Refactor default.nix to follow Nix Flakes patterns

2 files changed, 142 insertions, 0 deletions

diff --git a/nix/compile.nix b/nix/compile.nix
new file mode 100644
index 00000000..972e2f2e
--- /dev/null
+++ b/nix/compile.nix
@@ -0,0 +1,140 @@
+{
+  system ? builtins.currentSystem,
+  target ? "x86_64-unknown-linux-musl",
+  release ? false,
+  git_version ? null,
+}:
+
+with import ./common.nix;
+
+let
+  crossSystem = { config = target; };
+
+  log = v: builtins.trace v v;
+
+  pkgs = import pkgsSrc {
+    inherit system crossSystem;
+    overlays = [ cargo2nixOverlay ];
+  };
+
+
+  /*
+   Rust and Nix triples are not the same. Cargo2nix has a dedicated library
+   to convert Nix triples to Rust ones. We need this conversion as we want to
+   set later options linked to our (rust) target in a generic way. Not only
+   the triple terminology is different, but also the "roles" are named differently.
+   Nix uses a build/host/target terminology where Nix's "host" maps to Cargo's "target".
+  */
+  rustTarget = log (pkgs.rustBuilder.rustLib.rustTriple pkgs.stdenv.hostPlatform);
+
+  /*
+   Cargo2nix is built for rustOverlay which installs Rust from Mozilla releases.
+   We want our own Rust to avoid incompatibilities, like we had with musl 1.2.0.
+   rustc was built with musl < 1.2.0 and nix shipped musl >= 1.2.0 which lead to compilation breakage.
+   So we want a Rust release that is bound to our Nix repository to avoid these problems.
+   See here for more info: https://musl.libc.org/time64.html
+   Because Cargo2nix does not support the Rust environment shipped by NixOS,
+   we emulate the structure of the Rust object created by rustOverlay.
+   In practise, rustOverlay ships rustc+cargo in a single derivation while
+   NixOS ships them in separate ones. We reunite them with symlinkJoin.
+   */
+  rustChannel = pkgs.symlinkJoin {
+    name ="rust-channel";
+    paths = [ 
+      pkgs.rustPlatform.rust.rustc
+      pkgs.rustPlatform.rust.cargo
+    ];
+  };
+
+  /*
+   Cargo2nix provides many overrides by default, you can take inspiration from them:
+   https://github.com/cargo2nix/cargo2nix/blob/master/overlay/overrides.nix
+
+   You can have a complete list of the available options by looking at the overriden object, mkcrate:
+   https://github.com/cargo2nix/cargo2nix/blob/master/overlay/mkcrate.nix
+  */
+  overrides = pkgs.rustBuilder.overrides.all ++ [
+    /*
+     [1] We need to alter Nix hardening to make static binaries: PIE,
+     Position Independent Executables seems to be supported only on amd64. Having
+     this flag set either 1. make our executables crash or 2. compile as dynamic on some platforms.
+     Here, we deactivate it. Later (find `codegenOpts`), we reactivate it for supported targets
+     (only amd64 curently) through the `-static-pie` flag.
+     PIE is a feature used by ASLR, which helps mitigate security issues.
+     Learn more about Nix Hardening at: https://github.com/NixOS/nixpkgs/blob/master/pkgs/build-support/cc-wrapper/add-hardening.sh
+    */
+    (pkgs.rustBuilder.rustLib.makeOverride {
+      name = "garage";
+      overrideAttrs = drv: { hardeningDisable = [ "pie" ]; };
+    })
+
+    (pkgs.rustBuilder.rustLib.makeOverride {
+      name = "garage_rpc";
+
+      /*
+       [2] We want to inject the git version while keeping the build deterministic.
+       As we do not want to consider the .git folder as part of the input source,
+       we ask the user (the CI often) to pass the value to Nix.
+      */
+      overrideAttrs = drv:
+        (if git_version != null then {
+          preConfigure = ''
+            ${drv.preConfigure or ""}
+            export GIT_VERSION="${git_version}"
+          '';
+        } else {});
+
+      /*
+       [3] We ship some parts of the code disabled by default by putting them behind a flag.
+       It speeds up the compilation (when the feature is not required) and released crates have less dependency by default (less attack surface, disk space, etc.).
+       But we want to ship these additional features when we release Garage.
+       In the end, we chose to exclude all features from debug builds while putting (all of) them in the release builds.
+       Currently, the only feature of Garage is kubernetes-discovery from the garage_rpc crate.
+      */
+      overrideArgs = old: {
+        features = if release then [ "kubernetes-discovery" ] else [];
+      };
+    })
+
+  ];
+
+  packageFun = import ../Cargo.nix;
+
+  /*
+    We compile fully static binaries with musl to simplify deployment on most systems.
+    When possible, we reactivate PIE hardening (see above).
+
+    Also, if you set the RUSTFLAGS environment variable, the following parameters will
+    be ignored.
+
+    For more information on static builds, please refer to Rust's RFC 1721.
+    https://rust-lang.github.io/rfcs/1721-crt-static.html#specifying-dynamicstatic-c-runtime-linkage
+  */
+
+  codegenOpts = {
+   "armv6l-unknown-linux-musleabihf" = [ "target-feature=+crt-static" "link-arg=-static" ]; /* compile as dynamic with static-pie */
+   "aarch64-unknown-linux-musl" = [ "target-feature=+crt-static" "link-arg=-static" ]; /* segfault with static-pie */
+   "i686-unknown-linux-musl" = [ "target-feature=+crt-static" "link-arg=-static" ]; /* segfault with static-pie */
+   "x86_64-unknown-linux-musl" = [ "target-feature=+crt-static" "link-arg=-static-pie" ];
+  };
+
+in
+  /*
+   The following definition is not elegant as we use a low level function of Cargo2nix
+   that enables us to pass our custom rustChannel object. We need this low level definition
+   to pass Nix's Rust toolchains instead of Mozilla's one.
+
+   target is mandatory but must be kept to null to allow cargo2nix to set it to the appropriate value
+   for each crate.
+  */ 
+  pkgs.rustBuilder.makePackageSet {
+    inherit packageFun rustChannel release codegenOpts;
+    packageOverrides = overrides;
+    target = null;
+
+    buildRustPackages = pkgs.buildPackages.rustBuilder.makePackageSet {
+      inherit rustChannel packageFun codegenOpts;
+      packageOverrides = overrides;
+      target = null;
+    };
+  }
diff --git a/nix/nix.conf b/nix/nix.conf
index f3defe69..de2ede71 100644
--- a/nix/nix.conf
+++ b/nix/nix.conf
@@ -5,3 +5,5 @@ cores = 4
 log-lines = 200
 filter-syscalls = false
 sandbox = false
+keep-outputs = true
+keep-derivations = true