Add a thrift_version compiler option.

If you require a specific version of the Thrift compiler, you can specify a
version requirement using the `thrift_version` option. Version requirements
use the SemVer 2.0 schema.

README.md

@@ -37,7 +37,7 @@ Next, define the list of `:thrift_files` that should be compiled. In this
 example, we gather all of the `.thrift` files under the `thrift` directory:
 
 ```elixir
-thrift_files: Mix.Utils.extract_files(["thrift"], [:thrift]),
+thrift_files: Mix.Utils.extract_files(["thrift"], [:thrift])
 ```
 
 By default, the generated source files will be written to the `src` directory,
@@ -46,6 +46,14 @@ but you can change that using the `thrift_output` option.
 You can also pass additional options to the Thrift compiler by listing them in
 the `thrift_options` option.
 
+If you require a specific version of the Thrift compiler, you can specify a
+version requirement using the `thrift_version` option. Version requirements
+use the [SemVer 2.0 schema][semver]. For example:
+
+```elixir
+thrift_version: ">= 0.9.3"  # Erlang maps support
+```
+
 ## Thrift IDL Parsing
 
 This package also contains experimental support for parsing [Thrift IDL][idl]
@@ -60,4 +68,5 @@ provide more advanced parser support over time.
   {:ident, 1, 'BLUE'}, {:symbol, 1, '}'}], 1}
 ```
 
+[semver]: http://semver.org/
 [idl]: https://thrift.apache.org/docs/idl

lib/compile.thrift.ex

@@ -22,6 +22,8 @@ defmodule Mix.Tasks.Compile.Thrift do
 
     * `:thrift_options` - list of additional options that will be passed to
       the Thrift compiler.
+
+    * `:thrift_version` - thrift compiler `Version` requirement
   """
 
   @spec run(OptionParser.argv) :: :ok | :noop
@@ -32,17 +34,31 @@ defmodule Mix.Tasks.Compile.Thrift do
     project        = Mix.Project.config
     thrift_files   = project[:thrift_files]
     thrift_options = project[:thrift_options] || []
+    thrift_version = project[:thrift_version]
     output_dir     = project[:thrift_output] || "src"
 
     stale_files = Enum.filter(thrift_files, fn file ->
       force || stale?(file, output_dir)
     end)
 
+    if(thrift_version && !Enum.empty?(stale_files)) do
+      unless(Version.match?(v = get_thrift_version, thrift_version)) do
+        Mix.raise "Unsupported Thrift version #{v} (requires #{thrift_version})"
+      end
+    end
+
     unless(Enum.empty?(stale_files), do: File.mkdir_p!(output_dir))
 
     Enum.each stale_files, &generate(&1, output_dir, thrift_options)
   end
 
+  defp get_thrift_version do
+    case System.cmd("thrift", ~w[-version]) do
+      {s, 0} -> hd(Regex.run(~r/\b(\d+\.\d+\.\d+)\b/, s, capture: :first) || [])
+      {_, e} -> Mix.raise "Failed to execute `thrift -version` (error #{e})"
+    end
+  end
+
   defp get_generated_files(thrift_file, output_dir) do
     basename = Path.basename(thrift_file, ".thrift")
     pattern  = basename <> "_{constants,thrift,types}.{erl,hrl}"