pkg/apis/nfd: support templating of "vars"

Support templating of var names in a similar manner as labels. Add
support for a new 'varsTemplate' field to the feature rule spec which is
treated similarly to the 'labelsTemplate' field. The value of the field
is processed through the golang "text/template" template engine and the
expanded value must contain variables in a raw <key>[=<value>] format
(where 'value' defaults to "true"), separated by
newlines i.e.:

  - name: <rule-name>
    varsTemplate: |
      <label-1>[=<value-1>]
      <label-2>[=<value-2>]
      ...

Similar rules as for 'labelsTemplate' apply, i.e.

1. In case of matchAny is specified, the template is executed separately
   against each individual matchFeatures matcher.
2. 'vars' field has priority over 'varsTemplate'

deployment/base/nfd-crds/nodefeaturerule-crd.yaml

@@ -197,6 +197,12 @@ spec:
                         more complex rule hierarchies, without exposing intermediary
                         output values as labels.
                       type: object
+                    varsTemplate:
+                      description: VarsTemplate specifies a template to expand for
+                        dynamically generating multiple variables. Data (after template
+                        expansion) must be keys with an optional value (<key>[=<value>])
+                        separated by newlines.
+                      type: string
                   required:
                   - name
                   type: object

deployment/helm/node-feature-discovery/manifests/nodefeaturerule-crd.yaml

@@ -197,6 +197,12 @@ spec:
                         more complex rule hierarchies, without exposing intermediary
                         output values as labels.
                       type: object
+                    varsTemplate:
+                      description: VarsTemplate specifies a template to expand for
+                        dynamically generating multiple variables. Data (after template
+                        expansion) must be keys with an optional value (<key>[=<value>])
+                        separated by newlines.
+                      type: string
                   required:
                   - name
                   type: object

pkg/apis/nfd/v1alpha1/rule.go

@@ -58,7 +58,9 @@ func (r *Rule) Execute(features feature.Features) (RuleOutput, error) {
 				if err := r.executeLabelsTemplate(m, labels); err != nil {
 					return RuleOutput{}, err
 				}
-
+				if err := r.executeVarsTemplate(m, vars); err != nil {
+					return RuleOutput{}, err
+				}
 			}
 		}
 		if !matched {
@@ -78,6 +80,9 @@ func (r *Rule) Execute(features feature.Features) (RuleOutput, error) {
 			if err := r.executeLabelsTemplate(m, labels); err != nil {
 				return RuleOutput{}, err
 			}
+			if err := r.executeVarsTemplate(m, vars); err != nil {
+				return RuleOutput{}, err
+			}
 		}
 	}
 
@@ -117,6 +122,28 @@ func (r *Rule) executeLabelsTemplate(in matchedFeatures, out map[string]string)
 	return nil
 }
 
+func (r *Rule) executeVarsTemplate(in matchedFeatures, out map[string]string) error {
+	if r.VarsTemplate == "" {
+		return nil
+	}
+	if r.varsTemplate == nil {
+		t, err := newTemplateHelper(r.VarsTemplate)
+		if err != nil {
+			return err
+		}
+		r.varsTemplate = t
+	}
+
+	vars, err := r.varsTemplate.expandMap(in)
+	if err != nil {
+		return err
+	}
+	for k, v := range vars {
+		out[k] = v
+	}
+	return nil
+}
+
 type matchedFeatures map[string]domainMatchedFeatures
 
 type domainMatchedFeatures map[string]interface{}

pkg/apis/nfd/v1alpha1/rule_test.go

@@ -254,6 +254,12 @@ label-2=
 {{range .domain_1.vf_1}}vf-{{.Name}}=vf-{{.Value}}
 {{end}}
 {{range .domain_1.if_1}}if-{{index . "attr-1"}}_{{index . "attr-2"}}=present
+{{end}}`,
+		Vars: map[string]string{"var-1": "var-val-1"},
+		VarsTemplate: `
+var-1=value-will-be-overridden-by-vars
+var-2=
+{{range .domain_1.kf_1}}kf-{{.Name}}
 {{end}}`,
 		MatchFeatures: FeatureMatcher{
 			FeatureMatcherTerm{
@@ -297,8 +303,17 @@ label-2=
 		"if-1_val-2":   "present",
 		"if-10_val-20": "present",
 	}
+	expectedVars := map[string]string{
+		"var-1": "var-val-1",
+		"var-2": "",
+		// From template
+		"kf-key-a": "true",
+		"kf-key-c": "true",
+		"kf-foo":   "true",
+	}
 
 	m, err := r1.Execute(f)
 	assert.Nilf(t, err, "unexpected error: %v", err)
 	assert.Equal(t, expectedLabels, m.Labels, "instances should have matched")
+	assert.Equal(t, expectedVars, m.Vars, "instances should have matched")
 }

pkg/apis/nfd/v1alpha1/types.go

@@ -72,6 +72,12 @@ type Rule struct {
 	// +optional
 	Vars map[string]string `json:"vars"`
 
+	// VarsTemplate specifies a template to expand for dynamically generating
+	// multiple variables. Data (after template expansion) must be keys with an
+	// optional value (<key>[=<value>]) separated by newlines.
+	// +optional
+	VarsTemplate string `json:"varsTemplate"`
+
 	// MatchFeatures specifies a set of matcher terms all of which must match.
 	// +optional
 	MatchFeatures FeatureMatcher `json:"matchFeatures"`