identifiers: Allow to set ruma_identifiers_storage cfg setting with env variable

crates/ruma-common/CHANGELOG.md

@@ -1,5 +1,14 @@
 # [unreleased]
 
+Improvements:
+
+- The `ruma_identifiers_storage` compile-time `cfg` setting can also be
+  configured by setting the `RUMA_IDENTIFIERS_STORAGE` environment variable at
+  compile time. It has the benefit of not requiring to re-compile all the crates
+  of the dependency chain when the value is changed.
+
+# 0.14.1
+
 Bug fixes:
 
 - The `KeyId::key_name` method now returns the key name. In 0.14.0, `key_name`

crates/ruma-common/build.rs

@@ -0,0 +1,10 @@
+use std::env;
+
+fn main() {
+    // Set the `ruma_identifiers_storage` configuration from an environment variable.
+    if let Ok(value) = env::var("RUMA_IDENTIFIERS_STORAGE") {
+        println!("cargo:rustc-cfg=ruma_identifiers_storage={value}");
+    }
+
+    println!("cargo:rerun-if-env-changed=RUMA_IDENTIFIERS_STORAGE");
+}

crates/ruma-events/CHANGELOG.md

@@ -3,6 +3,10 @@
 Improvements:
 
 - Add unstable support for MSC4171 for the m.member_hints state event.
+- The `ruma_identifiers_storage` compile-time `cfg` setting can also be
+  configured by setting the `RUMA_IDENTIFIERS_STORAGE` environment variable at
+  compile time. It has the benefit of not requiring to re-compile all the crates
+  of the dependency chain when the value is changed.
 
 Breaking changes:
 

crates/ruma-events/build.rs

@@ -0,0 +1,10 @@
+use std::env;
+
+fn main() {
+    // Set the `ruma_identifiers_storage` configuration from an environment variable.
+    if let Ok(value) = env::var("RUMA_IDENTIFIERS_STORAGE") {
+        println!("cargo:rustc-cfg=ruma_identifiers_storage={value}");
+    }
+
+    println!("cargo:rerun-if-env-changed=RUMA_IDENTIFIERS_STORAGE");
+}

crates/ruma/src/lib.rs

@@ -73,6 +73,19 @@
 //!
 //! If you are viewing this on `docs.rs`, you can have a look at the feature dependencies by
 //! clicking **Feature flags** in the toolbar at the top.
+//!
+//! # Compile-time `cfg` settings
+//!
+//! These settings are accepted at compile time to configure the generated code. They can be set as
+//! `--cfg={key}={value}` using `RUSTFLAGS` or `.cargo/config.toml` (under `[build]` -> `rustflags =
+//! ["..."]`). They can also be configured using an environment variable at compile time, which has
+//! the benefit of not requiring to re-compile the whole dependency chain when their value is
+//! changed.
+//!
+//! * `ruma_identifiers_storage` -- Choose the inner representation of `Owned*` wrapper types for
+//!   identifiers. By default they use [`Box`], setting the value to `Arc` makes them use
+//!   [`Arc`](std::sync::Arc). This can also be configured by setting the `RUMA_IDENTIFIERS_STORAGE`
+//!   environment variable.
 
 #![warn(missing_docs)]
 #![cfg_attr(docsrs, feature(doc_auto_cfg))]