[clang] [llvm] Disable compiling and testing Flang on Clang changes (PR #92740)

[Aaron Ballman via cfe-commits]

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@@ -68,7 +68,7 @@ function compute-projects-to-test() {
       done
     ;;
     clang)
-      for p in clang-tools-extra compiler-rt flang lldb cross-project-tests; do
+      for p in clang-tools-extra compiler-rt lldb cross-project-tests; do
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AaronBallman wrote:

> But what are you arguing about here exactly? What is the core principle to use for testing the monorepo in a premerge context?

I am arguing two things. 1) to solve immediate needs, we need precommit CI to go back to a working state, which it has not been in since the transition to GitHub. This involves disabling tests. 2) to solve long-term needs, we need to rethink how we handle precommit CI because the current strategy of testing everything on every change is expensive and nonfunctional in practice. This patch is about #1 and I would like to see it land ASAP so we can debate the finer points of #2 while the community is not experiencing significant pain.

> What I see on PRs on my side is that it always ends up with the Linux build completing while Windows waits for an agent for hours. Hence "it's a windows problem".

I see the same outcomes you're seeing, but I'm coming from the perspective of seeing how that impacts PRs in general. What I'm seeing, at least in Clang, is that folks are not landing PRs until precommit CI goes green, and so patches have to undergo significantly more churn because of how slow precommit CI is to complete. The problem is that precommit CI is not finishing in a reasonable amount of time. That's not a Windows problem, that's a community problem caused by precommit CI and exacerbated by one part of the project having slow tests on Windows. Claiming it is a Windows problem makes it sound like the issue is with the OS when that's not actually (known to be) the case.

@joker-eph -- I'd like to make sure we're on the same page; this PR has been accepted and is set to be landed sometime soon to ease pain for the community. If you wish to block the PR from landing, please hit Request Changes and explain what you want to see done in order to move the PR forward in a timely manner.

https://github.com/llvm/llvm-project/pull/92740