handle typedesc params in VM (nim-lang#22581)

* handle typedesc params in VM

fixes nim-lang#15760

* add test

* fix getType(typedesc) test

compiler/vmgen.nim

@@ -1546,6 +1546,7 @@ proc checkCanEval(c: PCtx; n: PNode) =
     # little hack ahead for bug #12612: assume gensym'ed variables
     # are in the right scope:
     if sfGenSym in s.flags and c.prc.sym == nil: discard
+    elif s.kind == skParam and s.typ.kind == tyTypeDesc: discard
     else: cannotEval(c, n)
   elif s.kind in {skProc, skFunc, skConverter, skMethod,
                   skIterator} and sfForward in s.flags:
@@ -2102,8 +2103,13 @@ proc gen(c: PCtx; n: PNode; dest: var TDest; flags: TGenFlags = {}) =
     let s = n.sym
     checkCanEval(c, n)
     case s.kind
-    of skVar, skForVar, skTemp, skLet, skParam, skResult:
+    of skVar, skForVar, skTemp, skLet, skResult:
       genRdVar(c, n, dest, flags)
+    of skParam:
+      if s.typ.kind == tyTypeDesc:
+        genTypeLit(c, s.typ, dest)
+      else:
+        genRdVar(c, n, dest, flags)
     of skProc, skFunc, skConverter, skMacro, skTemplate, skMethod, skIterator:
       # 'skTemplate' is only allowed for 'getAst' support:
       if s.kind == skIterator and s.typ.callConv == TCallingConvention.ccClosure:

tests/vm/ttypedesc.nim

@@ -0,0 +1,18 @@
+block: # issue #15760
+  type
+    Banana = object
+    SpecialBanana = object
+
+  proc getName(_: type Banana): string = "Banana"
+  proc getName(_: type SpecialBanana): string = "SpecialBanana"
+
+  proc x[T](): string = 
+    const n = getName(T) # this one works
+    result = n
+
+  proc y(T: type): string =
+    const n = getName(T) # this one failed to compile
+    result = n
+
+  doAssert x[SpecialBanana]() == "SpecialBanana"
+  doAssert y(SpecialBanana) == "SpecialBanana"

tests/vm/tvmmisc.nim

@@ -1,10 +1,11 @@
-# bug #4462
 import macros
 import os
 
+# bug #4462
 block:
   proc foo(t: typedesc) {.compileTime.} =
-    assert sameType(getType(t), getType(int))
+    assert sameType(getType(t), getType(typedesc[int]))
+    assert sameType(getType(t), getType(type int))
 
   static:
     foo(int)