clockworklabs/SpacetimeDB · error · anyhow::Error

--uproject-dir is required for --lang unrealcpp

Error message

--uproject-dir is required for --lang unrealcpp

What it means

`spacetime generate --lang unrealcpp` produces an Unreal Engine C++ plugin that must live inside a .uproject-containing project, so the CLI validates Unreal-specific arguments up front. If the resolved uproject_dir is None (no --uproject-dir flag and nothing in the generate config), generation refuses to start with this focused error.

Solutions

1. Pass the path to your Unreal project directory: `spacetime generate --lang unrealcpp --uproject-dir /path/to/MyProject`
2. Or persist it in spacetime.json under the generate entry: `"uproject-dir": "../MyProject"`
3. Also provide --unreal-module-name at the same time, since it is validated immediately after (error 346)

Example fix

# before
spacetime generate --lang unrealcpp --bin-path module.wasm
# after
spacetime generate --lang unrealcpp --bin-path module.wasm \
  --uproject-dir ~/Projects/MyGame --unreal-module-name MyGame

#!/usr/bin/env bash
uproject="${UPROJECT_DIR:-}"
[ -n "$uproject" ] && [ -d "$uproject" ] || { echo '--uproject-dir <dir> required and must exist'; exit 2; }
spacetime generate --lang unrealcpp --uproject-dir "$uproject" --unreal-module-name "$MODULE_NAME"

When it happens

Trigger: Running `spacetime generate --lang unrealcpp` without `--uproject-dir` (and with no `uproject-dir` key in the spacetime.json generate config for this entry). The check runs before module-source validation so the missing Unreal argument is reported first.

Common situations: Copying a generate invocation from a Rust/TypeScript project where --uproject-dir doesn't exist; CI pipelines generating UE bindings against a workspace where the uproject path is passed via a variable that is empty; forgetting that unrealcpp has stricter requirements than other languages.

Understand the failure class

Background: "missing required argument" and "the following required arguments were not provided": what required-argument errors mean and how to fix them — this error's family across 20 libraries.

Related errors

• --unreal-module-name is required for --lang unrealcpp
• Either --out-dir or --uproject-dir is required
• --namespace is only supported with --lang csharp
• Unknown client language
• Unknown server language

AI-assisted analysis of clockworklabs/SpacetimeDB@eddf9f5014 (2026-08-20). Data as JSON: /api/errors/5f5880ad2967f15a. Report an issue: GitHub.

Appendix: source

Thrown at crates/cli/src/subcommands/generate.rs:344

        let namespace = command_config
            .get_one::<String>("namespace")?
            .unwrap_or_else(|| "SpacetimeDB.Types".to_string());
        let module_name = command_config.get_one::<String>("unreal_module_name")?;
        let module_prefix = command_config.get_one::<String>("module_prefix")?;
        let build_options = command_config
            .get_one::<String>("build_options")?
            .unwrap_or_else(String::new);
        let dotnet_version = if command_config.is_from_cli("dotnet_version") {
            command_config.get_one::<u8>("dotnet_version")?
        } else {
            let dotnet_version = command_config.get_one::<String>("dotnet_version")?;
            parse_optional_dotnet_version(dotnet_version.as_deref())?
        };

        // Validate Unreal-specific args first to preserve focused errors for this mode.
        if requested_lang == Some(Language::UnrealCpp) {
            if command_config.get_one::<PathBuf>("uproject_dir")?.is_none() {
                return Err(anyhow::anyhow!("--uproject-dir is required for --lang unrealcpp"));
            }
            if module_name.is_none() {
                return Err(anyhow::anyhow!("--unreal-module-name is required for --lang unrealcpp"));
            }
        }

        // Validate module source path for source-based generation.
        if wasm_file.is_none() && js_file.is_none() && !project_path.is_dir() {
            anyhow::bail!(
                "Could not find module source at '{}'. \
                 If this is not correct, pass --module-path or add module-path in spacetime.json. \
                 You can also pass --bin-path/--js-path to generate without building from source.",
                project_path.display()
            );
        }

        let lang = match requested_lang {
            Some(lang) => lang,

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