Deprecate availability key in nif_versions (#81)

PRECOMPILATION_GUIDE.md

@@ -43,8 +43,7 @@ def project do
     make_precompiler_filename: "nif",
     make_precompiler_priv_paths: ["nif.*"],
     make_precompiler_nif_versions: [
-      versions: ["2.14", "2.15", "2.16"],
-      availability: &target_available_for_nif_version?/2
+      versions: ["2.14", "2.15", "2.16"]
     ]
     # ...
   ]
@@ -113,22 +112,40 @@ The default value for `make_precompiler_nif_versions` is
 [versions: ["#{:erlang.system_info(:nif_version)}"]]
 ```
 
-There're three sub-keys for `make_precompiler_nif_versions`:
+There're two sub-keys for `make_precompiler_nif_versions`:
 
 - `versions` 
 - `fallback_version`
-- `availability`
 
 ##### `versions` sub-key
 
-The `versions` sub-key is a list of NIF versions that the precompiled artefacts are available for:
+The `versions` sub-key is either a list of NIF versions of a function that returns a list of NIF versions that the precompiled artefacts are available for:
 
 ```elixir
 make_precompiler_nif_versions: [
   versions: ["2.15", "2.16"]
 ]
 ```
 
+The above example tells `:elixir_make` that all targets have precompiled artefacts for NIF version `2.15` and `2.16`.
+
+For some platforms maybe we only have precompiled artefacts after a certain NIF version, say for x86_64 Windows we have precompiled artefacts available when NIF version >= `2.16` while other platforms have precompiled artefacts available from NIF version >= `2.15`.
+
+In such case we can inform `:elixir_make` that Windows targets don't have precompiled artefacts available except for NIF version `2.16` by passing a function to the `availability` sub-key. This function should accept two arguments, `target` and `nif_version`, and returns a boolean value indicating whether the precompiled artefacts for the target and NIF version are available.
+
+```elixir
+make_precompiler_nif_versions: [
+  versions: fn opts ->
+    target = opts.target
+    if String.contains?(target, "windows") do
+      ["2.16"]
+    else
+      ["2.15", "2.16"]
+    end
+  end
+]
+```
+
 The default behaviour is to use the exact NIF version that is available to the current target. If one is not available, it may fallback (see `fallback_version` next) to the highest matching major version prior to the current version. For example:
 
 - if the current host is using Erlang/OTP 23 (NIF version `2.15`), `elixir_make` will use the precompiled artefacts for NIF version `2.15`; 
@@ -139,25 +156,11 @@ If the current host is using Erlang/OTP with a new major Erlang NIF version (NIF
 
 ##### `fallback_version` sub-key
 
-The behaviour when `elixir_make` cannot find the exact NIF version of the precompiled binary can be customized by setting the `fallback_version` sub-key. The value of the `fallback_version` sub-key should be a function that accepts three arguments, `target`, `current_nif_version` and `target_versions`. The `target` is the target triplet (or other name format, defined by the precompiler of your choice), `current_nif_version` is the NIF version on the current host, and `target_versions` is a list of NIF versions that are available to the target.
-
-The `fallback_version` function should return either the NIF version that `elixir_make` should use from the `target_versions` list or the `current_nif_version`.
+The behaviour when `elixir_make` cannot find the exact NIF version of the precompiled binary can be customized by setting the `fallback_version` sub-key.
 
-##### `availability` sub-key
+The value of the `fallback_version` sub-key should be a function that accepts one argument, `opts`, which is a map that include one key `target`. The `target` is the target triplet (or other naming format, defined by the precompiler of your choice).
 
-For some platforms maybe we only have precompiled artefacts after a certain NIF version, say for x86_64 Windows we have precompiled artefacts available when NIF version >= `2.16` while other platforms have precompiled artefacts available from NIF version >= `2.15`.
-
-In such case we can inform `:elixir_make` that Windows targets don't have precompiled artefacts available except for NIF version `2.16` by passing a function to the `availability` sub-key. This function should accept two arguments, `target` and `nif_version`, and returns a boolean value indicating whether the precompiled artefacts for the target and NIF version are available.
-
-```elixir
-defp target_available_for_nif_version?(target, nif_version) do
-  if String.contains?(target, "windows") do
-    nif_version == "2.16"
-  else
-    true
-  end
-end
-```
+The `fallback_version` function should return the NIF version that is available and should be chosen for the current target.
 
 ### (Optional) Customise Precompilation Targets
 

lib/elixir_make/artefact.ex

@@ -146,13 +146,14 @@ defmodule ElixirMake.Artefact do
     {String.to_integer(major), String.to_integer(minor)}
   end
 
-  defp fallback_version(_current_target, current_nif_version, versions) do
+  defp fallback_version(opts) do
+    current_nif_version = "#{:erlang.system_info(:nif_version)}"
     {major, minor} = nif_version_to_tuple(current_nif_version)
 
     # Get all matching major versions, earlier than the current version
     # and their distance. We want the closest (smallest distance).
     candidates =
-      for version <- versions,
+      for version <- opts.versions,
           {^major, candidate_minor} <- [nif_version_to_tuple(version)],
           candidate_minor <= minor,
           do: {minor - candidate_minor, version}
@@ -163,6 +164,16 @@ defmodule ElixirMake.Artefact do
     end
   end
 
+  defp get_versions_for_target(versions, current_target) do
+    case versions do
+      version_list when is_list(version_list) ->
+        version_list
+
+      version_func when is_function(version_func, 1) ->
+        version_func.(%{target: current_target})
+    end
+  end
+
   @doc """
   Returns all available {{target, nif_version}, url} pairs available.
   """
@@ -179,15 +190,19 @@ defmodule ElixirMake.Artefact do
       config[:make_precompiler_nif_versions] ||
         [versions: [current_nif_version]]
 
-    versions = nif_versions[:versions]
-
     Enum.reduce(targets, [], fn target, archives ->
+      versions = get_versions_for_target(nif_versions[:versions], target)
+
       archive_filenames =
         Enum.reduce(versions, [], fn nif_version_for_target, acc ->
           availability = nif_versions[:availability]
 
           available? =
             if is_function(availability, 2) do
+              IO.warn(
+                ":availability key in elixir_make is deprecated, pass a function as :versions instead"
+              )
+
               availability.(target, nif_version_for_target)
             else
               true
@@ -220,14 +235,15 @@ defmodule ElixirMake.Artefact do
           config[:make_precompiler_nif_versions] ||
             [versions: []]
 
-        versions = nif_versions[:versions]
+        versions = get_versions_for_target(nif_versions[:versions], current_target)
 
         nif_version_to_use =
           if current_nif_version in versions do
             current_nif_version
           else
-            fallback_version = nif_versions[:fallback_version] || (&fallback_version/3)
-            fallback_version.(current_target, current_nif_version, versions)
+            fallback_version = nif_versions[:fallback_version] || (&fallback_version/1)
+            opts = %{target: current_target, versions: versions}
+            fallback_version.(opts)
           end
 
         available_urls = available_target_urls(config, precompiler)