Add List function for struct field names and map keys

tpl/debug/debug.go

@@ -16,6 +16,7 @@ package debug
 
 import (
 	"encoding/json"
+	"reflect"
 	"sort"
 	"sync"
 	"time"
@@ -120,6 +121,67 @@ func (ns *Namespace) VisualizeSpaces(val any) string {
 	return string(util.VisualizeSpaces([]byte(s)))
 }
 
+// List returns a string slice of field names and methods for structs/pointers,
+// or keys for maps. This function uses reflection and is non-recursive.
+// For structs and pointers to structs, it returns all exported field names and method names.
+// Method names include both value and pointer receiver methods.
+// For maps, it returns all keys converted to strings.
+// For other types, it returns an empty slice.
+func (ns *Namespace) List(val any) []string {
+	if val == nil {
+		return []string{}
+	}
+
+	v := reflect.ValueOf(val)
+	t := v.Type()
+
+	// Handle pointers by dereferencing them
+	if t.Kind() == reflect.Ptr {
+		if v.IsNil() {
+			return []string{}
+		}
+		v = v.Elem()
+		t = v.Type()
+	}
+
+	var names []string
+
+	switch t.Kind() {
+	case reflect.Struct:
+		// Get field names
+		for i := 0; i < t.NumField(); i++ {
+			field := t.Field(i)
+			if field.IsExported() {
+				names = append(names, field.Name)
+			}
+		}
+
+		// Get method names (use pointer type to get all methods)
+		ptrType := reflect.PointerTo(t)
+		for i := 0; i < ptrType.NumMethod(); i++ {
+			method := ptrType.Method(i)
+			if method.IsExported() {
+				names = append(names, method.Name)
+			}
+		}
+
+	case reflect.Map:
+		// Get map keys as strings
+		for _, key := range v.MapKeys() {
+			keyStr := cast.ToString(key.Interface())
+			names = append(names, keyStr)
+		}
+
+	default:
+		// For other types, return empty slice
+		return []string{}
+	}
+
+	// Sort the names for consistent output
+	sort.Strings(names)
+	return names
+}
+
 func (ns *Namespace) Timer(name string) Timer {
 	if ns.timers == nil {
 		return nopTimer

tpl/debug/debug_integration_test.go

@@ -73,3 +73,41 @@ Dump: {{ debug.Dump . | safeHTML }}
 	b := hugolib.TestRunning(t, files)
 	b.AssertFileContent("public/index.html", "Dump: {\n  \"Date\": \"2012-03-15T00:00:00Z\"")
 }
+
+func TestDebugList(t *testing.T) {
+	files := `
+-- hugo.toml --
+baseURL = "https://example.org/"
+disableLiveReload = true
+-- content/_index.md --
+---
+title: "The Index"
+---
+-- layouts/_default/list.html --
+{{ $dict := dict "name" "Hugo" "version" "0.120" "type" "SSG" }}
+Map Keys: {{ debug.List $dict }}
+
+{{ $page := . }}
+Page Fields: {{ debug.List $page }}
+
+Nil: {{ debug.List nil }}
+String: {{ debug.List "hello" }}
+Number: {{ debug.List 42 }}
+Slice: {{ debug.List (slice 1 2 3) }}
+`
+	b := hugolib.TestRunning(t, files)
+
+	// Test map keys
+	b.AssertFileContent("public/index.html", "Map Keys: [name type version]")
+
+	// Test that page struct returns field names and methods (should include common page fields)
+	b.AssertFileContent("public/index.html", "Page Fields:")
+	b.AssertFileContent("public/index.html", "Title")
+	b.AssertFileContent("public/index.html", "Content")
+
+	// Test edge cases
+	b.AssertFileContent("public/index.html", "Nil: []")
+	b.AssertFileContent("public/index.html", "String: []")
+	b.AssertFileContent("public/index.html", "Number: []")
+	b.AssertFileContent("public/index.html", "Slice: []")
+}

tpl/debug/init.go

@@ -40,6 +40,14 @@ func init() {
 			},
 		)
 
+		ns.AddMethodMapping(ctx.List,
+			nil,
+			[][2]string{
+				{`{{ $s := dict "name" "Hugo" "type" "SSG" }}
+{{ debug.List $s }}`, `[name type]`},
+			},
+		)
+
 		return ns
 	}