packwiz: re-load LOAD_ENV_FROM_FILE after the installer runs (#4137)

Author: ChipWolf

docs/mods-and-plugins/packwiz.md

@@ -13,6 +13,8 @@ docker run -d --pull=always \
 
 packwiz modpack definitions are processed before other mod definitions (`MODPACK`, `MODS`, etc.) to allow for additional processing/overrides you may want to perform (in case of mods not available via Modrinth/CurseForge, or you do not maintain the pack).
 
+If the pack ships a `.env` file that you reference with `LOAD_ENV_FROM_FILE`, that file is re-loaded immediately after the packwiz installer runs, so the freshly downloaded values are applied to the remaining startup stages. Note that `TYPE` and `VERSION` are resolved earlier (before the deploy is dispatched), so a pack-provided `.env` cannot change those from within packwiz; use `LOAD_ENV_FROM_GENERIC_PACK` or `LOAD_ENV_FROM_ARCHIVE` for those.
+
 !!! note 
 
     packwiz is pre-configured to only download server mods. If client-side mods are downloaded and cause issues, check your pack.toml configuration, and make sure any client-only mods are not set to `"both"`, but rather `"client"` for the side configuration item.

scripts/start-setupModpack

@@ -50,6 +50,16 @@ function handlePackwiz() {
       logError "Failed to run packwiz installer"
       exit 1
     fi
+
+    # packwiz may have just downloaded/updated the env file referenced by
+    # LOAD_ENV_FROM_FILE. The initial load in start-configuration happened
+    # before this point, so re-load it now to pick up the pack's values for
+    # the remaining setup stages (server.properties, JVM args, etc.).
+    if [[ ${LOAD_ENV_FROM_FILE:-} ]]; then
+      if ! loadEnvFromFile "${LOAD_ENV_FROM_FILE}"; then
+        exit 1
+      fi
+    fi
   fi
 }