remove ArrayDummySize with unchecked arrays (#5818)

doc/manual/ffi.txt

@@ -132,7 +132,7 @@ translated into a C array of undetermined size:
 
 .. code-block:: nim
   type
-    ArrayPart{.unchecked.} = array[0..0, int]
+    ArrayPart{.unchecked.} = array[0, int]
     MySeq = object
       len, cap: int
       data: ArrayPart
@@ -146,10 +146,6 @@ Produces roughly this C code:
     NI data[];
   } MySeq;
 
-The bounds checking done at compile time is not disabled for now, so to access
-``s.data[C]`` (where ``C`` is a constant) the array's index needs to
-include ``C``.
-
 The base type of the unchecked array may not contain any GC'ed memory but this
 is currently not checked.
 

lib/pure/collections/rtarrays.nim

@@ -19,7 +19,7 @@ type
     L: Natural
     spart: seq[T]
     apart: array[ArrayPartSize, T]
-  UncheckedArray* {.unchecked.}[T] = array[0..100_000_000, T]
+  UncheckedArray* {.unchecked.}[T] = array[0, T]
 
 template usesSeqPart(x): untyped = x.L > ArrayPartSize
 

lib/pure/collections/sharedstrings.nim

@@ -9,10 +9,8 @@
 
 ## Shared string support for Nim.
 
-const ArrayDummySize = when defined(cpu16): 10_000 else: 100_000_000
-
 type
-  UncheckedCharArray {.unchecked.} = array[0..ArrayDummySize, char]
+  UncheckedCharArray = UncheckedArray[char]
 
 type
   Buffer = ptr object

lib/pure/ioselectors.nim

@@ -208,7 +208,7 @@ else:
     import locks
 
     type
-      SharedArray {.unchecked.}[T] = array[0..100, T]
+      SharedArray[T] = UncheckedArray[T]
 
     proc allocSharedArray[T](nsize: int): ptr SharedArray[T] =
       result = cast[ptr SharedArray[T]](allocShared0(sizeof(T) * nsize))

lib/system.nim

@@ -268,6 +268,9 @@ type
   seq*{.magic: "Seq".}[T]  ## Generic type to construct sequences.
   set*{.magic: "Set".}[T]  ## Generic type to construct bit sets.
 
+  UncheckedArray* {.unchecked.}[T] = array[0, T]
+    ## Array with no boudns checking
+
 when defined(nimArrIdx):
   # :array|openarray|string|seq|cstring|tuple
   proc `[]`*[I: Ordinal;T](a: T; i: I): T {.
@@ -381,8 +384,6 @@ include "system/inclrtl"
 const NoFakeVars* = defined(nimscript) ## true if the backend doesn't support \
   ## "fake variables" like 'var EBADF {.importc.}: cint'.
 
-const ArrayDummySize = when defined(cpu16): 10_000 else: 100_000_000
-
 when not defined(JS):
   type
     TGenericSeq {.compilerproc, pure, inheritable.} = object
@@ -390,10 +391,9 @@ when not defined(JS):
       when defined(gogc):
         elemSize: int
     PGenericSeq {.exportc.} = ptr TGenericSeq
-    UncheckedCharArray {.unchecked.} = array[0..ArrayDummySize, char]
     # len and space without counting the terminating zero:
     NimStringDesc {.compilerproc, final.} = object of TGenericSeq
-      data: UncheckedCharArray
+      data: UncheckedArray[char]
     NimString = ptr NimStringDesc
 
 when not defined(JS) and not defined(nimscript):
@@ -1600,8 +1600,7 @@ type # these work for most platforms:
   culonglong* {.importc: "unsigned long long", nodecl.} = uint64
     ## This is the same as the type ``unsigned long long`` in *C*.
 
-  cstringArray* {.importc: "char**", nodecl.} = ptr
+  cstringArray* {.importc: "char**", nodecl.} = ptr UncheckedArray[cstring]
-    array[0..ArrayDummySize, cstring]
     ## This is binary compatible to the type ``char**`` in *C*. The array's
     ## high value is large enough to disable bounds checking in practice.
     ## Use `cstringArrayToSeq` to convert it into a ``seq[string]``.
@@ -3045,7 +3044,8 @@ when not defined(JS): #and not defined(nimscript):
       ## creates a NULL terminated cstringArray from `a`. The result has to
       ## be freed with `deallocCStringArray` after it's not needed anymore.
       result = cast[cstringArray](alloc0((a.len+1) * sizeof(cstring)))
-      let x = cast[ptr array[0..ArrayDummySize, string]](a)
+
+      let x = cast[ptr UncheckedArray[string]](a)
       for i in 0 .. a.high:
         result[i] = cast[cstring](alloc0(x[i].len+1))
         copyMem(result[i], addr(x[i][0]), x[i].len)

lib/system/cellsets.nim

@@ -30,13 +30,12 @@ type
     key: ByteAddress   # start address at bit 0
     bits: array[BitIndex, int] # a bit vector
 
-  PPageDescArray = ptr array[ArrayDummySize, PPageDesc]
+  PPageDescArray = ptr UncheckedArray[PPageDesc]
   CellSet {.final, pure.} = object
     counter, max: int
     head: PPageDesc
     data: PPageDescArray
-
+  PCellArray = ptr UncheckedArray[PCell]
-  PCellArray = ptr array[ArrayDummySize, PCell]
   CellSeq {.final, pure.} = object
     len, cap: int
     d: PCellArray

lib/system/mmdisp.nim

@@ -34,7 +34,7 @@ const
 
 type
   PPointer = ptr pointer
-  ByteArray = array[0..ArrayDummySize, byte]
+  ByteArray = UncheckedArray[byte]
   PByte = ptr ByteArray
   PString = ptr string
 {.deprecated: [TByteArray: ByteArray].}

lib/system/sysio.nim

@@ -86,11 +86,11 @@ proc writeBuffer(f: File, buffer: pointer, len: Natural): int =
   checkErr(f)
 
 proc writeBytes(f: File, a: openArray[int8|uint8], start, len: Natural): int =
-  var x = cast[ptr array[ArrayDummySize, int8]](a)
+  var x = cast[ptr UncheckedArray[int8]](a)
-  result = writeBuffer(f, addr(x[start]), len)
+  result = writeBuffer(f, addr(x[int(start)]), len)
 proc writeChars(f: File, a: openArray[char], start, len: Natural): int =
-  var x = cast[ptr array[ArrayDummySize, int8]](a)
+  var x = cast[ptr UncheckedArray[int8]](a)
-  result = writeBuffer(f, addr(x[start]), len)
+  result = writeBuffer(f, addr(x[int(start)]), len)
 
 proc write(f: File, s: string) =
   if writeBuffer(f, cstring(s), s.len) != s.len:

lib/system/widestrs.nim

@@ -15,7 +15,7 @@ when not declared(NimString):
 
 type
   Utf16Char* = distinct int16
-  WideCString* = ref array[ArrayDummySize, Utf16Char]
+  WideCString* = ref UncheckedArray[Utf16Char]
 {.deprecated: [TUtf16Char: Utf16Char].}
 
 proc len*(w: WideCString): int =

tests/array/tunchecked.nim

@@ -0,0 +1,5 @@
+{.boundchecks: on.}
+type Unchecked {.unchecked.} = array[0, char]
+
+var x = cast[ptr Unchecked](alloc(100))
+x[5] = 'x'

tests/metatype/ttypedesc2.nim

@@ -18,11 +18,10 @@ when true:
       uoffset_t* = uint32
       FlatBufferBuilder* = object
 
-      uarray* {.unchecked.} [T]  = array [0..0, T]
       Array* [T] = object
           o*: uoffset_t
           len*: int
-          data*: ptr uarray[T]
+          data*: ptr UncheckedArray[T]
 
   proc ca* (fbb: ptr FlatBufferBuilder, T: typedesc, len: int): Array[T] {.noinit.} =
       result.len = len