Create v3 compiler which respects declaration order of variables

Also, fix "<no value>" been printed when a non-existing variable is printed.

internal/compiler/v3/compiler_v3.go

@@ -0,0 +1,98 @@
+package v3
+
+import (
+	"bytes"
+	"context"
+	"fmt"
+	"strings"
+	"sync"
+
+	"github.com/go-task/task/v2/internal/compiler"
+	"github.com/go-task/task/v2/internal/execext"
+	"github.com/go-task/task/v2/internal/logger"
+	"github.com/go-task/task/v2/internal/taskfile"
+	"github.com/go-task/task/v2/internal/templater"
+)
+
+var _ compiler.Compiler = &CompilerV3{}
+
+type CompilerV3 struct {
+	Dir string
+
+	TaskfileVars *taskfile.Vars
+
+	Logger *logger.Logger
+
+	dynamicCache   map[string]string
+	muDynamicCache sync.Mutex
+}
+
+func (c *CompilerV3) GetVariables(t *taskfile.Task, call taskfile.Call) (*taskfile.Vars, error) {
+	result := compiler.GetEnviron()
+	result.Set("TASK", taskfile.Var{Static: t.Task})
+
+	rangeFunc := func(k string, v taskfile.Var) error {
+		tr := templater.Templater{Vars: result, RemoveNoValue: true}
+		v = taskfile.Var{
+			Static: tr.Replace(v.Static),
+			Sh:     tr.Replace(v.Sh),
+		}
+		if err := tr.Err(); err != nil {
+			return err
+		}
+		static, err := c.HandleDynamicVar(v)
+		if err != nil {
+			return err
+		}
+		result.Set(k, taskfile.Var{Static: static})
+		return nil
+	}
+
+	if err := c.TaskfileVars.Range(rangeFunc); err != nil {
+		return nil, err
+	}
+	if err := call.Vars.Range(rangeFunc); err != nil {
+		return nil, err
+	}
+	if err := t.Vars.Range(rangeFunc); err != nil {
+		return nil, err
+	}
+
+	return result, nil
+}
+
+func (c *CompilerV3) HandleDynamicVar(v taskfile.Var) (string, error) {
+	if v.Static != "" || v.Sh == "" {
+		return v.Static, nil
+	}
+
+	c.muDynamicCache.Lock()
+	defer c.muDynamicCache.Unlock()
+
+	if c.dynamicCache == nil {
+		c.dynamicCache = make(map[string]string, 30)
+	}
+	if result, ok := c.dynamicCache[v.Sh]; ok {
+		return result, nil
+	}
+
+	var stdout bytes.Buffer
+	opts := &execext.RunCommandOptions{
+		Command: v.Sh,
+		Dir:     c.Dir,
+		Stdout:  &stdout,
+		Stderr:  c.Logger.Stderr,
+	}
+	if err := execext.RunCommand(context.Background(), opts); err != nil {
+		return "", fmt.Errorf(`task: Command "%s" in taskvars file failed: %s`, opts.Command, err)
+	}
+
+	// Trim a single trailing newline from the result to make most command
+	// output easier to use in shell commands.
+	result := strings.TrimSuffix(stdout.String(), "\n")
+
+	c.dynamicCache[v.Sh] = result
+	c.Logger.VerboseErrf(logger.Magenta, `task: dynamic variable: '%s' result: '%s'`, v.Sh, result)
+
+	return result, nil
+}