Add MIX_INSTALL_DIR and use it in Mix.install/2 (#10825)

Author: wojtekmach

CHANGELOG.md

@@ -15,6 +15,8 @@ IO.puts Jason.encode!(%{hello: :world})
 
 `Mix.install/2` also performs protocol consolidation, which gives script developers an option to execute their code in the most performant format possible.
 
+**Note:** `Mix.install/2` is currently experimental and it may change in future releases.
+
 Another improvement to scripting is the ability to trap exit signals via `System.trap_signal/3`. All you need is the signal name and a callback that will be invoked when the signal triggers. For example, ExUnit leverages this functionality to print all currently running tests when you abort the test suite via SIGQUIT (`Ctrl+\\ `):
 
 ```

lib/mix/lib/mix.ex

@@ -251,6 +251,8 @@ defmodule Mix do
     * `MIX_EXS` - changes the full path to the `mix.exs` file
     * `MIX_HOME` - path to Mix's home directory, stores configuration files and scripts used by Mix
       (default: `~/.mix`)
+    * `MIX_INSTALL_DIR` - (since v1.12.0) specifies directory where `Mix.install/2` keeps
+      installs cache
     * `MIX_PATH` - appends extra code paths
     * `MIX_QUIET` - does not print information messages to the terminal
     * `MIX_REBAR` - path to rebar command that overrides the one Mix installs
@@ -470,12 +472,13 @@ defmodule Mix do
 
   The given `deps` should be in the same format as defined in a regular Mix
   project. See `mix help deps` for more information. As a shortcut, an atom
-  can be given as dependency to mean the latest version, e.g.: specifying
-  `:decimal` is the same as `{:decimal, ">= 0.0.0"}`.
+  can be given as dependency to mean the latest version. In other words,
+  specifying `:decimal` is the same as `{:decimal, ">= 0.0.0"}`.
 
   After each successful installation, a given set of dependencies is cached
-  so starting another VM and calling `Mix.install` with the same dependencies
-  will avoid unnecessary downloads and compilations.
+  so starting another VM and calling `Mix.install/2` with the same dependencies
+  will avoid unnecessary downloads and compilations. The location of the cache
+  directory can be controlled using the `MIX_INSTALL_DIR` environment variable.
 
   This function can only be called outside of a Mix project and only once in a
   given VM.
@@ -517,10 +520,13 @@ defmodule Mix do
       Mix.raise("Mix.install/2 can only be called once")
     end
 
+    installs_root =
+      System.get_env("MIX_INSTALL_DIR") ||
+        Path.join(Mix.Utils.mix_cache(), "installs")
+
     id = deps |> :erlang.term_to_binary() |> :erlang.md5() |> Base.encode16(case: :lower)
-    tmp_dir = System.tmp_dir()
     version = "elixir-#{System.version()}-erts-#{:erlang.system_info(:version)}"
-    dir = Path.join([tmp_dir, "mix_installs", version, id])
+    dir = Path.join([installs_root, version, id])
 
     if opts[:verbose] do
       Mix.shell().info("using #{dir}")

lib/mix/lib/mix/utils.ex

@@ -32,6 +32,24 @@ defmodule Mix.Utils do
     mix_home_xdg_lookup(:user_config)
   end
 
+  @doc """
+  Gets possible location of Mix cache.
+
+  Possible locations:
+
+   * `XDG_CACHE_HOME/mix` (if `MIX_XDG` is set)
+   * `:filename.basedir(:user_cache, "mix")`
+
+  """
+  def mix_cache do
+    if System.get_env("MIX_XDG") in ["1", "true"] do
+      # XDG lookups are only done for linux OS
+      :filename.basedir(:user_cache, "mix", %{os: :linux})
+    else
+      :filename.basedir(:user_cache, "mix")
+    end
+  end
+
   defp mix_home_xdg_lookup(xdg) do
     cond do
       dir = System.get_env("MIX_HOME") ->

lib/mix/test/mix/utils_test.exs

@@ -129,7 +129,7 @@ defmodule Mix.UtilsTest do
     end
 
     @tag :unix
-    test "falls back to XDG_DATA_HOME/mix" do
+    test "falls back to XDG_DATA_HOME/mix when MIX_XDG is set" do
       System.put_env("MIX_XDG", "1")
       assert Mix.Utils.mix_home() == :filename.basedir(:user_data, "mix", %{os: :linux})
     end
@@ -147,7 +147,7 @@ defmodule Mix.UtilsTest do
     end
 
     @tag :unix
-    test "falls back to XDG_CONFIG_HOME/mix" do
+    test "falls back to XDG_CONFIG_HOME/mix when MIX_XDG is set" do
       System.put_env("MIX_XDG", "1")
       assert Mix.Utils.mix_config() == :filename.basedir(:user_config, "mix", %{os: :linux})
     end
@@ -157,6 +157,18 @@ defmodule Mix.UtilsTest do
     end
   end
 
+  describe "mix_cache/0" do
+    @tag :unix
+    test "prefers XDG_CACHE_HOME/mix when MIX_XDG is set" do
+      System.put_env("MIX_XDG", "1")
+      assert Mix.Utils.mix_cache() == :filename.basedir(:user_cache, "mix", %{os: :linux})
+    end
+
+    test "falls back to user cache dir" do
+      assert Mix.Utils.mix_cache() == :filename.basedir(:user_cache, "mix")
+    end
+  end
+
   defp assert_ebin_symlinked_or_copied(result) do
     case result do
       {:ok, paths} ->

lib/mix/test/mix_test.exs

@@ -22,13 +22,20 @@ defmodule MixTest do
 
   describe "install" do
     @describetag :tmp_dir
+
+    setup %{tmp_dir: tmp_dir} do
+      System.put_env("MIX_INSTALL_DIR", Path.join(tmp_dir, "installs"))
+    end
+
     setup :test_project
 
     test "default options", %{tmp_dir: tmp_dir} do
       Mix.install([
         {:install_test, path: Path.join(tmp_dir, "install_test")}
       ])
 
+      assert File.dir?(Path.join(tmp_dir, "installs"))
+
       assert Protocol.consolidated?(InstallTest.Protocol)
 
       assert_received {:mix_shell, :info, ["==> install_test"]}

man/mix.1

@@ -94,13 +94,9 @@ environments
 .Pq see above
 are not enough to solve the problem.
 .It Ev MIX_HOME
-Stores configuration files and scripts shared by multiple
-.Nm
-implementations.
-.Pp
-See the
-.Sy Mix.Utils.mix_home/0
-function.
+path to Mix's home directory, stores configuration files and scripts used by Mix
+.It MIX_INSTALL_DIR
+Specifies directory where Mix.install/2 keeps installs cache
 .It Ev MIX_PATH
 Allows expanding the code path. If the MIX_PATH environment variable has a value which consists of multiple paths, they must be colon-separated
 .Pq for Unix-like operating systems