get git sha on install

report.js

@@ -193,6 +193,22 @@ function processDependencyTreeOutput (resolve, reject) {
   }
 }
 
+function processGitRevParseOutput (resolve, reject) {
+  return function (error, stdout, stderr) {
+    if (error && !stdout) {
+      return reject(new Error(`Scarf received an error from git rev-parse: ${error} | ${stderr}`))
+    }
+
+    const output = String(stdout).trim()
+
+    if (output.length > 0) {
+      return resolve(output)
+    } else {
+      return reject(new Error('Scarf did not receive usable output from git rev-parse'))
+    }
+  }
+}
+
 // packageJSONOverride: a test convenience to set a packageJSON explicitly.
 // Leave empty to use the actual root package.json.
 async function getDependencyInfo (packageJSONOverride) {
@@ -226,6 +242,18 @@ async function getDependencyInfo (packageJSONOverride) {
   })
 }
 
+async function getGitSha () {
+  const promise = new Promise((resolve, reject) => {
+    exec(`cd ${rootPath} && git rev-parse HEAD`, { timeout: execTimeout, maxBuffer: 1024 * 1024 * 1024 }, processGitRevParseOutput(resolve, reject))
+  })
+  try {
+    return await promise
+  } catch (e) {
+    logIfVerbose(e)
+    return undefined
+  }
+}
+
 async function reportPostInstall () {
   const scarfApiToken = process.env.SCARF_API_TOKEN
 
@@ -235,6 +263,10 @@ async function reportPostInstall () {
     return Promise.reject(new Error('No parent found, nothing to report'))
   }
 
+  const gitSha = await getGitSha()
+  logIfVerbose(`Injecting sha to parent: ${gitSha}`)
+  dependencyInfo.parent.gitSha = gitSha
+
   const rootPackage = dependencyInfo.rootPackage
 
   if (!userHasOptedIn(rootPackage) && isYarn()) {
@@ -512,8 +544,10 @@ module.exports = {
   tmpFileName,
   dirName,
   processDependencyTreeOutput,
+  processGitRevParseOutput,
   npmExecPath,
   getDependencyInfo,
+  getGitSha,
   reportPostInstall,
   hashWithDefault,
   findScarfInFullDependencyTree

test/report.test.js

@@ -147,6 +147,16 @@ describe('Reporting tests', () => {
       return report.processDependencyTreeOutput(resolve, reject)(null, JSON.stringify(parsedLsOutput), null)
     })).rejects.toEqual(new Error('The package depending on Scarf is the root package being installed, but Scarf is not configured to run in this case. To enable it, set `scarfSettings.allowTopLevel = true` in your package.json'))
   })
+
+  test('Can parse example git rev-parse HEAD output', async () => {
+    await expect(new Promise((resolve, reject) => {
+      return report.processGitRevParseOutput(resolve, reject)(null, '9ace16b9e3833ad4e761a49f17fe607723d5bd5e\n', null)
+    })).resolves.toEqual('9ace16b9e3833ad4e761a49f17fe607723d5bd5e')
+  })
+
+  test('getGitSha resolves in test run of cloned repository', async () => {
+    await expect(report.getGitSha()).resolves.toBeTruthy()
+  })
 })
 
 function dependencyTreeScarfEnabled () {