From 6310f9c609976a453707a793f855d2f5dd8adae7 Mon Sep 17 00:00:00 2001
From: Timothy Peterson <33550033+tmrp@users.noreply.github.com>
Date: Fri, 3 Apr 2026 09:55:18 +0200
Subject: [PATCH] fix(core): include extended env vars when skipValidation is
 true

When `skipValidation: true`, `createEnv` was returning `runtimeEnv`
directly, silently discarding variables contributed via `extends`.

Fix by hoisting the `extendedObj` reduction above the skip guard and
merging it with `runtimeEnv` before the early return, matching the
behaviour of the normal validation path (runtimeEnv takes precedence).

Adds three regression tests in smoke-zod4.test.ts covering:
- single preset vars are accessible
- runtimeEnv values override preset values
- multiple preset vars are all accessible
---
 .../fix-skip-validation-extended-env.md       | 10 +++
 packages/core/src/index.ts                    |  9 +--
 packages/core/test/smoke-zod4.test.ts         | 69 +++++++++++++++++++
 3 files changed, 84 insertions(+), 4 deletions(-)
 create mode 100644 .changeset/fix-skip-validation-extended-env.md

diff --git a/.changeset/fix-skip-validation-extended-env.md b/.changeset/fix-skip-validation-extended-env.md
new file mode 100644
index 00000000..3eee9ad0
--- /dev/null
+++ b/.changeset/fix-skip-validation-extended-env.md
@@ -0,0 +1,10 @@
+---
+"@t3-oss/env-core": patch
+---
+
+fix: include extended env vars when `skipValidation` is true
+
+Previously, calling `createEnv` with `skipValidation: true` returned only
+`runtimeEnv`, silently dropping any variables contributed by the `extends`
+array. Extended variables are now merged in (with `runtimeEnv` taking
+precedence), matching the behaviour of the normal validation path.
diff --git a/packages/core/src/index.ts b/packages/core/src/index.ts
index 05418a86..71ee070a 100644
--- a/packages/core/src/index.ts
+++ b/packages/core/src/index.ts
@@ -323,6 +323,10 @@ export function createEnv<
     }
   }
 
+  const extendedObj = (opts.extends ?? []).reduce((acc, curr) => {
+    return Object.assign(acc, curr);
+  }, {});
+
   const skip = !!opts.skipValidation;
   if (skip) {
     if (opts.extends) {
@@ -332,7 +336,7 @@ export function createEnv<
     }
 
     // biome-ignore lint/suspicious/noExplicitAny: <explanation>
-    return runtimeEnv as any;
+    return Object.assign(extendedObj, runtimeEnv) as any;
   }
 
   const _client = typeof opts.client === "object" ? opts.client : {};
@@ -386,9 +390,6 @@ export function createEnv<
     return prop === "__esModule" || prop === "$$typeof";
   };
 
-  const extendedObj = (opts.extends ?? []).reduce((acc, curr) => {
-    return Object.assign(acc, curr);
-  }, {});
   const fullObj = Object.assign(extendedObj, parsed.value);
 
   const env = new Proxy(fullObj, {
diff --git a/packages/core/test/smoke-zod4.test.ts b/packages/core/test/smoke-zod4.test.ts
index 5b5e90ac..6e92c841 100644
--- a/packages/core/test/smoke-zod4.test.ts
+++ b/packages/core/test/smoke-zod4.test.ts
@@ -787,6 +787,75 @@ test("overriding preset env var", () => {
   expect(env.PRESET_ENV).toBe(123);
 });
 
+describe("skipValidation with extends", () => {
+  test("includes extended env vars when skipValidation is true", () => {
+    const processEnv = {
+      PRESET_ENV: "preset",
+      MY_VAR: "myvar",
+    };
+
+    const preset = createEnv({
+      server: { PRESET_ENV: z.string() },
+      runtimeEnv: processEnv,
+    });
+
+    const env = createEnv({
+      server: { MY_VAR: z.string() },
+      extends: [preset],
+      runtimeEnv: processEnv,
+      skipValidation: true,
+    });
+
+    expect(env.MY_VAR).toBe("myvar");
+    expect(env.PRESET_ENV).toBe("preset");
+  });
+
+  test("runtimeEnv values take precedence over extended env vars when skipValidation is true", () => {
+    const preset = createEnv({
+      server: { SHARED_VAR: z.string() },
+      runtimeEnv: { SHARED_VAR: "from-preset" },
+    });
+
+    const env = createEnv({
+      server: { SHARED_VAR: z.string() },
+      extends: [preset],
+      runtimeEnv: { SHARED_VAR: "from-runtime" },
+      skipValidation: true,
+    });
+
+    expect(env.SHARED_VAR).toBe("from-runtime");
+  });
+
+  test("includes vars from multiple extended presets when skipValidation is true", () => {
+    const processEnv = {
+      PRESET_ENV1: "preset1",
+      PRESET_ENV2: "preset2",
+      MY_VAR: "myvar",
+    };
+
+    const preset1 = createEnv({
+      server: { PRESET_ENV1: z.string() },
+      runtimeEnv: processEnv,
+    });
+
+    const preset2 = createEnv({
+      server: { PRESET_ENV2: z.string() },
+      runtimeEnv: processEnv,
+    });
+
+    const env = createEnv({
+      server: { MY_VAR: z.string() },
+      extends: [preset1, preset2],
+      runtimeEnv: processEnv,
+      skipValidation: true,
+    });
+
+    expect(env.MY_VAR).toBe("myvar");
+    expect(env.PRESET_ENV1).toBe("preset1");
+    expect(env.PRESET_ENV2).toBe("preset2");
+  });
+});
+
 test("with built-in preset", () => {
   process.env.UPLOADTHING_TOKEN = "token";
   const env = createEnv({