[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 Always out of date, always regenerates on every doc build, but it's very cheap. 2.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 GitOrigin-RevId: 263280e39e6d968c9d610df8160dc49b4b62599f
Flang is a ground-up implementation of a Fortran front end written in modern C++. It started off as the f18 project (https://github.com/flang-compiler/f18) with an aim to replace the previous flang project (https://github.com/flang-compiler/flang) and address its various deficiencies. F18 was subsequently accepted into the LLVM project and rechristened as Flang.
Please note that flang is not ready yet for production usage.
Read more about flang in the docs directory. Start with the compiler overview.
To better understand Fortran as a language and the specific grammar accepted by flang, read Fortran For C Programmers and flang's specifications of the Fortran grammar and the OpenMP grammar.
Treatment of language extensions is covered in this document.
To understand the compilers handling of intrinsics, see the discussion of intrinsics.
To understand how a flang program communicates with libraries at runtime, see the discussion of runtime descriptors.
If you're interested in contributing to the compiler, read the style guide and also review how flang uses modern C++ features.
If you are interested in writing new documentation, follow LLVM's Markdown style guide.
Consult the Getting Started with Flang for information on building and running flang.