[rush] new "Build cache is only supported if running in a Git repository" error thrown on CI after Rush upgrade

[benkeen]

Summary

We updated to Rush 5.109.1 yesterday, from 5.88.2. Since then, one of our CI pipelines has been throwing the following error on the rush build command (this is with --debug added):

Executing a maximum of 16 simultaneous processes...
Error: Error: Build cache is only supported if running in a Git repository. Either disable the build cache or run Rush in a Git repository.
    at _rushstack_node_core_library__WEBPACK_IMPORTED_MODULE_1__.Async.forEachAsync.concurrency (/vsts/_work/1/s/common/temp/install-run/@microsoft+rush@5.109.1/node_modules/@microsoft/rush-lib/dist/commons.js:17752:27)
rush build - Errors! (0.05 seconds)

Error: An error occurred.
    at PhasedScriptAction._executeOperations (/vsts/_work/1/s/common/temp/install-run/@microsoft+rush@5.109.1/node_modules/@microsoft/rush-lib/dist/commons.js:11102:19)
    at async PhasedScriptAction._runInitialPhases (/vsts/_work/1/s/common/temp/install-run/@microsoft+rush@5.109.1/node_modules/@microsoft/rush-lib/dist/commons.js:10872:9)
    at async PhasedScriptAction.runAsync (/vsts/_work/1/s/common/temp/install-run/@microsoft+rush@5.109.1/node_modules/@microsoft/rush-lib/dist/commons.js:10848:13)
    at async RushCommandLineParser.onExecute (/vsts/_work/1/s/common/temp/install-run/@microsoft+rush@5.109.1/node_modules/@rushstack/ts-command-line/lib/providers/CommandLineParser.js:228:13)
    at async RushCommandLineParser._wrapOnExecuteAsync (/vsts/_work/1/s/common/temp/install-run/@microsoft+rush@5.109.1/node_modules/@microsoft/rush-lib/dist/commons.js:5431:9)
    at async RushCommandLineParser.onExecute (/vsts/_work/1/s/common/temp/install-run/@microsoft+rush@5.109.1/node_modules/@microsoft/rush-lib/dist/commons.js:5411:13)
    at async RushCommandLineParser.execute (/vsts/_work/1/s/common/temp/install-run/@microsoft+rush@5.109.1/node_modules/@rushstack/ts-command-line/lib/providers/CommandLineParser.js:101:13)
    at async RushCommandLineParser.execute (/vsts/_work/1/s/common/temp/install-run/@microsoft+rush@5.109.1/node_modules/@microsoft/rush-lib/dist/commons.js:5397:16)

Repro steps

Currently only occurs on a single one of our pipelines. All the others work fine. No devs have complained about their local machines.

Details

• I see this particular error message was added recently with the following cobuild PR on Aug 31st.
• I attempted to temporarily mitigate the problem by disabling the cache but the same error still occurs. [N.B. I tried multiple different ways through ENV vars, but also explicitly setting buildCacheEnabled to false in build-cache.json]

Standard questions

Any tips on how to debug this or information I could supply that would help?

Question	Answer
@microsoft/rush globally installed version?	N/A
rushVersion from rush.json?	5.109.1
useWorkspaces from rush.json?	Not defined
Operating system?	Linux (I think)
Would you consider contributing a PR?	Sure
Node.js version (node -v)?	18.17.1

[benkeen]

Never mind, apologies. We were doing something wild and woolly on that particular pipeline and copying the checked out repo into a separate folder. That was failing to copy over hidden files + this problem appeared after the Rush upgrade. (Amazing it worked before, quite frankly).