support for headers in a split prefix broken between 1.2.1 and 1.2.2

[vcunat]

In NixPkgs/NixOS we often put headers into a different prefix than libraries. But that broke for snappy when we attempted upgrade from 1.2.1 to 1.2.2.

In lib/cmake/Snappy/SnappyTargets.cmake this update added an INTERFACE_SOURCES line that assumes everything is in a single prefix. That's incorrect in our case and then (some) dependents would fail to find (some of) the headers.

I looked briefly into your sources and diff between the releases, but I have no idea how this difference originated. I can (try to) provide more info in you tell me what.

[trofi]

The regression bisected down to a688be4

[trofi]

I wonder if $<$<VERSION_GREATER:CMAKE_VERSION,3.2>:PUBLIC> should have been $<$<VERSION_GREATER:$<CMAKE_VERSION>,3.2>:PUBLIC> and it did nothing until the change. But I don't really know cmake. /cc @gruenich

[gruenich]

What happens when you remove the PUBLIC? Does this fix your issue?

Can you share the generated commands (using make VERBOSE=ON or similar) with and without the change?

[trofi]

Yeah, removing PUBLIC as below fixes arrow/cpp project build in nixpkgs:

--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -261,7 +261,6 @@ target_sources(snappy
     "snappy-stubs-internal.cc"
     "snappy.cc"
     "${PROJECT_BINARY_DIR}/config.h"
-  PUBLIC
     $<BUILD_INTERFACE:${PROJECT_SOURCE_DIR}/snappy-c.h>
     $<INSTALL_INTERFACE:include/snappy-c.h>
     $<BUILD_INTERFACE:${PROJECT_SOURCE_DIR}/snappy-sinksource.h>

Attaching both build logs for snappy with and without the patch:

• snappy-good.log.txt
• snappy-bad.log.txt

Both look identical (up to the target hashes)

[trofi]

The diff of generated lib/cmake/Snappy/SnappyTargets.cmake file:

diff -u <(cat /nix/store/01jb2nzykl5sv5j566v65r08qgjwjdh9-snappy-1.2.1-dev/lib/cmake/Snappy/SnappyTargets.cmake | unnix) <(cat /nix/store/mfviv2ysgxf3zbsipfr581wjmw2y7lpx-snappy-1.2.1-dev/lib/cmake/Snappy/SnappyTargets.cmake | unnix)
--- /dev/fd/63  2025-05-11 19:08:35.959094091 +0100
+++ /dev/fd/62  2025-05-11 19:08:35.959094091 +0100
@@ -1,13 +1,13 @@
 # Generated by CMake

 if("${CMAKE_MAJOR_VERSION}.${CMAKE_MINOR_VERSION}" LESS 2.8)
-   message(FATAL_ERROR "CMake >= 2.8.3 required")
+   message(FATAL_ERROR "CMake >= 3.1.0 required")
 endif()
-if(CMAKE_VERSION VERSION_LESS "2.8.3")
-   message(FATAL_ERROR "CMake >= 2.8.3 required")
+if(CMAKE_VERSION VERSION_LESS "3.1.0")
+   message(FATAL_ERROR "CMake >= 3.1.0 required")
 endif()
 cmake_policy(PUSH)
-cmake_policy(VERSION 2.8.3...3.29)
+cmake_policy(VERSION 3.1.0...3.29)
 #----------------------------------------------------------------
 # Generated CMake target import file.
 #----------------------------------------------------------------
@@ -54,6 +54,7 @@

 set_target_properties(Snappy::snappy PROPERTIES
   INTERFACE_INCLUDE_DIRECTORIES "/<<NIX>>/snappy-1.2.1-dev"
+  INTERFACE_SOURCES "${_IMPORT_PREFIX}/include/snappy-c.h;${_IMPORT_PREFIX}/include/snappy-sinksource.h;${_IMPORT_PREFIX}/include/snappy.h;${_IMPORT_PREFIX}/include/snappy-stubs-public.h"
 )

 # Load information for each installed configuration.

[gruenich]

1. What version of CMake are you using?
2. What do you mean by "In NixPkgs/NixOS we often put headers into a different prefix than libraries."? How do you "put"? By specifing according CMake variables?

[vcunat]

1. 3.31.6 right now by default.

[vcunat]

2. -DCMAKE_INSTALL_INCLUDEDIR=${!outputInclude}/include (and many other similar ones)
   https://github.com/NixOS/nixpkgs/blob/3b0374eb637ce2310218af0f36f4d7b25182ebb3/pkgs/by-name/cm/cmake/setup-hook.sh#L92

[gruenich]

I have no idea. Everything looks fine and should behave like prior to my change.