Compiler crashes when using string as object variant selector with else branch

[metagn]

Example

type Obj = object
  case str: string
  of "abc": discard
  else: discard

Current Output

Error: internal error: invalid kind for lastOrd(tyString)
Traceback (most recent call last)
compiler/nim.nim(104) nim
compiler/nim.nim(81) handleCmdLine
compiler/cmdlinehelper.nim(91) loadConfigsAndRunMainCommand
compiler/main.nim(196) mainCommand
compiler/main.nim(98) commandCompileToC
compiler/modules.nim(143) compileProject
compiler/modules.nim(84) compileModule
compiler/passes.nim(210) processModule
compiler/passes.nim(86) processTopLevelStmt
compiler/sem.nim(599) myProcess
compiler/sem.nim(567) semStmtAndGenerateGenerics
compiler/semstmts.nim(2308) semStmt
compiler/semexprs.nim(1014) semExprNoType
compiler/semexprs.nim(2776) semExpr
compiler/semstmts.nim(2248) semStmtList
compiler/semexprs.nim(2781) semExpr
compiler/semstmts.nim(1423) semTypeSection
compiler/semstmts.nim(1265) typeSectionRightSidePass
compiler/semtypes.nim(1916) semTypeNode
compiler/semtypes.nim(882) semObjectNode
compiler/semtypes.nim(755) semRecordNodeAux
compiler/semtypes.nim(748) semRecordNodeAux
compiler/semtypes.nim(685) semRecordCase
compiler/types.nim(841) lengthOrd
compiler/types.nim(802) lastOrd
compiler/msgs.nim(564) internalError
compiler/msgs.nim(442) rawMessage
compiler/msgs.nim(439) rawMessage
compiler/msgs.nim(356) handleError
compiler/msgs.nim(346) quit

Expected Output

Compiles or disallowed. There is an error message that says Error: selector must be of an ordinal type, float or string if you make the selector type anything but those types.

Possible Solution

To disallow, change:

Nim/compiler/semtypes.nim

Lines 673 to 681 in 9c33bca

	of tyFloat..tyFloat128, tyString, tyError:
	discard
	of tyRange:
	if skipTypes(typ[0], abstractInst).kind in shouldChckCovered:
	chckCovered = true
	of tyForward:
	errorUndeclaredIdentifier(c, n[0].info, typ.sym.name.s)
	elif not isOrdinalType(typ):
	localError(c.config, n[0].info, "selector must be of an ordinal type, float or string")

to:

  of tyFloat..tyFloat128, tyError:
    discard
  ...
  elif not isOrdinalType(typ):
    localError(c.config, n[0].info, "selector must be an ordinal type or float")

$ nim -v
Nim Compiler Version 1.3.1

[disruptek]

I believe the consensus is that strings should be disallowed in object variant typedefs. A pull to that effect would let us measure breakage, to some extent. It might need a documentation update, too.

[metagn]

Strings in object variants are not documented, so no need to update anything there. From the manual:

This analysis only works for immutable discriminators of an ordinal type

This error message is just randomly misleading. It's really easy to remove it, someone can make a PR with the proposed change above if they want