implement the special treatment of explicit type params in concepts

compiler/ast.nim

@@ -494,6 +494,8 @@ type
     tfGenericTypeParam
     tfImplicitTypeParam
     tfInferrableStatic
+    tfExplicit        # for typedescs, marks types explicitly prefixed with the
+                      # `type` operator (e.g. type int)
     tfWildcard        # consider a proc like foo[T, I](x: Type[T, I])
                       # T and I here can bind to both typedesc and static types
                       # before this is determined, we'll consider them to be a

compiler/semmagic.nim

@@ -24,7 +24,7 @@ proc semTypeOf(c: PContext; n: PNode): PNode =
   result = newNodeI(nkTypeOfExpr, n.info)
   let typExpr = semExprWithType(c, n, {efInTypeof})
   result.add typExpr
-  result.typ = makeTypeDesc(c, typExpr.typ.skipTypes({tyTypeDesc}))
+  result.typ = makeTypeDesc(c, typExpr.typ)
 
 type
   SemAsgnMode = enum asgnNormal, noOverloadedSubscript, noOverloadedAsgn

compiler/semtypes.nim

@@ -1239,6 +1239,7 @@ proc semTypeNode(c: PContext, n: PNode, prev: PType): PType =
     let typExpr = semExprWithType(c, n.sons[0], {efInTypeof})
     fixupTypeOf(c, prev, typExpr)
     result = typExpr.typ
+    if result.kind == tyTypeDesc: result.flags.incl tfExplicit
   of nkPar:
     if sonsLen(n) == 1: result = semTypeNode(c, n.sons[0], prev)
     else:

compiler/sigmatch.nim

@@ -638,6 +638,7 @@ proc matchUserTypeClass*(c: PContext, m: var TCandidate,
     if modifier != tyNone:
       dummyName = param[0]
       dummyType = c.makeTypeWithModifier(modifier, a)
+      if modifier == tyTypeDesc: dummyType.flags.incl tfExplicit
     else:
       dummyName = param
       dummyType = a
@@ -833,7 +834,8 @@ proc typeRel(c: var TCandidate, f, aOrig: PType, doBind = true): TTypeRelation =
   var
     useTypeLoweringRuleInTypeClass = c.c.inTypeClass > 0 and
                                      not c.isNoCall and
-                                     f.kind != tyTypeDesc
+                                     f.kind != tyTypeDesc and
+                                     tfExplicit notin aOrig.flags
 
     aOrig = if useTypeLoweringRuleInTypeClass:
           aOrig.skipTypes({tyTypeDesc, tyFieldAccessor})