ci: fix ambiguity issue during tokio releases (#7848)

docs/contributing/README.md

@@ -37,6 +37,7 @@ If you are unsure where to begin, use the following guides:
     - [Review a bit at a time](reviewing-pull-requests.md#review-a-bit-at-a-time)
     - [Be aware of the person behind the code](reviewing-pull-requests.md#be-aware-of-the-person-behind-the-code)
     - [Abandoned or Stalled Pull Requests](reviewing-pull-requests.md#abandoned-or-stalled-pull-requests)
+- [How to specify crates dependencies versions](how-to-specify-crates-dependencies-versions.md)
 - [Keeping track of issues and PRs](keeping-track-of-issues-and-prs.md)
     - [Area](keeping-track-of-issues-and-prs.md#area)
     - [Category](keeping-track-of-issues-and-prs.md#category)

docs/contributing/how-to-specify-crates-dependencies-versions.md

@@ -0,0 +1,31 @@
+# How to specify crates dependencies versions
+
+Each crate (e.g., `tokio-util`, `tokio-stream`, etc.) should specify dependencies
+according to these rules:
+
+1. The listed version should be the oldest version that the crate works with
+(e.g., if `tokio-util` works with `tokio` version `1.44` but not `1.43`, then
+`tokio-util` should specify version `1.44` for its `tokio` dependency).
+We don't require users to use the latest version unnecessarily.
+2. When a crate starts using a newer feature in a dependency, the version
+should be bumped to the version that introduced it.
+3. If a crate depends on an unreleased feature in a dependency, it may use
+`path = ` dependency to specify this. Since path dependencies must be removed
+during the release of the crate, this ensures that it can't be released until
+the dependency has a new version.
+
+Consider the following example from `tokio-stream`:
+
+```toml
+[dependencies]
+futures-core = { version = "0.3.0" }
+pin-project-lite = "0.2.11"
+tokio = { path = "../tokio", features = ["sync"] }
+```
+
+In this case, local development of `tokio-stream` uses the local version
+of `tokio` via the `path` dependency. This means that it's currently not
+possible to release `tokio-stream`. Once a new version of `tokio` is
+released, the path dependency will be removed from `tokio-stream`.
+As mentioned before, this version should only be bumped when adding a new
+feature in the crate that relies on a newer version.