Stricter checks for typedesc

compiler/semstmts.nim

@@ -409,6 +409,9 @@ proc semVarOrLet(c: PContext, n: PNode, symkind: TSymKind): PNode =
     var typ: PType
     if a.sons[length-2].kind != nkEmpty:
       typ = semTypeNode(c, a.sons[length-2], nil)
+      if typ.kind == tyTypeDesc and c.p.owner.kind != skMacro:
+        localError(c.config, a.sons[length-2].info, "'typedesc' metatype is not valid here")
+        continue
     else:
       typ = nil
     var def: PNode = c.graph.emptyNode
@@ -539,6 +542,9 @@ proc semConst(c: PContext, n: PNode): PNode =
     if typ == nil:
       localError(c.config, a.sons[2].info, errConstExprExpected)
       continue
+    if typ.kind == tyTypeDesc:
+      localError(c.config, a.info, "cannot have typedesc as const value, " &
+        "use 'type $1 = $2' instead", [$a.sons[0], typeToString(def.typ.skipTypes({tyTypeDesc}))])
     if typeAllowed(typ, skConst) != nil and def.kind != nkNilLit:
       localError(c.config, a.info, "invalid type for const: " & typeToString(typ))
       continue

compiler/types.nim

@@ -1188,8 +1188,8 @@ proc typeAllowedAux(marker: var IntSet, typ: PType, kind: TSymKind,
     if result.isNil and t.sons[0] != nil:
       result = typeAllowedAux(marker, t.sons[0], skResult, flags)
   of tyTypeDesc:
-    # XXX: This is still a horrible idea...
-    result = nil
+    # Could be inside a macro, so var and let are allowed here and checked later
+    if kind notin {skParam, skResult, skVar, skLet}: result = t
   of tyExpr, tyStmt, tyStatic:
     if kind notin {skParam, skResult}: result = t
   of tyVoid:

tests/errmsgs/t8610.nim

@@ -0,0 +1,8 @@
+discard """
+  errormsg: "cannot have typedesc as const value, use 'type Foo = int' instead"
+  line: 6
+"""
+
+const Foo=int
+echo Foo is int # true
+echo int is Foo # Error: type expected

tests/errmsgs/t8654_1.nim

@@ -0,0 +1,8 @@
+discard """
+  errormsg: "'typedesc' metatype is not valid here"
+  line: 6
+"""
+
+var a: typedesc
+a = typedesc[int]
+echo a is typedesc[int]

tests/errmsgs/t8654_2.nim

@@ -0,0 +1,7 @@
+discard """
+  errormsg: "cannot have typedesc as const value, use 'type a = int' instead"
+  line: 6
+"""
+
+const a: typedesc = typedesc[int]
+echo a is typedesc[int]