Add CODEOWNERS for review assignment (carbon-language#6153)

This disables the autoassign action so that the codeowners approach can
be tested without interference.

Trying this out because it might be a path for vacation handling. See
[GitHub
docs](https://docs.github.com/en/organizations/organizing-members-into-teams/managing-code-review-settings-for-your-team)
and
[#infra](https://discord.com/channels/655572317891461132/707150492370862090/1422985757311635620)

---------

Co-authored-by: Dana Jansens <[email protected]>

Author: jonmeow

.github/workflows/auto_assign_prs.yaml

@@ -0,0 +1,24 @@
+# Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+# Exceptions. See /LICENSE for license information.
+# SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+# This file is only used for PR autoassignment. Branch protections don't enforce
+# it.
+#
+# Syntax:
+# https://docs.github.com/en/repositories/managing-your-repositorys-settings-and-features/customizing-your-repository/about-code-owners#codeowners-syntax
+
+# Toolchain reviewers are used as a fallback.
+*                          @carbon-language/toolchain-reviewers
+
+# Key project documents should be reviewed by leads.
+/*.md                      @carbon-language/leads
+/LICENSE                   @carbon-language/leads
+/docs/project/evolution.md @carbon-language/leads
+/docs/project/goals.md     @carbon-language/leads
+/docs/project/principles/* @carbon-language/leads
+/docs/project/roadmap.md   @carbon-language/leads
+/proposals/*.md            @carbon-language/leads
+
+# Toolchain code.
+/toolchain                 @carbon-language/toolchain-reviewers

CODEOWNERS

@@ -86,11 +86,11 @@ In Carbon, developers will focus on particular areas, loosely broken down as:
     -   We split out auto-assignment by explorer, toolchain, and other files
         (including documentation).
 
-[Auto-assignment](/.github/workflows/auto_assign_prs.yaml) will help find
-owners, but won't always be perfect -- developers may take a PR they weren't
-auto-assigned in order to help review go quickly. Contributors can also request
-multiple reviewers, but it can be daunting to get feedback from a large number
-of reviewers, so we suggest keeping the number of reviewers reasonably small.
+[Auto-assignment](/CODEOWNERS) will help find owners, but won't always be
+perfect -- developers may take a PR they weren't auto-assigned in order to help
+review go quickly. Contributors can also request multiple reviewers, but it can
+be daunting to get feedback from a large number of reviewers, so we suggest
+keeping the number of reviewers reasonably small.
 
 Any reviews that explicitly request changes should be addressed, either with the
 changes or an explanation of why not, before a pull request is merged. Further,

docs/project/code_review.md

@@ -110,8 +110,9 @@ group access controls are the last word on who can commit PRs.
 
 ### Auto-assignment
 
-This PR [introduces auto-assignment](/.github/workflows/auto_assign_prs.yaml) in
-order to ensure PRs aren't lost. It provides categories of assignment, and a
+This PR
+[introduces auto-assignment](https://github.com/carbon-language/carbon-lang/pull/1367/files#diff-5e5db53c34ec04ba9da95c70d5c797f1be9f390f7e2bf18ca3149cbd99c277df)
+in order to ensure PRs aren't lost. It provides categories of assignment, and a
 fallback for other PRs that don't have explicit assignment.
 
 ### Stacked PRs