Merge pull request #1856 from indygreg/build-config-feature

pyo3-build-config: add a crate feature to control build script

CHANGELOG.md

@@ -16,6 +16,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 - Add implementation of `std::ops::Index<usize>` for `PyList`, `PyTuple` and `PySequence`. [#1825](https://github.com/PyO3/pyo3/pull/1825)
 - Add range indexing implementations of `std::ops::Index` for `PyList`, `PyTuple` and `PySequence`. [#1829](https://github.com/PyO3/pyo3/pull/1829)
 - Add commonly-used sequence methods to `PyList` and `PyTuple`. [#1849](https://github.com/PyO3/pyo3/pull/1849)
+- The `pyo3-build-config` crate now has a `resolve-config` feature to control whether its build script does anything. [#1856](https://github.com/PyO3/pyo3/pull/1856)
 
 ### Changed
 

Cargo.toml

@@ -43,7 +43,7 @@ pyo3 = { path = ".", default-features = false, features = ["macros", "auto-initi
 serde_json = "1.0.61"
 
 [build-dependencies]
-pyo3-build-config = { path = "pyo3-build-config", version = "0.14.4" }
+pyo3-build-config = { path = "pyo3-build-config", version = "0.14.4", features = ["resolve-config"] }
 
 [features]
 default = ["macros"]

guide/src/features.md

@@ -69,6 +69,14 @@ The `nightly` feature needs the nightly Rust compiler. This allows PyO3 to use R
 - `FromPyObject` for `Vec` and `[T;N]` can perform a `memcpy` when the object supports the Python buffer protocol.
 - `ToBorrowedObject` can skip a reference count increase when the provided object is a Python native type.
 
+### `resolve-config`
+
+The `resolve-config` feature of the `pyo3-build-config` crate controls whether that crate's
+build script automatically resolves a Python interpreter / build configuration. Disabling
+this feature enables this crate to be used in *library mode*. This may be desirable for
+use cases where you want to read or write PyO3 build configuration files or resolve
+metadata about a Python interpreter.
+
 ## Optional Dependencies
 
 These features enable conversions between Python types and types from other Rust crates, enabling easy access to the rest of the Rust ecosystem.

pyo3-build-config/Cargo.toml

@@ -14,7 +14,11 @@ edition = "2018"
 once_cell = "1"
 
 [features]
-default = []
+default = ["resolve-config"]
+
+# Attempt to resolve a Python interpreter config for building in the build
+# script. If this feature isn't enabled, the build script no-ops.
+resolve-config = []
 
 abi3 = []
 abi3-py36 = ["abi3-py37"]

pyo3-build-config/build.rs

@@ -91,8 +91,12 @@ fn generate_build_configs() -> Result<()> {
 }
 
 fn main() {
-    if let Err(e) = generate_build_configs() {
-        eprintln!("error: {}", e.report());
-        std::process::exit(1)
+    if std::env::var("CARGO_FEATURE_RESOLVE_CONFIG").is_ok() {
+        if let Err(e) = generate_build_configs() {
+            eprintln!("error: {}", e.report());
+            std::process::exit(1)
+        }
+    } else {
+        eprintln!("resolve-config feature not enabled; build script in no-op mode");
     }
 }

pyo3-macros-backend/Cargo.toml

@@ -16,7 +16,7 @@ edition = "2018"
 [dependencies]
 quote = { version = "1", default-features = false }
 proc-macro2 = { version = "1", default-features = false }
-pyo3-build-config = { path = "../pyo3-build-config", version = "0.14.4" }
+pyo3-build-config = { path = "../pyo3-build-config", version = "0.14.4", features = ["resolve-config"] }
 
 [dependencies.syn]
 version = "1"