JSON.stringify Runtime Error Prevention

[cs01]

JSON.stringify Runtime Error Prevention

Summary

Fixed JSON.stringify to properly handle string[] and number[] arrays, and now emits compile-time errors for unsupported types instead of silently producing garbage output.

Problem: When calling JSON.stringify() with types that weren't explicitly handled (like string[], number[], or arbitrary interfaces), the codegen would fall through to a number handler that treated pointer values as doubles, causing LLVM type errors or silent garbage output.

Solution:

• Added dispatch cases for string[] and number[] that iterate and call new C bridge functions
• Replaced silent fallback with compile-time error detection for truly unsupported types
• Added new C bridge functions csyyjson_arr_add_str and csyyjson_arr_add_num for array serialization

Test Plan

• All 259 existing tests pass
• Two new fixtures added:
  • json-stringify-string-array.ts — verifies string[] serialization
  • json-stringify-number-array.ts — verifies number[] serialization
• Existing mixed-type tests continue to pass

Implementation Details

Files Changed

1. c_bridges/yyjson-bridge.c

   • Added csyyjson_arr_add_str(doc, arr, val) — appends string to JSON array
   • Added csyyjson_arr_add_num(doc, arr, val) — appends number to JSON array

2. src/codegen/runtime/runtime.ts

   • Declared two new extern functions in generateJSONRuntime()

3. src/codegen/stdlib/json.ts

   • Enhanced generateStringifyArg() to detect and dispatch:
     • string[] via symbolTable.isStringArray() + isStringArrayExpression()
     • number[] via symbolTable.isNumberArray()
   • Added stringifyStringArray() method with loop-based array iteration
   • Added stringifyNumberArray() method with loop-based array iteration
   • Replaced silent number fallback with ctx.emitError() for unsupported types
   • Now correctly rejects unsupported types at compile time with clear error messages

4. tests/fixtures/builtins/json-stringify-string-array.ts

   • Tests JSON.stringify(["alpha", "beta", "gamma"])

5. tests/fixtures/builtins/json-stringify-number-array.ts

   • Tests JSON.stringify([1, 2, 3])

How It Works

String Array Serialization

• Load %StringArray struct (pointer to strings, length, capacity)
• Create yyjson array document
• Loop over elements calling csyyjson_arr_add_str per string
• Stringify the result

Number Array Serialization

• Load %Array struct (pointer to doubles, length, capacity)
• Create yyjson array document
• Loop over elements calling csyyjson_arr_add_num per number
• Stringify the result

Compile Error for Unsupported Types

Before returning a value, generateStringifyArg now checks if the expression is a number/boolean literal or variable:

• If arg.type === "number" or "boolean" → serialize as number
• If variable is number/boolean per symbol table → serialize as number
• Otherwise → emit compile error with clear message listing supported types

Verification

npm test  # All 259 tests pass

The implementation preserves existing behavior for supported types (objects, interfaces, ObjectArray, strings, numbers, booleans) while extending support to common array types and preventing silent failures.