From 282a3b502a0758bf3191f55dede8f0a69b01dce1 Mon Sep 17 00:00:00 2001
From: Ivan Petkov <ivanppetkov@gmail.com>
Date: Mon, 17 Jan 2022 15:01:21 -0800
Subject: [PATCH] Add README

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+# Crane
+
+A [Nix](https://nixos.org/) library for building [cargo](https://doc.rust-lang.org/cargo/) projects.
+
+* **No messing with hashes**: a Cargo.lock file is all you need
+* **Incremental**: never build a dependency twice with easy artifact caching
+* **Composable**: split builds and tests into granular steps. Gate CI without
+  burdening downstream consumers building from source.
+
+Detailed [API docs] are available.
+
+## Getting Started
+
+The easiest way to get started is to initialize a flake from a template:
+
+```sh
+# Start with a comprehensive suite of tests
+nix flake init -t github:ipetkov/crane#quick-start
+
+# Or if you want something simpler
+nix flake init -t github:ipetkov/crane#quick-start-simple
+
+# If you need a custom rust toolchain (e.g. to build WASM targets):
+nix flake init -t github:ipetkov/crane#custom-toolchain
+```
+
+For an even more lean, no frills set up, create a `flake.nix` file with the
+following contents at the root of your cargo workspace:
+
+```nix
+{
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
+    crane.url = "github:ipetkov/crane";
+    crane.inputs.nixpkgs.follows = "nixpkgs";
+    flake-utils.url = "github:numtide/flake-utils";
+    flake-utils.inputs.nixpkgs.follows = "nixpkgs";
+  };
+
+  outputs = { self, nixpkgs, crane, flake-utils, ... }:
+    flake-utils.lib.eachDefaultSystem (system: {
+      defaultPackage = crane.lib.${system}.buildPackage {
+        src = ./.;
+      };
+    });
+}
+```
+
+## FAQs
+
+### I want to use a custom version of nixpkgs or another specific system
+
+The crane library can be instantiated with a specific version of nixpkgs as
+follows. For more information, see the [API docs] for `mkLib`.
+
+```nix
+crane.mkLib (import nixpkgs { system = "armv7l-linux"; })
+```
+
+### I want to override a particular package used by the crane library
+
+Specific inputs can be overridden for the entire library via the
+`overrideScope'` API as follows. For more information, see the [API docs] for
+`mkLib` or checkout the [custom-toolchain] example.
+
+```nix
+crane.lib.${system}.overrideScope' (final: prev: {
+  cargo = myCustomCargoVersion;
+})
+```
+
+### My custom rust flags are getting ignored
+
+If you are using a `build.rustflags` definition in `.cargo/config.toml`,
+consider turning off source prefix remapping by adding
+`doRemapSourcePathPrefix = false;` in your derivation.
+
+See the [API docs] for `remapSourcePathPrefixHook` for more information.
+
+### Nix is complaining about IFD (import from derivation)
+
+If a derivation's `pname` and `version` attributes are not explicitly set,
+crane will inspect the project's `Cargo.toml` file to set them as a convenience
+to avoid duplicating that information by hand. This works well when the source
+is a local path, but can cause issues if the source is being fetched remotely,
+or flakes are not being used (since flakes have IFD enabled on by default).
+
+One easy workaround for this issue (besides enabling the
+`allow-import-from-derivation` option in Nix) is to explicitly set
+`{ pname = "..."; version = "..."; }` in the derivation.
+
+You'll know you've run into this issue if you see error messages along the lines
+of:
+* `cannot build '/nix/store/...-source.drv' during evaluation because the option 'allow-import-from-derivation' is disabled`
+* `a 'aarch64-darwin' with features {} is required to build '/nix/store/...', but I am a 'x86_64-linux' with features {}`
+
+[API docs]: ./docs/API.md
+[custom-toolchain]: ./examples/custom-toolchain/flake.nix