feat: implement thin vertical slice of system-generated notifications (#13537)

coderd/notifications/render/gotmpl.go

@@ -0,0 +1,26 @@
+package render
+
+import (
+	"strings"
+	"text/template"
+
+	"golang.org/x/xerrors"
+
+	"github.com/coder/coder/v2/coderd/notifications/types"
+)
+
+// GoTemplate attempts to substitute the given payload into the given template using Go's templating syntax.
+// TODO: memoize templates for memory efficiency?
+func GoTemplate(in string, payload types.MessagePayload, extraFuncs template.FuncMap) (string, error) {
+	tmpl, err := template.New("text").Funcs(extraFuncs).Parse(in)
+	if err != nil {
+		return "", xerrors.Errorf("template parse: %w", err)
+	}
+
+	var out strings.Builder
+	if err = tmpl.Execute(&out, payload); err != nil {
+		return "", xerrors.Errorf("template execute: %w", err)
+	}
+
+	return out.String(), nil
+}

coderd/notifications/render/gotmpl_test.go

@@ -0,0 +1,59 @@
+package render_test
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+
+	"github.com/coder/coder/v2/coderd/notifications/render"
+
+	"github.com/coder/coder/v2/coderd/notifications/types"
+)
+
+func TestGoTemplate(t *testing.T) {
+	t.Parallel()
+
+	const userEmail = "bob@xyz.com"
+
+	tests := []struct {
+		name           string
+		in             string
+		payload        types.MessagePayload
+		expectedOutput string
+		expectedErr    error
+	}{
+		{
+			name:           "top-level variables are accessible and substituted",
+			in:             "{{ .UserEmail }}",
+			payload:        types.MessagePayload{UserEmail: userEmail},
+			expectedOutput: userEmail,
+			expectedErr:    nil,
+		},
+		{
+			name: "input labels are accessible and substituted",
+			in:   "{{ .Labels.user_email }}",
+			payload: types.MessagePayload{Labels: map[string]string{
+				"user_email": userEmail,
+			}},
+			expectedOutput: userEmail,
+			expectedErr:    nil,
+		},
+	}
+
+	for _, tc := range tests {
+		tc := tc // unnecessary as of go1.22 but the linter is outdated
+
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+
+			out, err := render.GoTemplate(tc.in, tc.payload, nil)
+			if tc.expectedErr == nil {
+				require.NoError(t, err)
+			} else {
+				require.ErrorIs(t, err, tc.expectedErr)
+			}
+
+			require.Equal(t, tc.expectedOutput, out)
+		})
+	}
+}