Add a doc alias policy

Based on discussion in 2021-06-30 libs meeting.

Author: joshtriplett

src/SUMMARY.md

@@ -36,6 +36,11 @@
 
 ---
 
+- [Documentation](./documentation/summary.md)
+    - [doc alias policy](./documentation/doc-alias-policy.md)
+
+---
+
 - [Tools and bots](./tools-and-bots/summary.md)
     - [`@bors`](./tools-and-bots/bors.md)
     - [`@rust-timer`](./tools-and-bots/timer.md)

src/documentation/doc-alias-policy.md

@@ -0,0 +1,35 @@
+doc alias policy
+================
+
+Rust's documentation supports adding aliases to any declaration (such as a
+function, type, or constant), using the syntax `#[doc(alias = "name")]`. We
+want to use doc aliases to help people find what they're looking for, while
+keeping those aliases maintainable and high-value. This policy outlines the
+cases where we add doc aliases, and the cases where we omit those aliases.
+
+- We must have a reasonable expectation that people might search for the term
+  in the documentation search. Rust's documentation provides a name search, not
+  a full-text search; as such, we expect that people may search for plausible
+  names, but that for more general documentation searches they'll turn to a web
+  search engine.
+  - Related: we don't expect that people are currently searching Rust
+    documentation for language-specific name from arbitrary languages they're
+    familiar with, and we don't want to add that as a new documentation search
+    feature; please don't add aliases based on your favorite language. Those
+    mappings should live in separate guides or references. We do expect that
+    people might look for the Rust name of a function they reasonably expect to
+    exist in Rust (e.g. a system function or a C library function), to try to
+    figure out what Rust called that function.
+- The proposed alias must be a name we would plausibly have used for the
+  declaration. For instance, `delete` for `remove`, or `popcnt` and `popcount`
+  for `count_ones`, or `umask` for `mode`, or `mkdir` for `create_dir`. This
+  feeds into the reasonable expectation that someone might search for the name
+  and expect to find it ("what did Rust call `mkdir`").
+- There must be an obvious single target for the alias that is an *exact*
+  analogue of the aliased name. We will not add the same alias to multiple
+  declarations. We will also not add an alias for a function that's only
+  somewhat similar or related.
+- The alias must not conflict with the actual name of any existing declaration.
+- As a special case for stdarch, aliases from exact assembly instruction names
+  to the corresponding intrinsic function are welcome, as long as they don't
+  conflict with other names.

src/documentation/summary.md

@@ -0,0 +1 @@
+- [doc alias policy](./doc-alias-policy.md)