FindPNG: Create an imported PNG::PNG target (#15911)

Imported targets are now the recommended way of dealing with external
library dependencies.  Add one for FindPNG and update documentation
accordingly.  Also add a test case activated by CMake_TEST_FindPNG.

3 files changed, 46 insertions, 0 deletions

diff --git a/Tests/FindPNG/CMakeLists.txt b/Tests/FindPNG/CMakeLists.txt
new file mode 100644
index 0000000..c665b67
--- /dev/null
+++ b/Tests/FindPNG/CMakeLists.txt
@@ -0,0 +1,10 @@
+add_test(NAME FindPNG.Test COMMAND
+  ${CMAKE_CTEST_COMMAND} -C $<CONFIGURATION>
+  --build-and-test
+  "${CMake_SOURCE_DIR}/Tests/FindPNG/Test"
+  "${CMake_BINARY_DIR}/Tests/FindPNG/Test"
+  ${build_generator_args}
+  --build-project TestFindPNG
+  --build-options ${build_options}
+  --test-command ${CMAKE_CTEST_COMMAND} -V -C $<CONFIGURATION>
+  )
diff --git a/Tests/FindPNG/Test/CMakeLists.txt b/Tests/FindPNG/Test/CMakeLists.txt
new file mode 100644
index 0000000..ad50011
--- /dev/null
+++ b/Tests/FindPNG/Test/CMakeLists.txt
@@ -0,0 +1,16 @@
+cmake_minimum_required(VERSION 3.4)
+project(TestFindPNG C)
+include(CTest)
+
+find_package(PNG REQUIRED)
+
+add_definitions(-DCMAKE_EXPECTED_PNG_VERSION="${PNG_VERSION_STRING}")
+
+add_executable(test_tgt main.c)
+target_link_libraries(test_tgt PNG::PNG)
+add_test(NAME test_tgt COMMAND test_tgt)
+
+add_executable(test_var main.c)
+target_include_directories(test_var PRIVATE ${PNG_INCLUDE_DIRS})
+target_link_libraries(test_var PRIVATE ${PNG_LIBRARIES})
+add_test(NAME test_var COMMAND test_var)
diff --git a/Tests/FindPNG/Test/main.c b/Tests/FindPNG/Test/main.c
new file mode 100644
index 0000000..27e1478
--- /dev/null
+++ b/Tests/FindPNG/Test/main.c
@@ -0,0 +1,20 @@
+#include <assert.h>
+#include <string.h>
+#include <png.h>
+
+int main()
+{
+  png_uint_32 png_version;
+  char png_version_string[16];
+
+  png_version = png_access_version_number ();
+
+  snprintf (png_version_string, 16, "%i.%i.%i",
+            png_version / 10000,
+            (png_version % 10000) / 100,
+            png_version % 100);
+
+  assert (strcmp(png_version_string, CMAKE_EXPECTED_PNG_VERSION) == 0);
+
+  return 0;
+}