feat(beam): support Environment.CurrentDirectory and GetEnvironmentVariable (#4801)

Author: MangelMaxime

src/Fable.Transforms/Beam/Replacements.fs

@@ -5775,6 +5775,20 @@ let tryCall
     | "System.Environment" ->
         match info.CompiledName with
         | "get_NewLine" -> makeStrConst "\n" |> Some
+        | "GetEnvironmentVariable" ->
+            Helper.LibCall(
+                com,
+                "fable_environment",
+                "get_environment_variable",
+                t,
+                args,
+                info.SignatureArgTypes,
+                ?loc = r
+            )
+            |> Some
+        | "get_CurrentDirectory" ->
+            Helper.LibCall(com, "fable_environment", "get_current_directory", t, [], ?loc = r)
+            |> Some
         | _ -> None
     | Types.datetime -> dates com ctx r t info thisArg args
     | "System.Uri" -> uris com ctx r t info thisArg args

src/fable-library-beam/fable_environment.erl

@@ -0,0 +1,18 @@
+-module(fable_environment).
+-export([
+    get_environment_variable/1,
+    get_current_directory/0
+]).
+
+-spec get_environment_variable(binary()) -> binary() | undefined.
+-spec get_current_directory() -> binary().
+
+get_environment_variable(Name) ->
+    case os:getenv(unicode:characters_to_list(Name)) of
+        false -> undefined;
+        Value -> unicode:characters_to_binary(Value)
+    end.
+
+get_current_directory() ->
+    {ok, Dir} = file:get_cwd(),
+    unicode:characters_to_binary(Dir).

tests/Beam/EnvironmentTests.fs

@@ -0,0 +1,14 @@
+module Fable.Tests.Environment
+
+open System
+open Util.Testing
+
+[<Fact>]
+let ``test Environment.GetEnvironmentVariable returns null for a missing variable`` () =
+    Environment.GetEnvironmentVariable("__FABLE_NON_EXISTENT_VAR__")
+    |> equal null
+
+[<Fact>]
+let ``test Environment.CurrentDirectory works`` () =
+    Environment.CurrentDirectory.Length > 0
+    |> equal true

tests/Beam/Fable.Tests.Beam.fsproj

@@ -73,6 +73,7 @@
     <Compile Include="QueueTests.fs" />
     <Compile Include="StackTests.fs" />
     <Compile Include="EncodingTests.fs" />
+    <Compile Include="EnvironmentTests.fs" />
     <Compile Include="ApplicativeTests.fs" />
     <Compile Include="MiscTests.fs" />
     <Compile Include="TimeSpanTests.fs" />