build: Reuse nix from xrpld in Clio (#3247)

.envrc

@@ -0,0 +1,5 @@
+use flake
+
+# Optional, untracked local overrides. To use a different shell, put e.g.
+# `use flake .#gcc` in .envrc.local.
+source_env_if_exists .envrc.local

.gitignore

@@ -14,3 +14,7 @@ CLAUDE.md
 .claude/**
 .agents/**
 .augment/**
+# Direnv's directory
+/.direnv
+# Direnv's local, per-developer overrides
+/.envrc.local

docs/build-clio.md

@@ -12,7 +12,18 @@
 - [**Optional**] [CCache](https://ccache.dev/): speeds up compilation if you are going to compile Clio often
 
 We use the Nix-based Docker image `ghcr.io/xrplf/xrpld/nix-ubuntu` to build `Clio`, see [Building Clio with Docker](#building-clio-with-docker).
-This image is produced by [rippled](https://github.com/XRPLF/rippled) and ships the compilers and tools listed below.
+This image is produced by [xrpld](https://github.com/XRPLF/rippled) and ships the compilers and tools listed below.
+
+The same environment is available locally as a [Nix](https://nixos.org/) dev shell, reused from `xrpld` through [`flake.nix`](../flake.nix):
+
+```sh
+nix develop          # Clang on macOS, GCC on Linux
+nix develop .#clang  # or .#gcc, .#apple-clang
+```
+
+The shell uses its own Conan home, `~/.conan2-nix`, and sets it up on entry.
+With [direnv](https://direnv.net/), run `direnv allow` once to enter the shell automatically, using the provided `.envrc`.
+See [xrpld's Nix guide](https://github.com/XRPLF/rippled/blob/develop/docs/build/nix.md) for more details.
 
 The following compiler version are guaranteed to work.
 Any compiler with lower version may not be able to build Clio:
@@ -31,7 +42,7 @@ You can change it by using `$CONAN_HOME` env variable.
 
 > [!TIP]
 > To setup Conan automatically, you can run `conan/init.sh`.
-> This will delete Conan home directory (if it exists), set up profiles and add Artifactory remote.
+> This will set up the global configuration and profiles, and add the `xrplf` remote. It never deletes the Conan home directory.
 
 The instruction below assumes that `$CONAN_HOME` is not set.
 

flake.lock

@@ -0,0 +1,86 @@
+{
+  "nodes": {
+    "nixpkgs": {
+      "locked": {
+        "lastModified": 1791130267,
+        "narHash": "sha256-1sjwcQMcgAbmiip/VivBSiK8p2bTkQGOvCuO7vnwfx4=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "9013764fcc0ea99fa16cf7aa7decf8a5c3889dd2",
+        "type": "github"
+      },
+      "original": {
+        "owner": "NixOS",
+        "ref": "nixpkgs-unstable",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "nixpkgs-custom-glibc": {
+      "flake": false,
+      "locked": {
+        "lastModified": 1593520194,
+        "narHash": "sha256-+TZW+2I7kLL9JglPNOagm1ywjf9ua0JYGoptq/dzVn0=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "9cd98386a38891d1074fc18036b842dc4416f562",
+        "type": "github"
+      },
+      "original": {
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "9cd98386a38891d1074fc18036b842dc4416f562",
+        "type": "github"
+      }
+    },
+    "root": {
+      "inputs": {
+        "xrpld": "xrpld"
+      }
+    },
+    "rust-overlay": {
+      "inputs": {
+        "nixpkgs": [
+          "xrpld",
+          "nixpkgs"
+        ]
+      },
+      "locked": {
+        "lastModified": 1791189933,
+        "narHash": "sha256-Y8eN7ki0Urx4Ojf4w1xSpWg8uk/3lJqK+E0Oth77rH0=",
+        "owner": "oxalica",
+        "repo": "rust-overlay",
+        "rev": "e60029353d0c48d216bc4b065168ccd4079c166f",
+        "type": "github"
+      },
+      "original": {
+        "owner": "oxalica",
+        "repo": "rust-overlay",
+        "type": "github"
+      }
+    },
+    "xrpld": {
+      "inputs": {
+        "nixpkgs": "nixpkgs",
+        "nixpkgs-custom-glibc": "nixpkgs-custom-glibc",
+        "rust-overlay": "rust-overlay"
+      },
+      "locked": {
+        "lastModified": 1791321597,
+        "narHash": "sha256-AhcXqET1GyR9wp2ae0fdadZzRPpSB8KSLASwjMMthBQ=",
+        "owner": "XRPLF",
+        "repo": "rippled",
+        "rev": "3d526d456ecd54dfb83d34eda54f5e88df840d79",
+        "type": "github"
+      },
+      "original": {
+        "owner": "XRPLF",
+        "repo": "rippled",
+        "rev": "3d526d456ecd54dfb83d34eda54f5e88df840d79",
+        "type": "github"
+      }
+    }
+  },
+  "root": "root",
+  "version": 7
+}

flake.nix

@@ -0,0 +1,18 @@
+{
+  description = "Nix related things for Clio";
+
+  inputs = {
+    # Clio is built with the same toolchain as xrpld, so its dev shells are reused as is.
+    # Keep the revision in sync with the `ghcr.io/xrplf/xrpld/nix-ubuntu` image used in CI,
+    # so the local shell matches CI.
+    # Its nixpkgs is deliberately not overridden with `follows`:
+    # that would change the toolchain and lose the match with CI.
+    xrpld.url = "github:XRPLF/rippled/3d526d456ecd54dfb83d34eda54f5e88df840d79";
+  };
+
+  outputs =
+    { xrpld, ... }:
+    {
+      inherit (xrpld) devShells formatter;
+    };
+}