From 363467fc00d15b274ce963548532cb6330f8b3a5 Mon Sep 17 00:00:00 2001
From: Tanguy Cizain <tanguycizain@gmail.com>
Date: Thu, 15 Apr 2021 15:45:38 +0200
Subject: [PATCH] Fix array's high & low return type for empty arrays (#17705)

* fix array.high/low return type

* Add test for empty array low return type

Co-authored-by: konsumlamm <44230978+konsumlamm@users.noreply.github.com>

Co-authored-by: konsumlamm <44230978+konsumlamm@users.noreply.github.com>
---
 compiler/semexprs.nim  | 2 ++
 lib/system.nim         | 8 ++++++++
 tests/array/tarray.nim | 7 +++++++
 3 files changed, 17 insertions(+)

diff --git a/compiler/semexprs.nim b/compiler/semexprs.nim
index cbd4318f7..13b53ef32 100644
--- a/compiler/semexprs.nim
+++ b/compiler/semexprs.nim
@@ -379,6 +379,8 @@ proc semLowHigh(c: PContext, n: PNode, m: TMagic): PNode =
       n.typ = getSysType(c.graph, n.info, tyInt)
     of tyArray:
       n.typ = typ[0] # indextype
+      if n.typ.kind == tyRange and emptyRange(n.typ.n[0], n.typ.n[1]): #Invalid range
+        n.typ = getSysType(c.graph, n.info, tyInt)
     of tyInt..tyInt64, tyChar, tyBool, tyEnum, tyUInt..tyUInt64, tyFloat..tyFloat64:
       n.typ = n[1].typ.skipTypes({tyTypeDesc})
     of tyGenericParam:
diff --git a/lib/system.nim b/lib/system.nim
index 6e84aca66..38f6d64d3 100644
--- a/lib/system.nim
+++ b/lib/system.nim
@@ -348,6 +348,8 @@ proc high*[T](x: openArray[T]): int {.magic: "High", noSideEffect.}
 proc high*[I, T](x: array[I, T]): I {.magic: "High", noSideEffect.}
   ## Returns the highest possible index of an array `x`.
   ##
+  ## For empty arrays, the return type is `int`.
+  ##
   ## See also:
   ## * `low(array) <#low,array[I,T]>`_
   ##
@@ -360,6 +362,8 @@ proc high*[I, T](x: array[I, T]): I {.magic: "High", noSideEffect.}
 proc high*[I, T](x: typedesc[array[I, T]]): I {.magic: "High", noSideEffect.}
   ## Returns the highest possible index of an array type.
   ##
+  ## For empty arrays, the return type is `int`.
+  ##
   ## See also:
   ## * `low(typedesc[array]) <#low,typedesc[array[I,T]]>`_
   ##
@@ -420,6 +424,8 @@ proc low*[T](x: openArray[T]): int {.magic: "Low", noSideEffect.}
 proc low*[I, T](x: array[I, T]): I {.magic: "Low", noSideEffect.}
   ## Returns the lowest possible index of an array `x`.
   ##
+  ## For empty arrays, the return type is `int`.
+  ##
   ## See also:
   ## * `high(array) <#high,array[I,T]>`_
   ##
@@ -432,6 +438,8 @@ proc low*[I, T](x: array[I, T]): I {.magic: "Low", noSideEffect.}
 proc low*[I, T](x: typedesc[array[I, T]]): I {.magic: "Low", noSideEffect.}
   ## Returns the lowest possible index of an array type.
   ##
+  ## For empty arrays, the return type is `int`.
+  ##
   ## See also:
   ## * `high(typedesc[array]) <#high,typedesc[array[I,T]]>`_
   ##
diff --git a/tests/array/tarray.nim b/tests/array/tarray.nim
index 81a43f203..2765ad06d 100644
--- a/tests/array/tarray.nim
+++ b/tests/array/tarray.nim
@@ -587,3 +587,10 @@ block t12466:
     a[0'u16 + i] = i
   for i in 0'u16 ..< 8'u16:
     a[0'u16 + i] = i
+
+block t17705:
+  # https://github.com/nim-lang/Nim/pull/17705
+  var a = array[0, int].low
+  a = int(a)
+  var b = array[0, int].high
+  b = int(b)