Use Packet_ROOT to specify the Npcap or WinPcap SDK root directory.

That appears to be the only way to get the CMake that comes with Visual
Studio 2019 to reliably find it when we're working entirely through the
IDE.  I also infer that it might be what the CMake developers intend to
be the way to externally specify where to find a package.

(cherry picked from commit e230d63c8af6bfc5c85e15d1341be3258d60fb8c)

3 files changed, 17 insertions, 10 deletions

diff --git a/.appveyor.yml b/.appveyor.yml
index a644151c..ccf96c4f 100644
--- a/.appveyor.yml
+++ b/.appveyor.yml
@@ -32,5 +32,5 @@ build_script:
   - type NUL >.devel
   - md build
   - cd build
-  - cmake -DCMAKE_PREFIX_PATH=c:\projects\libpcap\Win32\%SDK% -G"%GENERATOR%" ..
+  - cmake -DPacket_ROOT=c:\projects\libpcap\Win32\%SDK% -G"%GENERATOR%" ..
   - msbuild /m /nologo /p:Configuration=Release pcap.sln
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 55b93f14..08025c8b 100644..100755
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -9,6 +9,16 @@ if(POLICY CMP0042)
     cmake_policy(SET CMP0042 OLD)
 endif()
 
+#
+# We want find_file() and find_library() to honor {packagename}_ROOT,
+# as that appears to be the only way, with the Visual Studio 2019 IDE
+# and its CMake support, to tell CMake where to look for the Npcap
+# or WinPcap SDK.
+#
+if(POLICY CMP0074)
+    cmake_policy(SET CMP0074 NEW)
+endif()
+
 set(CMAKE_MODULE_PATH ${CMAKE_CURRENT_SOURCE_DIR}/cmake/Modules)
 
 project(pcap)
@@ -107,7 +117,7 @@ if(WIN32)
 endif(WIN32)
 option(BUILD_SHARED_LIBS "Build shared libraries" ON)
 if(WIN32)
-    set(PACKET_DLL_DIR "" CACHE PATH "Path to directory with include and lib subdirectories for packet.dll")
+    set(Packet_ROOT "" CACHE PATH "Path to directory with include and lib subdirectories for packet.dll")
 endif(WIN32)
 
 # To pacify those who hate the protochain instruction
diff --git a/cmake/Modules/FindPacket.cmake b/cmake/Modules/FindPacket.cmake
index f114875b..5c398219 100644
--- a/cmake/Modules/FindPacket.cmake
+++ b/cmake/Modules/FindPacket.cmake
@@ -33,8 +33,7 @@
 # PACKET_LIBRARY         - relative or absolute path to the Packet library to
 #                          link with. An absolute path is will be used if the
 #                          Packet library is not located in the compiler's
-#                          default search path. See e.g. PACKET_DLL_DIR
-#                          variable below.
+#                          default search path.
 
 # PACKET_FOUND           - TRUE if the Packet library *and* header are found.
 #
@@ -42,10 +41,10 @@
 # ================================
 #
 # To tell this module where to look, a user may set the environment variable
-# PACKET_DLL_DIR to point cmake to the *root* of a directory with include and
-# lib subdirectories for packet.dll (e.g WpdPack/npcap-sdk).
-# Alternatively, PACKET_DLL_DIR may also be set from cmake command line or GUI
-# (e.g cmake -DPACKET_DLL_DIR=/path/to/packet [...])
+# Packet_ROOT to point cmake to the *root* of a directory with include and
+@ lib subdirectories for packet.dll (e.g WpdPack or npcap-sdk).
+# Alternatively, Packet_ROOT may also be set from cmake command line or GUI
+# (e.g cmake -DPacket_ROOT=C:\path\to\packet [...])
 #
 
 # The 64-bit Packet.lib is located under /x64
@@ -64,14 +63,12 @@ endif()
 
 # Find the header
 find_path(PACKET_INCLUDE_DIR Packet32.h
-  HINTS "${PACKET_DLL_DIR}" ENV PACKET_DLL_DIR
   PATH_SUFFIXES include Include
 )
 
 # Find the library
 find_library(PACKET_LIBRARY
   NAMES Packet packet
-  HINTS "${PACKET_DLL_DIR}" ENV PACKET_DLL_DIR
 )
 
 # Set PACKET_FOUND to TRUE if PACKET_INCLUDE_DIR and PACKET_LIBRARY are TRUE.