build: Install conan configuration/profiles inside Nix devshell (#7997)

.envrc

@@ -1,3 +1,7 @@
 watch_file nix/*.nix
 
+# The dev shell derivation includes all of conan/ (see nix/devshell.nix), so any
+# change in there has to invalidate direnv's cached environment.
+watch_dir conan
+
 use flake

BUILD.md

@@ -53,33 +53,25 @@ releases](https://github.com/XRPLF/rippled/releases).
 
 ### Set Up Conan
 
-Once your [development environment](./docs/build/environment.md) is ready, you
-may need to set up your Conan profile.
-
-#### Profiles
-
-We recommend that you install our Conan profiles:
+Once your [development environment](./docs/build/environment.md) is ready, set
+Conan up for this repository:
 
 ```bash
-conan config install conan/profiles/ -tf $(conan config home)/profiles/
+./conan/init.sh
 ```
 
-You can check your Conan profile by running:
+That installs our [`global.conf`](./conan/global.conf), our Conan
+[profiles](./conan/profiles), and the `xrplf` remote that hosts some of our
+dependencies. It honours `CONAN_HOME` and never deletes an existing Conan home,
+so it is safe to re-run — it only overwrites the files it manages.
 
-```bash
-conan profile show
-```
+> [!TIP]
+> In the [Nix development shell](./docs/build/nix.md#conan-configuration) this is
+> already done for you: the script runs on entry.
 
-If the default profile is not suitable for your environment, you can create a custom profile and pass it to Conan.
-More information on customizing Conan can be found in the [Advanced Conan configuration](./docs/build/advanced_conan.md).
-
-#### Add xrplf remote
-
-Run the following command to add the `xrplf` remote, which hosts some of our dependencies:
-
-```bash
-conan remote add --index 0 --force xrplf https://conan.xrplf.org/repository/conan/
-```
+You can inspect the resulting profile with `conan profile show`. If it is not
+suitable for your environment, create a custom profile and pass it to Conan — see
+[Advanced Conan configuration](./docs/build/advanced_conan.md).
 
 ### Set Up Ccache
 
@@ -368,14 +360,14 @@ After any updates or changes to dependencies, you may need to do the following:
 4. [Regenerate lockfile](./docs/build/advanced_conan.md#conan-lockfile).
 5. Re-run [conan install](#build-and-test).
 
-If you are using the Nix development shell, prebuilt Conan binaries may be
-incompatible with it — see
-[Building xrpld in the Nix shell](./docs/build/nix.md#building-xrpld-in-the-nix-shell).
+If you are using the Nix development shell, whether prebuilt Conan binaries apply
+depends on your platform — see
+[Prebuilt packages](./docs/build/nix.md#prebuilt-packages).
 
 #### ERROR: Package not resolved
 
 If you're seeing an error like `ERROR: Package 'snappy/1.1.10' not resolved: Unable to find 'snappy/1.1.10#968fef506ff261592ec30c574d4a7809%1756234314.246' in remotes.`,
-please [add `xrplf` remote](#add-xrplf-remote) or re-run `conan export` for [patched recipes](./docs/build/advanced_conan.md#patched-recipes).
+please [set Conan up](#set-up-conan) so the `xrplf` remote is configured, or re-run `conan export` for [patched recipes](./docs/build/advanced_conan.md#patched-recipes).
 
 ### `protobuf/port_def.inc` file not found
 

conan/init.sh

@@ -0,0 +1,21 @@
+#!/usr/bin/env bash
+# Install our Conan configuration, profiles and the xrplf remote into CONAN_HOME.
+# Safe to re-run; never deletes the Conan home.
+
+set -euo pipefail
+
+SCRIPT_DIR="$(cd -- "$(dirname -- "${BASH_SOURCE[0]}")" && pwd)"
+CONAN_DIR="$(conan config home)"
+
+echo "Installing Conan configuration into ${CONAN_DIR}"
+conan config install "${SCRIPT_DIR}/global.conf"
+conan config install "${SCRIPT_DIR}/profiles" -tf "${CONAN_DIR}/profiles"
+# This script manages these files, so make them read-only - Conan does not
+# preserve the source mode. Only the files: the directories must stay writable
+# for `conan config install` to replace them.
+chmod a-w "${CONAN_DIR}/global.conf"
+find "${CONAN_DIR}/profiles" -type f -exec chmod a-w {} +
+
+echo "Adding the xrplf Conan remote"
+# --index 0: our patched recipes must win over Conan Center.
+conan remote add --index 0 --force xrplf https://conan.xrplf.org/repository/conan/

conan/profiles/default

@@ -1,10 +1,7 @@
 {% set os = detect_api.detect_os() %}
 {% set arch = detect_api.detect_arch() %}
 {% set compiler, version, compiler_exe = detect_api.detect_default_compiler() %}
-{% set compiler_version = version %}
-{% if os == "Linux" %}
 {% set compiler_version = detect_api.default_compiler_version(compiler, version) %}
-{% endif %}
 {% if os == "Macos" %}
 {# Minimum macOS the dependencies target. #}
 {# Without this, Conan builds each dependency against the (possibly newer) host SDK, so the #}

docs/build/nix.md

@@ -124,14 +124,32 @@ nix develop -c "$SHELL"
 
 Once inside the Nix development shell, follow the standard [build instructions](../../BUILD.md#steps). The Nix shell provides all necessary tools (CMake, Ninja, Conan, etc.).
 
-Two things differ from a system environment:
-
-**Prebuilt Conan packages.** There is no guarantee that binaries from the Conan cache will work when using Nix. If you encounter any errors, add `--build '*'` to the `conan install` command in [Build and Test](../../BUILD.md#build-and-test) to force Conan to compile everything from source. Keep the rest of the command as it is there, so it rebuilds the `build_type` you are actually configuring.
-
-**Coverage builds.** `-Dcoverage=ON` works in the `gcc` shell (and `gcc-plain` on Linux):
+Coverage builds (`-Dcoverage=ON`) work in the `gcc` shell (and `gcc-plain` on Linux):
 each ships a `gcov` matching its compiler, since Nix's cc-wrapper does not expose one.
 The `clang` shells do not include `llvm-cov`, so use a `gcc` shell for coverage.
 
+## Conan configuration
+
+The shell runs [`conan/init.sh`](../../conan/init.sh) on entry, so
+[Set Up Conan](../../BUILD.md#set-up-conan) is already done for you. It installs
+into the shell's own Conan home: `CONAN_HOME=~/.conan2-nix`.
+
+### Prebuilt packages
+
+On **Linux**, the binaries on the `xrplf` remote are built in this same Nix
+environment — CI runs in Docker images that bundle the dev shell's toolchain (see
+[`nix/docker`](../../nix/docker)) — so `.#gcc` and `.#clang` can reuse them. The
+`-plain` shells do not match that toolchain's glibc, so binaries from the remote
+are not a reliable match there.
+
+On **macOS**, CI builds with Apple Clang, so the remote holds nothing for the Nix
+`clang` toolchain and dependencies are compiled locally. We do not publish
+Nix-built macOS binaries because a Conan package ID records the compiler version
+but not the nixpkgs revision.
+
+To compile everything from source, add `--build '*'` to the `conan install`
+command.
+
 ## Automatic Activation with direnv
 
 [direnv](https://direnv.net/) or [nix-direnv](https://github.com/nix-community/nix-direnv) can automatically activate the Nix development shell when you enter the repository directory.

nix/devshell.nix

@@ -30,10 +30,29 @@ let
   };
   customGccGcov = if pkgs.stdenv.isLinux then customCompilers.customGcov else plainGcov;
 
+  # Whole directory: init.sh locates the profiles relative to itself.
+  conanDir = ../conan;
+
+  # Own Conan home, so Nix-built packages never share a cache with a system
+  # Conan. The stamp holds a content-addressed store path, so init.sh re-runs
+  # only when something in conan/ changes.
+  conanHook = ''
+    export CONAN_HOME=~/.conan2-nix
+    _xrpl_conan_stamp="$CONAN_HOME/.xrpld-devshell"
+    if [ "$(cat "$_xrpl_conan_stamp" 2>/dev/null)" != "${conanDir}" ]; then
+      if ${conanDir}/init.sh; then
+        printf '%s' "${conanDir}" >"$_xrpl_conan_stamp"
+      else
+        echo "⚠️ Conan setup failed - run ./conan/init.sh from the repository root to retry."
+      fi
+    fi
+    unset _xrpl_conan_stamp
+  '';
+
   # Shown when entering a *-plain shell. These exist only on Linux (see below),
   # where the stock toolchain diverges from CI.
   plainWarningHook = ''
-    echo "⚠️  WARNING: this is the stock nixpkgs toolchain and does not match CI's glibc. Prefer 'nix develop .#gcc' / '.#clang' unless you need to skip the custom-glibc build."
+    echo "⚠️ WARNING: this is the stock nixpkgs toolchain and does not match CI's glibc. Prefer 'nix develop .#gcc' / '.#clang' unless you need to skip the custom-glibc build."
   '';
 
   # Tools to expose under version-suffixed names (see mkVersionedToolLinks).
@@ -87,6 +106,7 @@ let
         shellHook = ''
           echo "Welcome to xrpld development shell";
           ${compilerVersionHook}
+          ${conanHook}
           ${warningHook}
         '';
       }