fix #15958 (#15970) [backport:1.4]

* fix #15958

* also cover openArray and VarArgs

* more tests

* cover even more types

* cover even more types

* Trigger build

* Trigger build

* cover sets passed as arrays

(cherry picked from commit fcb2ec4)

compiler/ccgtypes.nim

@@ -282,7 +282,8 @@ proc ccgIntroducedPtr(conf: ConfigRef; s: PSym, retType: PType): bool =
     result = false
   # first parameter and return type is 'lent T'? --> use pass by pointer
   if s.position == 0 and retType != nil and retType.kind == tyLent:
-    result = pt.kind != tyVar
+    result = not (pt.kind in {tyVar, tyArray, tyOpenArray, tyVarargs, tyRef, tyPtr, tyPointer} or
+      pt.kind == tySet and mapSetType(conf, pt) == ctArray)
 
 proc fillResult(conf: ConfigRef; param: PNode) =
   fillLoc(param.sym.loc, locParam, param, ~"Result",

tests/lent/tbasic_lent_check.nim

@@ -1,4 +1,5 @@
 discard """
+  targets: "c cpp"
   output: "1"
 """
 
@@ -14,3 +15,41 @@ proc main =
   doAssert(not compiles(passToVar(viewInto(x))))
 
 main()
+
+
+#------------------------------------------------------------------------------
+# issue #15958
+
+block:
+  proc byLent[T](a: T): lent T = a
+  let a = [11,12]
+  let b = @[21,23]  
+  let ss = {1, 2, 3, 5}
+  doAssert byLent(a) == [11,12]
+  doAssert byLent(a).unsafeAddr == a.unsafeAddr
+  doAssert byLent(b) == @[21,23]
+  doAssert byLent(b).unsafeAddr == b.unsafeAddr
+  doAssert byLent(ss) == {1, 2, 3, 5}
+  doAssert byLent(ss).unsafeAddr == ss.unsafeAddr
+
+  let r = new(float)
+  r[] = 10.0
+  doAssert byLent(r)[] == 10.0
+
+  let p = create(float)
+  p[] = 20.0
+  doAssert byLent(p)[] == 20.0
+
+  proc byLent2[T](a: openarray[T]): lent T = a[0]
+  doAssert byLent2(a) == 11
+  doAssert byLent2(a).unsafeAddr == a[0].unsafeAddr
+  doAssert byLent2(b) == 21
+  doAssert byLent2(b).unsafeAddr == b[0].unsafeAddr
+
+  proc byLent3[T](a: varargs[T]): lent T = a[1]
+  let 
+    x = 10
+    y = 20
+    z = 30
+  doAssert byLent3(x, y, z) == 20
+