docker: add REPO_URL and ORG_NAME support

* REPO_URL allows to fetch rules from the target repo
* ORG_NAME allows to prefix review groups correctly

Author: shtrom

README.md

@@ -77,7 +77,10 @@ reviewers string is formatted for use with [GitHub's gh
 CLI](https://cli.github.com/).
 
     $ docker run --rm -i reviewer-selector < samples/sample.diff
+    No REPO_URL in environment, using built-in rules ...
     No DIFF_URL in environment, reading from stdin ...
+    No ORG_NAME in environment, using # as group prefix ...
+    No REPO_NAME or TARGET_BRANCH_NAME in environment, not matching repository-based rules ...
     No PR_URL or GITHUB_TOKEN in environment, outputing to stdout ...
     @example-group,shtrom
 
@@ -91,7 +94,10 @@ piped into the container.
        | docker run --rm -i \
          -v ./herald_rules.real.json:/app/herald_rules.json \
          reviewer-selector
+    No REPO_URL in environment, using built-in rules ...
     No DIFF_URL in environment, reading from stdin ...
+    No ORG_NAME in environment, using # as group prefix ...
+    No REPO_NAME or TARGET_BRANCH_NAME in environment, not matching repository-based rules ...
     No PR_URL or GITHUB_TOKEN in environment, outputing to stdout ...
     @android-reviewers
 
@@ -104,6 +110,16 @@ The container's behaviour can be entirely parametrised via environment variables
       -e GITHUB_TOKEN=[REDACTED] reviewer-selector
     Adding reviewers to https://github.com/mozilla-firefox/infra-testing/pull/30 ...
 
-If `DIFF_URL` is given, it will be fetched and passed into the selector's
-stdin. If `GITHUB_TOKEN` and `PR_URL` are provided, the container will attempt
-to set the reviewers on the target PR.
+* If `DIFF_URL` is given, it will be fetched and passed into the selector's
+stdin.
+* If `GITHUB_TOKEN` and `PR_URL` are provided, the container will attempt
+
+Some other optional behaviours can be triggered by providing additional context
+in environment variables:
+* If `ORG_NAME` is passed, it will be used to scope reviewers groups to that
+  org.
+* If `REPO_NAME` and `TARGET_BRANCH_NAME` are provided, rules that specifically
+  match a given repository and/or branch will also be applied.
+* If `REPO_URL` is given, the script will attempt to fetch a rules file from
+  the `main` branch of the repository. If it fails, it will fallback to
+  built-in rules. to set the reviewers on the target PR.

docker/entrypoint.sh

@@ -1,21 +1,65 @@
 #!/bin/sh -eu
+# Variables expected in environment:
+# * DIFF_URL (optional, will read stdin otherwise)
+# * GITHUB_TOKEN (optional, will output reviewers to stdout otherwise)
+# * PR_URL (optional, will output reviewers to stdout otherwise)
+# * ORG_NAME (optional, will use # as a group prefix otherwise)
+# * REPO_NAME (optional, for more rule matching with TARGET_BRANCH_NAME)
+# * TARGET_BRANCH_NAME (optional, for more rule matching with REPO_NAME)
+# * REPO_URL (optional, to fetch specific rules)
 
-HERALD_RULES_JSON="${1}"
+CURL="curl --fail --show-error --silent --location"
+
+if [ -n "${REPO_URL:-}" ]; then
+  HERALD_RULES_JSON=$(mktemp)
+  # We always fetch the rules from the main branch.
+  RULES_URL="${REPO_URL}/refs/heads/main/herald_rules.json"
+
+	if ! ${CURL} "${RULES_URL}" --output "${HERALD_RULES_JSON}"; then
+    echo "Failed to fetch rules from ${RULES_URL}, using built-in rules ..." >&2
+    HERALD_RULES_JSON=""
+
+  fi
+
+else
+	echo "No REPO_URL in environment, using built-in rules ..." >&2
+
+fi
+
+if [ -z "${HERALD_RULES_JSON:-}" ]; then
+  HERALD_RULES_JSON="${1}"
+fi
 
 DIFF=$(mktemp)
 if [ -n "${DIFF_URL:-}" ]; then
-	curl --show-error --silent --location "${DIFF_URL}" --output "${DIFF}"
+  ${CURL} "${DIFF_URL}" --output "${DIFF}"
 
 else
 	echo "No DIFF_URL in environment, reading from stdin ..." >&2
 	cat > "${DIFF}"
 
 fi
 
+if [ -n "${ORG_NAME:-}" ]; then
+  GROUP_PREFIX="${ORG_NAME}/"
+
+else
+  GROUP_PREFIX="#"
+	echo "No ORG_NAME in environment, using ${GROUP_PREFIX} as group prefix ..." >&2
+
+fi
+
+if [ -n "${REPO_NAME:-}" ] && [ -n "${TARGET_BRANCH_NAME:-}" ]; then
+  REPO_BRANCH=${REPO_NAME}-${TARGET_BRANCH_NAME}
+
+else
+	echo "No REPO_NAME or TARGET_BRANCH_NAME in environment, not matching repository-based rules ..." >&2
+fi
+
 REVIEWERS=$(cat "${DIFF}" \
 	| /app/reviewer_selector.py \
-    ${REPO_NAME:+--repo "${REPO_NAME}"} \
-    --group-prefix @ --reviewer-separator , \
+    ${REPO_BRANCH:+--repo "${REPO_BRANCH}"} \
+    --group-prefix "${GROUP_PREFIX}" --reviewer-separator , \
     "${HERALD_RULES_JSON}" \
 )