Rules Coffee

Compiles CoffeeScript files and exposes them as JavaScript targets.

coffee_src

The lowest level rule transpiles CoffeeScript into JavaScript. It comes in two flavors, coffee_srcs, which transpiles an arbitrary number of CoffeeScript sources in arbitrary directories, and coffee_src, which transpiles exactly one CoffeeScript into one JavaScript output.

```python
load('@com_vistarmedia_rules_coffee//coffee:def.bzl',
  'coffee_src',
  'coffee_srcs')

# Generates:
#   bazel-bin/{pkg}/file-a.js
coffee_src(
  name = 'src',
  src  = 'file-a.coffee',
)

# Generates:
#   bazel-bin/{pkg}/file-a.js
#   bazel-bin/{pkg}/file-b.js
coffee_srcs(
  name = 'srcs',
  srcs = [
    'file-a.coffee',
    'file-b.coffee',
  ],
)
```

coffee_library

Translates a collection of CoffeeScript sources files into a js_library.

```python
load('@com_vistarmedia_rules_coffee//coffee:def.bzl', 'coffee_library')

# Generates:
#  //{pkg}:lib js_library target
coffee_library(
  name = 'lib',
  srcs = [
    'file-a.coffee',
    'file-b.coffee',
  ],
  deps = [
    ':local',
    '//dep/in:rep',
    '@external//:lib',
  ],
)
```

coffee_binary

Translates a CoffeeScript source file into a js_binary.

```python
load('@com_vistarmedia_rules_coffee//coffee:def.bzl', 'coffee_binary')

# Generates:
#  //{pkg}:bin js_binary target
coffee_binary(
  name = 'bin',
  src  = 'main.coffee',
  deps = [
    ':local',
    '//dep/in:rep',
    '@external//:lib',
  ],
)
```

coffee_test

Translates a collection of CoffeeScript sources files into a js_test.

```python
load('@com_vistarmedia_rules_coffee//coffee:def.bzl', 'coffee_test')

# Generates:
#  //{pkg}:test js_test target
coffee_test(
  name = 'test',
  size = 'small',
  srcs  = [
    'lib-a_test.coffee',
    'lib-b_test.coffee',
  ]
  deps = [
    ':lib',
  ],
)
```

Implementation weirdness

The CoffeeScript compiler handles source files in different directories kind of strangely. Namely, it tries to find the longest path prefix shared by all input files and uses that as the root source directory. The output directory structure is based on that.

Though it's rare that a coffee_* rule would encounter rules in multiple directories, there's no way to inform the compiler of a strict root. Instead, these rules group all sources by their directory, and performs a compilation for each.