Rscons

Rscons (https://github.com/holtrop/rscons) is a software construction framework inspired by SCons and waf but implemented in Ruby.

Installation

Rscons is distributed as a standalone Ruby script named rscons. This file (containing the complete rscons build system) can be checked into your project and versioned along with your project.

Usage

Standalone

Rscons provides a standalone executable ("rscons") with a command-line interface. The rscons executable will read a build script (by default named Rsconsfile or Rsconsfile.rb) and execute its contents.

With Rake

Rscons can be used with rake as well. The same content that would be written in Rsconsfile can be placed in a Rakefile. It could be placed within a rake task block or split among multiple tasks.

Example Build Scripts

Example: Building a C Program

Rscons::Environment.new do |env|
  env["CFLAGS"] << "-Wall"
  env.Program("program", Rscons.glob("src/**/*.c"))
end

Example: Building a D Program

Rscons::Environment.new do |env|
  env["DFLAGS"] << "-Wall"
  env.Program("program", Rscons.glob("src/**/*.d"))
end

Example: Cloning an Environment

main_env = Rscons::Environment.new do |env|
  # Store object files from sources under "src" in "build/main"
  env.build_dir("src", "build/main")
  env["CFLAGS"] = ["-DSOME_DEFINE", "-O3"]
  env["LIBS"] = ["SDL"]
  env.Program("program", Rscons.glob("src/**/*.cc"))
end

debug_env = main_env.clone do |env|
  # Store object files from sources under "src" in "build/debug"
  env.build_dir("src", "build/debug")
  env["CFLAGS"] -= ["-O3"]
  env["CFLAGS"] += ["-g", "-O0"]
  env.Program("program-debug", Rscons.glob("src/**/*.cc"))
end

Example: Custom Builder

Custom builders are implemented as classes which extend from Rscons::Builder. The builder must have a run method which is called to invoke the builder. The run method should return the name of the target built on success, and false on failure.

class GenerateFoo < Rscons::Builder
  def run(target, sources, cache, env, vars)
    cache.mkdir_p(File.dirname(target))
    File.open(target, "w") do |fh|
      fh.puts <<EOF
#define GENERATED 42
EOF
    end
    target
  end
end

Rscons::Environment.new do |env|
  env.add_builder(GenerateFoo.new)
  env.GenerateFoo("foo.h", [])
  env.Program("a.out", Rscons.glob("*.c"))
end

Example: Custom Builder That Only Regenerates When Necessary

class CmdBuilder < Rscons::Builder
  def run(target, sources, cache, env, vars)
    cmd = ["cmd", "-i", sources.first, "-o", target]
    unless cache.up_to_date?(target, cmd, sources, env)
      cache.mkdir_p(File.dirname(target))
      system(cmd)
      cache.register_build(target, cmd, sources, env)
    end
    target
  end
end

Rscons::Environment.new do |env|
  env.add_builder(CmdBuilder.new)
  env.CmdBuilder("foo.gen", "foo_gen.cfg")
end

The Cache#up_to_date? method accepts an optional 5th parameter which is an options Hash. The :debug option can be specified in this Hash with a value of true to aid in debugging builders while developing them. For example:

unless cache.up_to_date?(target, cmd, sources, env, debug: true)
end

Example: Custom Builder That Generates Multiple Output Files

class CModuleGenerator < Rscons::Builder
  def run(target, sources, cache, env, vars)
    c_fname = target
    h_fname = target.sub(/\.c$/, ".h")
    cmd = ["generate_c_and_h", sources.first, c_fname, h_fname]
    unless cache.up_to_date?([c_fname, h_fname], cmd, sources, env)
      cache.mkdir_p(File.dirname(target))
      system(cmd)
      cache.register_build([c_fname, h_fname], cmd, sources, env)
    end
    target
  end
end

Rscons::Environment.new do |env|
  env.add_builder(CModuleGenerator.new)
  env.CModuleGenerator("build/foo.c", "foo_gen.cfg")
end

Example: Custom Builder Using Builder#standard_build()

The standard_build method from the Rscons::Builder base class can be used when the builder needs to execute a system command to produce the target file. The standard_build method will return the correct value so its return value can be used as the return value from the run method.

class CmdBuilder < Rscons::Builder
  def run(target, sources, cache, env, vars)
    cmd = ["cmd", "-i", sources.first, "-o", target]
    standard_build("CmdBld #{target}", target, cmd, sources, env, cache)
  end
end

Rscons::Environment.new do |env|
  env.add_builder(CmdBuilder.new)
  env.CmdBuilder("foo.gen", "foo_gen.cfg")
end

Example: Custom Builder Using Environment#add_builder()

The add_builder method of the Rscons::Environment class optionally allows you to define and register a builder by providing a name and action block. This can be useful if the builder you are trying to define is easily expressed as a short ruby procedure. When add_builder is called in this manner a new builder will be registered with the environment with the given name. When this builder is used it will call the provided block in order to build the target.

Rscons::Environment.new do |env|
  env.add_builder(:JsonToYaml) do |target, sources, cache, env, vars|
    unless cache.up_to_date?(target, :JsonToYaml, sources, env)
      cache.mkdir_p(File.dirname(target))
      File.open(target, 'w') do |f|
        f.write(YAML.dump(JSON.load(IO.read(sources.first))))
      end
      cache.register_build(target, :JsonToYaml, sources, env)
    end
    target
  end
  env.JsonToYaml('foo.yml','foo.json')
end

Example: Using different compilation flags for some sources

Rscons::Environment.new do |env|
  env["CFLAGS"] = ["-O3", "-Wall", "-DDEFINE"]
  env.add_build_hook do |build_op|
    if build_op[:target] =~ %r{build/third-party}
      build_op[:vars]["CFLAGS"] -= ["-Wall"]
    end
  end
  env.build_dir("src", "build")
  env.Program("program", Rscons.glob("**/*.cc"))
end

Example: Creating a static library

Rscons::Environment.new do |env|
  env.Library("mylib.a", Rscons.glob("src/**/*.c"))
end

Example: Creating a C++ parser source from a Yacc/Bison input file

Rscons::Environment.new do |env|
  env.CFile("#{env.build_root}/parser.tab.cc", "parser.yy")
end

Details

Environments

The Environment is the main top-level object that Rscons operates with. An Environment must be created by the user in order to build anything. All build targets are registered within an Environment. In many cases only a single Environment will be needed, but more than one can be created (either from scratch or by cloning another existing Environment) if needed.

An Environment consists of:

• a collection of builders
• a collection of construction variables used by those builders
• a mapping of build directories from source directories
• a default build root to apply if no specific build directories are matched
• a collection of user-defined build targets
• a collection of user-defined build hooks

When cloning an environment, by default the construction variables, builders, build hooks, build directories, and build root are cloned, but the new environment does not inherit any of the registered build targets.

The set of environment attributes that are cloned is controllable via the :clone option to the #clone method. For example, env.clone(clone: [:variables, :builders]) will include construction variables, and builders but not build hooks, build directories, or the build root.

The set of pending targets is never cloned.

Cloned environments contain "deep copies" of construction variables. For example, in:

base_env = Rscons::Environment.new
base_env["CPPPATH"] = ["one", "two"]
cloned_env = base_env.clone
cloned_env["CPPPATH"] << "three"

base_env["CPPPATH"] will not include "three".

Builders

Builders are the workhorses that Rscons uses to execute build operations. Each builder is specialized to perform a particular operation.

Rscons ships with a number of builders:

• Command, which executes a user-defined command to produce the target.
• Copy, which is identical to Install.
• CFile, which builds a C or C++ source file from a lex or yacc input file.
• Disassemble, which disassembles an object file to a disassembly listing.
• Install, which installs files or directories to a specified destination.
• Library, which collects object files into a static library archive file.
• Object, which compiles source files to produce an object file.
• Preprocess, which invokes the C/C++ preprocessor on a source file.
• Program, which links object files to produce an executable.
• SharedLibrary, which links object files to produce a dynamically loadable library.
• SharedObject, which compiles source files to produce an object file, in a way that is able to be used to create a shared library.

If you want to create an Environment that does not contain any builders, you can use the :exclude_builders key to the Environment constructor.

Command

env.Command(target, sources, "CMD" => command)
# Example
env.Command("docs.html", "docs.md",
    "CMD" => ["pandoc", "-fmarkdown", "-thtml", "-o${_TARGET}", "${_SOURCES}"],
    "CMD_DESC" => "PANDOC")

The command builder executes a user-defined command in order to produce the desired target file based on the provided source files.

CFile

env.CFile(target, source)
# Example
env.CFile("parser.c", "parser.y")

The CFile builder will generate a C or C++ source file from a lex (.l, .ll) or yacc (.y, .yy) input file.

Disassemble

env.Disassemble(target, source)
# Example
env.Disassemble("module.dis", "module.o")

The Disassemble builder generates a disassembly listing using objdump from and object file.

Install

env.Install(destination, sources)
# Example
env.Install("dist/bin", "app.exe")
env.Install("dist/share", "share")

Library

env.Library(target, sources)
# Example
env.Library("lib.a", Rscons.glob("src/**/*.c"))

The Library builder creates a static library archive from the given source files.

Object

env.Object(target, sources)
# Example
env.Object("module.o", "module.c")

The Object builder compiles the given sources to an object file. Although it can be called explicitly, it is more commonly implicitly called by the Program builder.

Preprocess

env.Preprocess(target, source)
# Example
env.Preprocess("module-preprocessed.cc", "module.cc")

The Preprocess builder invokes either ${CC} or ${CXX} (depending on if the source contains an extension in ${CXXSUFFIX} or not) and writes the preprocessed output to the target file.

Program

env.Program(target, sources)
# Example
env.Program("myprog", Rscons.glob("src/**/*.cc"))

The Program builder compiles and links the given sources to an executable file. Object files or source files can be given as sources. A platform-dependent program suffix will be appended to the target name if one is not specified. This can be controlled with the PROGSUFFIX construction variable.

SharedLibrary

env.SharedLibrary(target, sources)
# Example
env.SharedLibrary("mydll", Rscons.glob("src/**/*.cc"))

The SharedLibrary builder compiles and links the given sources to a dynamically loadable library. Object files or source files can be given as sources. A platform-dependent prefix and suffix will be appended to the target name if they are not specified by the user. These values can be controlled by overriding the SHLIBPREFIX and SHLIBSUFFIX construction variables.

SharedObject

env.SharedObject(target, sources)
# Example
env.SharedObject("lib_module.o", "lib_module.c")

The SharedObject builder compiles the given sources to an object file. Any compilation flags necessary to build the object file in a manner that allows it to be used to create a shared library are added. Although it can be called explicitly, it is more commonly implicitly called by the SharedLibrary builder.

Construction Variables

Construction variables are used to define the toolset and any build options that Rscons will use to build a project. The default construction variable values are configured to build applications using gcc. However, all construction variables can be overridden by the user.

Name	Type	Description	Default
AR	String	Static library archiver executable	"ar"
ARCMD	Array	Static library archiver command line	["${AR}", "${ARFLAGS}", "${_TARGET}", "${_SOURCES}"]
ARFLAGS	Array	Static library archiver flags	["rcs"]
AS	String	Assembler executable	"${CC}"
ASCMD	Array	Assembler command line	["${AS}", "-c", "-o", "${_TARGET}", "${ASDEPGEN}", "${INCPREFIX}${ASPPPATH}", "${ASPPFLAGS}", "${ASFLAGS}", "${_SOURCES}"]
ASDEPGEN	Array	Assembly dependency generation flags	["-MMD", "-MF", "${_DEPFILE}", "-MT", "TARGET"]
ASFLAGS	Array	Assembler flags	[]
ASPPFLAGS	Array	Assembler preprocessor flags	["${CPPFLAGS}"]
ASPPPATH	Array	Assembler preprocessor path	["${CPPPATH}"]
ASSUFFIX	Array	Assembly file suffixes	[".S"]
CC	String	C compiler executable	"gcc"
CCCMD	Array	C compiler command line	["${CC}", "-c", "-o", "${_TARGET}", "${CCDEPGEN}", "${INCPREFIX}${CPPPATH}", "${CPPFLAGS}", "${CFLAGS}", "${CCFLAGS}", "${_SOURCES}"]
CCDEPGEN	Array	C compiler dependency generation flags	["-MMD", "-MF", "${_DEPFILE}", "-MT", "TARGET"]
CCFLAGS	Array	Common flags for both C and C++ compiler	[]
CFLAGS	Array	C compiler flags	[]
CPP_CMD	Array	Preprocess command line	["${_PREPROCESS_CC}", "-E", "${_PREPROCESS_DEPGEN}", "-o", "${_TARGET}", "${INCPREFIX}${CPPPATH}", "${CPPFLAGS}", "${_SOURCES}"]
CPP_TARGET_SUFFIX	String	Suffix used for crt:preprocess target filename.	".c"
CPPDEFINES	Array	C preprocessor defines	[]
CPPDEFPREFIX	String	Prefix used for C preprocessor to introduce a define	"-D"
CPPFLAGS	Array	C preprocessor flags	["${CPPDEFPREFIX}${CPPDEFINES}"]
CPPPATH	Array	C preprocessor path	[]
CSUFFIX	Array	C source file suffixes	[".c"]
CXX	String	C++ compiler executable	"g++"
CXXCMD	Array	C++ compiler command line	["${CXX}", "-c", "-o", "${_TARGET}", "${CXXDEPGEN}", "${INCPREFIX}${CPPPATH}", "${CPPFLAGS}", "${CXXFLAGS}", "${CCFLAGS}", "${_SOURCES}"]
CXXDEPGEN	Array	C++ compiler dependency generation flags	["-MMD", "-MF", "${_DEPFILE}", "-MT", "TARGET"]
CXXFLAGS	Array	C++ compiler flags	[]
CXXSUFFIX	Array	C++ source file suffixes	[".cc", ".cpp", ".cxx", ".C"]
D_IMPORT_PATH	Array	D compiler import path	[]
DC	String	D compiler executable	"gdc"
DCCMD	Array	D compiler command line	["${DC}", "-c", "-o", "${_TARGET}", "${DDEPGEN}", "${INCPREFIX}${D_IMPORT_PATH}", "${DFLAGS}", "${_SOURCES}"]
DDEPGEN	Array	D compiler dependency generation flags	["-MMD", "-MF", "${_DEPFILE}", "-MT", "TARGET"]
DEPFILESUFFIX	String	Dependency file suffix for Makefile-style dependency rules emitted by the compiler (used internally for temporary dependency files used to determine a source file's dependencies)	".mf"
DFLAGS	Array	D compiler flags	[]
DISASM_CMD	Array	Disassemble command line	["${OBJDUMP}", "${DISASM_FLAGS}", "${_SOURCES}"]
DISASM_FLAGS	Array	Disassemble flags	["--disassemble", "--source"]
DSUFFIX	String/Array	Default D source file suffix	".d"
INCPREFIX	String	Prefix used for C preprocessor to add an include path	"-I"
LD	String	nil	Linker executable (automatically determined when nil)
LDCMD	Array	Link command line	["${LD}", "-o", "${_TARGET}", "${LDFLAGS}", "${_SOURCES}", "${LIBDIRPREFIX}${LIBPATH}", "${LIBLINKPREFIX}${LIBS}"]
LDFLAGS	Array	Linker flags	[]
LEX	String	Lex executable	"flex"
LEX_CMD	Array	Lex command line	["${LEX}", "${LEX_FLAGS}", "-o", "${_TARGET}", "${_SOURCES}"]
LEX_FLAGS	Array	Lex flags	[]
LEXSUFFIX	Array	Lex input file suffixes	[".l", ".ll"]
LIBDIRPREFIX	String	Prefix given to linker to add a library search path	"-L"
LIBLINKPREFIX	String	Prefix given to linker to add a library to link with	"-l"
LIBPATH	Array	Library load path	[]
LIBS	Array	Libraries to link with	[]
LIBSUFFIX	String/Array	Default static library file suffix	".a"
OBJDUMP	String	Objdump executable	"objdump"
OBJSUFFIX	String/Array	Default object file suffix	".o"
PROGSUFFIX	String	Default program suffix.	Windows: ".exe", POSIX: ""
SHCC	String	Shared object C compiler	"${CC}"
SHCCCMD	Array	Shared object C compiler command line	["${SHCC}", "-c", "-o", "${_TARGET}", "${CCDEPGEN}", "${INCPREFIX}${CPPPATH}", "${CPPFLAGS}", "${SHCFLAGS}", "${SHCCFLAGS}", "${_SOURCES}"]
SHCCFLAGS	Array	Shared object C and C++ compiler flags	Windows: ["${CCFLAGS}"], POSIX: ["${CCFLAGS}", -fPIC"]
SHCFLAGS	Array	Shared object C compiler flags	["${CFLAGS}"]
SHCXX	String	Shared object C++ compiler	"${CXX}"
SHCXXCMD	Array	Shared object C++ compiler command line	["${SHCXX}", "-c", "-o", "${_TARGET}", "${CXXDEPGEN}", "${INCPREFIX}${CPPPATH}", "${CPPFLAGS}", "${SHCXXFLAGS}", "${SHCCFLAGS}", "${_SOURCES}"]
SHCXXFLAGS	Array	Shared object C++ compiler flags	["${CXXFLAGS}"]
SHDC	String	Shared object D compiler	"gdc"
SHDCCMD	Array	Shared object D compiler command line	["${SHDC}", "-c", "-o", "${_TARGET}", "${INCPREFIX}${D_IMPORT_PATH}", "${SHDFLAGS}", "${_SOURCES}"]
SHDFLAGS	Array	Shared object D compiler flags	Windows: ["${DFLAGS}"], POSIX: ["${DFLAGS}", "-fPIC"]
SHLD	String	Shared library linker	nil (if nil, ${SHCC}, ${SHCXX}, or ${SHDC} is used depending on the sources being linked)
SHLDCMD	Array	Shared library linker command line	["${SHLD}", "-o", "${_TARGET}", "${SHLDFLAGS}", "${_SOURCES}", "${SHLIBDIRPREFIX}${LIBPATH}", "${SHLIBLINKPREFIX}${LIBS}"]
SHLDFLAGS	Array	Shared library linker flags	["${LDFLAGS}", "-shared"]
SHLIBDIRPREFIX	String	Prefix given to shared library linker to add a library search path	"-L"
SHLIBLINKPREFIX	String	Prefix given to shared library linker to add a library to link with	"-l"
SHLIBPREFIX	String	Shared library file name prefix	Windows: "", POSIX: "lib"
SHLIBSUFFIX	String	Shared library file name suffix	Windows: ".dll", POSIX: ".so"
SIZE	String	Size executable.	"size"
YACC	String	Yacc executable	"bison"
YACC_CMD	Array	Yacc command line	["${YACC}", "${YACC_FLAGS}", "-o", "${_TARGET}", "${_SOURCES}"]
YACC_FLAGS	Array	Yacc flags	["-d"]
YACCSUFFIX	Array	Yacc input file suffixes	[".y", ".yy"]

Build Hooks

Environments can have build hooks which are added with env.add_build_hook(). Build hooks are invoked immediately before a builder executes. Build hooks can modify the construction variables in use for the build operation. They can also register new build targets.

Environments can also have post-build hooks added with env.add_post_build_hook(). Post-build hooks are only invoked if the build operation was a success. Post-build hooks can invoke commands using the newly-built files, or register new build targets.

Each build hook block will be invoked for every build operation, so the block should test the target or sources if its action should only apply to some subset of build targets or source files.

Example build hook:

Rscons::Environment.new do |env|
  # Build third party sources without -Wall
  env.add_build_hook do |build_op|
    if build_op[:builder].name == "Object" and
      build_op[:sources].first =~ %r{src/third-party}
      build_op[:vars]["CFLAGS"] -= ["-Wall"]
    end
  end
end

The build_op parameter to the build hook block is a Hash describing the build operation with the following keys:

• :builder - Builder instance in use
• :env - Environment calling the build hook; note that this may be different from the Environment that the build hook was added to in the case that the original Environment was cloned with build hooks!
• :target - String name of the target file
• :sources - Array of the source files
• :vars - Rscons::VarSet containing the construction variables to use. The build hook can overwrite entries in build_op[:vars] to alter the construction variables in use for this specific build operation.

Phony Targets

A build target name given as a Symbol instead of a String is interpreted as a "phony" target. Phony targets operate similarly to normal build targets, except that a file is not expected to be produced by the builder. Phony targets will still be "rebuilt" if any source or the command is out of date.

Explicit Dependencies

A target can be marked as depending on another file that Rscons would not otherwise know about via the Environment#depends function. For example, to force the linker to re-link a Program output when a linker script changes:

Rscons::Environment.new do |env|
  env.Program("a.out", "foo.c", "LDFLAGS" => %w[-T linker_script.ld])
  env.depends("a.out", "linker_script.ld")
end

You can pass multiple dependency files to Environment#depends:

env.depends("my_app", "config/link.ld", "README.txt", *Rscons.glob("assets/**/*"))

Command-Line Variables

Variables can be specified on the rscons command line. For example:

rscons VAR=val

These variables are accessible in a global VarSet called Rscons.vars.

Construction Variable Naming

• uppercase strings - the default construction variables that Rscons uses
• strings beginning with "_" - set and used internally by builders
• symbols, lowercase strings - reserved as user-defined construction variables

API documentation

Documentation for the complete Rscons API can be found at http://www.rubydoc.info/github/holtrop/rscons/master.

Contributing

1. Fork it
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Add some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create new Pull Request