v2.2.0 - yyyy-mm-dd

Changes affecting backward compatibility

-d:nimStrictDelete becomes the default. An index error is produced when the index passed to system.delete was out of bounds. Use -d:nimAuditDelete to mimic the old behavior for backwards compatibility.
The default user-agent in std/httpclient has been changed to Nim-httpclient/<version> instead of Nim httpclient/<version> which was incorrect according to the HTTP spec.
Methods now support implementations based on a VTable by using --experimental:vtables. Methods are then confined to be in the same module where their type has been defined.
With -d:nimPreviewNonVarDestructor, non-var destructors become the default.
A bug where tuple unpacking assignment with a longer tuple on the RHS than the LHS was allowed has been fixed, i.e. code like:
```
var a, b: int
(a, b) = (1, 2, 3, 4)
```
will no longer compile.
internalNew is removed from system, use new instead.
bindMethod in std/jsffi is deprecated, don't use it with closures.
JS backend now supports lambda lifting for closures. Use --legacy:jsNoLambdaLifting to emulate old behavior.
owner in std/macros is deprecated.

Standard library additions and changes

Changed std/osfiles.copyFile to allow to specify bufferSize instead of a hardcoded one.
Changed std/osfiles.copyFile to use POSIX_FADV_SEQUENTIAL hints for kernel-level aggressive sequential read-aheads.
std/htmlparser has been moved to a nimble package, use nimble or atlas to install it.

Added newStringUninit to system, which creates a new string of length len like newString but with uninitialized content.
Added setLenUninit to system, which doesn't initialize slots when enlarging a sequence.
Added hasDefaultValue to std/typetraits to check if a type has a valid default value.
Added Viewport API for the JavaScript targets in the dom module.
Added toSinglyLinkedRing and toDoublyLinkedRing to std/lists to convert from openArrays.
ORC: To be enabled via nimOrcStats there is a new API called GC_orcStats that can be used to query how many objects the cyclic collector did free. If the number is zero that is a strong indicator that you can use --mm:arc instead of --mm:orc.
A $ template is provided for Path in std/paths.
std/hashes.hash(x:string) changed to produce a 64-bit string Hash (based on Google's Farm Hash) which is also often faster than the present one. Define nimStringHash2 to get the old values back. --jsbigint=off mode always only produces the old values. This may impact your automated tests if they depend on hash order in some obvious or indirect way. Using sorted or OrderedTable is often an easy workaround.

Deprecates system.newSeqUninitialized, which is replaced by newSeqUninit.

Language changes

noInit can be used in types and fields to disable member initializers in the C++ backend.
C++ custom constructors initializers see https://nim-lang.org/docs/manual_experimental.htm#constructor-initializer
member can be used to attach a procedure to a C++ type.
C++ constructor now reuses result instead creating this.
Tuple unpacking changes:
- Tuple unpacking assignment now supports using underscores to discard values.
```
var a, c: int
(a, _, c) = (1, 2, 3)
```
- Tuple unpacking variable declarations now support type annotations, but only for the entire tuple.
```
let (a, b): (int, int) = (1, 2)
let (a, (b, c)): (byte, (float, cstring)) = (1, (2, "abc"))
```

An experimental option genericsOpenSym has been added to allow captured symbols in generic routine bodies to be replaced by symbols injected locally by templates/macros at instantiation time. bind may be used to keep the captured symbols over the injected ones regardless of enabling the option.

Since this change may affect runtime behavior, the experimental switch genericsOpenSym needs to be enabled, and a warning is given in the case where an injected symbol would replace a captured symbol not bound by bind and the experimental switch isn't enabled.

const value = "captured"
template foo(x: int, body: untyped) =
  let value {.inject.} = "injected"
  body

proc old[T](): string =
  foo(123):
    return value # warning: a new `value` has been injected, use `bind` or turn on `experimental:genericsOpenSym`
echo old[int]() # "captured"

{.experimental: "genericsOpenSym".}

proc bar[T](): string =
  foo(123):
    return value
assert bar[int]() == "injected" # previously it would be "captured"

proc baz[T](): string =
  bind value
  foo(123):
    return value
assert baz[int]() == "captured"

Compiler changes

--nimcache using a relative path as the argument in a config file is now relative to the config file instead of the current directory.

Tool changes

koch now allows bootstrapping with -d:nimHasLibFFI, replacing the older option of building the compiler directly w/ the libffi nimble package in tow.

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