Add options to run `ldd -u -r` as a "link-what-you-use" tool

Create a LINK_WHAT_YOU_USE target property and corresponding
CMAKE_LINK_WHAT_YOU_USE variable to enable this behavior.
Extend link commands by running `ldd -u -r` to detect shared
libraries that are linked but not needed.

13 files changed, 62 insertions, 0 deletions

diff --git a/Tests/RunCMake/CMakeLists.txt b/Tests/RunCMake/CMakeLists.txt
index d16e5e7..b6d1c38 100644
--- a/Tests/RunCMake/CMakeLists.txt
+++ b/Tests/RunCMake/CMakeLists.txt
@@ -307,6 +307,14 @@ if(CMAKE_OSX_ARCHITECTURES AND XCODE AND NOT "${XCODE_VERSION}" MATCHES "^[^12]"
 endif()
 
 if("${CMAKE_GENERATOR}" MATCHES "Make|Ninja")
+  if(UNIX AND NOT CYGWIN)
+    execute_process(COMMAND ldd --help
+      OUTPUT_VARIABLE LDD_HELP)
+    if("${LDD_HELP}" MATCHES
+        "(-r, --function-relocs.*process data and function relocations.*-u, --unused.*print unused direct dependencies)")
+      add_RunCMake_test(LinkWhatYouUse)
+    endif()
+  endif()
   add_executable(pseudo_tidy pseudo_tidy.c)
   add_executable(pseudo_iwyu pseudo_iwyu.c)
   add_RunCMake_test(ClangTidy -DPSEUDO_TIDY=$<TARGET_FILE:pseudo_tidy>)
diff --git a/Tests/RunCMake/LinkWhatYouUse/C-Build-stdout.txt b/Tests/RunCMake/LinkWhatYouUse/C-Build-stdout.txt
new file mode 100644
index 0000000..95eafad
--- /dev/null
+++ b/Tests/RunCMake/LinkWhatYouUse/C-Build-stdout.txt
@@ -0,0 +1,2 @@
+.*Warning: Unused direct dependencies.*
+.*libm.*
diff --git a/Tests/RunCMake/LinkWhatYouUse/C-launch-Build-stdout.txt b/Tests/RunCMake/LinkWhatYouUse/C-launch-Build-stdout.txt
new file mode 100644
index 0000000..95eafad
--- /dev/null
+++ b/Tests/RunCMake/LinkWhatYouUse/C-launch-Build-stdout.txt
@@ -0,0 +1,2 @@
+.*Warning: Unused direct dependencies.*
+.*libm.*
diff --git a/Tests/RunCMake/LinkWhatYouUse/C-launch.cmake b/Tests/RunCMake/LinkWhatYouUse/C-launch.cmake
new file mode 100644
index 0000000..e66ca20
--- /dev/null
+++ b/Tests/RunCMake/LinkWhatYouUse/C-launch.cmake
@@ -0,0 +1,3 @@
+set(CTEST_USE_LAUNCHERS 1)
+include(CTestUseLaunchers)
+include(C.cmake)
diff --git a/Tests/RunCMake/LinkWhatYouUse/C.cmake b/Tests/RunCMake/LinkWhatYouUse/C.cmake
new file mode 100644
index 0000000..4c3f428
--- /dev/null
+++ b/Tests/RunCMake/LinkWhatYouUse/C.cmake
@@ -0,0 +1,4 @@
+enable_language(C)
+set(CMAKE_LINK_WHAT_YOU_USE TRUE)
+add_executable(main main.c)
+target_link_libraries(main m)
diff --git a/Tests/RunCMake/LinkWhatYouUse/CMakeLists.txt b/Tests/RunCMake/LinkWhatYouUse/CMakeLists.txt
new file mode 100644
index 0000000..18dfd26
--- /dev/null
+++ b/Tests/RunCMake/LinkWhatYouUse/CMakeLists.txt
@@ -0,0 +1,3 @@
+cmake_minimum_required(VERSION 3.2)
+project(${RunCMake_TEST} NONE)
+include(${RunCMake_TEST}.cmake)
diff --git a/Tests/RunCMake/LinkWhatYouUse/CXX-Build-stdout.txt b/Tests/RunCMake/LinkWhatYouUse/CXX-Build-stdout.txt
new file mode 100644
index 0000000..95eafad
--- /dev/null
+++ b/Tests/RunCMake/LinkWhatYouUse/CXX-Build-stdout.txt
@@ -0,0 +1,2 @@
+.*Warning: Unused direct dependencies.*
+.*libm.*
diff --git a/Tests/RunCMake/LinkWhatYouUse/CXX-launch-Build-stdout.txt b/Tests/RunCMake/LinkWhatYouUse/CXX-launch-Build-stdout.txt
new file mode 100644
index 0000000..95eafad
--- /dev/null
+++ b/Tests/RunCMake/LinkWhatYouUse/CXX-launch-Build-stdout.txt
@@ -0,0 +1,2 @@
+.*Warning: Unused direct dependencies.*
+.*libm.*
diff --git a/Tests/RunCMake/LinkWhatYouUse/CXX-launch.cmake b/Tests/RunCMake/LinkWhatYouUse/CXX-launch.cmake
new file mode 100644
index 0000000..3002c9d
--- /dev/null
+++ b/Tests/RunCMake/LinkWhatYouUse/CXX-launch.cmake
@@ -0,0 +1,3 @@
+set(CTEST_USE_LAUNCHERS 1)
+include(CTestUseLaunchers)
+include(CXX.cmake)
diff --git a/Tests/RunCMake/LinkWhatYouUse/CXX.cmake b/Tests/RunCMake/LinkWhatYouUse/CXX.cmake
new file mode 100644
index 0000000..9555832
--- /dev/null
+++ b/Tests/RunCMake/LinkWhatYouUse/CXX.cmake
@@ -0,0 +1,4 @@
+enable_language(CXX)
+set(CMAKE_LINK_WHAT_YOU_USE TRUE)
+add_executable(main main.cxx)
+target_link_libraries(main m)
diff --git a/Tests/RunCMake/LinkWhatYouUse/RunCMakeTest.cmake b/Tests/RunCMake/LinkWhatYouUse/RunCMakeTest.cmake
new file mode 100644
index 0000000..897f568
--- /dev/null
+++ b/Tests/RunCMake/LinkWhatYouUse/RunCMakeTest.cmake
@@ -0,0 +1,21 @@
+include(RunCMake)
+
+
+function(run_lwyu lang)
+  # Use a single build tree for tests without cleaning.
+  set(RunCMake_TEST_BINARY_DIR ${RunCMake_BINARY_DIR}/${lang}-build)
+  set(RunCMake_TEST_NO_CLEAN 1)
+  file(REMOVE_RECURSE "${RunCMake_TEST_BINARY_DIR}")
+  file(MAKE_DIRECTORY "${RunCMake_TEST_BINARY_DIR}")
+  run_cmake(${lang})
+
+  set(RunCMake_TEST_OUTPUT_MERGE 1)
+  run_cmake_command(${lang}-Build ${CMAKE_COMMAND} --build .)
+endfunction()
+
+run_lwyu(CXX)
+run_lwyu(C)
+if (NOT RunCMake_GENERATOR STREQUAL "Watcom WMake")
+  run_lwyu(C-launch)
+  run_lwyu(CXX-launch)
+endif()
diff --git a/Tests/RunCMake/LinkWhatYouUse/main.c b/Tests/RunCMake/LinkWhatYouUse/main.c
new file mode 100644
index 0000000..8488f4e
--- /dev/null
+++ b/Tests/RunCMake/LinkWhatYouUse/main.c
@@ -0,0 +1,4 @@
+int main(void)
+{
+  return 0;
+}
diff --git a/Tests/RunCMake/LinkWhatYouUse/main.cxx b/Tests/RunCMake/LinkWhatYouUse/main.cxx
new file mode 100644
index 0000000..f8b643a
--- /dev/null
+++ b/Tests/RunCMake/LinkWhatYouUse/main.cxx
@@ -0,0 +1,4 @@
+int main()
+{
+  return 0;
+}