fix #18990 Regression in proc symbol resolution; Error: attempting to… (#20554)

fix #18990 Regression in proc symbol resolution; Error: attempting to call routine

compiler/semtypes.nim

@@ -1298,7 +1298,7 @@ proc semProcTypeNode(c: PContext, n, genericParams: PNode,
     if hasDefault:
       def = a[^1]
       block determineType:
-        if genericParams.isGenericParams:
+        if genericParams != nil and genericParams.len > 0:
           def = semGenericStmt(c, def)
           if hasUnresolvedArgs(c, def):
             def.typ = makeTypeFromExpr(c, def.copyTree)
@@ -1426,7 +1426,7 @@ proc semProcTypeNode(c: PContext, n, genericParams: PNode,
           result.flags.excl tfHasMeta
       result.n.typ = r
 
-  if genericParams.isGenericParams:
+  if genericParams != nil and genericParams.len > 0:
     for n in genericParams:
       if {sfUsed, sfAnon} * n.sym.flags == {}:
         result.flags.incl tfUnresolved

tests/constr/a.nim

@@ -0,0 +1,2 @@
+type A* = object
+  a: uint8

tests/constr/b.nim

@@ -0,0 +1,2 @@
+type B* = object
+proc A*(a, b: float): B = discard

tests/constr/t18990.nim

@@ -0,0 +1,3 @@
+import a, b
+discard A(1f, 1f) # works
+proc x(b = A(1f, 1f)) = discard # doesn't work