Add branch matching (#2329)

scripts/branch-match.sh

@@ -0,0 +1,48 @@
+#!/bin/bash
+
+# Script for downloading a branch of element-web matching the branch a PR is contributed from
+
+set -x
+
+deforg="element-hq"
+defrepo="element-web"
+
+# The PR_NUMBER variable must be set explicitly.
+default_org_repo=${GITHUB_REPOSITORY:-"$deforg/$defrepo"}
+PR_ORG=${PR_ORG:-${default_org_repo%%/*}}
+PR_REPO=${PR_REPO:-${default_org_repo##*/}}
+
+# A function that clones a branch of a repo based on the org, repo and branch
+clone() {
+    org=$1
+    repo=$2
+    branch=$3
+    if [ -n "$branch" ]
+    then
+        echo "Trying to use $org/$repo#$branch"
+        # Disable auth prompts: https://serverfault.com/a/665959
+        GIT_TERMINAL_PROMPT=0 git clone https://github.com/$org/$repo.git $repo --branch "$branch" --depth 1 && exit 0
+    fi
+}
+
+echo "Getting info about a PR with number $PR_NUMBER"
+apiEndpoint="https://api.github.com/repos/$PR_ORG/$PR_REPO/pulls/$PR_NUMBER"
+head=$(curl "$apiEndpoint" | jq -r '.head.label')
+
+# for forks, $head will be in the format "fork:branch", so we split it by ":"
+# into an array. On non-forks, this has the effect of splitting into a single
+# element array given ":" shouldn't appear in the head - it'll just be the
+# branch name. Based on the results, we clone.
+BRANCH_ARRAY=(${head//:/ })
+TRY_ORG=$deforg
+TRY_BRANCH=${BRANCH_ARRAY[0]}
+if [[ "$head" == *":"* ]]; then
+    # ... but only match that fork if it's a real fork
+    if [ "${BRANCH_ARRAY[0]}" != "$PR_ORG" ]; then
+        TRY_ORG=${BRANCH_ARRAY[0]}
+    fi
+    TRY_BRANCH=${BRANCH_ARRAY[1]}
+fi
+clone "$TRY_ORG" "$defrepo" "$TRY_BRANCH"
+
+exit 1