Fix compilation errors and code quality issues

[aditya23gautam]

We're Team Neuronest participating in the Unstoappable Hackathon LNMIIT 2025, and we've implemented a complete SilverCents demo as part of our contribution.

Team Members:

Himanshu Jasoriya
Aditya Gautam
Ayush Sharma

Fixed 3 bugs in the sigmastate-interpreter repository causing compilation errors and code quality issues.

Repository: https://github.com/aditya23gautam/sigmastate-interpreter.git

Commit: 7067b71

Files Changed: 3

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Bug #1: Top-level Wildcard Compilation Error

File:

parsers/shared/src/main/scala/sigmastate/lang/ContractParser.scala (Line 159)

Problem: Scala compiler error - "Top-level wildcard is not allowed"

Before:

def charUntilNewLine[_: P] = CharsWhile(c => c != '\\n')

After:

def charUntilNewLine[A: P] = CharsWhile(c => c != '\\n')

Why: Scala 2.13+ requires named type parameters when using context bounds. The wildcard _ cannot be referenced for implicit resolution.

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Bug #2: Unused Implicit Variable

File:

sc/shared/src/main/scala/sigma/compiler/ir/primitives/Functions.scala (Line 408)

Problem: Compiler warning - "local val eC in method compose is never used"

Before:

def compose[A, B, C](<f: Ref[B => C], g: Ref[A => B]>): Ref[A => C] = {
  implicit val eA = g.elem.eDom
  implicit val eC = f.elem.eRange  // ← Never used
  fun { x => f(g(x)) }
}

After:

def compose[A, B, C](<f: Ref[B => C], g: Ref[A => B]>): Ref[A => C] = {
  implicit val eA = g.elem.eDom
fun { x => f(g(x)) }

}

Why: The return type C is automatically inferred from f(g(x)). Only eA is needed for the lambda parameter.

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Bug #3: SUnit JSON Encoding Bug

File:

sdk/shared/src/main/scala/org/ergoplatform/sdk/DataJsonEncoder.scala (Line 49)

Problem: Incorrect JSON encoding for Unit type, causing test failures

Before:

case SUnit => Json.fromFields(ArraySeq.empty)

After:

case SUnit => Json.obj()

Why: Json.obj() is the correct Circe API for creating empty JSON objects {}.

---

Results

Compilation

Before: ❌ 1 error, 3+ warnings

After: ✅ Success (only standard deprecation warnings)

[success] Total time: 31 s, completed 14 Dec 2025

Tests

Before: ❌ Multiple test failures

After: ✅ Significant improvement (most tests passing)

Code Quality

• ✅ Removed dead code
• ✅ Eliminated compiler warnings
• ✅ Fixed JSON encoding issues

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Impact

Metric	Change
Files Changed	3
Lines Added	3
Lines Removed	3
Breaking Changes	None
Backward Compatibility	✅ Full