Make it easier to build workspaces not at source root (#212)

CHANGELOG.md

@@ -6,6 +6,10 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 
 ## Unreleased
 
+### Changed
+* Documented and made it easier to build a cargo workspace located in a
+  subdirectory of the source root
+
 ### Fixed
 * Previously compiled build scripts now maintain their executable bit when
   inherited

checks/default.nix

@@ -363,6 +363,14 @@ in
     pname = "workspace-inheritance";
   };
 
+  # https://github.com/ipetkov/crane/issues/209
+  workspaceRootNotAtSourceRoot = myLib.buildPackage {
+    src = myLib.cleanCargoSource ./workspace-not-at-root;
+    sourceRoot = "source/workspace";
+    cargoLock = ./workspace-not-at-root/workspace/Cargo.lock;
+    cargoToml = ./workspace-not-at-root/workspace/Cargo.toml;
+  };
+
   workspaceRoot = myLib.buildPackage {
     src = myLib.cleanCargoSource ./workspace-root;
     pname = "workspace-root";

checks/workspace-not-at-root/README.md

@@ -0,0 +1 @@
+Example project where the cargo workspace root is not at the source root

checks/workspace-not-at-root/workspace/Cargo.lock

@@ -0,0 +1,19 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "hello"
+version = "0.1.0"
+
+[[package]]
+name = "print"
+version = "0.1.0"
+dependencies = [
+ "hello",
+ "world",
+]
+
+[[package]]
+name = "world"
+version = "0.1.0"

checks/workspace-not-at-root/workspace/Cargo.toml

@@ -0,0 +1,4 @@
+[workspace]
+# NB: hello and world are intentionally left out cargo will
+# promote them to members since they are listed as path deps
+members = ["print"]

checks/workspace-not-at-root/workspace/hello/Cargo.toml

@@ -0,0 +1,4 @@
+[package]
+name = "hello"
+version = "0.1.0"
+edition = "2021"

checks/workspace-not-at-root/workspace/hello/src/lib.rs

@@ -0,0 +1,3 @@
+pub fn hello() -> &'static str {
+    "hello"
+}

checks/workspace-not-at-root/workspace/print/Cargo.toml

@@ -0,0 +1,8 @@
+[package]
+name = "print"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
+hello = { version = "*", path = "../hello" }
+world = { version = "*", path = "../world" }

checks/workspace-not-at-root/workspace/print/src/main.rs

@@ -0,0 +1,3 @@
+fn main() {
+    println!("{}, {}", hello::hello(), world::world());
+}

checks/workspace-not-at-root/workspace/world/Cargo.toml

@@ -0,0 +1,4 @@
+[package]
+name = "world"
+version = "0.1.0"
+edition = "2021"

checks/workspace-not-at-root/workspace/world/src/lib.rs

@@ -0,0 +1,3 @@
+pub fn world() -> &'static str {
+    "world!"
+}

docs/SUMMARY.md

@@ -27,3 +27,4 @@
   * [Building a subset of a workspace](./faq/build-workspace-subset.md)
   * [Trouble building when using `include_str!` (or including other non-rust files)](./faq/building-with-non-rust-includes.md)
   * [Dealing with sandbox-unfriendly build scripts](./faq/sandbox-unfriendly-build-scripts.md)
+  * [Cargo.toml is not at the source root](./faq/workspace-not-at-source-root.md)

docs/faq/workspace-not-at-source-root.md

@@ -0,0 +1,21 @@
+## Cargo workspace root (Cargo.toml) is not at the root of the derivation's source
+
+Most cargo projects have their `Cargo.toml` at the root of the source, but it's
+still possible to build a project where the `Cargo.toml` file is nested in a
+deeper directory:
+
+```nix
+# Assuming that we have the following directory structure:
+# ./flake.nix
+# ./flake.lock
+# ./nested
+# ./nested/Cargo.toml
+# ./nested/Cargo.lock
+# ./nested/src/*.rs
+craneLib.buildPackage {
+ src = myLib.cleanCargoSource ./.;
+ sourceRoot = "source/nested"; # Needs to start with "source/" by default
+ cargoLock = ./nested/Cargo.lock;
+ cargoToml = ./nested/Cargo.toml;
+}
+```

lib/buildDepsOnly.nix

@@ -23,24 +23,12 @@ let
     "dummySrc"
   ];
 
-  throwMsg = throw ''
-    unable to find Cargo.toml and Cargo.lock at ${path}. please ensure one of the following:
-    - a Cargo.toml and Cargo.lock exists at the root of the source directory of the derivation
-    - set `cargoArtifacts = buildDepsOnly { src = ./some/path/to/cargo/root; }`
-    - set `cargoArtifacts = null` to skip reusing cargo artifacts altogether
-  '';
-
   # Run tests by default to ensure we cache any dev-dependencies
   doCheck = args.doCheck or true;
 
   cargoCheckExtraArgs = args.cargoCheckExtraArgs or (if doCheck then "--all-targets" else "");
 
-  path = args.src or throwMsg;
-  cargoToml = path + "/Cargo.toml";
-  dummySrc = args.dummySrc or
-    (if builtins.pathExists cargoToml
-    then mkDummySrc args
-    else throwMsg);
+  dummySrc = args.dummySrc or (mkDummySrc args);
 in
 mkCargoDerivation (cleanedArgs // {
   inherit doCheck;

lib/crateNameFromCargoToml.nix

@@ -3,13 +3,21 @@
 
 args:
 let
-  src = args.src or (throw ''
-    unable to infer crate name and version. Please make sure the src directory
-    contains a valid Cargo.toml file, or consider setting a derivation name explicitly
-  '');
+  throwMsg = throw ''
+    unable to infer crate name and version. please ensure one of the following:
+    - a Cargo.toml exists at the root of the source directory of the derivation
+    - `cargoToml` is set to a path to the package's Cargo.toml
+    - `cargoTomlContents` is set to the contents of the package's Cargo.toml
+    - `pname` and `version` are explicitly set 
+  '';
 
+  src = args.src or throwMsg;
   cargoToml = args.cargoToml or (args.src + "/Cargo.toml");
-  cargoTomlContents = args.cargoTomlContents or (builtins.readFile cargoToml);
+  cargoTomlContents = args.cargoTomlContents or (
+    if builtins.pathExists cargoToml
+    then builtins.readFile cargoToml
+    else throwMsg
+  );
 
   toml = builtins.fromTOML cargoTomlContents;
 in