# v2.0.0 - yyyy-mm-dd


## Changes affecting backward compatibility
- `httpclient.contentLength` default to `-1` if the Content-Length header is not set in the response. It follows Apache HttpClient(Java), http(go) and .Net HttpWebResponse(C#) behavior. Previously it raised `ValueError`.

- `addr` is now available for all addressable locations,
  `unsafeAddr` is now deprecated and an alias for `addr`.

- Certain definitions from the default `system` module have been moved to
  the following new modules:

  - `std/syncio`
  - `std/assertions`
  - `std/formatfloat`
  - `std/objectdollar`
  - `std/widestrs`
  - `std/typedthreads`
  - `std/sysatomics`

  In the future, these definitions will be removed from the `system` module,
  and their respective modules will have to be imported to use them.
  Currently, to make these imports required, the `-d:nimPreviewSlimSystem` option
  may be used.

- Enabling `-d:nimPreviewSlimSystem` also removes the following deprecated
  symbols in the `system` module:
  - Aliases with `Error` suffix to exception types that have a `Defect` suffix
    (see [exceptions](https://nim-lang.github.io/Nim/exceptions.html)):
    `ArithmeticError`, `DivByZeroError`, `OverflowError`,
    `AccessViolationError`, `AssertionError`, `OutOfMemError`, `IndexError`,
    `FieldError`, `RangeError`, `StackOverflowError`, `ReraiseError`,
    `ObjectAssignmentError`, `ObjectConversionError`, `FloatingPointError`,
    `FloatOverflowError`, `FloatUnderflowError`, `FloatInexactError`,
    `DeadThreadError`, `NilAccessError`
  - `addQuitProc`, replaced by `exitprocs.addExitProc`
  - Legacy unsigned conversion operations: `ze`, `ze64`, `toU8`, `toU16`, `toU32`
  - `TaintedString`, formerly a distinct alias to `string`
  - `PInt32`, `PInt64`, `PFloat32`, `PFloat64`, aliases to
    `ptr int32`, `ptr int64`, `ptr float32`, `ptr float64`

- Enabling `-d:nimPreviewSlimSystem` removes the import of `channels_builtin` in
  in the `system` module.

- Enabling `-d:nimPreviewCstringConversion`, `ptr char`, `ptr array[N, char]` and `ptr UncheckedArray[N, char]` don't support conversion to cstring anymore.

- The `gc:v2` option is removed.

- The `mainmodule` and `m` options are removed.

- The `threads:on` option is now the default.

- Optional parameters in combination with `: body` syntax (RFC #405) are now opt-in via
  `experimental:flexibleOptionalParams`.

- Automatic dereferencing (experimental feature) is removed.

- The `Math.trunc` polyfill for targeting Internet Explorer was
  previously included in most JavaScript output files.
  Now, it is only included with `-d:nimJsMathTruncPolyfill`.
  If you are targeting Internet Explorer, you may choose to enable this option
  or define your own `Math.trunc` polyfill using the [`emit` pragma](https://nim-lang.org/docs/manual.html#implementation-specific-pragmas-emit-pragma).
  Nim uses `Math.trunc` for the division and modulo operators for integers.

- `shallowCopy` and `shallow` are removed for ARC/ORC. Use `move` when possible or combine assignment and
`sink` for optimization purposes.

- The experimental `nimPreviewDotLikeOps` switch is going to be removed or deprecated because it didn't fullfill its promises.

- The `{.this.}` pragma, deprecated since 0.19, has been removed.
- `nil` literals can no longer be directly assigned to variables or fields of `distinct` pointer types. They must be converted instead.
  ```nim
  type Foo = distinct ptr int

  # Before:
  var x: Foo = nil
  # After:
  var x: Foo = Foo(nil)
  ```
- Removed two type pragma syntaxes deprecated since 0.20, namely
  `type Foo = object {.final.}`, and `type Foo {.final.} [T] = object`.

- `foo a = b` now means `foo(a = b)` rather than `foo(a) = b`. This is consistent
  with the existing behavior of `foo a, b = c` meaning `foo(a, b = c)`.
  This decision was made with the assumption that the old syntax was used rarely;
  if your code used the old syntax, please be aware of this change.

- [Overloadable enums](https://nim-lang.github.io/Nim/manual.html#overloadable-enum-value-names) and Unicode Operators
  are no longer experimental.

- Removed the `nimIncrSeqV3` define.

- `macros.getImpl` for `const` symbols now returns the full definition node
  (as `nnkConstDef`) rather than the AST of the constant value.

- Lock levels are deprecated, now a noop.

- ORC is now the default memory management strategy. Use
  `--mm:refc` for a transition period.

- `strictEffects` are no longer experimental.
  Use `legacy:laxEffects` to keep backward compatibility.

- The `gorge`/`staticExec` calls will now return a descriptive message in the output
  if the execution fails for whatever reason. To get back legacy behaviour use `-d:nimLegacyGorgeErrors`.

- Pointer to `cstring` conversion now triggers a `[PtrToCstringConv]` warning.
  This warning will become an error in future versions! Use a `cast` operation
  like `cast[cstring](x)` instead.

- `logging` will default to flushing all log level messages. To get the legacy behaviour of only flushing Error and Fatal messages, use `-d:nimV1LogFlushBehavior`.

- Redefining templates with the same signature was previously
  allowed to support certain macro code. To do this explicitly, the
  `{.redefine.}` pragma has been added. Note that this is only for templates.
  Implicit redefinition of templates is now deprecated and will give an error in the future.

- Using an unnamed break in a block is deprecated. This warning will become an error in future versions! Use a named block with a named break instead.

- Several Standard libraries are moved to nimble packages, use `nimble` to install them:
  - `std/punycode` => `punycode`
  - `std/asyncftpclient` => `asyncftpclient`
  - `std/smtp` => `smtp`
  - `std/db_common` => `db_connector/db_common`
  - `std/db_sqlite` => `db_connector/db_sqlite`
  - `std/db_mysql` => `db_connector/db_mysql`
  - `std/db_postgres` => `db_connector/db_postgres`
  - `std/db_odbc` => `db_connector/db_odbc`

- Previously, calls like `foo(a, b): ...` or `foo(a, b) do: ...` where the final argument of
  `foo` had type `proc ()` were assumed by the compiler to mean `foo(a, b, proc () = ...)`.
  This behavior is now deprecated. Use `foo(a, b) do (): ...` or `foo(a, b, proc () = ...)` instead.

- If no exception or any exception deriving from Exception but not Defect or CatchableError given in except, a `warnBareExcept` warning will be triggered.

- The experimental strictFuncs feature now disallows a store to the heap via a `ref` or `ptr` indirection.

- The underscore identifier (`_`) is now generally not added to scope when
  used as the name of a definition. While this was already the case for
  variables, it is now also the case for routine parameters, generic
  parameters, routine declarations, type declarations, etc. This means that the following code now does not compile:

  ```nim
  proc foo(_: int): int = _ + 1
  echo foo(1)

  proc foo[_](t: typedesc[_]): seq[_] = @[default(_)]
  echo foo[int]()

  proc _() = echo "_"
  _()

  type _ = int
  let x: _ = 3
  ```

  Whereas the following code now compiles:

  ```nim
  proc foo(_, _: int): int = 123
  echo foo(1, 2)

  proc foo[_, _](): int = 123
  echo foo[int, bool]()

  proc foo[T, U](_: typedesc[T], _: typedesc[U]): (T, U) = (default(T), default(U))
  echo foo(int, bool)

  proc _() = echo "one"
  proc _() = echo "two"

  type _ = int
  type _ = float
  ```

- - Added the `--legacy:verboseTypeMismatch` switch to get legacy type mismatch error messages.

- The JavaScript backend now uses [BigInt](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigInt)
  for 64-bit integer types (`int64` and `uint64`) by default. As this affects
  JS code generation, code using these types to interface with the JS backend
  may need to be updated. Note that `int` and `uint` are not affected.
  
  For compatibility with [platforms that do not support BigInt](https://caniuse.com/bigint)
  and in the case of potential bugs with the new implementation, the
  old behavior is currently still supported with the command line option
  `--jsbigint64:off`.

- The `proc` and `iterator` type classes now respectively only match
  procs and iterators. Previously both type classes matched any of
  procs or iterators.

  ```nim
  proc prc(): int =
    123

  iterator iter(): int =
    yield 123
  
  proc takesProc[T: proc](x: T) = discard
  proc takesIter[T: iterator](x: T) = discard

  # always compiled:
  takesProc(prc)
  takesIter(iter)
  # no longer compiles:
  takesProc(iter)
  takesIter(prc)
  ```

- The `proc` and `iterator` type classes now accept a calling convention pragma
  (i.e. `proc {.closure.}`) that must be shared by matching proc or iterator
  types. Previously pragmas were parsed but discarded if no parameter list
  was given.

  This is represented in the AST by an `nnkProcTy`/`nnkIteratorTy` node with
  an `nnkEmpty` node in the place of the `nnkFormalParams` node, and the pragma
  node in the same place as in a concrete `proc` or `iterator` type node. This
  state of the AST may be unexpected to existing code, both due to the
  replacement of the `nnkFormalParams` node as well as having child nodes
  unlike other type class AST.

## Standard library additions and changes

[//]: # "Changes:"
- OpenSSL 3 is now supported.
- `macros.parseExpr` and `macros.parseStmt` now accept an optional
  filename argument for more informative errors.
- Module `colors` expanded with missing colors from the CSS color standard.
  `colPaleVioletRed` and `colMediumPurple` have also been changed to match the CSS color standard.
- Fixed `lists.SinglyLinkedList` being broken after removing the last node ([#19353](https://github.com/nim-lang/Nim/pull/19353)).
- The `md5` module now works at compile time and in JavaScript.
- Changed `mimedb` to use an `OrderedTable` instead of `OrderedTableRef` to support `const` tables.
- `strutils.find` now uses and defaults to `last = -1` for whole string searches,
  making limiting it to just the first char (`last = 0`) valid.
- `random.rand` now works with `Ordinal`s.
- Undeprecated `os.isvalidfilename`.
- `std/oids` now uses `int64` to store time internally (before it was int32).
- `std/uri.Uri` dollar `$` improved, precalculates the `string` result length from the `Uri`.
- `std/uri.Uri.isIpv6` is now exported.
- `std/logging.ConsoleLogger` and `FileLogger` now have a `flushThreshold` attribute to set what log message levels are automatically flushed. For Nim v1 use `-d:nimFlushAllLogs` to automatically flush all message levels. Flushing all logs is the default behavior for Nim v2.


- `std/net.IpAddress` dollar `$` improved, uses a fixed capacity for the `string` result based from the `IpAddressFamily`.
- `std/jsfetch.newFetchOptions` now has default values for all parameters
- `std/jsformdata` now accepts `Blob` data type.

- `std/sharedlist` and `std/sharedtables` are now deprecated, see RFC [#433](https://github.com/nim-lang/RFCs/issues/433).

- New compile flag (`-d:nimNoGetRandom`) when building `std/sysrand` to remove dependency on linux `getrandom` syscall.

  This compile flag only affects linux builds and is necessary if either compiling on a linux kernel version < 3.17, or if code built will be executing on kernel < 3.17.

  On linux kernels < 3.17 (such as kernel 3.10 in RHEL7 and CentOS7), the `getrandom` syscall was not yet introduced. Without this, the `std/sysrand` module will not build properly, and if code is built on a kernel >= 3.17 without the flag, any usage of the `std/sysrand` module will fail to execute on a kernel < 3.17 (since it attempts to perform a syscall to `getrandom`, which isn't present in the current kernel). A compile flag has been added to force the `std/sysrand` module to use /dev/urandom (available since linux kernel 1.3.30), rather than the `getrandom` syscall. This allows for use of a cryptographically secure PRNG, regardless of kernel support for the `getrandom` syscall.

  When building for RHEL7/CentOS7 for example, the entire build process for nim from a source package would then be:
  ```sh
  $ yum install devtoolset-8 # Install GCC version 8 vs the standard 4.8.5 on RHEL7/CentOS7. Alternatively use -d:nimEmulateOverflowChecks. See issue #13692 for details
  $ scl enable devtoolset-8 bash # Run bash shell with default toolchain of gcc 8
  $ sh build.sh  # per unix install instructions
  $ bin/nim c koch  # per unix install instructions
  $ ./koch boot -d:release  # per unix install instructions
  $ ./koch tools -d:nimNoGetRandom  # pass the nimNoGetRandom flag to compile std/sysrand without support for getrandom syscall
  ```

  This is necessary to pass when building nim on kernel versions < 3.17 in particular to avoid an error of "SYS_getrandom undeclared" during the build process for stdlib (sysrand in particular).

[//]: # "Additions:"
- Added ISO 8601 week date utilities in `times`:
  - Added `IsoWeekRange`, a range type for weeks in a week-based year.
  - Added `IsoYear`, a distinct type for a week-based year in contrast to a regular year.
  - Added a `initDateTime` overload to create a datetime from an ISO week date.
  - Added `getIsoWeekAndYear` to get an ISO week number and week-based year from a datetime.
  - Added `getIsoWeeksInYear` to return the number of weeks in a week-based year.
- Added new modules which were part of `std/os`:
  - Added `std/oserrors` for OS error reporting. Added `std/envvars` for environment variables handling.
  - Added `std/paths`, `std/dirs`, `std/files`, `std/symlinks` and `std/appdirs`.
  - Added `std/cmdline` for reading command line parameters.
- Added `sep` parameter in `std/uri` to specify the query separator.
- Added bindings to [`Array.shift`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/shift)
  and [`queueMicrotask`](https://developer.mozilla.org/en-US/docs/Web/API/queueMicrotask)
  in `jscore` for JavaScript targets.
- Added `UppercaseLetters`, `LowercaseLetters`, `PunctuationChars`, `PrintableChars` sets to `std/strutils`.
- Added `complex.sgn` for obtaining the phase of complex numbers.
- Added `insertAdjacentText`, `insertAdjacentElement`, `insertAdjacentHTML`,
  `after`, `before`, `closest`, `append`, `hasAttributeNS`, `removeAttributeNS`,
  `hasPointerCapture`, `releasePointerCapture`, `requestPointerLock`,
  `replaceChildren`, `replaceWith`, `scrollIntoViewIfNeeded`, `setHTML`,
  `toggleAttribute`, and `matches` to `std/dom`.
- Added [`jsre.hasIndices`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/RegExp/hasIndices)
- Added `capacity` for `string` and `seq` to return the current capacity, see https://github.com/nim-lang/RFCs/issues/460
- Added `openArray[char]` overloads for `std/parseutils` allowing more code reuse.
- Added `openArray[char]` overloads for `std/unicode` allowing more code reuse.
- Added `safe` parameter to `base64.encodeMime`.
- Added `parseutils.parseSize` - inverse to `strutils.formatSize` - to parse human readable sizes.

[//]: # "Deprecations:"
- Deprecated `selfExe` for Nimscript.
- Deprecated `std/sums`.
- Deprecated `std/base64.encode` for collections of arbitrary integer element type.
  Now only `byte` and `char` are supported.

[//]: # "Removals:"
- Removed deprecated module `parseopt2`.
- Removed deprecated module `sharedstrings`.
- Removed deprecated module `dom_extensions`.
- Removed deprecated module `LockFreeHash`.
- Removed deprecated module `events`.
- Removed deprecated `oids.oidToString`.
- Removed define `nimExperimentalAsyncjsThen` for `std/asyncjs.then` and `std/jsfetch`.
- Removed deprecated `jsre.test` and `jsre.toString`.
- Removed deprecated `math.c_frexp`.
- Removed deprecated `` httpcore.`==` ``.
- Removed deprecated `std/posix.CMSG_SPACE` and `std/posix.CMSG_LEN` that takes wrong argument types.
- Removed deprecated `osproc.poDemon`, symbol with typo.
- Removed deprecated `tables.rightSize`.


- Removed deprecated `posix.CLONE_STOPPED`.


## Language changes

- [Tag tracking](https://nim-lang.github.io/Nim/manual.html#effect-system-tag-tracking) supports the definition of forbidden tags by the `.forbids` pragma
  which can be used to disable certain effects in proc types.
- [Case statement macros](https://nim-lang.github.io/Nim/manual.html#macros-case-statement-macros) are no longer experimental,
  meaning you no longer need to enable the experimental switch `caseStmtMacros` to use them.
- Full command syntax and block arguments i.e. `foo a, b: c` are now allowed
  for the right-hand side of type definitions in type sections. Previously
  they would error with "invalid indentation".

- Compile-time define changes:
  - `defined` now accepts identifiers separated by dots, i.e. `defined(a.b.c)`.
    In the command line, this is defined as `-d:a.b.c`. Older versions can
    use accents as in ``defined(`a.b.c`)`` to access such defines.
  - [Define pragmas for constants](https://nim-lang.github.io/Nim/manual.html#implementation-specific-pragmas-compileminustime-define-pragmas)
    now support a string argument for qualified define names.

    ```nim
    # -d:package.FooBar=42
    const FooBar {.intdefine: "package.FooBar".}: int = 5
    echo FooBar # 42
    ```

    This was added to help disambiguate similar define names for different packages.
    In older versions, this could only be achieved with something like the following:

    ```nim
    const FooBar = block:
      const `package.FooBar` {.intdefine.}: int = 5
      `package.FooBar`
    ```
  - A generic `define` pragma for constants has been added that interprets
    the value of the define based on the type of the constant value.
    See the [experimental manual](https://nim-lang.github.io/Nim/manual_experimental.html#generic-define-pragma)
    for a list of supported types.

- [Macro pragmas](https://nim-lang.github.io/Nim/manual.html#userminusdefined-pragmas-macro-pragmas) changes:
  - Templates now accept macro pragmas.
  - Macro pragmas for var/let/const sections have been redesigned in a way that works
    similarly to routine macro pragmas. The new behavior is documented in the
    [experimental manual](https://nim-lang.github.io/Nim/manual_experimental.html#extended-macro-pragmas).
  - Pragma macros on type definitions can now return `nnkTypeSection` nodes as well as `nnkTypeDef`,
    allowing multiple type definitions to be injected in place of the original type definition.

    ```nim
    import macros
    macro multiply(amount: static int, s: untyped): untyped =
      let name = $s[0].basename
      result = newNimNode(nnkTypeSection)
      for i in 1 .. amount:
        result.add(newTree(nnkTypeDef, ident(name & $i), s[1], s[2]))
    type
      Foo = object
      Bar {.multiply: 3.} = object
        x, y, z: int
      Baz = object
    # becomes
    type
      Foo = object
      Bar1 = object
        x, y, z: int
      Bar2 = object
        x, y, z: int
      Bar3 = object
        x, y, z: int
      Baz = object
    ```

- A new form of type inference called [top-down inference](https://nim-lang.github.io/Nim/manual_experimental.html#topminusdown-type-inference)
  has been implemented for a variety of basic cases. For example, code like the following now compiles:

  ```nim
  let foo: seq[(float, byte, cstring)] = @[(1, 2, "abc")]
  ```

- `cstring` is now accepted as a selector in `case` statements, removing the
  need to convert to `string`. On the JS backend, this is translated directly
  to a `switch` statement.

- Nim now supports `out` parameters and ["strict definitions"](https://nim-lang.github.io/Nim/manual_experimental.html#strict-definitions-and-nimout-parameters).
- Nim now offers a [strict mode](https://nim-lang.github.io/Nim/manual_experimental.html#strict-case-objects) for `case objects`.

- IBM Z architecture and macOS m1 arm64 architecture are supported.

- `=wasMoved` can be overridden by users.

- Tuple unpacking for variables is now treated as syntax sugar that directly
  expands into multiple assignments. Along with this, tuple unpacking for
  variables can now be nested.

  ```nim
  proc returnsNestedTuple(): (int, (int, int), int, int) = (4, (5, 7), 2, 3)

  let (x, (_, y), _, z) = returnsNestedTuple()
  # roughly becomes
  let
    tmpTup1 = returnsNestedTuple()
    x = tmpTup1[0]
    tmpTup2 = tmpTup1[1]
    y = tmpTup2[1]
    z = tmpTup1[3]
  ```

  As a result `nnkVarTuple` nodes in variable sections will no longer be
  reflected in `typed` AST.

## Compiler changes

- The `gc` switch has been renamed to `mm` ("memory management") in order to reflect the
  reality better. (Nim moved away from all techniques based on "tracing".)

- Defines the `gcRefc` symbol which allows writing specific code for the refc GC.

- `nim` can now compile version 1.4.0 as follows: `nim c --lib:lib --stylecheck:off compiler/nim`,
  without requiring `-d:nimVersion140` which is now a noop.

- `--styleCheck`, `--hintAsError` and `--warningAsError` now only apply to the current package.

- The switch `--nimMainPrefix:prefix` has been added to add a prefix to the names of `NimMain` and
  related functions produced on the backend. This prevents conflicts with other Nim
  static libraries.

- When compiling for Release the flag `-fno-math-errno` is used for GCC.


## Tool changes

- Nim now ships Nimble version 0.14 which added support for lock-files. Libraries are stored in `$nimbleDir/pkgs2` (it was `$nimbleDir/pkgs`). Use `nimble develop --global` to create an old style link file in the special links directory documented at https://github.com/nim-lang/nimble#nimble-develop.
