rscons/README.md

# Rscons

Rscons is a software construction framework inspired by SCons and implemented
in Ruby.

[![Gem Version](https://badge.fury.io/rb/rscons.png)](http://badge.fury.io/rb/rscons)

## Installation

Add this line to your application's Gemfile:

    gem "rscons"

And then execute:

    $ bundle install

Or install it yourself as:

    $ gem install rscons

## Usage

Rscons is implemented as a Ruby library and distributed as a gem.
It also provides a "rscons" executable which can evaluate a build script (by
default named Rsconsfile or Rsconsfile.rb).
It can also be used from rake or from a standalone Ruby script.

### Example: Building a C Program

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

### Example: Building a D Program

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

### Example: Cloning an Environment

```ruby
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", Dir["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", Dir["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.

```ruby
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", Dir["*.c"])
end
```

### Example: Custom Builder That Only Regenerates When Necessary

```ruby
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
```

### Example: Custom Builder That Generates Multiple Output Files

```ruby
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.

```ruby
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.

```ruby
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

```ruby
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", Dir["**/*.cc"])
end
```

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.

Build hooks can alter construction variable values for a particular build
operation. Build hooks can also register new build targets.

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.

### Example: Creating a static library

```ruby
Rscons::Environment.new do |env|
  env.Library("mylib.a", Dir["src/**/*.c"])
end
```

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

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

## Details

### Builders

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.

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

```ruby
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

```ruby
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

```ruby
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

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

#### Library

```ruby
env.Library(target, sources)
# Example
env.Library("lib.a", Dir["src/**/*.c"])
```

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

#### Object

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

The Object builder compiles the given sources to an object file.

#### Preprocess

```ruby
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

```ruby
env.Program(target, sources)
# Example
env.Program("myprog", Dir["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`.

### Managing Environments

An Rscons::Environment consists of:

* a collection of construction variables
* a collection of builders
* a mapping of build directories from source directories
* a default build root to apply if no build directories are matched
* a collection of targets to build
* a collection of build hooks

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

The set of environment attributes that are cloned is controllable via the
`:clone` option to the `#clone` method.
For example, `env.clone(clone: :all)` will include construction variables,
builders, build hooks, build directories, and the build root.

The set of pending targets is never cloned.

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

```ruby
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".

#### 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.

### 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:

```ruby
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`:

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

### Construction Variable Naming

* uppercase strings - the default construction variables that Rscons uses
* symbols, lowercase strings - reserved as user-defined construction variables

### API documentation

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

## Release Notes

### v1.9.2

- allow phony targets in conjunction with build roots

### v1.9.1

- change *SUFFIX defaults to arrays
- add various C++ file suffixes
- use ${INCPREFIX} instead of hard-coded "-I" in Preprocess builder

### v1.9.0

#### New Features

- #6 - add Install and Copy builders
- #22 - allow overriding Command builder short description with CMD_DESC variable
- #24 - add "rscons" executable
- #25 - add support for phony targets given as Symbols instead of Strings
- #26 - support registering multiple build targets with the same target name
- #27 - add Directory builder

#### Fixes

- #20 - fix variable references that expand to arrays in build target sources
- #21 - rework Preprocess builder to consider deep dependencies
- fix Rscons.set_suffix to append the given suffix if the filename has none
- remove ${CFLAGS} from default CPP_CMD

### v1.8.1

- fix Environment#dump when construction variables are symbols

### v1.8.0

- new Command builder to execute arbitrary user commands
- new SimpleBuilder class
  - create new builders quickly by passing a block to Environment#add_builder
- improved YARD documentation
- add Environment#dump to debug Environment construction variables

### v1.7.0

- allow build hooks to register new build targets
- add post-build hooks (register with Environment#add_post_build_hook)
- clear all build targets after processing an Environment
- allow trailing slashes in arguments to Environment#build_dir

### v1.6.1

- add DEPFILESUFFIX construction variable to override dependency file suffix
- fix Environment#depends to expand its arguments for construction variables

### v1.6.0

- support lambdas as construction variable values

### v1.5.0

- add "json" as a runtime dependency
- update construction variables to match SCons more closely
  - add CPPDEFPREFIX, INCPREFIX, CPPDEFINES, CCFLAGS, LIBDIRPREFIX, and LIBLINKPREFIX
- add Environment#shell
- add Environment#parse_flags, #parse_flags!, #merge_flags
- unbuffer $stdout by default
- add PROGSUFFIX construction variable (defaults to .exe on MinGW/Cygwin)
- add Rscons::BuildTarget and Builder#create_build_target
- update specs to RSpec 3.x and fix to run on MinGW/Cygwin/Linux
- add YARD documentation to get to 100% coverage

### v1.4.3

- fix builders properly using construction variable overrides
- expand nil construction variables to empty strings

### v1.4.2

- add Environment#expand_path
- expand construction variable references in builder targets and sources before invoking builder

### v1.4.1

- fix invoking a builder with no sources while a build root defined

### v1.4.0

- add CFile builder
- add Disassemble builder
- add Preprocess builder
- pass the Environment object to build hooks in the :env key of the build_op parameter
- expand target/source paths beginning with "^/" to be relative to the Environment's build root
- many performance improvements, including:
  - use JSON instead of YAML for the cache to improve loading speed (Issue #7)
  - store a hash of the build command instead of the full command contents in the cache
  - implement copy-on-write semantics for construction variables when cloning Environments
  - only load the cache once instead of on each Environment#process
  - only write the cache when something has changed
- fix Cache#mkdir_p to handle relative paths (Issue #5)
- flush the cache to disk if a builder raises an exception (Issue #4)

### v1.3.0

- change Environment#execute() options parameter to accept the following options keys:
  - :env to pass an environment Hash to Kernel#system
  - :options to pass an options Hash to Kernel#system

### v1.2.0

- add :clone option to Environment#clone to control exactly which Environment attributes are cloned
- allow nil to be passed in to Environment#build_root=

### v1.1.0

- Change Cache#up_to_date?() and #register_build() to accept a single target
  file or an array of target file names

## 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