ci: add labeler (#846)

Fixes #830

Author: ricochet

.github/labeler.yml

@@ -0,0 +1,46 @@
+# Configuration for actions/labeler
+# Labels PRs based on changed files
+#
+# Proposal labels use the P- prefix to identify which WASI proposal is affected.
+# See CONTRIBUTING.md for documentation on label conventions.
+
+# Proposal labels (P-)
+P-cli:
+  - changed-files:
+      - any-glob-to-any-file: 'proposals/cli/**'
+
+P-clocks:
+  - changed-files:
+      - any-glob-to-any-file: 'proposals/clocks/**'
+
+P-filesystem:
+  - changed-files:
+      - any-glob-to-any-file: 'proposals/filesystem/**'
+
+P-http:
+  - changed-files:
+      - any-glob-to-any-file: 'proposals/http/**'
+
+P-io:
+  - changed-files:
+      - any-glob-to-any-file: 'proposals/io/**'
+
+P-random:
+  - changed-files:
+      - any-glob-to-any-file: 'proposals/random/**'
+
+P-sockets:
+  - changed-files:
+      - any-glob-to-any-file: 'proposals/sockets/**'
+
+# GitHub Actions label
+github_actions:
+  - changed-files:
+      - any-glob-to-any-file: '.github/**'
+
+# Dependencies label (already exists, used by dependabot)
+dependencies:
+  - changed-files:
+      - any-glob-to-any-file:
+          - '**/deps.toml'
+          - '**/deps.lock'

.github/workflows/labeler.yml

@@ -0,0 +1,15 @@
+name: Labeler
+
+on:
+  pull_request_target:
+
+jobs:
+  labeler:
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+      pull-requests: write
+
+    steps:
+      - name: Apply labels
+        uses: actions/labeler@634933edcd8ababfe52f92936142cc22ac488b1b # v6.0.1

CONTRIBUTING.md

@@ -7,6 +7,31 @@ Interested in participating? Please follow
 
 Also, please be sure to read [the README.md](README.md) for this repository.
 
+## Labels
+
+This repository uses a categorized label system inspired by [the Rust project].
+Proposal labels use the `P-` prefix to identify which WASI proposal an issue or
+pull request relates to.
+
+### Proposal Labels (P-)
+
+| Label | Proposal |
+| ----- | -------- |
+| `P-cli` | [cli](proposals/cli/) |
+| `P-clocks` | [clocks](proposals/clocks/) |
+| `P-filesystem` | [filesystem](proposals/filesystem/) |
+| `P-http` | [http](proposals/http/) |
+| `P-io` | [io](proposals/io/) |
+| `P-random` | [random](proposals/random/) |
+| `P-sockets` | [sockets](proposals/sockets/) |
+
+Pull requests that modify files in a proposal directory are automatically
+labeled by the [labeler workflow](.github/workflows/labeler.yml).
+
+[the Rust project]: https://github.com/rust-lang/rust/labels
+
+## Contributing to Proposals
+
 To contribute to an [existing proposal](https://github.com/WebAssembly/WASI/blob/main/docs/Proposals.md),
 refer to the linked proposal repository.