Adjust mix nerves.system.shell` for OTP 26

OTP 26 made some big changes around serial interface and it breaks the
`mix nerves.system.shell` task. In the end, the main issue is that we
no longer have an easy way to take over the STDIN of the task to forward
it to a shell running in the system build directory.

Many attempts were made to recapture STDIN, but decided that for now we
need to move on. Instead, this adjusts the task to do _all_ the setup
for the build directory as before and outputs a warning to the user for
the command that can be manually run in order to get the same shell that
was previously started with `mix nerves.system.shell`

lib/nerves/artifact/build_runners/docker.ex

@@ -125,30 +125,62 @@ defmodule Nerves.Artifact.BuildRunners.Docker do
 
   @doc """
   Connect to a system configuration shell in a Docker container
+
+  Unsupported in >= OTP 26. However, the Docker env will still be created
+  and a command output to IO which can be used manually.
   """
   @spec system_shell(Nerves.Package.t()) :: :ok
   def system_shell(pkg) do
     _ = preflight(pkg)
     {_, image} = config(pkg)
-    platform_config = pkg.config[:platform_config][:defconfig]
-    defconfig = Path.join("/nerves/env/#{pkg.app}", platform_config)
-
-    initial_input = [
-      "echo Updating build directory.",
-      "echo This will take a while if it is the first time...",
-      "/nerves/env/platform/create-build.sh #{defconfig} #{@working_dir} >/dev/null"
-    ]
 
     mounts = Enum.join(mounts(pkg), " ")
     ssh_agent = Enum.join(ssh_agent(), " ")
     env_vars = Enum.join(env(), " ")
 
-    cmd =
+    shell =
       "docker run --rm -it -w #{@working_dir} #{env_vars} #{mounts} #{ssh_agent} #{image} /bin/bash"
 
     set_volume_permissions(pkg)
 
-    Mix.Nerves.Shell.open(cmd, initial_input)
+    create_build = create_build_cmd(pkg) |> Enum.join(" ")
+
+    if String.to_integer(System.otp_release()) < 26 do
+      # Legacy shell support
+      initial_input = [
+        "echo Updating build directory.",
+        "echo This will take a while if it is the first time...",
+        "#{create_build} >/dev/null"
+      ]
+
+      Mix.Nerves.Shell.open(shell, initial_input)
+    else
+      Mix.Nerves.IO.shell_warn("shell start deprecated", """
+      OTP 26 made several changes to the serial interface handling. Unfortunately, this
+      is a regression in preventing the Nerves tooling from starting a system sub-shell.
+
+      However, the Docker environment has been configured and can be used the same as
+      before by manually running the command below which creates the build directory
+      and gives you a shell running in the container to interact with the system:
+      """)
+
+      exec_input = [
+        "echo -e '\\e[25F\\e[0J\\e[1;7m\\n  Preparing Nerves Shell  \\e[0m'",
+        "echo -e '\\e]0;Nerves Shell\\a'",
+        "echo \\\"PS1='\\e[1;7m Nerves \\e[0;1m \\W > \\e[0m'\\\" >> ~/.bashrc",
+        "echo \\\"PS2='\\e[1;7m Nerves \\e[0;1m \\W ..\\e[0m'\\\" >> ~/.bashrc",
+        "echo 'Updating build directory.'",
+        "echo 'This will take a while if it is the first time...'",
+        "#{create_build} >/dev/null",
+        "echo -e '\\nUse \\e[33mctrl+d\\e[0m or \\e[33mexit\\e[0m to leave the container shell\\n'",
+        "exec /bin/bash"
+      ]
+
+      # >= OTP 26 will just output this command to the user for them to run
+      # With Docker, we want create-build.sh to run and then to exec the shell
+      # to keep the docker container open as an interactive shell
+      Mix.shell().info(~s(#{shell} -c "#{Enum.join(exec_input, " ; ")}"))
+    end
   end
 
   defp preflight(pkg) do
@@ -162,10 +194,14 @@ defmodule Nerves.Artifact.BuildRunners.Docker do
 
   # Build Commands
 
-  defp create_build(pkg, stream) do
+  defp create_build_cmd(pkg) do
     platform_config = pkg.config[:platform_config][:defconfig]
     defconfig = Path.join("/nerves/env/#{pkg.app}", platform_config)
-    cmd = ["/nerves/env/platform/create-build.sh", defconfig, @working_dir]
+    ["/nerves/env/platform/create-build.sh", defconfig, @working_dir]
+  end
+
+  defp create_build(pkg, stream) do
+    cmd = create_build_cmd(pkg)
     shell_info("Starting Build... (this may take a while)")
     run(pkg, cmd, stream)
   end

lib/nerves/artifact/build_runners/local.ex

@@ -51,6 +51,8 @@ defmodule Nerves.Artifact.BuildRunners.Local do
 
   @doc """
   Connect to a system configuration sub-shell
+
+  Unsupported in >= OTP 26
   """
   @spec system_shell(Nerves.Package.t()) :: :ok
   def system_shell(pkg) do
@@ -67,13 +69,28 @@ defmodule Nerves.Artifact.BuildRunners.Local do
     platform_config = pkg.config[:platform_config][:defconfig]
     defconfig = Path.join("#{pkg.path}", platform_config)
 
-    initial_input = [
-      "echo Updating build directory.",
-      "echo This will take a while if it is the first time...",
-      "#{script} #{defconfig} #{dest} >/dev/null",
-      "cd #{dest}"
-    ]
+    if String.to_integer(System.otp_release()) < 26 do
+      initial_input = [
+        "echo Updating build directory.",
+        "echo This will take a while if it is the first time...",
+        "#{script} #{defconfig} #{dest} >/dev/null",
+        "cd #{dest}"
+      ]
+
+      Mix.Nerves.Shell.open(shell, initial_input)
+    else
+      Mix.Nerves.IO.shell_warn("shell start deprecated", """
+      OTP 26 made several changes to the serial interface handling. Unfortunately, this
+      is a regression in preventing the Nerves tooling from starting a system sub-shell.
+
+      However, compilation is supported on this host and this native shell can be used.
+      Run the commands below to create the build directory and perform all the same
+      interactions as before within it:
+      """)
 
-    Mix.Nerves.Shell.open(shell, initial_input)
+      # Leave as it's own info line so users could pipe/eval this as a workaround
+      # i.e eval "$(mix nerves.system.shell | tail -n 1)"
+      Mix.shell().info("  #{script} #{defconfig} #{dest} >/dev/null && cd #{dest}")
+    end
   end
 end