ci: add label check script

Author: Stebalien

.github/scripts/check-labels.sh

@@ -0,0 +1,41 @@
+#!/bin/bash
+#
+# This script checks the local label table (ISSUE_LABELS.md) against canonical label file in the
+# protocol/.github repo.
+
+set -euo pipefail
+set -x
+
+# The canonical source of labels.
+CANONICAl_LABELS="https://raw.githubusercontent.com/protocol/.github/master/ISSUE_LABELS.json"
+
+# Matches labels in label tables. Assumes table rows have the form:
+# | `label name` | Some description... | ...`#hexcolor`... |
+LABEL_REGEXP='s/|.*`\([^`]*\)`.*| *\([^|]*[^ |]\) *|.*`\(#[a-f0-9]*\)`.*|/\1\t\3\t\2/p'
+
+# Reads a label markdown file on stdin and prints a JSON version on stdout.
+parse_labels() {
+    while IFS=$'\t' read -r label color description; do
+        jq -n \
+           --arg name "$label" \
+           --arg color "${color##\#}" \
+           --arg description "$description" \
+           '{"name": $name, "color": $color, "description": $description}'
+    done < <(sed -ne "$LABEL_REGEXP" - ) |
+        jq 'select(.name | startswith("area/") == false)' | # area labels are not synced.
+        jq -s 'sort_by(.name)' # sort into a canonical order for comparison.
+}
+
+# Extract labels.
+parse_labels < ISSUE_LABELS.md > ISSUE_LABELS.json
+
+# Download canonical labels.
+curl "$CANONICAl_LABELS" |
+    jq 'del(.aliases)|sort_by(.name)' > CANONICAL_LABELS.json
+
+# Compare.
+if ! diff -u CANONICAL_LABELS.json ISSUE_LABELS.json; then
+    echo "Please update the labels defined at https://github.com/protocol/.github/blob/master/ISSUE_LABELS.json."
+    exit 1
+fi
+