fixes #18059 (#18140)

* fixes #18059

compiler/semexprs.nim

@@ -54,7 +54,8 @@ proc semOperand(c: PContext, n: PNode, flags: TExprFlags = {}): PNode =
   result = semExpr(c, n, flags + {efOperand})
   if result.typ != nil:
     # XXX tyGenericInst here?
-    if result.typ.kind == tyProc and tfUnresolved in result.typ.flags:
+    if result.typ.kind == tyProc and hasUnresolvedParams(result, {efOperand}):
+      #and tfUnresolved in result.typ.flags:
       localError(c.config, n.info, errProcHasNoConcreteType % n.renderTree)
     if result.typ.kind in {tyVar, tyLent}: result = newDeref(result)
   elif {efWantStmt, efAllowStmt} * flags != {}:
@@ -2649,6 +2650,23 @@ proc shouldBeBracketExpr(n: PNode): bool =
           n[0] = be
           return true
 
+proc asBracketExpr(c: PContext; n: PNode): PNode =
+  proc isGeneric(c: PContext; n: PNode): bool =
+    if n.kind in {nkIdent, nkAccQuoted}:
+      let s = qualifiedLookUp(c, n, {})
+      result = s != nil and isGenericRoutineStrict(s)
+
+  assert n.kind in nkCallKinds
+  if n.len > 1 and isGeneric(c, n[1]):
+    let b = n[0]
+    if b.kind in nkSymChoices:
+      for i in 0..<b.len:
+        if b[i].kind == nkSym and b[i].sym.magic == mArrGet:
+          result = newNodeI(nkBracketExpr, n.info)
+          for i in 1..<n.len: result.add(n[i])
+          return result
+  return nil
+
 proc hoistParamsUsedInDefault(c: PContext, call, letSection, defExpr: var PNode) =
   # This takes care of complicated signatures such as:
   # proc foo(a: int, b = a)
@@ -2820,7 +2838,13 @@ proc semExpr(c: PContext, n: PNode, flags: TExprFlags = {}): PNode =
       # the 'newSeq[T](x)' bug
       setGenericParams(c, n[0])
       result = semDirectOp(c, n, flags)
-    elif isSymChoice(n[0]) or nfDotField in n.flags:
+    elif nfDotField in n.flags:
+      result = semDirectOp(c, n, flags)
+    elif isSymChoice(n[0]):
+      let b = asBracketExpr(c, n)
+      if b != nil:
+        result = semExpr(c, b, flags)
+      else:
         result = semDirectOp(c, n, flags)
     else:
       result = semIndirectOp(c, n, flags)

compiler/semstmts.nim

@@ -385,6 +385,23 @@ proc hasEmpty(typ: PType): bool =
     for s in typ.sons:
       result = result or hasEmpty(s)
 
+proc hasUnresolvedParams(n: PNode; flags: TExprFlags): bool =
+  result = tfUnresolved in n.typ.flags
+  when false:
+    case n.kind
+    of nkSym:
+      result = isGenericRoutineStrict(n.sym)
+    of nkSymChoices:
+      for ch in n:
+        if hasUnresolvedParams(ch, flags):
+          return true
+      result = false
+    else:
+      result = false
+    if efOperand in flags:
+      if tfUnresolved notin n.typ.flags:
+        result = false
+
 proc makeDeref(n: PNode): PNode =
   var t = n.typ
   if t.kind in tyUserTypeClasses and t.isResolvedUserTypeClass:
@@ -517,7 +534,8 @@ proc semVarOrLet(c: PContext, n: PNode, symkind: TSymKind): PNode =
           typ = typ.lastSon
         if hasEmpty(typ):
           localError(c.config, def.info, errCannotInferTypeOfTheLiteral % typ.kind.toHumanStr)
-        elif typ.kind == tyProc and tfUnresolved in typ.flags:
+        elif typ.kind == tyProc and hasUnresolvedParams(def, {}):
+          # tfUnresolved in typ.flags:
           localError(c.config, def.info, errProcHasNoConcreteType % def.renderTree)
         when false:
           # XXX This typing rule is neither documented nor complete enough to

tests/metatype/tcps.nim

@@ -0,0 +1,35 @@
+discard """
+  output: '''10
+string'''
+"""
+
+# bug #18059
+type
+  C = ref object of RootObj
+    fn: ContProc
+    ex: ref Exception
+
+  ContProc = proc (c: C): C {.nimcall.}
+
+proc noop(c: C): C = c
+
+type
+  Env[T] = ref object of C
+    x: T
+
+proc foo_cont[U](c: C): C =
+  proc afterCall[V](c: C): C =
+    echo Env[V](c).x
+
+  c.fn = afterCall[U]
+  return noop(c)
+
+proc foo[T](x: T): C =
+  return Env[T](fn: foo_cont[T], x: x)
+
+proc tramp(c: sink C) =
+  while c != nil and c.fn != nil:
+    c = c.fn(c)
+
+tramp foo(10)
+tramp foo("string")