feat(template): add toJson function

docs/notifications.md

@@ -83,20 +83,21 @@ templating.
 
 ## Strings
 
-| Name          | Arguments     | Returns  | Notes    |
-| ------------- | ------------- | -------- | -------- |
-| title | string |[strings.Title](http://golang.org/pkg/strings/#Title), capitalises first character of each word. |
-| toUpper | string | [strings.ToUpper](http://golang.org/pkg/strings/#ToUpper), converts all characters to upper case. |
-| toLower | string | [strings.ToLower](http://golang.org/pkg/strings/#ToLower), converts all characters to lower case. |
-| trimSpace | string | [strings.TrimSpace](https://pkg.go.dev/strings#TrimSpace), removes leading and trailing white spaces. |
-| match | pattern, string | [Regexp.MatchString](https://golang.org/pkg/regexp/#MatchString). Match a string using Regexp. |
-| reReplaceAll | pattern, replacement, text | [Regexp.ReplaceAllString](http://golang.org/pkg/regexp/#Regexp.ReplaceAllString) Regexp substitution, unanchored. |
-| join | sep string, s []string | [strings.Join](http://golang.org/pkg/strings/#Join), concatenates the elements of s to create a single string. The separator string sep is placed between elements in the resulting string. (note: argument order inverted for easier pipelining in templates.) |
-| safeHtml | text string | [html/template.HTML](https://golang.org/pkg/html/template/#HTML), Marks string as HTML not requiring auto-escaping. |
-| safeUrl | text string | [html/template.URL](https://golang.org/pkg/html/template/#URL), Marks string as URL not requiring auto-escaping. |
-| urlUnescape | text string | [url.QueryUnescape](https://pkg.go.dev/net/url#QueryUnescape), unescapes a URL with % encoding |
-| stringSlice | ...string | Returns the passed strings as a slice of strings. |
-| date | string, time.Time | Returns the text representation of the time in the specified format. For documentation on formats refer to [pkg.go.dev/time](https://pkg.go.dev/time#pkg-constants). |
-| tz | string, time.Time | Returns the time in the timezone. For example, Europe/Paris. |
-| since | time.Time | [time.Duration](https://pkg.go.dev/time#Since), returns the duration of how much time passed from the provided time till the current system time. |
-| humanizeDuration | number or string | Returns a human-readable string representing the duration, and the error if it happened. |
+| Name             | Arguments                  | Description |
+| ---------------- | -------------------------- | ----------- |
+| date             | string, time.Time          | Returns the text representation of the time in the specified format. For documentation on formats refer to [pkg.go.dev/time](https://pkg.go.dev/time#pkg-constants). |
+| humanizeDuration | number or string           | Returns a human-readable string representing the duration, and the error if it happened. |
+| join             | sep string, s []string     | [strings.Join](http://golang.org/pkg/strings/#Join), concatenates the elements of s to create a single string. The separator string sep is placed between elements in the resulting string. (note: argument order inverted for easier pipelining in templates.) |
+| match            | pattern, string            | [Regexp.MatchString](https://golang.org/pkg/regexp/#MatchString). Match a string using Regexp. |
+| reReplaceAll     | pattern, replacement, text | [Regexp.ReplaceAllString](http://golang.org/pkg/regexp/#Regexp.ReplaceAllString) Regexp substitution, unanchored. |
+| safeHtml         | text string                | [html/template.HTML](https://golang.org/pkg/html/template/#HTML), Marks string as HTML not requiring auto-escaping. |
+| safeUrl          | text string                | [html/template.URL](https://golang.org/pkg/html/template/#URL), Marks string as URL not requiring auto-escaping. |
+| since            | time.Time                  | [time.Since](https://pkg.go.dev/time#Since), returns the duration of how much time passed from the provided time till the current system time. |
+| stringSlice      | ...string                  | Returns the passed strings as a slice of strings. |
+| title            | string                     | [strings.Title](http://golang.org/pkg/strings/#Title), capitalises first character of each word. |
+| toJson           | any                        | [json.Marshal](https://pkg.go.dev/encoding/json#Marshal), returns the JSON encoding of the value. |
+| toLower          | string                     | [strings.ToLower](http://golang.org/pkg/strings/#ToLower), converts all characters to lower case. |
+| toUpper          | string                     | [strings.ToUpper](http://golang.org/pkg/strings/#ToUpper), converts all characters to upper case. |
+| trimSpace        | string                     | [strings.TrimSpace](https://pkg.go.dev/strings#TrimSpace), removes leading and trailing white spaces. |
+| tz               | string, time.Time          | Returns the time in the timezone. For example, Europe/Paris. |
+| urlUnescape      | text string                | [url.QueryUnescape](https://pkg.go.dev/net/url#QueryUnescape), unescapes a URL with % encoding |

template/template.go

@@ -15,6 +15,7 @@ package template
 
 import (
 	"bytes"
+	"encoding/json"
 	tmplhtml "html/template"
 	"io"
 	"net/url"
@@ -213,6 +214,13 @@ var DefaultFuncs = FuncMap{
 	},
 	"since":            time.Since,
 	"humanizeDuration": commonTemplates.HumanizeDuration,
+	"toJson": func(v any) (string, error) {
+		bytes, err := json.Marshal(v)
+		if err != nil {
+			return "", err
+		}
+		return string(bytes), nil
+	},
 }
 
 // Pair is a key/value string pair.

template/template_test.go

@@ -401,6 +401,65 @@ func TestTemplateExpansion(t *testing.T) {
 			},
 			exp: "[key2 key4]",
 		},
+		{
+			title: "Template using toJson with string",
+			in:    `{{ "test" | toJson }}`,
+			exp:   `"test"`,
+		},
+		{
+			title: "Template using toJson with number",
+			in:    `{{ 42 | toJson }}`,
+			exp:   `42`,
+		},
+		{
+			title: "Template using toJson with boolean",
+			in:    `{{ true | toJson }}`,
+			exp:   `true`,
+		},
+		{
+			title: "Template using toJson with map",
+			in:    `{{ . | toJson }}`,
+			data:  map[string]any{"key": "value", "number": 123},
+			exp:   `{"key":"value","number":123}`,
+		},
+		{
+			title: "Template using toJson with slice",
+			in:    `{{ . | toJson }}`,
+			data:  []string{"a", "b", "c"},
+			exp:   `["a","b","c"]`,
+		},
+		{
+			title: "Template using toJson with KV",
+			in:    `{{ .CommonLabels | toJson }}`,
+			data: Data{
+				CommonLabels: KV{"severity": "critical", "job": "foo"},
+			},
+			exp: `{"job":"foo","severity":"critical"}`,
+		},
+		{
+			title: "Template using toJson with Alerts",
+			in:    `{{ .Alerts | toJson }}`,
+			data: Data{
+				Alerts: Alerts{
+					{
+						Status: "firing",
+						Labels: KV{"alertname": "test"},
+					},
+				},
+			},
+			exp: `[{"status":"firing","labels":{"alertname":"test"},"annotations":null,"startsAt":"0001-01-01T00:00:00Z","endsAt":"0001-01-01T00:00:00Z","generatorURL":"","fingerprint":""}]`,
+		},
+		{
+			title: "Template using toJson with Alerts.Firing()",
+			in:    `{{ .Alerts.Firing | toJson }}`,
+			data: Data{
+				Alerts: Alerts{
+					{Status: "firing"},
+					{Status: "resolved"},
+				},
+			},
+			exp: `[{"status":"firing","labels":null,"annotations":null,"startsAt":"0001-01-01T00:00:00Z","endsAt":"0001-01-01T00:00:00Z","generatorURL":"","fingerprint":""}]`,
+		},
 	} {
 		t.Run(tc.title, func(t *testing.T) {
 			f := tmpl.ExecuteTextString
@@ -575,6 +634,25 @@ func TestTemplateFuncs(t *testing.T) {
 		in:    "{{ . | since | humanizeDuration }}",
 		data:  time.Now().Add(-1 * time.Hour),
 		exp:   "1h 0m 0s",
+	}, {
+		title: "Template using toJson with string",
+		in:    `{{ "hello" | toJson }}`,
+		exp:   `"hello"`,
+	}, {
+		title: "Template using toJson with map",
+		in:    `{{ . | toJson }}`,
+		data:  map[string]string{"key": "value"},
+		exp:   `{"key":"value"}`,
+	}, {
+		title: "Template using toJson with Alerts.Firing()",
+		in:    `{{ .Alerts.Firing | toJson }}`,
+		data: Data{
+			Alerts: Alerts{
+				{Status: "firing", Labels: KV{"alertname": "test"}},
+				{Status: "resolved"},
+			},
+		},
+		exp: `[{"status":"firing","labels":{"alertname":"test"},"annotations":null,"startsAt":"0001-01-01T00:00:00Z","endsAt":"0001-01-01T00:00:00Z","generatorURL":"","fingerprint":""}]`,
 	}} {
 		t.Run(tc.title, func(t *testing.T) {
 			wg := sync.WaitGroup{}