1 files changed, 71 insertions, 0 deletions
diff --git a/tests/generics/t23854.nim b/tests/generics/t23854.nim
new file mode 100644
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+++ b/tests/generics/t23854.nim
@@ -0,0 +1,71 @@
+# issue #23854, not entirely fixed
+
+import std/bitops
+
+const WordBitWidth = sizeof(pointer) * 8
+
+func wordsRequired*(bits: int): int {.inline.} =
+  const divShiftor = fastLog2(uint32(WordBitWidth))
+  result = (bits + WordBitWidth - 1) shr divShiftor
+
+type
+  Algebra* = enum
+    BLS12_381
+
+  BigInt*[bits: static int] = object
+    limbs*: array[wordsRequired(bits), uint]
+
+  Fr*[Name: static Algebra] = object
+    residue_form*: BigInt[255]
+
+  Fp*[Name: static Algebra] = object
+    residue_form*: BigInt[381]
+
+  FF*[Name: static Algebra] = Fp[Name] or Fr[Name]
+
+template getBigInt*[Name: static Algebra](T: type FF[Name]): untyped =
+  ## Get the underlying BigInt type.
+  typeof(default(T).residue_form)
+
+type
+  EC_ShortW_Aff*[F] = object
+    ## Elliptic curve point for a curve in Short Weierstrass form
+    ##   y² = x³ + a x + b
+    ##
+    ## over a field F
+    x*, y*: F
+
+type FieldKind* = enum
+  kBaseField
+  kScalarField
+
+func bits*[Name: static Algebra](T: type FF[Name]): static int =
+  T.getBigInt().bits
+
+template getScalarField*(EC: type EC_ShortW_Aff): untyped =
+  Fr[EC.F.Name]
+
+# ------------------------------------------------------------------------------
+
+type
+  ECFFT_Descriptor*[EC] = object
+    ## Metadata for FFT on Elliptic Curve
+    order*: int
+    rootsOfUnity1*: ptr UncheckedArray[BigInt[EC.getScalarField().bits()]]  # Error: in expression 'EC.getScalarField()': identifier expected, but found 'EC.getScalarField'
+    rootsOfUnity2*: ptr UncheckedArray[BigInt[getScalarField(EC).bits()]] # Compiler SIGSEGV: Illegal Storage Access
+
+func new*(T: type ECFFT_Descriptor): T =
+  discard
+
+# ------------------------------------------------------------------------------
+
+template getBits[bits: static int](x: ptr UncheckedArray[BigInt[bits]]): int = bits
+
+proc main() =
+  let ctx = ECFFT_Descriptor[EC_ShortW_Aff[Fp[BLS12_381]]].new()
+  doAssert getBits(ctx.rootsOfUnity1) == 255
+  doAssert getBits(ctx.rootsOfUnity2) == 255
+  doAssert ctx.rootsOfUnity1[0].limbs.len == wordsRequired(255)
+  doAssert ctx.rootsOfUnity2[0].limbs.len == wordsRequired(255)
+
+main()