From 92c284bb8d8d155db5bbe1c2d7d8af987f0a92df Mon Sep 17 00:00:00 2001
From: Justin Magaram <justin@magaram.com>
Date: Sat, 10 May 2025 15:14:45 -0700
Subject: [PATCH] Add RegExp.flags external and corresponding tests

---
 runtime/Stdlib_RegExp.res                |  1 +
 runtime/Stdlib_RegExp.resi               | 15 +++++++++++++++
 tests/tests/src/core/Core_RegExpTest.res | 18 ++++++++++++++++++
 tests/tests/src/core/Core_TestSuite.res  |  1 +
 4 files changed, 35 insertions(+)
 create mode 100644 tests/tests/src/core/Core_RegExpTest.res

diff --git a/runtime/Stdlib_RegExp.res b/runtime/Stdlib_RegExp.res
index ff24abab95..94cde1ea2f 100644
--- a/runtime/Stdlib_RegExp.res
+++ b/runtime/Stdlib_RegExp.res
@@ -22,5 +22,6 @@ module Result = {
 @get external source: t => string = "source"
 @get external sticky: t => bool = "sticky"
 @get external unicode: t => bool = "unicode"
+@get external flags: t => string = "flags"
 
 external ignore: t => unit = "%ignore"
diff --git a/runtime/Stdlib_RegExp.resi b/runtime/Stdlib_RegExp.resi
index 5415ab1d3a..79a351b888 100644
--- a/runtime/Stdlib_RegExp.resi
+++ b/runtime/Stdlib_RegExp.resi
@@ -298,6 +298,20 @@ Console.log(regexp2->RegExp.unicode) // Logs `true`, since `u` is set
 @get
 external unicode: t => bool = "unicode"
 
+/**
+`flags(regexp)` returns a string consisting of all the flags set on this `RegExp`.
+
+See [`RegExp.flags`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/RegExp/flags) on MDN.
+
+## Examples
+```rescript
+let regexp = RegExp.fromString("\\w+", ~flags="gi")
+Console.log(regexp->RegExp.flags) // Logs "gi", all the flags set on the RegExp
+```
+*/
+@get
+external flags: t => string = "flags"
+
 /**
   `ignore(regExp)` ignores the provided regExp and returns unit.
 
@@ -305,3 +319,4 @@ external unicode: t => bool = "unicode"
   without having to store or process it further.
 */
 external ignore: t => unit = "%ignore"
+//
diff --git a/tests/tests/src/core/Core_RegExpTest.res b/tests/tests/src/core/Core_RegExpTest.res
new file mode 100644
index 0000000000..dd1c844f7c
--- /dev/null
+++ b/tests/tests/src/core/Core_RegExpTest.res
@@ -0,0 +1,18 @@
+// Test for RegExp.flags
+Test.run(
+  __POS_OF__("RegExp.flags basic"),
+  RegExp.fromStringWithFlags("\\w+", ~flags="gi")->RegExp.flags,
+  eq,
+  "gi",
+)
+
+// Test for alphabetical sorting of flags
+Test.run(
+  __POS_OF__("RegExp.flags sorting"),
+  RegExp.fromStringWithFlags("\\w+", ~flags="igd")->RegExp.flags,
+  eq,
+  "dgi",
+)
+
+// Test with no flags
+Test.run(__POS_OF__("RegExp.flags empty"), RegExp.fromString("\\w+")->RegExp.flags, eq, "")
diff --git a/tests/tests/src/core/Core_TestSuite.res b/tests/tests/src/core/Core_TestSuite.res
index e048a3bd56..9b9c997f7e 100644
--- a/tests/tests/src/core/Core_TestSuite.res
+++ b/tests/tests/src/core/Core_TestSuite.res
@@ -11,3 +11,4 @@ include Core_JsonTests
 include Core_NullableTests
 include Core_DictTests
 include Core_IteratorTests
+include Core_RegExpTest