fix(NIM-BUG): cast[char] not trunc on JS

Author: litlighilit

Modules/unicodedata/decimalAndSpace.nim

@@ -3,13 +3,14 @@
 from std/unicode import `<%`
 include ./common_h
 import ./[rune_decl, decimal, space]
+import ../../Utils/castChar
 
 const AsciiDigits = "0123456789"
 proc transformDecimalAndSpaceToASCII*(unicodeStr: openArray[Rune]): string =
   result = (when declared(newStringUninit): newStringUninit else: newString)(unicodeStr.len)
   for i, rune in unicodeStr:
     template st(val) = result[i] = val
-    if rune <% Rune(127): st cast[char](rune)
+    if rune <% Rune(127): st castChar(rune)
     elif rune.isspace(): st ' '
     else:
       decimalItOr(rune):

Objects/stringobject.nim

@@ -3,9 +3,10 @@ import ./hash_def
 import std/unicode
 export Rune, unicode.`==`, toRunes
 from std/strutils import join
-import macros
+import std/macros
 
-import pyobject
+import ./pyobject
+import ../Utils/castChar
 
 type UnicodeVariant* = ref object
   ## UCS1 or UCS4 variant
@@ -366,7 +367,7 @@ proc copy_characters(dest: PyStrObject, dest_start: int, frm: PyStrObject, frm_s
     loopAsgn dest.str.asciiStr:
       if it >% Rune(255):
         when check_maxchar: return true
-        else: cast[char](it)
+        else: castChar(it)
       else:
         cast[char](it)
   else:

Utils/castChar.nim

@@ -0,0 +1,7 @@
+
+from std/unicode import Rune
+when defined(js):
+  template castChar*(i: SomeInteger): char = cast[char](i and 255)
+  template castChar*(i: Rune): char = char cast[uint8](i)
+else:
+  template castChar*(i: SomeInteger|Rune): char = cast[char](i)