fixes #3799

compiler/semcall.nim

@@ -255,12 +255,13 @@ proc resolveOverloads(c: PContext, n, orig: PNode,
 
 
 proc instGenericConvertersArg*(c: PContext, a: PNode, x: TCandidate) =
-  if a.kind == nkHiddenCallConv and a.sons[0].kind == nkSym and
-      isGenericRoutine(a.sons[0].sym):
-    let finalCallee = generateInstance(c, a.sons[0].sym, x.bindings, a.info)
-    a.sons[0].sym = finalCallee
-    a.sons[0].typ = finalCallee.typ
-    #a.typ = finalCallee.typ.sons[0]
+  if a.kind == nkHiddenCallConv and a.sons[0].kind == nkSym:
+    let s = a.sons[0].sym
+    if s.ast != nil and s.ast[genericParamsPos].kind != nkEmpty:
+      let finalCallee = generateInstance(c, s, x.bindings, a.info)
+      a.sons[0].sym = finalCallee
+      a.sons[0].typ = finalCallee.typ
+      #a.typ = finalCallee.typ.sons[0]
 
 proc instGenericConvertersSons*(c: PContext, n: PNode, x: TCandidate) =
   assert n.kind in nkCallKinds

tests/converter/tgenericconverter2.nim

@@ -0,0 +1,49 @@
+# bug #3799
+
+import macros
+
+const nmax = 500
+
+type
+  Complex*[T] = object
+    re*: T
+    im*: T
+
+converter toComplex*[T](x: tuple[re, im: T]): Complex[T] =
+  result.re = x.re
+  result.im = x.im
+
+
+proc julia*[T](z0, c: Complex[T], er2: T, nmax: int): int =
+  result = 0
+  var z = z0
+  var sre = z0.re * z0.re
+  var sim = z0.im * z0.im
+  while (result < nmax) and (sre + sim < er2):
+    z.im = z.re * z.im
+    z.im = z.im + z.im
+    z.im = z.im + c.im
+    z.re = sre - sim + c.re
+    sre = z.re * z.re
+    sim = z.im * z.im
+    inc result
+
+template dendriteFractal*[T](z0: Complex[T], er2: T, nmax: int): int =
+  julia(z0, (T(0.0), T(1.0)), er2, nmax)
+
+iterator stepIt[T](start, step: T, iterations: int): T =
+  for i in 0 .. iterations:
+    yield start + T(i) * step
+
+
+let c = (0.36237, 0.32)
+for y in stepIt(2.0, -0.0375, 107):
+  var row = ""
+  for x in stepIt(-2.0, 0.025, 160):
+    #let n = julia((x, y), c, 4.0, nmax)         ### this works
+    let n = dendriteFractal((x, y), 4.0, nmax)
+    if n < nmax:
+      row.add($(n mod 10))
+    else:
+      row.add(' ')
+  echo row