terraform: expose providers to terraform 0.13

Terraform 0.13 adopts a new filesystem layout for plugins (illustrated below).

Terraform 0.12 and earlier
`plugins-dir/terraform-provider-aws_v3.7.0`

Terraform 0.13
`plugins-dir/registry.terraform.io/hashicorp/aws/3.7.0/linux_amd64/terraform-provider-aws_v3.7.0`

To support all packaged Terraform versions a shim is created at both locations.

This approach was inspired by https://github.com/numtide/generate-terraform-provider-shim

Terraform 0.13 provider documentation https://www.terraform.io/upgrade-guides/0-13.html#new-filesystem-layout-for-local-copies-of-providers

layout terraform providers filesystem in withPlugins

pkgs/applications/networking/cluster/terraform-providers/default.nix

@@ -2,11 +2,16 @@
 , buildGoPackage
 , fetchFromGitHub
 , callPackage
+, runtimeShell
 }:
 let
   list = lib.importJSON ./providers.json;
 
-  toDrv = data:
+  toDrv = name: data:
+    let
+      fallbackProviderSourceAddress = "nixpkgs/${data.owner}/${name}";
+      providerSourceAddress = data.provider-source-address or fallbackProviderSourceAddress;
+    in
     buildGoPackage rec {
       inherit (data) owner repo rev version sha256;
       name = "${repo}-${version}";
@@ -18,6 +23,9 @@ let
       # Terraform allow checking the provider versions, but this breaks
       # if the versions are not provided via file paths.
       postBuild = "mv $NIX_BUILD_TOP/go/bin/${repo}{,_v${version}}";
+      passthru = {
+        inherit providerSourceAddress;
+      };
     };
 
   # Google is now using the vendored go modules, which works a bit differently
@@ -48,7 +56,7 @@ let
     });
 
   # These providers are managed with the ./update-all script
-  automated-providers = lib.mapAttrs (_: toDrv) list;
+  automated-providers = lib.mapAttrs (toDrv) list;
 
   # These are the providers that don't fall in line with the default model
   special-providers = {

pkgs/applications/networking/cluster/terraform/default.nix

@@ -1,5 +1,5 @@
 { stdenv, lib, buildEnv, buildGoPackage, fetchFromGitHub, makeWrapper, coreutils
-, runCommand, writeText, terraform-providers, fetchpatch }:
+, runCommand, runtimeShell, writeText, terraform-providers, fetchpatch }:
 
 let
   goPackagePath = "github.com/hashicorp/terraform";
@@ -59,6 +59,29 @@ let
         let
           actualPlugins = plugins terraform.plugins;
 
+          # Make providers available in Terraform 0.13 and 0.12 search paths.
+          pluginDir = lib.concatMapStrings (pl: let
+            inherit (pl) repo version GOOS GOARCH;
+            inherit (pl.passthru) providerSourceAddress;
+
+            shim = writeText "shim" ''
+              #!${runtimeShell}
+              exec ${pl}/bin/${repo}_v${version} \$@
+            '';
+            in ''
+              TF_0_13_PROVIDER_PATH=$out/plugins/${providerSourceAddress}/${version}/${GOOS}_${GOARCH}/${repo}_v${version}
+              mkdir -p "$(dirname $TF_0_13_PROVIDER_PATH)"
+
+              cp ${shim} "$TF_0_13_PROVIDER_PATH"
+              chmod +x "$TF_0_13_PROVIDER_PATH"
+
+              TF_0_12_PROVIDER_PATH=$out/plugins/${repo}_v${version}
+
+              cp ${shim} "$TF_0_12_PROVIDER_PATH"
+              chmod +x "$TF_0_12_PROVIDER_PATH"
+          ''
+          ) actualPlugins;
+
           # Wrap PATH of plugins propagatedBuildInputs, plugins may have runtime dependencies on external binaries
           wrapperInputs = lib.unique (lib.flatten
             (lib.catAttrs "propagatedBuildInputs"
@@ -87,15 +110,10 @@ let
             inherit (terraform) name;
             buildInputs = [ makeWrapper ];
 
-            buildCommand = ''
+            buildCommand = pluginDir + ''
               mkdir -p $out/bin/
               makeWrapper "${terraform}/bin/terraform" "$out/bin/terraform" \
-                --set NIX_TERRAFORM_PLUGIN_DIR "${
+                --set NIX_TERRAFORM_PLUGIN_DIR $out/plugins \
-                  buildEnv {
-                    name = "tf-plugin-env";
-                    paths = actualPlugins;
-                  }
-                }/bin" \
                 --prefix PATH : "${lib.makeBinPath wrapperInputs}"
             '';