feat(templates-repo): add support for stdlib template options

templates-repo/options.go

@@ -29,13 +29,14 @@ type (
 	// options holds the settings of a repository, the sources it is yet to read, and the first
 	// option that rejected its arguments.
 	options struct {
-		sources     []source
-		funcs       template.FuncMap
-		extensions  []string
-		roots       []string
-		coverPrefix string
-		err         error
-		coverage    bool
+		sources        []source
+		funcs          template.FuncMap
+		extensions     []string
+		roots          []string
+		coverPrefix    string
+		err            error
+		coverage       bool
+		templateOption string
 	}
 )
 
@@ -258,3 +259,25 @@ func WithCoverage(prefix string) Option {
 		return o
 	}
 }
+
+// MissingKeyBehavior exposes the options provided by [template.Template].
+type MissingKeyBehavior string
+
+const (
+	MissingKeyBehaviorDefault MissingKeyBehavior = "missingkey=default"
+	MissingKeyBehaviorZero    MissingKeyBehavior = "missingkey=zero"
+	MissingKeyBehaviorError   MissingKeyBehavior = "missingkey=error"
+)
+
+// WithMissingKey instructs templates to be built with the options provided by [template.Template]:
+//
+//   - [MissingKeyBehaviorDefault]: execution continues on missing keys on maps, the value is set to "<no value>".
+//   - [MissingKeyBehaviorZero]: execution continues with the value set to the zero value of the element type.
+//   - [MissingKeyBehaviorError]: execution stops with an error
+func WithMissingKey(onMissingKey MissingKeyBehavior) Option {
+	return func(o options) options {
+		o.templateOption = string(onMissingKey)
+
+		return o
+	}
+}

templates-repo/repository.go

@@ -434,6 +434,10 @@ func parseAssets(assets []asset, settings options) (parsedAssets, error) {
 				fmt.Errorf("could not parse template %q from asset %q: %w: %w", owner, item.path, err, ErrTemplateRepo)
 		}
 
+		if settings.templateOption != "" {
+			tpl = tpl.Option(settings.templateOption)
+		}
+
 		declaredHere := make(map[string]*declared, len(tpl.Templates()))
 		for _, found := range tpl.Templates() {
 			if found.Tree == nil {