From 2eec4b5daaf663d616d54199aa86a3056d5833cb Mon Sep 17 00:00:00 2001
From: Jon Parise <jon@indelible.org>
Date: Mon, 17 May 2021 10:25:09 -0700
Subject: [PATCH] Add regexp.Regexp support

It's useful to support validated regular expressions in configuration
files. Previously, we could represent these fields as raw pattern
strings and compile them in application code. By supporting Regexp as a
first-class field type, we get a smaller application code and more
immediate error reporting without complicating the API.
---
 README.md   |  7 ++++---
 fig.go      |  7 +++++++
 fig_test.go | 45 +++++++++++++++++++++++++++++++++++++++++++--
 3 files changed, 54 insertions(+), 5 deletions(-)

diff --git a/README.md b/README.md
index c1e5b15..fb80df6 100644
--- a/README.md
+++ b/README.md
@@ -20,7 +20,7 @@ fig is a tiny library for loading an application's config file and its environme
 - Define your **configuration**, **validations** and **defaults** in a single location
 - Optionally **load from the environment** as well
 - Only **3** external dependencies
-- Full support for`time.Time` & `time.Duration`
+- Full support for`time.Time`, `time.Duration` & `regexp.Regexp`
 - Tiny API
 - Decoders for `.yaml`, `.json` and `.toml` files
 
@@ -64,8 +64,9 @@ type Config struct {
     Cleanup time.Duration `fig:"cleanup" default:"30m"`
   }
   Logger struct {
-    Level string `fig:"level" default:"info"`
-    Trace bool   `fig:"trace"`
+    Level   string         `fig:"level" default:"info"`
+    Pattern *regexp.Regexp `fig:"pattern" default:".*"`
+    Trace   bool           `fig:"trace"`
   }
 }
 
diff --git a/fig.go b/fig.go
index 510a4f4..6281dc9 100644
--- a/fig.go
+++ b/fig.go
@@ -6,6 +6,7 @@ import (
 	"os"
 	"path/filepath"
 	"reflect"
+	"regexp"
 	"strconv"
 	"strings"
 	"time"
@@ -289,6 +290,12 @@ func (f *fig) setValue(fv reflect.Value, val string) error {
 				return err
 			}
 			fv.Set(reflect.ValueOf(t))
+		} else if _, ok := fv.Interface().(regexp.Regexp); ok {
+			re, err := regexp.Compile(val)
+			if err != nil {
+				return err
+			}
+			fv.Set(reflect.ValueOf(*re))
 		} else {
 			return fmt.Errorf("unsupported type %s", fv.Kind())
 		}
diff --git a/fig_test.go b/fig_test.go
index 35c3826..8d53849 100644
--- a/fig_test.go
+++ b/fig_test.go
@@ -6,6 +6,7 @@ import (
 	"os"
 	"path/filepath"
 	"reflect"
+	"regexp"
 	"strings"
 	"testing"
 	"time"
@@ -221,8 +222,9 @@ func Test_fig_Load_Defaults(t *testing.T) {
 					Host   string `fig:"host" default:"127.0.0.1"`
 					Ports  []int  `fig:"ports" default:"[80,443]"`
 					Logger struct {
-						LogLevel   string `fig:"log_level" default:"info"`
-						Production bool   `fig:"production"`
+						LogLevel   string         `fig:"log_level" default:"info"`
+						Pattern    *regexp.Regexp `fig:"pattern" default:".*"`
+						Production bool           `fig:"production"`
 						Metadata   struct {
 							Keys []string `fig:"keys" default:"[ts]"`
 						}
@@ -236,6 +238,7 @@ func Test_fig_Load_Defaults(t *testing.T) {
 				want.Host = "0.0.0.0"
 				want.Ports = []int{80, 443}
 				want.Logger.LogLevel = "debug"
+				want.Logger.Pattern = regexp.MustCompile(".*")
 				want.Logger.Production = false
 				want.Logger.Metadata.Keys = []string{"ts"}
 				want.Application.BuildDate = time.Date(2020, 1, 1, 12, 0, 0, 0, time.UTC)
@@ -1014,6 +1017,35 @@ func Test_fig_setValue(t *testing.T) {
 		}
 	})
 
+	t.Run("regexp", func(t *testing.T) {
+		var re regexp.Regexp
+		fv := reflect.ValueOf(&re).Elem()
+
+		err := fig.setValue(fv, "[a-z]+")
+		if err != nil {
+			t.Fatalf("unexpected err: %v", err)
+		}
+
+		want, err := regexp.Compile("[a-z]+")
+		if err != nil {
+			t.Fatalf("error parsing time: %v", err)
+		}
+
+		if re.String() != want.String() {
+			t.Fatalf("want %v, got %v", want, re)
+		}
+	})
+
+	t.Run("bad regexp", func(t *testing.T) {
+		var re regexp.Regexp
+		fv := reflect.ValueOf(&re).Elem()
+
+		err := fig.setValue(fv, "[a-")
+		if err == nil {
+			t.Fatalf("expected err")
+		}
+	})
+
 	t.Run("interface returns error", func(t *testing.T) {
 		var i interface{}
 		fv := reflect.ValueOf(i)
@@ -1089,6 +1121,15 @@ func Test_fig_setSlice(t *testing.T) {
 			},
 			Val: "[2019-12-25T10:30:30Z,2020-01-01T00:00:00Z]",
 		},
+		{
+			Name:    "regexps",
+			InSlice: &[]*regexp.Regexp{},
+			WantSlice: &[]*regexp.Regexp{
+				regexp.MustCompile("[a-z]+"),
+				regexp.MustCompile(".*"),
+			},
+			Val: "[[a-z]+,.*]",
+		},
 	} {
 		t.Run(tc.Val, func(t *testing.T) {
 			in := reflect.ValueOf(tc.InSlice).Elem()