TypeScript Strict Migration

What this skill does

Walks a TypeScript project from strict: false to strict: true one sub-flag at a time. Each pass enables a single flag, fixes the resulting errors, and commits — keeping diffs reviewable and easy to revert.

Inputs

• tsconfig_path: path to the active tsconfig.json.
• repo_dir: repo root.
• branch_prefix (optional): defaults to ts-strict/. Each flag gets its own branch.

Steps

1. Read the current tsconfig.json with cat. Parse to confirm strict is unset or false.
2. Determine flag order: noImplicitAny, strictNullChecks, strictFunctionTypes, strictBindCallApply, strictPropertyInitialization, noImplicitThis, useUnknownInCatchVariables, alwaysStrict. Easiest first.
3. For each flag, create a branch: git checkout -b <branch_prefix><flag>.
4. Set the flag to true in tsconfig.json (preserve all other settings).
5. Run npx tsc --noEmit -p <tsconfig_path> and capture errors to /tmp/strict-<flag>.log.
6. Group errors by file via awk -F: '{print $1}' | sort | uniq -c | sort -rn. Tackle highest-count files first.
7. For noImplicitAny: add explicit any (or a real type) to each unannotated parameter. For strictNullChecks: add ? to optional fields and if (x == null) guards. For strictPropertyInitialization: use ! only on truly DI-injected fields, prefer initializers.
8. Re-run tsc --noEmit after each file; commit when the file is clean.
9. When the flag is fully clean, commit the tsconfig change separately and merge to main.
10. Move to the next flag and repeat until all eight are enabled, then replace them with "strict": true.

Output

A series of commits (one per flag) plus a final report ts-strict-report.md listing the error count entering and exiting each flag, the files most touched, and any // @ts-expect-error exits taken with TODO references.

Verification

After all flags pass, run tsc --noEmit -p <tsconfig_path> from a clean checkout — exit 0 confirms the migration. Grep for // @ts-expect-error and count: each occurrence must reference a tracking issue. Run the test suite (npm test); type-only changes shouldn't change runtime behavior, so a regression here is a real bug introduced by overzealous typing.

Edge cases

• Generated code (e.g., *.gen.ts): exclude via tsconfig's exclude, don't try to retype.
• Third-party types missing strict-safe .d.ts: use skipLibCheck: true and report unaffected.
• Project references with composite builds: enable the flag in leaf projects first, then propagate.
• Codebases relying on any at framework boundaries (e.g., older Express middleware): keep any localized behind a typed wrapper rather than fanning the relaxation out.