| Author: | Andreas Rumpf |
|---|---|
| Version: | 0.20.0 |
"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 (therefore is the manual).
Nim is free software; it is licensed under the MIT License.
Compiler Usage
Command line switches
Basic command line switches are:
Usage:
nim command [options] [projectfile] [arguments]
- Command:
compile, c compile project with default code generator (C) doc generate the documentation for inputfile - Arguments:
- arguments are passed to the program being run (if --run option is selected)
- Options:
-p, --path:PATH add path to search paths -d, --define:SYMBOL(:VAL) define a conditional symbol (Optionally: Define the value for that symbol, see: "compile time define pragmas") -u, --undef:SYMBOL undefine a conditional symbol -f, --forceBuild:on|off force rebuilding of all modules --stackTrace:on|off turn stack tracing on|off --lineTrace:on|off turn line tracing on|off --threads:on|off turn support for multi-threading on|off -x, --checks:on|off turn all runtime checks on|off -a, --assertions:on|off turn assertions on|off --opt:none|speed|size optimize not at all or for speed|size Note: use -d:release for a release build! --debugger:native|endb use native debugger (gdb) | ENDB (experimental) --app:console|gui|lib|staticlib generate a console app|GUI app|DLL|static library -r, --run run the compiled program with given arguments --fullhelp show all command line switches -h, --help show this help -v, --version show detailed version information
Note, single letter options that take an argument require a colon. E.g. -p:PATH.
Advanced command line switches are:
- Advanced commands:
compileToC, cc compile project with C code generator compileToCpp, cpp compile project to C++ code compileToOC, objc compile project to Objective C code js compile project to Javascript e run a Nimscript file rst2html convert a reStructuredText file to HTML rst2tex convert a reStructuredText file to TeX jsondoc extract the documentation to a json file ctags create a tags file buildIndex build an index for the whole documentation run run the project (with Tiny C backend; buggy!) genDepend generate a DOT file containing the module dependency graph dump dump all defined conditionals and search paths see also: --dump.format:json (useful with: ` | jq`) check checks the project for syntax and semantic - Runtime checks (see -x):
--objChecks:on|off turn obj conversion checks on|off --fieldChecks:on|off turn case variant field checks on|off --rangeChecks:on|off turn range checks on|off --boundChecks:on|off turn bound checks on|off --overflowChecks:on|off turn int over-/underflow checks on|off --floatChecks:on|off turn all floating point (NaN/Inf) checks on|off --nanChecks:on|off turn NaN checks on|off --infChecks:on|off turn Inf checks on|off --nilChecks:on|off turn nil checks on|off - Advanced options:
-o:FILE, --out:FILE set the output filename --outdir:DIR set the path where the output file will be written --stdout:on|off output to stdout --colors:on|off turn compiler messages coloring on|off --listFullPaths:on|off list full paths in messages -w:on|off|list, --warnings:on|off|list turn all warnings on|off or list all available --warning[X]:on|off turn specific warning X on|off --hints:on|off|list turn all hints on|off or list all available --hint[X]:on|off turn specific hint X on|off --styleCheck:off|hint|error produce hints or errors for Nim identifiers that do not adhere to Nim's official style guide https://nim-lang.org/docs/nep1.html --showAllMismatches:on|off show all mismatching candidates in overloading resolution --lib:PATH set the system library path --import:PATH add an automatically imported module --include:PATH add an automatically included module --nimcache:PATH set the path used for generated files -c, --compileOnly:on|off compile Nim files only; do not assemble or link --noLinking:on|off compile Nim and generated files but do not link --noMain:on|off do not generate a main procedure --genScript:on|off generate a compile script (in the 'nimcache' subdirectory named 'compile_$$project$$scriptext'), implies --compileOnly --genDeps:on|off generate a '.deps' file containing the dependencies --os:SYMBOL set the target operating system (cross-compilation) --cpu:SYMBOL set the target processor (cross-compilation) --debuginfo:on|off enables debug information -t, --passC:OPTION pass an option to the C compiler -l, --passL:OPTION pass an option to the linker --cincludes:DIR modify the C compiler header search path --clibdir:DIR modify the linker library search path --clib:LIBNAME link an additional C library (you should omit platform-specific extensions) --project document the whole project (doc2) --docSeeSrcUrl:url activate 'see source' for doc and doc2 commands (see doc.item.seesrc in config/nimdoc.cfg) --docInternal also generate documentation for non-exported symbols --lineDir:on|off generation of #line directive on|off --embedsrc:on|off embeds the original source code as comments in the generated output --threadanalysis:on|off turn thread analysis on|off --tlsEmulation:on|off turn thread local storage emulation on|off --taintMode:on|off turn taint mode on|off --implicitStatic:on|off turn implicit compile time evaluation on|off --trmacros:on|off turn term rewriting macros on|off --multimethods:on|off turn multi-methods on|off --memTracker:on|off turn memory tracker on|off --hotCodeReloading:on|off turn support for hot code reloading on|off --excessiveStackTrace:on|off stack traces use full file paths --oldNewlines:on|off turn on|off the old behaviour of "n" --laxStrings:on|off when turned on, accessing the zero terminator in strings is allowed; only for backwards compatibility --nilseqs:on|off allow 'nil' for strings/seqs for backwards compatibility --oldast:on|off use old AST for backwards compatibility --skipCfg:on|off do not read the nim installation's configuration file --skipUserCfg:on|off do not read the user's configuration file --skipParentCfg:on|off do not read the parent dirs' configuration files --skipProjCfg:on|off do not read the project's configuration file --gc:refc|markAndSweep|boehm|go|none|regions select the GC to use; default is 'refc' --index:on|off turn index file generation on|off --putenv:key=value set an environment variable --NimblePath:PATH add a path for Nimble support --noNimblePath deactivate the Nimble path --noCppExceptions use default exception handling with C++ backend --cppCompileToNamespace:namespace use the provided namespace for the generated C++ code, if no namespace is provided "Nim" will be used --expandMacro:MACRO dump every generated AST from MACRO --excludePath:PATH exclude a path from the list of search paths --dynlibOverride:SYMBOL marks SYMBOL so that dynlib:SYMBOL has no effect and can be statically linked instead; symbol matching is fuzzy so that --dynlibOverride:lua matches dynlib: "liblua.so.3" --dynlibOverrideAll disables the effects of the dynlib pragma --listCmd list the commands used to execute external programs --parallelBuild:0|1|... perform a parallel build value = number of processors (0 for auto-detect) --incremental:on|off only recompile the changed modules (experimental!) --verbosity:0|1|2|3 set Nim's verbosity level (1 is default) --errorMax:N stop compilation after N errors; 0 means unlimited --experimental:$1 enable experimental language feature --profiler:on|off Enable profiling; requires import nimprof, and works better with --stackTrace:on see also https://nim-lang.github.io/Nim/estp.html
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 certain safety checks are omitted 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.
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):
- $nim/config/nim.cfg, /etc/nim/nim.cfg (UNIX) or <Nim's installation director>\config\nim.cfg (Windows). This file can be skipped with the --skipCfg command line option.
- 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.
- $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.
- $projectDir/nim.cfg where $projectDir stands for the project file's path. This file can be skipped with the --skipProjCfg command line option.
- 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. To compile a release build define the release symbol:
nim c -d:release 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 and so the compiler should reject it. Currently however this check is not implemented and instead the first matching file is used.
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. Files generated in this directory follow a naming logic which you can read about in the Nim Backend Integration document.
The --nimcache compiler switch 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.$cc (for example arm.linux.gcc) and the configuration system is used to provide meaningful defaults. For example for ARM your configuration file should contain something like:
arm.linux.gcc.path = "/usr/bin" arm.linux.gcc.exe = "arm-linux-gcc" arm.linux.gcc.linkerexe = "arm-linux-gcc"
Cross compilation for Windows
To cross compile for Windows from Linux or OSX using the MinGW-w64 toolchain:
nim c -d:mingw myproject.nim
Use --cpu:i386 or --cpu:amd64 to switch the cpu arch.
The MinGW-w64 toolchain can be installed as follows:
Ubuntu: apt install mingw-w64 CentOS: yum install mingw32-gcc | mingw64-gcc - requires EPEL OSX: brew install mingw-w64
Cross compilation for Nintendo Switch
Simply add --os:nintendoswitch to your usual nim c or nim cpp command and set the passC and passL command line switches to something like:
nim c ... --passC="-I$DEVKITPRO/libnx/include" ... --passL="-specs=$DEVKITPRO/libnx/switch.specs -L$DEVKITPRO/libnx/lib -lnx"
or setup a nim.cfg file like so:
#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:
- 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
- Dynamic calls. DevkitPro libraries have no dlopen/dlclose functions.
- Command line parameters. It doesn't make sense to have these for a console anyways, so no big deal here.
- mqueue. Sadly there are no mqueue headers.
- ucontext. No headers for these either. No coroutines for now :(
- 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 off runtime checks and turns on the optimizer. More aggressive optimizations are possible, eg: --passC:-ffast-math (but see issue #10305) --stacktrace:off |
| useFork | Makes osproc use fork instead of posix_spawn. |
| useNimRtl | Compile and link against nimrtl.dll. |
| useMalloc | Makes Nim use C's malloc 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 (requires a C compiler with _Static_assert support, like any C11 compiler) |
| 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.
Hot code reloading
The hotCodeReloading option enables special compilation mode where changes in the code can be applied automatically to a running program. The code reloading happens at the granularity of an individual module. When a module is reloaded, any newly added global variables will be initialized, but all other top-level code appearing in the module won't be re-executed and the state of all existing global variables will be preserved. One can use the special event handlers beforeCodeReload and afterCodeReload to reset the state of a particular variable or to force the execution of certain statements:
var settings = initTable[string, string]() lastReload: Time for k, v in loadSettings(): settings[k] = v initProgram() afterCodeReload: lastReload = now() resetProgramState()
On each code reload, Nim will first execute all beforeCodeReload handlers registered in the previous version of the program and then all afterCodeReload:idx handlers appearing in the newly loaded code. Please note that any handlers appearing in modules that weren't reloaded will also be executed. To prevent this behavior, one can guard the code with the hasModuleChanged() API:
import mydb var myCache = initTable[Key, Value]() afterCodeReload: if hasModuleChanged(mydb): resetCache(myCache)
The hot code reloading is based on dynamic library hot swapping in the native targets and direct manipulation of the global namespace in the JavaScript target. The Nim compiler does not specify the mechanism for detecting the conditions when the code must be reloaded. Instead, the program code is expected to call performCodeReload():idx every time it wishes to reload its code.
It's expected that most projects will implement the reloading with a suitable build-system triggered IPC notification mechanism, but a polling solution is also possible through the provided hasAnyModuleChanged():idx API.
In order to access beforeCodeReload, afterCodeReload, hasModuleChanged or hasAnyModuleChanged one must import the hotcodereloading:idx module.
Usage in Native projects:
Native projects using the hot code reloading option will be implicitly compiled with the -d:useNimRtl option and they will depend on both the nimrtl library and the nimhcr library which implements the hot code reloading run-time.
All modules of the project will be compiled to separate dynamic link libraries placed in the nimcache directory. Please note that during the execution of the program, the hot code reloading run-time will load only copies of these libraries in order to not interfere with any newly issued build commands.
The main module of the program is considered non-reloadable. Please note that procs from reloadable modules should not appear in the call stack of program while performCodeReload is being called. Thus, the main module is a suitable place for implementing a program loop capable of calling performCodeReload.
Please note that reloading won't be possible when any of the type definitions in the program has been changed. When closure iterators are used (directly or through async code), the reloaded refinitions will affect only newly created instances. Existing iterator instancess will execute their original code to completion.
Usage in JavaScript projects:
Once your code is compiled for hot reloading, the nim-livereload NPM package provides a convenient solution for implementing the actual reloading in the browser using a framework such as LiveReload or BrowserSync.
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
Cursor pragma
The .cursor pragma is a temporary tool for optimization purposes and this property will be computed by Nim's optimizer eventually. Thus it remains undocumented.
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 and doc2 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 for embedded systems
The standard library can be avoided to a point where C code generation for 16bit micro controllers is feasible. Use the standalone target (--os:standalone) for a bare bones standard library that lacks any OS features.
To make the compiler output code for a 16bit target use the --cpu:avr target.
For example, to generate code for an AVR processor use this command:
nim c --cpu:avr --os:standalone --genScript x.nim
For the standalone target one needs to provide a file panicoverride.nim. See tests/manyloc/standalone/panicoverride.nim for an example implementation. Additionally, users should specify the amount of heap space to use with the -d:StandaloneHeapSize=<size> command line switch. Note that the total heap size will be <size> * sizeof(float64).
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:
- switch off the embedded debugger (it is slow!)
- turn on the optimizer and turn off runtime checks
- profile your code to find where the bottlenecks are
- try to find a better algorithm
- 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:
var s = procA() # assignment will not copy the string; procA allocates a new # string already
However it is not efficient to do:
var s = varA # assignment has to copy the whole string into a new buffer!
For let symbols a copy is not always necessary:
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:
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.
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:
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))