lang: core, funcs: Remove facts API

This started because it was possible, not because it was very useful.
The overhead of using the full function API, is lessened by the function
API helpers, and the upcoming improvements in the function API.

It's much easier to have one fewer API's to manage and so on.

It's also a stark reminder of how weak tools like "puppet" are which
only really have data collection systems that don't take arguments.

lang/core/test/fastcount.go

@@ -0,0 +1,137 @@
+// Mgmt
+// Copyright (C) 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 coretest
+
+import (
+	"context"
+	"fmt"
+	"sync"
+
+	"github.com/purpleidea/mgmt/lang/funcs"
+	"github.com/purpleidea/mgmt/lang/interfaces"
+	"github.com/purpleidea/mgmt/lang/types"
+)
+
+const (
+	// FastCountFuncName 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.
+	FastCountFuncName = "fastcount"
+)
+
+func init() {
+	funcs.ModuleRegister(ModuleName, FastCountFuncName, func() interfaces.Func { return &FastCount{} }) // must register the fact and name
+}
+
+// FastCount is a fact that counts up as fast as possible from zero forever.
+type FastCount struct {
+	init *interfaces.Init
+
+	mutex *sync.Mutex
+	count int
+}
+
+// String returns a simple name for this fact. This is needed so this struct can
+// satisfy the pgraph.Vertex interface.
+func (obj *FastCount) String() string {
+	return FastCountFuncName
+}
+
+// Validate makes sure we've built our struct properly.
+func (obj *FastCount) Validate() error {
+	return nil
+}
+
+// Info returns some static info about itself.
+func (obj *FastCount) Info() *interfaces.Info {
+	return &interfaces.Info{
+		Pure: false, // non-constant facts can't be pure!
+		Memo: false,
+		Fast: false,
+		Spec: false,
+		Sig:  types.NewType("func() int"),
+	}
+}
+
+// Init runs some startup code for this fact.
+func (obj *FastCount) Init(init *interfaces.Init) error {
+	obj.init = init
+	obj.mutex = &sync.Mutex{}
+	return nil
+}
+
+// Stream returns the changing values that this fact has over time.
+func (obj *FastCount) Stream(ctx context.Context) error {
+	defer close(obj.init.Output) // always signal when we're done
+
+	// We always wait for our initial event to start.
+	select {
+	case _, ok := <-obj.init.Input:
+		if ok {
+			return fmt.Errorf("unexpected input")
+		}
+		obj.init.Input = nil
+
+	case <-ctx.Done():
+		return nil
+	}
+
+	// streams must generate an initial event on startup
+	for {
+		result, err := obj.Call(ctx, nil)
+		if err != nil {
+			return err
+		}
+
+		obj.mutex.Lock()
+		obj.count++
+		obj.mutex.Unlock()
+
+		select {
+		case obj.init.Output <- result:
+
+		case <-ctx.Done():
+			return nil
+		}
+	}
+}
+
+// Call this fact and return the value if it is possible to do so at this time.
+func (obj *FastCount) Call(ctx context.Context, args []types.Value) (types.Value, error) {
+	if obj.mutex == nil {
+		return nil, funcs.ErrCantSpeculate
+	}
+	obj.mutex.Lock() // TODO: could be a read lock
+	count := obj.count
+	obj.mutex.Unlock()
+	return &types.IntValue{
+		V: int64(count),
+	}, nil
+}