Simple type definition crash

[Clyybber]

The following crashes the compiler (assertion fails in int128)

Example

type
  TileCT[n: static int] = object
    a: array[n, int]
  Tile = TileCT #Commenting this out to make it work

Current Output

/home/clyybber/builds/nim/compiler/nim.nim(106) nim
/home/clyybber/builds/nim/compiler/nim.nim(83) handleCmdLine
/home/clyybber/builds/nim/compiler/cmdlinehelper.nim(98) loadConfigsAndRunMainCommand
/home/clyybber/builds/nim/compiler/main.nim(188) mainCommand
/home/clyybber/builds/nim/compiler/main.nim(92) commandCompileToC
/home/clyybber/builds/nim/compiler/modules.nim(144) compileProject
/home/clyybber/builds/nim/compiler/modules.nim(85) compileModule
/home/clyybber/builds/nim/compiler/passes.nim(210) processModule
/home/clyybber/builds/nim/compiler/passes.nim(86) processTopLevelStmt
/home/clyybber/builds/nim/compiler/sem.nim(600) myProcess
/home/clyybber/builds/nim/compiler/sem.nim(568) semStmtAndGenerateGenerics
/home/clyybber/builds/nim/compiler/semstmts.nim(2218) semStmt
/home/clyybber/builds/nim/compiler/semexprs.nim(986) semExprNoType
/home/clyybber/builds/nim/compiler/semexprs.nim(2740) semExpr
/home/clyybber/builds/nim/compiler/semstmts.nim(2158) semStmtList
/home/clyybber/builds/nim/compiler/semexprs.nim(2745) semExpr
/home/clyybber/builds/nim/compiler/semstmts.nim(1359) semTypeSection
/home/clyybber/builds/nim/compiler/semstmts.nim(1297) typeSectionFinalPass
/home/clyybber/builds/nim/compiler/semtypinst.nim(27) checkConstructedType
/home/clyybber/builds/nim/compiler/types.nim(1390) computeSize
/home/clyybber/builds/nim/compiler/sizealignoffsetimpl.nim(405) computeSizeAlign
/home/clyybber/builds/nim/compiler/sizealignoffsetimpl.nim(382) computeSizeAlign
/home/clyybber/builds/nim/compiler/sizealignoffsetimpl.nim(150) computeObjectOffsetsFoldFunction
/home/clyybber/builds/nim/compiler/sizealignoffsetimpl.nim(155) computeObjectOffsetsFoldFunction
/home/clyybber/builds/nim/compiler/sizealignoffsetimpl.nim(264) computeSizeAlign
/home/clyybber/builds/nim/compiler/int128.nim(338) *
/home/clyybber/builds/nim/compiler/int128.nim(330) *
/home/clyybber/builds/nim/lib/system/assertions.nim(27) failedAssertImpl
/home/clyybber/builds/nim/lib/system/assertions.nim(20) raiseAssert
/home/clyybber/builds/nim/lib/system/fatal.nim(39) sysFatal
Error: unhandled exception: /home/clyybber/builds/nim/compiler/int128.nim(330, 11) `false` overflow [AssertionError]

$ nim -v
Nim Compiler Version 1.1.1 (#devel)

[Clyybber]

Using Tile[n: static int] = TileCT[n] works as a workaround for now, but shouldn't be needed.

[krux02]

The following condition tests if a type has generic parameters in typeSectionFinalPass.

Nim/compiler/semstmts.nim

Line 1277 in e5ed4c1

if a[1].kind == nkEmpty:

Generic types should be skipped in this pass. Since the expression Tile = TileCT has no explicit generic parameters, it isn't skipped here even though it should. The incomplete type gets size computation and that causes an int128 undorflow (crash in debug mode). This also explains why Tile[n: static int] = TileCT[n] does prevent the crash, because here the generic parameters are explicitly listed.

My recommended solution to this problem is that the type alias infers the generic parameters in the way that Tile = TileCT is internally converted into Tile[n: static int] = TileCT[n]. size computation and the listed condition doesn't need to be touched.