[flang-commits] [flang] [Flang] Add a Fortran Standards Support doc (PR #132195)

[Kelvin Li via flang-commits]

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+<!--===- docs/FortranStandardsSupport.md 
+  
+   Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+   See https://llvm.org/LICENSE.txt for license information.
+   SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+  
+-->
+
+# Flang's Fortran standards support
+
+```{contents}
+---
+local:
+---
+```
+
+This document summarizes Flang's Fortran standards support. The information is only provided as a guideline. The compiler emits
+TODOs/Not Yet Implemented messages for unimplemented features and that should be treated as the authoratative information. 
+Standards support is provided upto Fortran 2008 for now. It will be later extended for Fortran 2018 and Fortran 2023.
+
+The standards support information is provided as a table with three columns that are self explanatory. The Status column uses
+the letters **P**, **Y**, **N** for the various implementation status.
+- **P** : When the implementation is incomplete for a few cases
+- **Y** : When the implementation is complete
+- **N** : When the implementation is absent
+
+Note 1 : No distinction is made between the support in the Parser/Semantics and MLIR or Lowering support.
+Note 2 : Besides the features listed below a few intrinsics like MIN/MAX are not supported for a few cases with CHARACTER type.
+
----------------
kkwli wrote:

Since all the contents in the first three sections are the same, I suggest to consolidate to the `FORTRAN77, Fortran 90 and Fortran 95` section. In addition, if we take Michael's suggestion to populate the `Fortran 2018` and `Fortran 2023` sections, I suggest to re-order the sections to start with `Fortran 2023` first. I think people are more interested in which newer features that flang support nowadays.

https://github.com/llvm/llvm-project/pull/132195