v2.0.0 - 2023-08-01

Changes affecting backward compatibility

ORC is now the default memory management strategy. Use --mm:refc for a transition period.
The threads:on option is now the default.
httpclient.contentLength default to -1 if the Content-Length header is not set in the response. It follows Apache's HttpClient (Java), http (go) and .NET HttpWebResponse (C#) behaviors. Previously it raised a 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 an Error suffix to exception types that have a Defect suffix (see exceptions): 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, which is replaced by threading/channels. Use the command nimble install threading and import threading/channels.
Enabling -d:nimPreviewCstringConversion causes ptr char, ptr array[N, char] and ptr UncheckedArray[N, char] to not support conversion to cstring anymore.
Enabling -d:nimPreviewProcConversion causes proc to not support conversion to pointer anymore. cast may be used instead.
The gc:v2 option is removed.
The mainmodule and m options are removed.
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. 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`. Instead,
  use `type Foo[T] {.final.} = 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.

- `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.

- `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` conversions now trigger 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 have been 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`
  - `std/md5` => `checksums/md5`
  - `std/sha1` => `checksums/sha1`
  - `std/sums` => `std/sums`

- 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.

- When `--warning[BareExcept]:on` is enabled, if an `except` specifies no exception or any exception not inheriting from `Defect` or `CatchableError`, a `warnBareExcept` warning will be triggered. For example, the following code will emit a warning:
  ```nim
  try:
    discard
  except: # Warning: The bare except clause is deprecated; use `except CatchableError:` instead [BareExcept]
    discard

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:

  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:

  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 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 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.

  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.

Signed integer literals in set literals now default to a range type of 0..255 instead of 0..65535 (the maximum size of sets).
case statements with else branches put before elif/of branches in macros are rejected with "invalid order of case branches".
Destructors now default to .raises: [] (i.e. destructors must not raise unlisted exceptions) and explicitly raising destructors are implementation defined behavior.
The very old, undocumented deprecated pragma statement syntax for deprecated aliases is now a no-op. The regular deprecated pragma syntax is generally sufficient instead.

  # now does nothing:
  {.deprecated: [OldName: NewName].}

  # instead use:
  type OldName* {.deprecated: "use NewName instead".} = NewName
  const oldName* {.deprecated: "use newName instead".} = newName

defined(nimalias) can be used to check for versions when this syntax was available; however since code that used this syntax is usually very old, these deprecated aliases are likely not used anymore and it may make sense to simply remove these statements.

getProgramResult and setProgramResult in std/exitprocs are no longer declared when they are not available on the backend. Previously it would call doAssert false at runtime despite the condition being checkable at compile-time.
Custom destructors now supports non-var parameters, e.g. proc `=destroy`[T: object](x: T) is valid. proc `=destroy`[T: object](x: var T) is deprecated.
Relative imports will not resolve to searched paths anymore, e.g. import ./tables now reports an error properly.

Standard library additions and changes

OpenSSL 3 is now supported.
macros.parseExpr and macros.parseStmt now accept an optional filename argument for more informative errors.
The colors module is 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).
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.
strutils.split and strutils.rsplit now return the source string as a single element for an empty separator.
random.rand now works with Ordinals.
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/jsfetch.newFetchOptions now has default values for all parameters.
std/jsformdata now accepts the Blob data type.
std/sharedlist and std/sharedtables are now deprecated, see RFC #433.
There is a new compile flag (-d:nimNoGetRandom) when building std/sysrand to remove the dependency on the 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:

  $ 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 the stdlib (sysrand in particular).

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 an 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 previously part of std/os:
- Added std/oserrors for OS error reporting.
- Added std/envvars for environment variables handling.
- Added std/cmdline for reading command line parameters.
- Added std/paths, std/dirs, std/files, std/symlinks and std/appdirs.
Added sep parameter in std/uri to specify the query separator.
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.
Added capacity for string and seq to return the current capacity, see RFC #460.
Added openArray[char] overloads for std/parseutils and std/unicode, allowing for more code reuse.
Added a safe parameter to base64.encodeMime.
Added parseutils.parseSize - inverse to strutils.formatSize - to parse human readable sizes.
Added minmax to sequtils, as a more efficient (min(_), max(_)) over sequences.
std/jscore for the JavaScript target:
- Added bindings to Array.shift and queueMicrotask.
- Added toDateString, toISOString, toJSON, toTimeString, toUTCString converters for DateTime.
Added BackwardsIndex overload for CacheSeq.
Added support for nested with blocks in std/with.
Added ensureMove to the system module. It ensures that the passed argument is moved, otherwise an error is given at the compile time.
Deprecated selfExe for Nimscript.
Deprecated std/base64.encode for collections of arbitrary integer element type. Now only byte and char are supported.
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 take wrong argument types.
Removed deprecated osproc.poDemon, symbol with typo.
Removed deprecated tables.rightSize.
Removed deprecated posix.CLONE_STOPPED.

Language changes

Tag tracking now supports the definition of forbidden tags by the .forbids pragma which can be used to disable certain effects in proc types.
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 backticks as in defined(`a.b.c`) to access such defines.
- Define pragmas for constants now support a string argument for qualified define names.
```
# -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:
```
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 for a list of supported types.

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.
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.

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 has been implemented for a variety of basic cases. For example, code like the following now compiles:

  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".
Nim now offers a strict mode for case objects.
IBM Z architecture and macOS m1 arm64 architecture are supported.
=wasMoved can now be overridden by users.
There is a new pragma called quirky that can be used to affect the code generation of goto based exception handling. It can improve the produced code size but its effects can be subtle so use it with care.
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.

  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.

C++ interoperability:
- New virtual pragma added.
- Improvements to constructor pragma.

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.
Removed deprecated LineTooLong hint.
Line numbers and file names of source files work correctly inside templates for JavaScript targets.
Removed support for LCC (Local C), Pelles C, Digital Mars and Watcom compilers.

Docgen

Markdown is now the default markup language of doc comments (instead of the legacy RstMarkdown mode). In this release we begin to separate RST and Markdown features to better follow specification of each language, with the focus on Markdown development. See also the docs.
- Added a {.doctype: Markdown | RST | RstMarkdown.} pragma allowing to select the markup language mode in the doc comments of the current .nim file for processing by nim doc:
  1. Markdown (default) is basically CommonMark (standard Markdown) + some Pandoc Markdown features + some RST features that are missing in our current implementation of CommonMark and Pandoc Markdown.
  2. RST closely follows the RST spec with few additional Nim features.
  3. RstMarkdown is a maximum mix of RST and Markdown features, which is kept for the sake of compatibility and ease of migration.
- Added separate md2html and rst2html commands for processing standalone .md and .rst files respectively (and also md2tex/rst2tex).
Added Pandoc Markdown bracket syntax [...] for making anchor-less links.
Docgen now supports concise syntax for referencing Nim symbols: instead of specifying HTML anchors directly one can use original Nim symbol declarations (adding the aforementioned link brackets [...] around them).
- To use this feature across modules, a new importdoc directive was added. Using this feature for referencing also helps to ensure that links (inside one module or the whole project) are not broken.
Added support for RST & Markdown quote blocks (blocks starting with >).
Added a popular Markdown definition lists extension.
Added Markdown indented code blocks (blocks indented by >= 4 spaces).
Added syntax for additional parameters to Markdown code blocks:

nim test="nim c $1" ...

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 before). 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.
nimgrep added the option --inContext (and --notInContext), which allows to filter only matches with the context block containing a given pattern.
nimgrep: names of options containing "include/exclude" are deprecated, e.g. instead of --includeFile and --excludeFile we have --filename and --notFilename respectively. Also the semantics are now consistent for such positive/negative filters.
koch now supports the --skipIntegrityCheck option. The command koch --skipIntegrityCheck boot -d:release always builds the compiler twice.

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