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Platforms

envy installs for the machine it is running on. There is no cross-building and no target triple. A cross-platform repo gets its coverage from a CI matrix, and every machine resolves its own packages.

Platform filters decide which packages a given machine instantiates.

Vocabulary​

FormExampleMatches
OS"linux"that OS, any architecture
OS and arch"darwin-arm64"that pair only

The OS names are darwin, linux, and windows. The architectures are arm64 and x86_64. In Lua:

NameValue on an Apple-silicon Mac
envy.PLATFORM"darwin"
envy.ARCH"arm64"
envy.PLATFORM_ARCH"darwin-arm64"
envy.EXE_EXT"", and ".exe" on Windows

An empty or absent filter means everywhere. A filter list matches if any entry matches.

The four places filters apply​

#WhereMeaning
1Manifest entry platforms = { ... }This project only needs it here.
2Spec PLATFORMS = { ... }This package only exists here.
3SETUP pair PLATFORMS = { ... }This host tweak only applies here.
4Product platforms = { ... }This tool only ships here.
envy.lua: (1) the project only wants apt on Linux
PACKAGES = {
  { spec = "acme.apt@r0", source = specs .. "acme.apt.lua",
    platforms = { "linux" },
    options = { packages = { "libudev-dev" } },
    setup = { "packages" } },
}
acme.jlink.lua: (2), (3) and (4)
PLATFORMS = { "darwin", "linux", "windows" }     -- (2) all three, explicitly

SETUP = {
  udev_rules = {
    PLATFORMS = { "linux" },                     -- (3) kernel rules are Linux-only
    CHECK = ..., INSTALL = ...,
  },
}

PRODUCTS = function(opts)
  local products = { JLinkExe = exe("JLink") }
  if envy.PLATFORM == "linux" then
    products.jlink_udev_rules = { value = "99-jlink.rules", script = false }  -- (4)
  end
  return products
end

How (1) and (2) combine​

envy intersects the entry's list with the spec's list. If both are non-empty and share nothing, the package never instantiates: no error, no scripts, no work.

Entry platformsSpec PLATFORMSResult
absentabsenteverywhere
{ "linux" }absentLinux only
absent{ "darwin" }macOS only
{ "linux", "darwin" }{ "darwin" }macOS only
{ "linux" }{ "darwin" }nowhere

Naming an excluded package explicitly is different. envy install acme.apt@r0 on macOS is an error, because you asked for something specific that cannot happen. A filter that does less is fine. A query that silently does nothing is not.

Switching inside a spec​

Platform logic is ordinary Lua, and it can define different verbs per platform:

if envy.PLATFORM == "windows" then
  FETCH = "https://github.com/PolarGoose/Ragel-for-Windows/releases/download/ragel-6.10/Ragel.zip"
  PRODUCTS = { ragel = "Ragel.exe" }
else
  FETCH = "https://www.colm.net/files/ragel/ragel-6.10.tar.gz"
  STAGE = { strip = 1 }
  BUILD = function(install_dir) return "./configure --prefix=" .. install_dir .. "\nmake -j" end
  INSTALL = "make install"
  PRODUCTS = { ragel = "bin/ragel" }
end

Two smaller patterns:

-- Fail loudly on a platform the vendor does not publish for.
FETCH = function(tmp_dir, opts)
  local key = ({ darwin = "macos", linux = "linux", windows = "win64" })[envy.PLATFORM]
  assert(key, "unsupported platform: " .. envy.PLATFORM)
  return base .. "tool-" .. opts.version .. "-" .. key .. ".tar.gz"
end

-- Vendor arch naming rarely matches envy's, so normalize once.
local arch = (envy.ARCH == "arm64") and "aarch64" or envy.ARCH

Not the same thing: --platform​

envy init, sync, and deploy take a --platform flag. It selects which script flavors get written into the bin directory: POSIX shell scripts, Windows .bat files, or both.

envy sync --platform all      # commit wrappers for POSIX and Windows

It says nothing about which packages install. A macOS machine still installs macOS packages. The flag exists so a cross-platform repo can commit working wrappers for colleagues on other systems.

See also​