llvm-project

263280e3 - [cmake][docs] Fix incremental docs builds under deletion and renames (#211411)

[cmake][docs] Fix incremental docs builds under deletion and renames (#211411) Currently clang, flang, and libc all copy documentation from the source tree into the build tree in preparation to build it, usually to create a combined tree that includes generated documentation files, like AttributeReference.md. However, renaming a document and rebuilding without cleaning the docs tree leaves behind stale documentation files that can accumulate. This patch fixes the problem with two build actions: 1. List source documentation files. Always out of date, always regenerates on every doc build, but it's very cheap. 2. Copy all source documents to the output, and delete any file that neither originates from the source directory nor is mentioned as a generated source to preserve. These actions are implemented as CMake script files (`cmake -P`) since they do things not covered by the builtin tools (`cmake -E copy_if_different`). They could be simplified if we were willing to tolerate more process launch overhead, but for something that runs on the critical path to every doc rebuild, I decided it was worth spending lines of CMake script on it. Assisted-by: a coding tool