Fix percy target branch for PRs (#43160)

* Fix percy target branch for PRs

* Add debug logging

* Try diff branch name

* Use PR_TARGET_BRANCH instead

* renable visReg jobs

* parse target branch from `branch_specifier`

* rename debugging print out

* set `PERCY_BRANCH` and `PERCY_TARGET_BRANCH`

* log PERCY_TARGET_BRANCH

* cleanup error messages

.ci/jobs.yml

@@ -14,7 +14,7 @@ JOB:
   - kibana-ciGroup10
   - kibana-ciGroup11
   - kibana-ciGroup12
-  # - kibana-visualRegression
+  - kibana-visualRegression
 
   # make sure all x-pack-ciGroups are listed in test/scripts/jenkins_xpack_ci_group.sh
   - x-pack-firefoxSmoke
@@ -28,7 +28,7 @@ JOB:
   - x-pack-ciGroup8
   - x-pack-ciGroup9
   - x-pack-ciGroup10
-  # - x-pack-visualRegression
+  - x-pack-visualRegression
 
 # `~` is yaml for `null`
 exclude: ~

src/dev/ci_setup/get_percy_env.js

@@ -23,7 +23,36 @@ const pkg = require('../../../package.json');
 const { stdout: commit } = execa.sync('git', ['rev-parse', 'HEAD']);
 const shortCommit = commit.slice(0, 8);
 
+if (!process.env.JOB_NAME) {
+  throw new Error('getPercyEnv: [JOB_NAME] environment variable required');
+}
+
 const isPr = process.env.JOB_NAME.includes('elastic+kibana+pull-request');
+if (isPr && !(process.env.PR_TARGET_BRANCH && process.env.PR_SOURCE_BRANCH)) {
+  throw new Error(
+    'getPercyEnv: Unable to determine percy environment in prs without [PR_TARGET_BRANCH] and [PR_SOURCE_BRANCH] environment variables'
+  );
+}
+
+let branch;
+if (isPr) {
+  branch = process.env.PR_SOURCE_BRANCH;
+} else {
+  if (!process.env.branch_specifier) {
+    throw new Error('getPercyEnv: [branch_specifier] environment variable required');
+  }
+
+  branch = process.env.branch_specifier.split('refs/heads/')[1];
+
+  if (!branch) {
+    throw new Error(
+      `getPercyEnv: [branch_specifier=${process.env.branch_specifier}] must start with 'refs/heads/'`
+    );
+  }
+}
 
 console.log(`export PERCY_PARALLEL_TOTAL=2;`);
-console.log(`export PERCY_PARALLEL_NONCE="${shortCommit}/${isPr ? 'PR' : pkg.branch}/${process.env.BUILD_ID}";`);
+console.log(`export PERCY_PARALLEL_NONCE="${shortCommit}/${isPr ? 'PR' : branch}/${process.env.BUILD_ID}";`);
+console.log(`export PERCY_BRANCH="${branch}";`);
+// percy snapshots always target pkg.branch, so that feature branches can be based on master/7.x/etc.
+console.log(`export PERCY_TARGET_BRANCH="${isPr ? process.env.PR_TARGET_BRANCH : pkg.branch}";`);

src/dev/ci_setup/setup_percy.sh

@@ -15,3 +15,5 @@ export PUPPETEER_EXECUTABLE_PATH
 eval "$(node ./src/dev/ci_setup/get_percy_env)"
 echo " -- PERCY_PARALLEL_NONCE='$PERCY_PARALLEL_NONCE'"
 echo " -- PERCY_PARALLEL_TOTAL='$PERCY_PARALLEL_TOTAL'"
+echo " -- PERCY_BRANCH='$PERCY_BRANCH'"
+echo " -- PERCY_TARGET_BRANCH='$PERCY_TARGET_BRANCH'"