From b680e4a219618ce88be2e4e3b7816f13fdf2d8da Mon Sep 17 00:00:00 2001
From: Stefan Stefanov <stefan.stefanov@randstad.com>
Date: Mon, 3 Jun 2024 22:56:56 +0300
Subject: [PATCH] Fix self-expanding undefined variable with default value.

---
 lib/main.js   |  4 +---
 tests/main.js | 17 +++++++++++++++--
 2 files changed, 16 insertions(+), 5 deletions(-)

diff --git a/lib/main.js b/lib/main.js
index 33e38db..e57074e 100644
--- a/lib/main.js
+++ b/lib/main.js
@@ -32,9 +32,7 @@ function interpolate (value, processEnv, parsed) {
 
       if (parsed[key]) {
         // avoid recursion from EXPAND_SELF=$EXPAND_SELF
-        if (parsed[key] === value) {
-          return parsed[key]
-        } else {
+        if (parsed[key] !== value) {
           return interpolate(parsed[key], processEnv, parsed)
         }
       }
diff --git a/tests/main.js b/tests/main.js
index 3db8947..f8f7755 100644
--- a/tests/main.js
+++ b/tests/main.js
@@ -42,7 +42,20 @@ t.test('expands self without a recursive call stack error', ct => {
   }
   const parsed = dotenvExpand.expand(dotenv).parsed
 
-  ct.equal(parsed.EXPAND_SELF, '$EXPAND_SELF') // because it ends up accessing parsed[key].
+  ct.equal(parsed.EXPAND_SELF, '') // because it ends up accessing parsed[key].
+
+  ct.end()
+})
+
+t.test('expands self with undefined variable and default value', ct => {
+  const dotenv = {
+    parsed: {
+      EXPAND_SELF: '${EXPAND_SELF:-default}'
+    }
+  }
+  const parsed = dotenvExpand.expand(dotenv).parsed
+
+  ct.equal(parsed.EXPAND_SELF, 'default')
 
   ct.end()
 })
@@ -466,7 +479,7 @@ t.test('expands self without a recursive call stack error (process.env)', ct =>
   const dotenv = require('dotenv').config({ path: 'tests/.env.test', processEnv: {} })
   const parsed = dotenvExpand.expand(dotenv).parsed
 
-  ct.equal(parsed.EXPAND_SELF, '$EXPAND_SELF') // because it ends up accessing parsed[key].
+  ct.equal(parsed.EXPAND_SELF, '') // because it ends up accessing parsed[key].
 
   ct.end()
 })