj *VarDirFunc) Info() *interfaces.Info {
+	return &interfaces.Info{
+		Pure: true,
+		Memo: false,
+		Sig:  types.NewType(fmt.Sprintf("func(%s str) str", absPathArgNamePath)),
+	}
+}
+
+// Init runs some startup code for this function.
+func (obj *VarDirFunc) Init(init *interfaces.Init) error {
+	obj.init = init
+	if obj.data == nil {
+		// programming error
+		return fmt.Errorf("missing function data")
+	}
+	return nil
+}
+
+// Stream returns the changing values that this func has over time.
+func (obj *VarDirFunc) Stream(ctx context.Context) error {
+	defer close(obj.init.Output) // the sender closes
+	var value types.Value
+	for {
+		select {
+		case input, ok := <-obj.init.Input:
+			if !ok {
+				obj.init.Input = nil // don't infinite loop back
+				continue             // no more inputs, but don't return!
+			}
+			//if err := input.Type().Cmp(obj.Info().Sig.Input); err != nil {
+			//	return errwrap.Wrapf(err, "wrong function input")
+			//}
+
+			if obj.last != nil && input.Cmp(obj.last) == nil {
+				continue // value didn't change, skip it
+			}
+			obj.last = input // store for next
+
+			args, err := interfaces.StructToCallableArgs(input) // []types.Value, error)
+			if err != nil {
+				return err
+			}
+			result, err := obj.Call(ctx, args)
+			if err != nil {
+				return err
+			}
+			value = result
+
+		case <-ctx.Done():
+			return nil
+		}
+
+		select {
+		case obj.init.Output <- value:
+		case <-ctx.Done():
+			return nil
+		}
+	}
+}
+
+// Call this function with the input args and return the value if it is possible
+// to do so at this time.
+func (obj *VarDirFunc) Call(ctx context.Context, input []types.Value) (types.Value, error) {
+	reldir := input[0].Str()
+	if strings.HasPrefix(reldir, "/") {
+		return nil, fmt.Errorf("path must be relative")
+	}
+	if !strings.HasSuffix(reldir, "/") {
+		return nil, fmt.Errorf("path must be a dir")
+	}
+	// NOTE: The above checks ensure we don't get either "" or "/" as input!
+
+	p := fmt.Sprintf("%s/", path.Join(prefix, reldir))
+
+	result, err := obj.init.Local.VarDir(ctx, p)
+	if err != nil {
+		return nil, err
+	}
+	return &types.StrValue{
+		V: result,
+	}, nil
+}