Add policy detailing review procedure for target-specific code

src/SUMMARY.md

@@ -20,6 +20,7 @@
     - [When to `#[inline]`](./policy/inline.md)
     - [Doc alias policy](./policy/doc-alias.md)
     - [Safety comments policy](./policy/safety-comments.md)
+    - [Reviewing target-specific code](./policy/target-code.md)
 
 - [Tricky situations]()
     - [Drop and `#[may_dangle]`](./tricky/may-dangle.md)

src/policy/target-code.md

@@ -0,0 +1,25 @@
+# Reviewing target-specific code
+
+When reviewing target-specific code, depending on the [tier] of the target in
+question, different level of scrutiny is expected from reviewers.
+
+For tier 1 targets, the reviewer should perform a full review of the code.
+Essentially treat the code as *not* platform specific.
+
+For tier 2 and tier 3 targets, the reviewer should confirm that the code:
+
+* Only affects 1 or more of such targets (i.e., is truly target-specific)
+* Does not introduce new licensing hazards (e.g., license headers or similar)
+* Is either proposed by a target maintainer[^1] or has pinged and received +1s
+  from at least one target maintainer. Where no maintainer is present, look for
+  whether the author is reputable and/or affiliated with the target in some way
+  (e.g., authored original code, works for a company maintaining the target, etc.).
+
+Note that this review does *not* include checking for correctness or for code
+quality. We lack the review bandwidth or expertise to perform detailed reviews
+of tier 2 and tier 3 targets.
+
+[^1]: Target maintainers are listed for most targets in the [platform support] documentation.
+
+[tier]: https://doc.rust-lang.org/nightly/rustc/platform-support.html
+[platform support]: https://doc.rust-lang.org/nightly/rustc/platform-support.html