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v2.x.x - yyyy-mm-dd

Changes affecting backward compatibility

  • Solaris and illumos are now separate targets (--os:solaris and --os:illumos). Both define sunos, posix, and unix; illumos no longer defines solaris. Use defined(sunos) for code shared by both systems. Native illumos compilers report hostOS == "illumos", and NimScript exposes OsPlatform.illumos. niminst distinguishes SunOS systems using uname -o, falling back to Solaris when that query is unavailable or unrecognized. koch boot handles the transition from bootstrap compilers that identify illumos as Solaris; source distributions must regenerate their csources with the updated compiler and niminst.

  • --compileOnly no longer implies the host's C compiler settings and no longer omits the /* Compiled for ... */ header comment: cross compilation settings (cpu.os.cc.*) are honored, which also fixes cross compilation with --spawnCodegen. The old behavior, needed by niminst to generate C code that can be shared among targets, is available via the new --mergeableCcode switch.

  • -d:nimPreviewFloatRoundtrip becomes the default. system.addFloat and system.$ now can produce string representations of floating point numbers that are minimal in size and possess round-trip and correct rounding guarantees (via the Dragonbox algorithm). Use -d:nimLegacySprintf to emulate old behaviors.

  • The default parameter of tables.getOrDefault has been renamed to def to avoid conflicts with system.default, so named argument usage for this parameter like getOrDefault(..., default = ...) will have to be changed.

  • With -d:nimPreviewCheckedClose, the close function in the std/syncio module now raises an IO exception in case of an error.

  • With -d:nimPreviewCheckedFlush, the flushFile function in the std/syncio module raises an IO exception when the buffered data cannot be written.

  • Unknown warnings and hints now gives warnings warnUnknownNotes instead of errors.

  • With -d:nimPreviewAsmSemSymbol, backticked symbols are type checked in the asm/emit statements.

  • The bare except: now panics on Defect. Use except Exception: or except Defect: to catch Defect. --legacy:noPanicOnExcept is provided for a transition period.

  • With -d:nimPreviewCStringComparisons, comparsions (<, >, <=, >=) between cstrings switch from reference semantics to value semantics like == and !=.

  • std/parsesql has been moved to a nimble package, use nimble or atlas to install it.

  • With -d:nimPreviewDuplicateModuleError, importing two modules that share the same name becomes a compile-time error. This includes importing the same module more than once. Use import foo as foo1 (or other aliases) to avoid collisions.

  • Adds the switch --mangle:nim|cpp, which selects nim or cpp style name mangling when used with debuginfo on, defaults to cpp.

  • The second parameter of succ, pred, inc, and dec in system now accepts SomeInteger (previously Ordinal).

  • Bitshift operators (shl, shr, ashr) now apply bitmasking to the right operand in the C/C++/VM/JS backends.

  • Adds a new warning --warning:ImplicitRangeConversion that detects downsizing implicit conversions to range types (e.g., int -> range[0..255] or range[1..256] -> range[0..255]) that could cause runtime panics. Safe conversions like range[0..255] -> range[0..65535] and explicit casts do not trigger warnings. int to Natural and Positive conversions do not trigger warnings, which can be enabled with --warning:systemRangeConversion.

  • Procedure compatibility also checks the backend representation of the parameter and result types, not just their source-level shape. Use --legacy:procParamTypeBackendAliases to restore the older behavior.

  • items for array now yields lent T, as it already did for seq and openArray, instead of a copy of each element. A closure cannot capture a lent value, so a closure that captures the loop variable of such a for loop no longer compiles ("cannot be captured as it would violate memory safety"). Copy the variable first (for x in a: let x = x), or use -d:nimNoLentIterators to restore the old behavior. The JS backend and NimScript are unaffected: there items yields copies.

  • std/asyncnet (and AsyncHttpClient with it) now checks that the server certificate matches the host name when the context uses CVerifyPeer, as std/net already does. Before, any certificate signed by a trusted CA was accepted for any host. A mismatch now raises SslError from AsyncSocket.connect, or from the first send or recv after wrapConnectedSocket. Connections to IP addresses and contexts created with CVerifyNone are not checked. A failed TLS handshake now also raises SslError from AsyncSocket.connect instead of being ignored.

  • std/net and std/asyncnet now also check the certificate host name on Windows. Before, the check was skipped there because X509_check_host was imported from the wrong DLL (libssl instead of libcrypto).

Standard library additions and changes

  • Added system.readRawDataStable, a companion to readRawData that returns a raw ptr UncheckedArray[char] into a string's character data which stays valid across moves and copies of the string value. It is available under every string implementation (refc, ARC/ORC and --strings:sso) with the same signature, so code can pin an interior buffer pointer today and be ready for --strings:sso without when declared guards. Under --strings:sso it promotes a small inline string to its heap representation first; under the other implementations the data is already heap-resident, so it is equivalent to readRawData.

  • setutils.symmetricDifference along with its operator version setutils.`-+-` and in-place version setutils.toggle have been added to more efficiently calculate the symmetric difference of bitsets.

  • strutils.multiReplace overload for character set replacements in a single pass. Useful for string sanitation. Follows existing multiReplace semantics.

  • std/files adds:

    • Exports CopyFlag enum and FilePermission type for fine-grained control of file operations
    • New file operation procs with Path support:
      • getFilePermissions, setFilePermissions for managing permissions
      • tryRemoveFile for file deletion
      • copyFile with configurable buffer size and symlink handling
      • copyFileWithPermissions to preserve file attributes
      • copyFileToDir for copying files into directories

  • std/dirs adds:

    • New directory operation procs with Path support:
      • copyDir with special file handling options
      • copyDirWithPermissions to recursively preserve attributes

  • system.setLenUninit now supports refc, JS and VM backends.

  • system.setLenUninit for the string type. Allows setting length without initializing new memory on growth.

  • std/parseopt now supports multiple parser modes via a CliMode enum. Modes include Nim (default, fully compatible) and two new experimental modes: Lax and Gnu for different option parsing behaviors.

  • std/symlinks.expandSymlink now supports Windows symlinks and junctions with POSIX-like single-hop readlink semantics.

  • std/nre2 is added to replace deprecated NRE.

  • system.typeof adds a new parameter modifierMode to specify how type modifiers are handled.

  • std/asynchttpserver.newAsyncHttpServer adds a parameter readTimeout, the number of milliseconds a client has to deliver a complete request. A client that is slower is disconnected (after a 408 Request Timeout response once its request line was received). The default of 0 keeps waiting indefinitely.

  • uri.decodeQuery now honours a non-default sep when splitting keys. Previously only the value was terminated by sep; the key was terminated by '=' or a hardcoded '&', so decodeQuery("a;b=2;c", ';') yielded the key "a;b". A literal '&' in a query with a custom separator is now data rather than a separator.

  • std/math The ^ symbol now supports floating-point as exponent in addition to the Natural type.

  • min, max, and sequtils' minIndex, maxIndex and minmax for openArrays now accept a comparison function.

  • system.substr implementation now uses copymem (wrapped C memcpy) for copying data, if available at compilation.

  • system.newStringUninit is now considered free of side-effects allowing it to be used with --experimental:strictFuncs.

  • os.moveFile, os.copyFileWithPermissions and os.copyDirWithPermissions no longer have the effect Exception; they raise OSError and IOError.

  • dynlib.loadLibPattern and dynlib.checkedSymAddr no longer have the effect Exception: they raise what the platform's loadLib and symAddr raise (nothing on POSIX and Windows). The OpenSSL procs that std/openssl loads at run time are declared raises: [], so net.newContext and httpclient.newHttpClient can be called from a {.raises: [CatchableError].} proc.

  • std/re and std/nre are deprecated as PCRE library is obsolete. Use https://github.com/nitely/nim-regex or std/nre2. See: nim-lang#23668.

  • std/pegs now correctly lexes UTF-8 bytes inside bare identifier-style terminals, so case-insensitive matching of non-ASCII terms (e.g. \i café) works without single-quoting.

  • std/uri: The ? operator now appends query parameters to an existing query string instead of replacing it. Fixes #19782.

  • std/jsonutils: fromJson now throws an exception when converting to array/seq if the JSON isn't an array instead of silently failing

  • std/strutils: rsplit with a string separator that can overlap itself (e.g. "..", "aa") no longer matches bytes already consumed by the separator to its right, so "a...b".rsplit("..") is @["a.", "b"] instead of @["a", "", "b"]. Fixes #24949.

  • std/pegs no longer crashes on some patterns: repetition of an expression that can match the empty input (e.g. ('a'?)*) is now valid (the matcher terminates on zero-length matches) instead of aborting with AssertionDefect; unknown builtin escapes inside character classes (e.g. [^\n]) raise EInvalidPeg instead of IndexDefect. An empty capture {} with no previous capture is now a no-op instead of underflowing the matcher's capture array.

Language changes

  • An experimental option --experimental:typeBoundOps has been added that implements the RFC nim-lang/RFCs#380. This makes the behavior of interfaces like hash, $, == etc. more reliable for nominal types across indirect/restricted imports.

    # objs.nim
import std/hashes

type
  Obj* = object
    x*, y*: int
    z*: string # to be ignored for equality

proc `==`*(a, b: Obj): bool =
  a.x == b.x and a.y == b.y

proc hash*(a: Obj): Hash =
  $!(hash(a.x) &! hash(a.y))
    # main.nim
{.experimental: "typeBoundOps".}
from objs import Obj # objs.hash, objs.`==` not imported
import std/tables

var t: Table[Obj, int]
t[Obj(x: 3, y: 4, z: "debug")] = 34
echo t[Obj(x: 3, y: 4, z: "ignored")] # 34

    See the experimental manual for more information.

  • Seven more Unicode characters are now parsed as operators, implementing the RFC nim-lang/RFCs#571: ⟑ ⟇ ⩓ ⩔ ■ □ ☆. They all have the same priority as * (multiplication). As with the other Unicode operators, Nim only lexes them; their meaning is up to user code.

  • An experimental option --experimental:ownedRefs has been added that implements the RFC nim-lang/RFCs#575: owned ref T and owned proc are statically checked unique ownership annotations on top of ARC/ORC/YRC. Converting an owned reference to an unowned one produces a counted reference, so there is no runtime failure mode. A type whose references are all owned or .cursor cannot form a cycle and stays out of the cycle collector, so for example a callback field of type owned proc () no longer makes its enclosing type cyclic. Without the feature owned continues to be erased.

  • Sum types, ported from Nimony: an object case without a discriminator declares a sum type. The branch names construct values, and a pattern matching case binds the fields of a branch:

    type
  Node = ref object
    case
    of AddOpr, SubOpr:
      a, b: Node
    of Value:
      val: int

proc eval(n: Node): int =
  case n
  of Value(v): v
  of AddOpr(a, b): eval(a) + eval(b)
  of SubOpr(a, b): eval(a) - eval(b)

echo eval(AddOpr(a: Value(val: 40), b: Value(val: 2))) # 42

    The fields of a branch can only be accessed through such a case, or in a {.cast(uncheckedAccess).} section. $ and repr render a sum type like its constructor. See the manual for more information.

Compiler changes

  • An import annotated with {.cyclic.} (import b {.cyclic.}) makes the modules of an import cycle a group whose types and leading routines are visible to each other regardless of declaration order, so procs of different modules can call each other. See the manual's section about cyclic imports. An import cycle without {.cyclic.} is deprecated; the new warning ImplicitCyclicImport (off by default) reports it.

  • Fixed a bug where sizeof(T) inside a typedesc template called from a generic type's when clause would error with "'sizeof' requires '.importc' types to be '.completeStruct'". The issue was that hasValuelessStatics in semtypinst.nim didn't recognize tyTypeDesc(tyGenericParam) as an unresolved generic parameter.

  • The JS backend now implements write-through for var openArray parameters that receive a toOpenArray view (bug #15952): mutations reach the caller's storage instead of silently writing to a copy. Fixed homogeneous numeric arrays (array[N, T], JS typed arrays) slice via subarray; seq and non-numeric arrays slice via a {base, off, len} view. This also covers seq/non-numeric-array write-through, pass-through, re-slicing and @ (openArray-to-seq) of such views.

  • On --os:ios, the default file name for --app:lib is now libfoo.dylib instead of libfoo.so, matching --os:macosx and the Darwin convention.

  • With --hotCodeReloading:on, a module can use the thread-local variables and the methods of another module, which made the program fail to link or to dispatch before; std/logging works with it now. A thread-local variable keeps its value, for each thread, when its module is reloaded.

Tool changes

  • Added --raw flag when generating JSON docs to not render markup.
  • Added --stdinfile flag to name of the file used when running program from stdin (defaults to stdinfile.nim)
  • Added --styleCheck:warning flag to treat style check violations as warnings.

Documentation changes

  • Added documentation for the completeStruct pragma in the manual.
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