Re: [PR] AVRO-4171: [c++] find system installed fmt first [avro]

["KalleOlaviNiemitalo (via GitHub)" <gi...@apache.org>]

KalleOlaviNiemitalo commented on code in PR #3447:
URL: https://github.com/apache/avro/pull/3447#discussion_r2249153168


##########
lang/c++/CMakeLists.txt:
##########
@@ -79,15 +79,18 @@ if (AVRO_BUILD_TESTS OR AVRO_USE_BOOST)
     find_package (Boost 1.70 REQUIRED CONFIG COMPONENTS system)
 endif ()
 
-include(FetchContent)
-FetchContent_Declare(
-        fmt
-        GIT_REPOSITORY  https://github.com/fmtlib/fmt.git
-        GIT_TAG         10.2.1
-        GIT_PROGRESS    TRUE
-        USES_TERMINAL_DOWNLOAD TRUE
-)
-FetchContent_MakeAvailable(fmt)
+find_package(fmt)
+if (NOT fmt_FOUND)
+    include(FetchContent)
+    FetchContent_Declare(
+            fmt
+            GIT_REPOSITORY  https://github.com/fmtlib/fmt.git
+            GIT_TAG         10.2.1
+            GIT_PROGRESS    TRUE
+            USES_TERMINAL_DOWNLOAD TRUE
+    )
+    FetchContent_MakeAvailable(fmt)
+endif (NOT fmt_FOUND)

Review Comment:
   Most other `endif` lines in this file don't repeat the condition.  According to <https://cmake.org/cmake/help/v3.14/command/if.html> and <https://cmake.org/cmake/help/v3.14/command/endif.html>, repeating the condition has been "legacy" and "supported for backward compatibility only" since CMake 3.14, and was already optional in CMake 3.0.
   
   However, two other `endif` lines in this file do repeat the condition, so the style is already inconsistent.
   
   It's not important to me what you choose here, but it caught my eye and I was curious about CMake best practices.



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