From 10e06da896809607321ea74faa151827eb99dd69 Mon Sep 17 00:00:00 2001
From: Michael Witten <mfwitten@gmail.com>
Date: Thu, 25 Apr 2024 21:21:50 +0000
Subject: [PATCH] build: Tell cmake to set 'rpath' so the installed 'cmark' can
 find 'libcmark.so'

Before this commit, the 'cmark' executable didn't inform the
dynamic linker where to look for the 'libcmark' shared object;
this becomes an irritation when libcmark is installed in an
unorthodox location:

  $ ldd /path/to/installed/files/bin/cmark
          linux-gate.so.1 (0xb7ed7000)
          libcmark.so.0.31.0 => not found
          libc.so.6 => /usr/lib/libc.so.6 (0xb7cf3000)
          /lib/ld-linux.so.2 => /usr/lib/ld-linux.so.2 (0xb7ed8000)

Because of this commit, the cmark executable's 'rpath' setting
(or equivalent) is set upon installation, thereby providing the
required search directory:

  $ ldd /path/to/installed/files/bin/cmark
          linux-gate.so.1 (0xb7ef2000)
          libcmark.so.0.31.0 => /path/to/installed/files/lib/libcmark.so.0.31.0 (0xb7e95000)
          libc.so.6 => /usr/lib/libc.so.6 (0xb7cbc000)
          /lib/ld-linux.so.2 => /usr/lib/ld-linux.so.2 (0xb7ef3000)

There is some intelligence behind whether rpath is set at all:

  * If 'CMAKE_INSTALL_RPATH' is set, then it is used; this
    allows the user to set a single, overriding value in
    the expected way.

  * Otherwise, the base case rpath is determined by the following:

      "${CMAKE_INSTALL_FULL_LIBDIR}"

    If that path is a standard location, then the base case rpath
    is the empty string; otherwise, the base case rpath is that
    path.

  * The cmark executable's rpath is set to the base case rpath.

  * Currently, libcmark's rpath is set to the empty string.

  * In addition, cmake has been instructed to add to each target's
    rpath any directories that it thinks might contain potential
    dependencies from outside the project; most of the time, there
    will be none, and so nothing will be added.

Of course, this will only help on a system that supports an rpath
feature known to cmake; for example, Windows has no such feature,
and so all of this will presumably be ignored when building under
that system.
---
 CMakeLists.txt     | 15 +++++++++++++++
 src/CMakeLists.txt |  3 ++-
 2 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index ce54658c8..262116a1d 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -69,6 +69,21 @@ set(CMAKE_VISIBILITY_INLINES_HIDDEN 1)
 
 set(CMAKE_INCLUDE_CURRENT_DIR ON)
 
+if (DEFINED CMAKE_INSTALL_RPATH)
+  set(Base_rpath "${CMAKE_INSTALL_RPATH}")
+else()
+  if(BUILD_SHARED_LIBS)
+    set(p "${CMAKE_INSTALL_FULL_LIBDIR}")
+    list(FIND CMAKE_PLATFORM_IMPLICIT_LINK_DIRECTORIES "${p}" i)
+    if("${i}" STREQUAL "-1")
+      set(Base_rpath "${p}")
+    endif()
+  endif()
+endif()
+
+# Append non-standard external dependency directories, if any.
+set(CMAKE_INSTALL_RPATH_USE_LINK_PATH TRUE)
+
 # Check integrity of node structure when compiled as debug
 add_compile_options($<$<CONFIG:Debug>:-DCMARK_DEBUG_NODES>)
 
diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index d98a4079e..523b2cb82 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -55,7 +55,8 @@ add_executable(cmark_exe
   main.c)
 cmark_add_compile_options(cmark_exe)
 set_target_properties(cmark_exe PROPERTIES
-  OUTPUT_NAME "cmark")
+  OUTPUT_NAME "cmark"
+  INSTALL_RPATH "${Base_rpath}")
 target_link_libraries(cmark_exe PRIVATE
   cmark)