typescript-typecheck-fallback

TypeScript Type-Check with shell_agent Fallback

When verifying TypeScript compilation as part of a build or validation workflow, run_shell may fail with unknown errors due to shell environment issues, missing PATH entries, timeout constraints, or other transient problems. This skill describes a two-step pattern: attempt the check with run_shell first, then fall back to shell_agent if it fails.

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When to Use

• After creating or modifying TypeScript source files and you need to confirm there are no type errors.
• As part of a CI-like verification step inside an autonomous workflow.
• Any time run_shell returns an unexpected or unclear error for a tsc invocation.

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Step-by-Step Pattern

Step 1 — Attempt with run_shell (fast path)

Try the direct command first. This is fast and gives immediate output when the environment is well-configured.

run_shell: npx tsc --noEmit

Evaluate the result:

• ✅ Exit code 0, no errors → Type-check passed. Done.
• ❌ Exit code non-zero with TypeScript diagnostics → Real type errors exist; surface them and fix.
• ⚠️ Unknown error, timeout, or no useful output → Proceed to Step 2.

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Step 2 — Fall back to shell_agent (reliable path)

When run_shell fails in an ambiguous or environmental way, delegate to shell_agent with a natural-language task. shell_agent can autonomously:

• Locate the correct npx/tsc binary
• Retry on transient failures
• Navigate PATH or permission issues
• Return a structured summary of any type errors

Task string to pass to shell_agent:

Run `npx tsc --noEmit` in the project root and report all TypeScript type errors found. If there are no errors, confirm the compilation succeeded. If tsc is not available, attempt to install TypeScript locally with `npm install --save-dev typescript` first.

Evaluate the result:

• ✅ "No errors found" / exit 0 → Type-check passed.
• ❌ Type errors listed → Collect and fix the reported diagnostics, then re-run.
• ⚠️ tsconfig.json missing → Ensure the file exists in the project root before re-running.

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Decision Flowchart

run_shell("npx tsc --noEmit")
        │
        ├─ success (exit 0) ──────────────────► ✅ PASS
        │
        ├─ type errors reported ──────────────► ❌ Fix errors, retry
        │
        └─ unknown/env error ─────────────────► shell_agent(natural-language task)
                                                        │
                                                        ├─ success ───► ✅ PASS
                                                        └─ errors  ───► ❌ Fix & retry

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Example Implementation

# Pseudo-code for an autonomous agent loop

result = run_shell("npx tsc --noEmit", timeout=60)

if result.exit_code == 0:
    print("TypeScript check passed.")

elif result.exit_code != 0 and result.stderr contains "TS\d+":
    # Real TypeScript diagnostics — surface and fix them
    raise TypeScriptError(result.stderr)

else:
    # Ambiguous failure — delegate to shell_agent
    shell_agent(
        task="Run `npx tsc --noEmit` in the project root and report all TypeScript "
             "type errors found. If there are no errors, confirm compilation succeeded. "
             "If tsc is not available, install it first with `npm install --save-dev typescript`."
    )

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Tips

• Always have a tsconfig.json: tsc --noEmit requires a valid config. If none exists, generate one first with npx tsc --init.
• Set a reasonable timeout: TypeScript compilation on large projects can take 30–120 seconds. Give run_shell at least timeout=90.
• Scope to changed files when possible: Use --project tsconfig.json or a path glob to limit what tsc checks if only a subset of files changed.
• Prefer shell_agent for first-time setups: If the project environment is freshly created and dependencies may not be fully installed, start with shell_agent directly to avoid a predictable run_shell failure.

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Generalizing Beyond TypeScript

This same fallback pattern applies to any build/lint/type-check command that may be sensitive to shell environment:

Tool	Primary run_shell command	shell_agent fallback task
TypeScript	npx tsc --noEmit	"Run npx tsc --noEmit and report errors"
ESLint	npx eslint src/	"Run npx eslint on the src directory and report lint errors"
Python mypy	python -m mypy src/	"Run mypy on the src directory and report type errors"
Go build	go build ./...	"Run go build and report compilation errors"

The core principle: run_shell for speed; shell_agent for resilience.