use SETUPTOOLS_RUST_CARGO_PROFILE=dev for main matrix, document it (#527)

* use `SETUPTOOLS_RUST_CARGO_PROFILE=dev` for main matrix, document it

* also set a common target dir

Author: davidhewitt

.github/workflows/ci.yml

@@ -9,6 +9,10 @@ concurrency:
   group: ${{ github.workflow }}-${{ github.ref_name }}-${{ github.event.pull_request.number || github.sha }}
   cancel-in-progress: true
 
+# Setting a fixed target dir ensures that all builds of examples re-use the same common dependencies
+env:
+  CARGO_TARGET_DIR: ${{ github.workspace }}/target
+
 jobs:
   ruff:
     runs-on: "ubuntu-latest"
@@ -110,6 +114,8 @@ jobs:
                 rust-target: "aarch64-apple-darwin",
               }
 
+    env:
+      SETUPTOOLS_RUST_CARGO_PROFILE: dev
     steps:
       - uses: actions/checkout@v4
 

README.md

@@ -107,6 +107,12 @@ python
 # ... better write some tests with pytest ...
 ```
 
+## Environment variables for configuration
+
+As well as all [environment variables supported by Cargo](https://doc.rust-lang.org/cargo/reference/environment-variables.html#environment-variables-cargo-reads), `setuptools-rust` also supports the following:
+
+- `SETUPTOOLS_RUST_CARGO_PROFILE`: used to override the profile of the Rust build. Defaults to `release`, e.g. set to `dev` to do a debug build.
+
 ## Next steps and final remarks
 
 - When you are ready to distribute your project, have a look on