fix #19304 Borrowing std/times.format causes Error: illformed AST (#20659)

* fix #19304 Borrowing std/times.format causes Error: illformed AST

* follow suggestions

* mitigate for #4121

* improve error message

tests/distinct/tinvalidborrow.nim

@@ -2,12 +2,19 @@ discard """
   cmd: "nim check --hints:off --warnings:off $file"
   action: "reject"
   nimout:'''
-tinvalidborrow.nim(18, 3) Error: only a 'distinct' type can borrow `.`
-tinvalidborrow.nim(19, 3) Error: only a 'distinct' type can borrow `.`
-tinvalidborrow.nim(20, 1) Error: no symbol to borrow from found
+tinvalidborrow.nim(25, 3) Error: only a 'distinct' type can borrow `.`
+tinvalidborrow.nim(26, 3) Error: only a 'distinct' type can borrow `.`
+tinvalidborrow.nim(27, 1) Error: borrow proc without distinct type parameter is meaningless
+tinvalidborrow.nim(36, 1) Error: borrow with generic parameter is not supported
+tinvalidborrow.nim(41, 1) Error: borrow from proc return type mismatch: 'T'
+tinvalidborrow.nim(42, 1) Error: borrow from '[]=' is not supported
 '''
 """
 
+
+
+
+
 # bug #516
 
 type
@@ -23,3 +30,13 @@ var
   d, e: TAtom
 
 discard( $(d == e) )
+
+# issue #4121
+type HeapQueue[T] = distinct seq[T]
+proc len*[T](h: HeapQueue[T]): int {.borrow.}
+
+# issue #3564
+type vec4[T] = distinct array[4, float32]
+
+proc `[]`(v: vec4, i: int): float32 {.borrow.}
+proc `[]=`(v: vec4, i: int, va: float32) {.borrow.}

tests/stdlib/t19304.nim

@@ -0,0 +1,7 @@
+import times
+
+type DjangoDateTime* = distinct DateTime
+
+# proc toTime*(x: DjangoDateTime): Time  {.borrow.} # <-- works
+proc format*(x: DjangoDateTime, f: TimeFormat,
+    loc: DateTimeLocale = DefaultLocale): string {.borrow.}