=================================== Nim Compiler User Guide =================================== :Author: Andreas Rumpf :Version: |nimversion| .. contents:: "Look at you, hacker. A pathetic creature of meat and bone, panting and sweating as you run through my corridors. How can you challenge a perfect, immortal machine?" Introduction ============ This document describes the usage of the *Nim compiler* on the different supported platforms. It is not a definition of the Nim programming language (which is covered in the `manual `_). Nim is free software; it is licensed under the `MIT License `_. Compiler Usage ============== Command line switches --------------------- Basic command line switches are: Usage: .. include:: basicopt.txt ---- Advanced command line switches are: .. include:: advopt.txt List of warnings ---------------- Each warning can be activated individually with ``--warning[NAME]:on|off`` or in a ``push`` pragma. ========================== ============================================ Name Description ========================== ============================================ CannotOpenFile Some file not essential for the compiler's working could not be opened. OctalEscape The code contains an unsupported octal sequence. Deprecated The code uses a deprecated symbol. ConfigDeprecated The project makes use of a deprecated config file. SmallLshouldNotBeUsed The letter 'l' should not be used as an identifier. EachIdentIsTuple The code contains a confusing ``var`` declaration. User Some user defined warning. ========================== ============================================ List of hints ------------- Each hint can be activated individually with ``--hint[NAME]:on|off`` or in a ``push`` pragma. ========================== ============================================ Name Description ========================== ============================================ CC Shows when the C compiler is called. CodeBegin CodeEnd CondTrue Conf A config file was loaded. ConvToBaseNotNeeded ConvFromXtoItselfNotNeeded Dependency Exec Program is executed. ExprAlwaysX ExtendedContext GCStats Dumps statistics about the Garbage Collector. GlobalVar Shows global variables declarations. LineTooLong Line exceeds the maximum length. Link Linking phase. Name Path Search paths modifications. Pattern Performance Processing Artifact being compiled. QuitCalled Source The source line that triggered a diagnostic message. StackTrace Success, SuccessX Successful compilation of a library or a binary. User UserRaw XDeclaredButNotUsed Unused symbols in the code. ========================== ============================================ Verbosity levels ---------------- ===== ============================================ Level Description ===== ============================================ 0 Minimal output level for the compiler. 1 Displays compilation of all the compiled files, including those imported by other modules or through the `compile pragma `_. This is the default level. 2 Displays compilation statistics, enumerates the dynamic libraries that will be loaded by the final binary and dumps to standard output the result of applying `a filter to the source code `_ if any filter was used during compilation. 3 In addition to the previous levels dumps a debug stack trace for compiler developers. ===== ============================================ Compile time symbols -------------------- Through the ``-d:x`` or ``--define:x`` switch you can define compile time symbols for conditional compilation. The defined switches can be checked in source code with the `when statement `_ and `defined proc `_. The typical use of this switch is to enable builds in release mode (``-d:release``) where optimizations are enabled for better performance. Another common use is the ``-d:ssl`` switch to activate SSL sockets. Additionally, you may pass a value along with the symbol: ``-d:x=y`` which may be used in conjunction with the `compile time define pragmas`_ to override symbols during build time. Compile time symbols are completely **case insensitive** and underscores are ignored too. ``--define:FOO`` and ``--define:foo`` are identical. Compile time symbols starting with the ``nim`` prefix are reserved for the implementation and should not be used elsewhere. Configuration files ------------------- **Note:** The *project file name* is the name of the ``.nim`` file that is passed as a command line argument to the compiler. The ``nim`` executable processes configuration files in the following directories (in this order; later files overwrite previous settings): 1) ``$nim/config/nim.cfg``, ``/etc/nim/nim.cfg`` (UNIX) or ``\config\nim.cfg`` (Windows). This file can be skipped with the ``--skipCfg`` command line option. 2) If environment variable ``XDG_CONFIG_HOME`` is defined, ``$XDG_CONFIG_HOME/nim/nim.cfg`` or ``~/.config/nim/nim.cfg`` (POSIX) or ``%APPDATA%/nim/nim.cfg`` (Windows). This file can be skipped with the ``--skipUserCfg`` command line option. 3) ``$parentDir/nim.cfg`` where ``$parentDir`` stands for any parent directory of the project file's path. These files can be skipped with the ``--skipParentCfg`` command line option. 4) ``$projectDir/nim.cfg`` where ``$projectDir`` stands for the project file's path. This file can be skipped with the ``--skipProjCfg`` command line option. 5) A project can also have a project specific configuration file named ``$project.nim.cfg`` that resides in the same directory as ``$project.nim``. This file can be skipped with the ``--skipProjCfg`` command line option. Command line settings have priority over configuration file settings. The default build of a project is a `debug build`:idx:. To compile a `release build`:idx: define the ``release`` symbol:: nim c -d:release myproject.nim To compile a `dangerous release build`:idx: define the ``danger`` symbol:: nim c -d:danger myproject.nim Search path handling -------------------- Nim has the concept of a global search path (PATH) that is queried to determine where to find imported modules or include files. If multiple files are found an ambiguity error is produced. ``nim dump`` shows the contents of the PATH. However before the PATH is used the current directory is checked for the file's existence. So if PATH contains ``$lib`` and ``$lib/bar`` and the directory structure looks like this:: $lib/x.nim $lib/bar/x.nim foo/x.nim foo/main.nim other.nim And ``main`` imports ``x``, ``foo/x`` is imported. If ``other`` imports ``x`` then both ``$lib/x.nim`` and ``$lib/bar/x.nim`` match but ``$lib/x.nim`` is used as it is the first match. Generated C code directory -------------------------- The generated files that Nim produces all go into a subdirectory called ``nimcache``. Its full path is - ``$XDG_CACHE_HOME/nim/$projectname(_r|_d)`` or ``~/.cache/nim/$projectname(_r|_d)`` on Posix - ``$HOME/nimcache/$projectname(_r|_d)`` on Windows. The ``_r`` suffix is used for release builds, ``_d`` is for debug builds. This makes it easy to delete all generated files. The ``--nimcache`` `compiler switch <#compiler-usage-command-line-switches>`_ can be used to to change the ``nimcache`` directory. However, the generated C code is not platform independent. C code generated for Linux does not compile on Windows, for instance. The comment on top of the C file lists the OS, CPU and CC the file has been compiled for. Compiler Selection ================== To change the compiler from the default compiler (at the command line):: nim c --cc:llvm_gcc --compile_only myfile.nim This uses the configuration defined in ``config\nim.cfg`` for ``lvm_gcc``. If nimcache already contains compiled code from a different compiler for the same project, add the ``-f`` flag to force all files to be recompiled. The default compiler is defined at the top of ``config\nim.cfg``. Changing this setting affects the compiler used by ``koch`` to (re)build Nim. Cross compilation ================= To cross compile, use for example:: nim c --cpu:i386 --os:linux --compileOnly --genScript myproject.nim Then move the C code and the compile script ``compile_myproject.sh`` to your Linux i386 machine and run the script. Another way is to make Nim invoke a cross compiler toolchain:: nim c --cpu:arm --os:linux myproject.nim For cross compilation, the compiler invokes a C compiler named like ``$cpu.$os.$cc`` (for example arm.linux.gcc) and the configuration system is used to provide meaningful defaults. For example for ``ARM`` your configuration file should contain something like:: arm.linux.gcc.path = "/usr/bin" arm.linux.gcc.exe = "arm-linux-gcc" arm.linux.gcc.linkerexe = "arm-linux-gcc" Cross compilation for Windows ============================= To cross compile for Windows from Linux or macOS using the MinGW-w64 toolchain:: nim c -d:mingw myproject.nim Use ``--cpu:i386`` or ``--cpu:amd64`` to switch the CPU architecture. The MinGW-w64 toolchain can be installed as follows:: Ubuntu: apt install mingw-w64 CentOS: yum install mingw32-gcc | mingw64-gcc - requires EPEL OSX: brew install mingw-w64 Cross compilation for Android ============================= There are two ways to compile for Android: terminal programs (Termux) and with the NDK (Android Native Development Kit). First one is to treat Android as a simple Linux and use `Termux `_ to connect and run the Nim compiler directly on android as if it was Linux. These programs are console only programs that can't be distributed in the Play Store. Use regular ``nim c`` inside termux to make Android terminal programs. Normal Android apps are written in Java, to use Nim inside an Android app you need a small Java stub that calls out to a native library written in Nim using the `NDK `_. You can also use `native-acitivty `_ to have the Java stub be auto generated for you. Use ``nim c -c --cpu:arm --os:android -d:androidNDK --noMain:on`` to generate the C source files you need to include in your Android Studio project. Add the generated C files to CMake build script in your Android project. Then do the final compile with Android Studio which uses Gradle to call CMake to compile the project. Because Nim is part of a library it can't have its own c style ``main()`` so you would need to define your own ``android_main`` and init the Java environment, or use a library like SDL2 or GLFM to do it. After the Android stuff is done, it's very important to call ``NimMain()`` in order to initialize Nim's garbage collector and to run the top level statements of your program. .. code-block:: Nim proc NimMain() {.importc.} proc glfmMain*(display: ptr GLFMDisplay) {.exportc.} = NimMain() # initialize garbage collector memory, types and stack Cross compilation for iOS ========================= To cross compile for iOS you need to be on a MacOS computer and use XCode. Normal languages for iOS development are Swift and Objective C. Both of these use LLVM and can be compiled into object files linked together with C, C++ or Objective C code produced by Nim. Use ``nim c -c --os:ios --noMain:on`` to generate C files and include them in your XCode project. Then you can use XCode to compile, link, package and sign everything. Because Nim is part of a library it can't have its own c style ``main()`` so you would need to define `main` that calls ``autoreleasepool`` and ``UIApplicationMain`` to do it, or use a library like SDL2 or GLFM. After the iOS setup is done, it's very important to call ``NimMain()`` in order to initialize Nim's garbage collector and to run the top level statements of your program. .. code-block:: Nim proc NimMain() {.importc.} proc glfmMain*(display: ptr GLFMDisplay) {.exportc.} = NimMain() # initialize garbage collector memory, types and stack Note: XCodes "make clean" gets confused about the genreated nim.c files, so you need to clean those files manually to do a clean build. Cross compilation for Nintendo Switch ===================================== Simply add --os:nintendoswitch to your usual ``nim c`` or ``nim cpp`` command and set the ``passC`` and ``passL`` command line switches to something like: .. code-block:: console nim c ... --passC="-I$DEVKITPRO/libnx/include" ... --passL="-specs=$DEVKITPRO/libnx/switch.specs -L$DEVKITPRO/libnx/lib -lnx" or setup a nim.cfg file like so: .. code-block:: Nim #nim.cfg --passC="-I$DEVKITPRO/libnx/include" --passL="-specs=$DEVKITPRO/libnx/switch.specs -L$DEVKITPRO/libnx/lib -lnx" The DevkitPro setup must be the same as the default with their new installer `here for Mac/Linux `_ or `here for Windows `_. For example, with the above mentioned config:: nim c --os:nintendoswitch switchhomebrew.nim This will generate a file called ``switchhomebrew.elf`` which can then be turned into an nro file with the ``elf2nro`` tool in the DevkitPro release. Examples can be found at `the nim-libnx github repo `_. There are a few things that don't work because the DevkitPro libraries don't support them. They are: 1. Waiting for a subprocess to finish. A subprocess can be started, but right now it can't be waited on, which sort of makes subprocesses a bit hard to use 2. Dynamic calls. DevkitPro libraries have no dlopen/dlclose functions. 3. Command line parameters. It doesn't make sense to have these for a console anyways, so no big deal here. 4. mqueue. Sadly there are no mqueue headers. 5. ucontext. No headers for these either. No coroutines for now :( 6. nl_types. No headers for this. DLL generation ============== Nim supports the generation of DLLs. However, there must be only one instance of the GC per process/address space. This instance is contained in ``nimrtl.dll``. This means that every generated Nim DLL depends on ``nimrtl.dll``. To generate the "nimrtl.dll" file, use the command:: nim c -d:release lib/nimrtl.nim To link against ``nimrtl.dll`` use the command:: nim c -d:useNimRtl myprog.nim **Note**: Currently the creation of ``nimrtl.dll`` with thread support has never been tested and is unlikely to work! Additional compilation switches =============================== The standard library supports a growing number of ``useX`` conditional defines affecting how some features are implemented. This section tries to give a complete list. ====================== ========================================================= Define Effect ====================== ========================================================= ``release`` Turns on the optimizer. More aggressive optimizations are possible, eg: ``--passC:-ffast-math`` (but see issue #10305) ``danger`` Turns off all runtime checks and turns on the optimizer. ``useFork`` Makes ``osproc`` use ``fork`` instead of ``posix_spawn``. ``useNimRtl`` Compile and link against ``nimrtl.dll``. ``useMalloc`` Makes Nim use C's `malloc`:idx: instead of Nim's own memory manager, albeit prefixing each allocation with its size to support clearing memory on reallocation. This only works with ``gc:none`` and with ``--newruntime``. ``useRealtimeGC`` Enables support of Nim's GC for *soft* realtime systems. See the documentation of the `gc `_ for further information. ``logGC`` Enable GC logging to stdout. ``nodejs`` The JS target is actually ``node.js``. ``ssl`` Enables OpenSSL support for the sockets module. ``memProfiler`` Enables memory profiling for the native GC. ``uClibc`` Use uClibc instead of libc. (Relevant for Unix-like OSes) ``checkAbi`` When using types from C headers, add checks that compare what's in the Nim file with what's in the C header. This may become enabled by default in the future. ``tempDir`` This symbol takes a string as its value, like ``--define:tempDir:/some/temp/path`` to override the temporary directory returned by ``os.getTempDir()``. The value **should** end with a directory separator character. (Relevant for the Android platform) ``useShPath`` This symbol takes a string as its value, like ``--define:useShPath:/opt/sh/bin/sh`` to override the path for the ``sh`` binary, in cases where it is not located in the default location ``/bin/sh``. ``noSignalHandler`` Disable the crash handler from ``system.nim``. ====================== ========================================================= Additional Features =================== This section describes Nim's additional features that are not listed in the Nim manual. Some of the features here only make sense for the C code generator and are subject to change. LineDir option -------------- The ``lineDir`` option can be turned on or off. If turned on the generated C code contains ``#line`` directives. This may be helpful for debugging with GDB. StackTrace option ----------------- If the ``stackTrace`` option is turned on, the generated C contains code to ensure that proper stack traces are given if the program crashes or an uncaught exception is raised. LineTrace option ---------------- The ``lineTrace`` option implies the ``stackTrace`` option. If turned on, the generated C contains code to ensure that proper stack traces with line number information are given if the program crashes or an uncaught exception is raised. DynlibOverride ============== By default Nim's ``dynlib`` pragma causes the compiler to generate ``GetProcAddress`` (or their Unix counterparts) calls to bind to a DLL. With the ``dynlibOverride`` command line switch this can be prevented and then via ``--passL`` the static library can be linked against. For instance, to link statically against Lua this command might work on Linux:: nim c --dynlibOverride:lua --passL:liblua.lib program.nim Backend language options ======================== The typical compiler usage involves using the ``compile`` or ``c`` command to transform a ``.nim`` file into one or more ``.c`` files which are then compiled with the platform's C compiler into a static binary. However there are other commands to compile to C++, Objective-C or JavaScript. More details can be read in the `Nim Backend Integration document `_. Nim documentation tools ======================= Nim provides the `doc`:idx: and `doc2`:idx: commands to generate HTML documentation from ``.nim`` source files. Only exported symbols will appear in the output. For more details `see the docgen documentation `_. Nim idetools integration ======================== Nim provides language integration with external IDEs through the idetools command. See the documentation of `idetools `_ for further information. .. Nim interactive mode ==================== The Nim compiler supports an interactive mode. This is also known as a `REPL`:idx: (*read eval print loop*). If Nim has been built with the ``-d:nimUseLinenoise`` switch, it uses the GNU readline library for terminal input management. To start Nim in interactive mode use the command ``nim secret``. To quit use the ``quit()`` command. To determine whether an input line is an incomplete statement to be continued these rules are used: 1. The line ends with ``[-+*/\\<>!\?\|%&$@~,;:=#^]\s*$`` (operator symbol followed by optional whitespace). 2. The line starts with a space (indentation). 3. The line is within a triple quoted string literal. However, the detection does not work if the line contains more than one ``"""``. Nim for embedded systems ======================== While the default Nim configuration is targeted for optimal performance on modern PC hardware and operating systems with ample memory, it is very well possible to run Nim code and a good part of the Nim standard libraries on small embedded microprocessors with only a few kilobytes of memory. A good start is to use the ``any`` operating target together with the ``malloc`` memory allocator and the ``arc`` garbage collector. For example: ``nim c --os:any --gc:arc -d:useMalloc [...] x.nim`` - ``--gc:arc`` will enable the reference counting memory management instead of the default garbage collector. This enables Nim to use heap memory which is required for strings and seqs, for example. - The ``--os:any`` target makes sure Nim does not depend on any specific operating system primitives. Your platform should support only some basic ANSI C library ``stdlib`` and ``stdio`` functions which should be available on almost any platform. - The ``-d:useMalloc`` option configures Nim to use only the standard C memory manage primitives ``malloc()``, ``free()``, ``realloc()``. If your platform does not provide these functions it should be trivial to provide an implementation for them and link these to your program. For targets with very restricted memory, it might be beneficial to pass some additional flags to both the Nim compiler and the C compiler and/or linker to optimize the build for size. For example, the following flags can be used when targeting a gcc compiler: ``--opt:size --passC:-flto --passL:-flto`` The ``--opt:size`` flag instructs Nim to optimize code generation for small size (with the help of the C compiler), the ``flto`` flags enable link-time optimization in the compiler and linker. Check the `Cross compilation` section for instructions how to compile the program for your target. Nim for realtime systems ======================== See the documentation of Nim's soft realtime `GC `_ for further information. Signal handling in Nim ====================== The Nim programming language has no concept of Posix's signal handling mechanisms. However, the standard library offers some rudimentary support for signal handling, in particular, segmentation faults are turned into fatal errors that produce a stack trace. This can be disabled with the ``-d:noSignalHandler`` switch. Optimizing for Nim ================== Nim has no separate optimizer, but the C code that is produced is very efficient. Most C compilers have excellent optimizers, so usually it is not needed to optimize one's code. Nim has been designed to encourage efficient code: The most readable code in Nim is often the most efficient too. However, sometimes one has to optimize. Do it in the following order: 1. switch off the embedded debugger (it is **slow**!) 2. turn on the optimizer and turn off runtime checks 3. profile your code to find where the bottlenecks are 4. try to find a better algorithm 5. do low-level optimizations This section can only help you with the last item. Optimizing string handling -------------------------- String assignments are sometimes expensive in Nim: They are required to copy the whole string. However, the compiler is often smart enough to not copy strings. Due to the argument passing semantics, strings are never copied when passed to subroutines. The compiler does not copy strings that are a result from a procedure call, because the callee returns a new string anyway. Thus it is efficient to do: .. code-block:: Nim var s = procA() # assignment will not copy the string; procA allocates a new # string already However it is not efficient to do: .. code-block:: Nim var s = varA # assignment has to copy the whole string into a new buffer! For ``let`` symbols a copy is not always necessary: .. code-block:: Nim let s = varA # may only copy a pointer if it safe to do so If you know what you're doing, you can also mark single string (or sequence) objects as `shallow`:idx:\: .. code-block:: Nim var s = "abc" shallow(s) # mark 's' as shallow string var x = s # now might not copy the string! Usage of ``shallow`` is always safe once you know the string won't be modified anymore, similar to Ruby's `freeze`:idx:. The compiler optimizes string case statements: A hashing scheme is used for them if several different string constants are used. So code like this is reasonably efficient: .. code-block:: Nim case normalize(k.key) of "name": c.name = v of "displayname": c.displayName = v of "version": c.version = v of "os": c.oses = split(v, {';'}) of "cpu": c.cpus = split(v, {';'}) of "authors": c.authors = split(v, {';'}) of "description": c.description = v of "app": case normalize(v) of "console": c.app = appConsole of "gui": c.app = appGUI else: quit(errorStr(p, "expected: console or gui")) of "license": c.license = UnixToNativePath(k.value) else: quit(errorStr(p, "unknown variable: " & k.key))