eqValues/assertEqValues: Clean up assertions

It's still paranoid, and probably a waste of words, but at least
now it's consistent and readily identifyable from a log.

src/libexpr/eval.cc

@@ -2631,17 +2631,12 @@ void EvalState::assertEqValues(Value & v1, Value & v2, const PosIdx pos, std::st
  return;
 
  case nThunk: // Must not be left by forceValue
- default:
- // This should never happen, because eqValues already throws an
- // error for this, and this function should only be called when
- // eqValues has found a difference, and it should match
- // its behavior.
- // Note that as of writing, we make the compiler require that all enum
- // values are handled explicitly with `case`s, _despite_ having a
- // `default:`.
- error<EvalBaseError>(
- "BUG: cannot compare %1% with %2%; did forceValue leave a thunk, or might assertEqValues be out of sync with eqValues?", showType(v1), showType(v2))
- .debugThrow();
+ assert(false);
+ default: // Note that we pass compiler flags that should make `default:` unreachable.
+ // Also note that this probably ran after `eqValues`, which implements
+ // the same logic more efficiently (without having to unwind stacks),
+ // so maybe `assertEqValues` and `eqValues` are out of sync. Check it for solutions.
+ error<EvalError>("assertEqValues: cannot compare %1% with %2%", showType(v1), showType(v2)).withTrace(pos, errorCtx).panic();
  }
 }
 
@@ -2723,8 +2718,9 @@ bool EvalState::eqValues(Value & v1, Value & v2, const PosIdx pos, std::string_v
  return v1.fpoint() == v2.fpoint();
 
  case nThunk: // Must not be left by forceValue
- default:
- error<EvalError>("cannot compare %1% with %2%", showType(v1), showType(v2)).withTrace(pos, errorCtx).debugThrow();
+ assert(false);
+ default: // Note that we pass compiler flags that should make `default:` unreachable.
+ error<EvalError>("eqValues: cannot compare %1% with %2%", showType(v1), showType(v2)).withTrace(pos, errorCtx).panic();
  }
 }
 
@@ -2978,7 +2974,7 @@ SourcePath EvalState::findFile(const LookupPath & lookupPath, const std::string_
  ? "cannot look up '<%s>' in pure evaluation mode (use '--impure' to override)"
  : "file '%s' was not found in the Nix search path (add it using $NIX_PATH or -I)",
  path
- ).atPos(pos).debugThrow();
+ ).atPos(pos).panic();
 }