[flang-commits] [flang] [flang][docs] Fix cmake warning when building documentation (PR #175597)

[Tarun Prabhu via flang-commits]

https://github.com/tarunprabhu updated https://github.com/llvm/llvm-project/pull/175597

>From c2336f60c61efc1e7572f3f5f7b1cafb6e9cac47 Mon Sep 17 00:00:00 2001
From: Tarun Prabhu <tarun at lanl.gov>
Date: Mon, 12 Jan 2026 11:00:11 -0700
Subject: [PATCH] [flang][docs] Fix cmake warning when building documentation

CMake issues the following warning when configuring with support for building
documentation enabled.

  Exactly one of PRE_BUILD, PRE_LINK, or POST_BUILD must be given.  Assuming
    POST_BUILD to preserve backward compatibility.

The offending command add_custom_command call in flang/docs/CMakeLists.txt has
been fixed to ensure that this warning is not issued. The comment describing
the purpose of the command was expanded to provide a more detailed explanation
of the command's purpose.
---
 flang/docs/CMakeLists.txt | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/flang/docs/CMakeLists.txt b/flang/docs/CMakeLists.txt
index b183d6add1059..09219b2bad811 100644
--- a/flang/docs/CMakeLists.txt
+++ b/flang/docs/CMakeLists.txt
@@ -129,11 +129,16 @@ if (LLVM_ENABLE_SPHINX)
           "${FLANG_DOCS_HTML_DIR}/FlangCommandLineReference.rst"
         DEPENDS flang-doc gen-FlangCommandLineReference.rst)
 
-      # Run Python preprocessing ONLY for HTML build
-      # This script prepends headers to FIRLangRef.md for proper formatting
-      add_custom_command(TARGET copy-flang-src-docs-html
+      # ${CMAKE_CURRENT_BINARY_DIR}/Dialect/FIRLangRef.md is generated by
+      # mlir-tblgen. The script executed in the command below adds some text to
+      # this document providing a brief overview of its contents in order to
+      # make it a bit more user-friendly. The result is written to
+      # ${FLANG_DOCS_HTML_DIR}/FIRLangRef.md. The original file in
+      # ${CMAKE_CURRENT_BINARY_DIR}/Dialect is *not* modified.
+      add_custom_command(TARGET copy-flang-src-docs-html POST_BUILD
         COMMAND "${Python3_EXECUTABLE}"
-        ARGS "${FLANG_DOCS_HTML_DIR}/FIR/CreateFIRLangRef.py")
+        ARGS "${FLANG_DOCS_HTML_DIR}/FIR/CreateFIRLangRef.py"
+        BYPRODUCTS ${FLANG_DOCS_HTML_DIR}/FIRLangRef.md)
 
       add_sphinx_target(html flang SOURCE_DIR "${FLANG_DOCS_HTML_DIR}")
       add_dependencies(docs-flang-html copy-flang-src-docs-html)