ADR 002: TypeScript Strict Configuration for Generated Projects

Status: Accepted

Date: 2026-02-21

Context

Generated TypeScript projects ship with a tsconfig.json produced by scaffold.rs. The original config used strict: true but immediately overrode one of its key sub-flags with noImplicitAny: false, leaving the generated codebases under-checked. We audited all TypeScript strict options against the full DoL (SugarCube) and GML output to determine what was safe to enable.

Decisions

Options added

Option	Reason
verbatimModuleSyntax	Enforces import type for type-only imports; zero new errors across all test projects
noImplicitReturns	All code paths must return; zero new errors
noImplicitOverride	Overriding methods must carry override keyword; zero new errors
noUncheckedIndexedAccess	Array/map indexing returns T | undefined; surfaces real null-safety gaps in runtime code
exactOptionalPropertyTypes	prop?: T cannot be set to undefined explicitly; surfaces sloppy optional-field handling
allowUnusedLabels: false	Catches dead labels
allowUnreachableCode: false	Catches dead code

Options deferred

Option	Reason
noImplicitAny: false removed	Only one runtime error surfaced (xml.ts Symbol-indexed array read, fixed with (v as any)[XML_LIST_TAG]). Implicit any in emitted game code now surfaces as TS7053 — correct diagnostics of missing type info in the emitter, not errors to suppress.
noFallthroughCasesInSwitch not added	The JsStmt::Dispatch node (structurizer output for irreducible control flow) uses an intentional switch ($block) { case N: { ... } /* falls through */ } loop pattern. Every non-terminal block in the dispatch switch would be flagged. Enabling this flag would require rearchitecting the dispatch emitter — a separate, non-trivial task.

Why not @tsconfig/strictest?

The @tsconfig/strictest package would add a devDependency to every generated project and require an npm install before the config can be resolved. Generated projects should be self-contained — the tsconfig must work without extra installs. Inlining the options explicitly is cleaner and more auditable.

Consequences

• Generated tsconfig.json now catches a wider class of type errors at compile time.
• Runtime source files (runtime/*/ts/) need ~293 fixes (primarily noUncheckedIndexedAccess null guards and exactOptionalPropertyTypes object literal adjustments). These are tracked as follow-on work.
• The Dispatch emitter is a known source of noFallthroughCasesInSwitch violations; any future restructuring of that node should reconsider enabling that flag.