Follow upstream support for variables (#66)

Because the upstream [PR](https://github.com/nektos/act/pull/1833) already supports variables, so this PR revert #43 (commit de529139af), and cherry-pick commit [6ce45e3](6ce45e3f24).

Co-authored-by: Kuan Yong <wong0514@gmail.com>
Reviewed-on: https://gitea.com/gitea/act/pulls/66
Reviewed-by: Jason Song <i@wolfogre.com>
Co-authored-by: sillyguodong <gedong_1994@163.com>
Co-committed-by: sillyguodong <gedong_1994@163.com>

pkg/exprparser/interpreter.go

@@ -19,12 +19,11 @@ type EvaluationEnvironment struct {
 	Steps    map[string]*model.StepResult
 	Runner   map[string]interface{}
 	Secrets  map[string]string
+	Vars     map[string]string
 	Strategy map[string]interface{}
 	Matrix   map[string]interface{}
 	Needs    map[string]Needs
 	Inputs   map[string]interface{}
-
-	Vars map[string]string
 }
 
 type Needs struct {
@@ -150,6 +149,7 @@ func (impl *interperterImpl) evaluateNode(exprNode actionlint.ExprNode) (interfa
 	}
 }
 
+// nolint:gocyclo
 func (impl *interperterImpl) evaluateVariable(variableNode *actionlint.VariableNode) (interface{}, error) {
 	switch strings.ToLower(variableNode.Name) {
 	case "github":
@@ -171,6 +171,8 @@ func (impl *interperterImpl) evaluateVariable(variableNode *actionlint.VariableN
 		return impl.env.Runner, nil
 	case "secrets":
 		return impl.env.Secrets, nil
+	case "vars":
+		return impl.env.Vars, nil
 	case "strategy":
 		return impl.env.Strategy, nil
 	case "matrix":
@@ -183,8 +185,6 @@ func (impl *interperterImpl) evaluateVariable(variableNode *actionlint.VariableN
 		return math.Inf(1), nil
 	case "nan":
 		return math.NaN(), nil
-	case "vars":
-		return impl.env.Vars, nil
 	default:
 		return nil, fmt.Errorf("Unavailable context: %s", variableNode.Name)
 	}

pkg/exprparser/interpreter_test.go

@@ -557,6 +557,7 @@ func TestContexts(t *testing.T) {
 		// {"contains(steps.*.outputs.name, 'value')", true, "steps-context-array-outputs"},
 		{"runner.os", "Linux", "runner-context"},
 		{"secrets.name", "value", "secrets-context"},
+		{"vars.name", "value", "vars-context"},
 		{"strategy.fail-fast", true, "strategy-context"},
 		{"matrix.os", "Linux", "matrix-context"},
 		{"needs.job-id.outputs.output-name", "value", "needs-context"},
@@ -593,6 +594,9 @@ func TestContexts(t *testing.T) {
 		Secrets: map[string]string{
 			"name": "value",
 		},
+		Vars: map[string]string{
+			"name": "value",
+		},
 		Strategy: map[string]interface{}{
 			"fail-fast": true,
 		},