From c3405c27b450570e760b42d8f3bba49f67c43df6 Mon Sep 17 00:00:00 2001
From: Greg Pfeil <greg@technomadic.org>
Date: Tue, 9 Jul 2024 13:50:32 -0600
Subject: [PATCH] Pin Haskell tool versions for VS Code

This also has the flake get its version pins (when possible) from the VS
Code settings. And we pin Cabal now, too.
---
 .vscode/settings.json     |  7 +++++++
 flake.nix                 | 12 ++++++++----
 nix/haskell-nix-flake.nix |  2 +-
 3 files changed, 16 insertions(+), 5 deletions(-)
 create mode 100644 .vscode/settings.json

diff --git a/.vscode/settings.json b/.vscode/settings.json
new file mode 100644
index 0000000000..6002d51193
--- /dev/null
+++ b/.vscode/settings.json
@@ -0,0 +1,7 @@
+{
+  "haskell.toolchain": {
+    "cabal": "3.10.3.0",
+    "hls": "2.8.0.0",
+    "stack": "2.15.7"
+  }
+}
diff --git a/flake.nix b/flake.nix
index 0be2f8da81..a266bd2e29 100644
--- a/flake.nix
+++ b/flake.nix
@@ -26,11 +26,15 @@
       "aarch64-darwin"
     ]
     (system: let
-      versions = {
-        ormolu = "0.7.2.0";
-        hls = "2.8.0.0";
-        stack = "2.15.7";
+      ## It’s much easier to read from a JSON file than to have JSON import from some other file, so we extract some
+      ## configuration from the VS Code settings to avoid duplication.
+      vscodeSettings = nixpkgs-release.lib.importJSON ./.vscode/settings.json;
+      versions =
+        vscodeSettings."haskell.toolchain"
+        ## There are some things we want to pin that the VS Code Haskell extension doesn’t let us control.
+        // {
         hpack = "0.35.2";
+        ormolu = "0.7.2.0";
       };
       pkgs = import nixpkgs-haskellNix {
         inherit system;
diff --git a/nix/haskell-nix-flake.nix b/nix/haskell-nix-flake.nix
index 25930790c1..97c8f1ebc0 100644
--- a/nix/haskell-nix-flake.nix
+++ b/nix/haskell-nix-flake.nix
@@ -28,7 +28,7 @@
       tools =
         (args.tools or {})
         // {
-          cabal = {};
+          cabal = {version = versions.cabal;};
           ormolu = {version = versions.ormolu;};
           haskell-language-server = {
             version = versions.hls;