Concrete MSRV policy (#683)

.github/workflows/ci.yml

@@ -41,7 +41,7 @@ jobs:
       run: rustup install 1.71 --profile minimal
 
     - name: Check
-      run: cargo +1.71 check -p diplomat -p diplomat-runtime --verbose
+      run: cargo +1.71 check -p diplomat -p diplomat-runtime -p diplomat_core --verbose
 
   gen:
     runs-on: ubuntu-latest

Cargo.toml

@@ -1,4 +1,6 @@
 [workspace]
+# Applies to diplomat-core, diplomat, and diplomat-runtime
+# Diplomat-tool has no MSRV for now
 resolver = "2"
 members = [
   "core",
@@ -8,3 +10,6 @@ members = [
   "example",
   "feature_tests",
 ]
+
+[workspace.package]
+rust-version = "1.71"

core/Cargo.toml

@@ -2,6 +2,7 @@
 name = "diplomat_core"
 description = "Shared utilities between Diplomat macros and code generation"
 version = "0.8.0"
+rust-version.workspace = true
 authors = [
     "Shadaj Laddad <[email protected]>",
     "Manish Goregaokar <[email protected]>",

docs/msrv_policy.md

@@ -0,0 +1,22 @@
+# Minimum Supported Rust Versions policy
+
+The diplomat libraries that end up as dependencies of diplomat-using crates (`diplomat`, `diplomat_core`, `diplomat-runtime`) attempt to maintain a reasonable Minimum Supported Rust Version policy for its users.
+
+At the moment, the primary user of Diplomat is [ICU4X](https://github.com/unicode-org/icu4x), and as such Diplomat matches ICU4X's [MSRV polic
+y], with a tweak:
+
+ - Diplomat releases must have an MSRV that is 4 or more releases before the current stable Rust (the version that Rust will be when Diplomat is released)
+ - Diplomat maintainers may upgrade MSRV to something that will be 6 or more releases before current stable Rust without needing justification.
+ - Upgrading MSRV to something between 4 and 6 releases before current stable Rust requires justification listing the concrete benefit Diplomat gets from this change.
+ - When a Diplomat MSRV update on Diplomat `main` will affect MSRV on ICU4X `main`, ICU4X must sign off on the MSRV update, either by policy, or by discussion when needed.
+
+When it comes to dependencies, Diplomat's MSRV implies that _some_ combination of dependency versions satisfies that MSRV. This combination can usually be found in Diplomat's lockfile, which is tested by CI.
+
+
+The tool library, `diplomat-tool`, does not maintain any MSRV.
+
+
+Diplomat is open to tweaking this policy to support the needs of other downstream users.
+
+
+ [MSRV policy]: https://github.com/unicode-org/icu4x/blob/main/documents/process/rust_versions.md

macro/Cargo.toml

@@ -2,6 +2,7 @@
 name = "diplomat"
 description = "The diplomat FFI generation macro"
 version = "0.8.0"
+rust-version.workspace = true
 authors = [
     "Shadaj Laddad <[email protected]>",
     "Manish Goregaokar <[email protected]>",

runtime/Cargo.toml

@@ -2,6 +2,7 @@
 name = "diplomat-runtime"
 description = "Common runtime utilities used by diplomat codegen"
 version = "0.8.1"
+rust-version.workspace = true
 authors = [
     "Shadaj Laddad <[email protected]>",
     "Manish Goregaokar <[email protected]>",