fixes #10542; suppresses varargs conversion warnings (#22757)

fixes #10542
revives and close #20169

compiler/semexprs.nim

@@ -390,7 +390,8 @@ proc semConv(c: PContext, n: PNode; flags: TExprFlags = {}, expectedType: PType
  elif op.kind in {nkPar, nkTupleConstr} and targetType.kind == tyTuple:
  op = fitNode(c, targetType, op, result.info)
  of convNotNeedeed:
- message(c.config, n.info, hintConvFromXtoItselfNotNeeded, result.typ.typeToString)
+ if efNoSem2Check notin flags:
+ message(c.config, n.info, hintConvFromXtoItselfNotNeeded, result.typ.typeToString)
  of convNotLegal:
  result = fitNode(c, result.typ, result[1], result.info)
  if result == nil:

compiler/sigmatch.nim

@@ -2060,7 +2060,7 @@ proc localConvMatch(c: PContext, m: var TCandidate, f, a: PType,
  if result != nil:
  if result.typ == nil: return nil
  # bug #13378, ensure we produce a real generic instantiation:
- result = c.semExpr(c, call)
+ result = c.semExpr(c, call, {efNoSem2Check})
  # resulting type must be consistent with the other arguments:
  var r = typeRel(m, f[0], result.typ)
  if r < isGeneric: return nil

tests/errmsgs/t10542.nim

@@ -0,0 +1,24 @@
+discard """
+ matrix: "--hintaserror:ConvFromXtoItselfNotNeeded"
+"""
+
+# bug #10542
+
+proc f(args: varargs[string, string], length: int) =
+ doAssert args.len == length
+
+# main use case that requires type conversion (no warning here)
+f("a", "b", 2)
+f("a", 1)
+
+
+proc m(args: varargs[cstring, cstring]) =
+ doAssert args.len == 2
+
+# main use case that requires type conversion (no warning here)
+m("a", "b")
+
+# if an argument already is cstring there's a warning
+let x: cstring = "x"
+m("a", x)
+m(x, "a")