feat: add fly.io preset (#254)

Co-authored-by: Julius Marminge <julius0216@outlook.com>

Author: dburdan

.changeset/giant-kids-promise.md

@@ -0,0 +1,5 @@
+---
+"@t3-oss/env-core": patch
+---
+
+fly.io preset

docs/src/app/docs/customization/page.mdx

@@ -100,6 +100,7 @@ T3 Env ships the following presets out of the box, all importable from the `/pre
 - `uploadthing` - All environment variables required to use [UploadThing](https://uploadthing.com/). More info [here](https://docs.uploadthing.com/getting-started/appdir#add-env-variables).
 - `render` - Render environment variables. See full list [here](https://docs.render.com/environment-variables#all-runtimes).
 - `railway` - Railway provided system environment variables. See full list [here](https://docs.railway.app/reference/variables#railway-provided-variables).
+- `fly.io` - Fly.io provided machine runtime environment variables. See full list [here](https://fly.io/docs/machines/runtime-environment/#environment-variables).
 
 <Callout type="info">
   Feel free to open a PR with more presets!

packages/core/src/presets.ts

@@ -100,3 +100,25 @@ export const railway = () =>
     },
     runtimeEnv: process.env,
   });
+
+/**
+ * Fly.io Environment Variables
+ * @see https://fly.io/docs/machines/runtime-environment/#environment-variables
+ */
+export const fly = () =>
+  createEnv({
+    server: {
+      FLY_APP_NAME: z.string().optional(),
+      FLY_MACHINE_ID: z.string().optional(),
+      FLY_ALLOC_ID: z.string().optional(),
+      FLY_REGION: z.string().optional(),
+      FLY_PUBLIC_IP: z.string().optional(),
+      FLY_IMAGE_REF: z.string().optional(),
+      FLY_MACHINE_VERSION: z.string().optional(),
+      FLY_PRIVATE_IP: z.string().optional(),
+      FLY_PROCESS_GROUP: z.string().optional(),
+      FLY_VM_MEMORY_MB: z.string().optional(),
+      PRIMARY_REGION: z.string().optional(),
+    },
+    runtimeEnv: process.env,
+  });