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

[Mehdi Amini via llvm-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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joker-eph wrote:

This is exactly the same for a lot of dependencies that this file encodes.

The principle here is conservative: if a change to clang *might* affect another project, then it should be tested.
Basically take the finest grain dependency in your head, then collapse the dependency graph per top-level projects.
"clangDriver" and "clangBasic" aren't projects, right now we can only track dependencies at this granularity (patches welcome of course, but that seems hard to keep maintained).

Note the situation is exactly the same for MLIR: Flang uses a small part of MLIR, many dialects are never used by Flang yet we encode the dependency at the granularity of the project.

(the granularity goes both ways also: many tests in Flang don't depend on the clang driver, yet we're still running them because it's really hard to disentangle when the project isn't setup specifically with this in mind)

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