Improve template helper functions: string/slice (#24266)

Follow #23328

The improvements:

1. The `contains` functions are covered by tests
2. The inconsistent behavior of `containGeneric` is replaced by
`StringUtils.Contains` and `SliceUtils.Contains`
3. In the future we can move more help functions into XxxUtils to
simplify the `helper.go` and reduce unnecessary global functions.

FAQ:

1. Why it's called `StringUtils.Contains` but not `strings.Contains`
like Golang?

Because our `StringUtils` is not Golang's `strings` package. There will
be our own string functions.

---------

Co-authored-by: silverwind <me@silverwind.io>

modules/templates/util_dict.go

@@ -0,0 +1,121 @@
+// Copyright 2023 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package templates
+
+import (
+	"fmt"
+	"html"
+	"html/template"
+	"reflect"
+
+	"code.gitea.io/gitea/modules/json"
+	"code.gitea.io/gitea/modules/setting"
+)
+
+func dictMerge(base map[string]any, arg any) bool {
+	if arg == nil {
+		return true
+	}
+	rv := reflect.ValueOf(arg)
+	if rv.Kind() == reflect.Map {
+		for _, k := range rv.MapKeys() {
+			base[k.String()] = rv.MapIndex(k).Interface()
+		}
+		return true
+	}
+	return false
+}
+
+// dict is a helper function for creating a map[string]any from a list of key-value pairs.
+// If the key is dot ".", the value is merged into the base map, just like Golang template's dot syntax: dot means current
+// The dot syntax is highly discouraged because it might cause unclear key conflicts. It's always good to use explicit keys.
+func dict(args ...any) (map[string]any, error) {
+	if len(args)%2 != 0 {
+		return nil, fmt.Errorf("invalid dict constructor syntax: must have key-value pairs")
+	}
+	m := make(map[string]any, len(args)/2)
+	for i := 0; i < len(args); i += 2 {
+		key, ok := args[i].(string)
+		if !ok {
+			return nil, fmt.Errorf("invalid dict constructor syntax: unable to merge args[%d]", i)
+		}
+		if key == "." {
+			if ok = dictMerge(m, args[i+1]); !ok {
+				return nil, fmt.Errorf("invalid dict constructor syntax: dot arg[%d] must be followed by a dict", i)
+			}
+		} else {
+			m[key] = args[i+1]
+		}
+	}
+	return m, nil
+}
+
+func dumpVarMarshalable(v any, dumped map[uintptr]bool) (ret any, ok bool) {
+	if v == nil {
+		return nil, true
+	}
+	e := reflect.ValueOf(v)
+	for e.Kind() == reflect.Pointer {
+		e = e.Elem()
+	}
+	if e.CanAddr() {
+		addr := e.UnsafeAddr()
+		if dumped[addr] {
+			return "[dumped]", false
+		}
+		dumped[addr] = true
+		defer delete(dumped, addr)
+	}
+	switch e.Kind() {
+	case reflect.Bool, reflect.String,
+		reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64,
+		reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64,
+		reflect.Float32, reflect.Float64:
+		return e.Interface(), true
+	case reflect.Struct:
+		m := map[string]any{}
+		for i := 0; i < e.NumField(); i++ {
+			k := e.Type().Field(i).Name
+			if !e.Type().Field(i).IsExported() {
+				continue
+			}
+			v := e.Field(i).Interface()
+			m[k], _ = dumpVarMarshalable(v, dumped)
+		}
+		return m, true
+	case reflect.Map:
+		m := map[string]any{}
+		for _, k := range e.MapKeys() {
+			m[k.String()], _ = dumpVarMarshalable(e.MapIndex(k).Interface(), dumped)
+		}
+		return m, true
+	case reflect.Array, reflect.Slice:
+		var m []any
+		for i := 0; i < e.Len(); i++ {
+			v, _ := dumpVarMarshalable(e.Index(i).Interface(), dumped)
+			m = append(m, v)
+		}
+		return m, true
+	default:
+		return "[" + reflect.TypeOf(v).String() + "]", false
+	}
+}
+
+// dumpVar helps to dump a variable in a template, to help debugging and development.
+func dumpVar(v any) template.HTML {
+	if setting.IsProd {
+		return "<pre>dumpVar: only available in dev mode</pre>"
+	}
+	m, ok := dumpVarMarshalable(v, map[uintptr]bool{})
+	dumpStr := ""
+	jsonBytes, err := json.MarshalIndent(m, "", "  ")
+	if err != nil {
+		dumpStr = fmt.Sprintf("dumpVar: unable to marshal %T: %v", v, err)
+	} else if ok {
+		dumpStr = fmt.Sprintf("dumpVar: %T\n%s", v, string(jsonBytes))
+	} else {
+		dumpStr = fmt.Sprintf("dumpVar: unmarshalable %T\n%s", v, string(jsonBytes))
+	}
+	return template.HTML("<pre>" + html.EscapeString(dumpStr) + "</pre>")
+}