Teach find_(library|file|path) to get prefixes from PATH (#15370)

The find_package command already knows how to compute installation
prefixes from PATH.  Use the same approach to establish prefixes for
find_library, find_file, and find_path to use to look in directories
like "<prefix>/lib[/<arch>]" and "<prefix>/include" for libraries and
headers.  This will reduce the amount of configuration end users need to
do to establish a work environment rooted under a specific prefix.

Tests/RunCMake/CMakeLists.txt

@@ -131,8 +131,10 @@ add_RunCMake_test(export)
 add_RunCMake_test(cmake_minimum_required)
 add_RunCMake_test(continue)
 add_RunCMake_test(file)
+add_RunCMake_test(find_file)
 add_RunCMake_test(find_library)
 add_RunCMake_test(find_package)
+add_RunCMake_test(find_path)
 add_RunCMake_test(get_filename_component)
 add_RunCMake_test(get_property)
 add_RunCMake_test(if)

Tests/RunCMake/find_file/CMakeLists.txt

@@ -0,0 +1,3 @@
+cmake_minimum_required(VERSION 3.1)
+project(${RunCMake_TEST} NONE)
+include(${RunCMake_TEST}.cmake)

Tests/RunCMake/find_file/PrefixInPATH-stdout.txt

@@ -0,0 +1,4 @@
+-- PrefixInPATH_INCLUDE_DIR='PrefixInPATH_INCLUDE_DIR-NOTFOUND'
+-- PrefixInPATH_INCLUDE_DIR='.*/Tests/RunCMake/find_file/include/PrefixInPATH.h'
+-- PrefixInPATH_INCLUDE_DIR='.*/Tests/RunCMake/find_file/include/PrefixInPATH.h'
+-- PrefixInPATH_INCLUDE_DIR='.*/Tests/RunCMake/find_file/include/PrefixInPATH.h'

Tests/RunCMake/find_file/PrefixInPATH.cmake

@@ -0,0 +1,8 @@
+set(ENV_PATH "$ENV{PATH}")
+foreach(path "/does_not_exist" "" "/bin" "/sbin")
+  unset(PrefixInPATH_INCLUDE_DIR CACHE)
+  set(ENV{PATH} "${CMAKE_CURRENT_SOURCE_DIR}${path}")
+  find_file(PrefixInPATH_INCLUDE_DIR NAMES PrefixInPATH.h)
+  message(STATUS "PrefixInPATH_INCLUDE_DIR='${PrefixInPATH_INCLUDE_DIR}'")
+endforeach()
+set(ENV{PATH} "${ENV_PATH}")

Tests/RunCMake/find_file/RunCMakeTest.cmake

@@ -0,0 +1,3 @@
+include(RunCMake)
+
+run_cmake(PrefixInPATH)

Tests/RunCMake/find_library/PrefixInPATH-stdout.txt

@@ -0,0 +1,4 @@
+-- PrefixInPATH_LIBRARY='PrefixInPATH_LIBRARY-NOTFOUND'
+-- PrefixInPATH_LIBRARY='.*/Tests/RunCMake/find_library/lib/libPrefixInPATH.a'
+-- PrefixInPATH_LIBRARY='.*/Tests/RunCMake/find_library/lib/libPrefixInPATH.a'
+-- PrefixInPATH_LIBRARY='.*/Tests/RunCMake/find_library/lib/libPrefixInPATH.a'

Tests/RunCMake/find_library/PrefixInPATH.cmake

@@ -0,0 +1,11 @@
+list(APPEND CMAKE_FIND_LIBRARY_PREFIXES lib)
+list(APPEND CMAKE_FIND_LIBRARY_SUFFIXES .a)
+
+set(ENV_PATH "$ENV{PATH}")
+foreach(path "/does_not_exist" "" "/bin" "/sbin")
+  unset(PrefixInPATH_LIBRARY CACHE)
+  set(ENV{PATH} "${CMAKE_CURRENT_SOURCE_DIR}${path}")
+  find_library(PrefixInPATH_LIBRARY NAMES PrefixInPATH)
+  message(STATUS "PrefixInPATH_LIBRARY='${PrefixInPATH_LIBRARY}'")
+endforeach()
+set(ENV{PATH} "${ENV_PATH}")

Tests/RunCMake/find_library/RunCMakeTest.cmake

@@ -1,3 +1,4 @@
 include(RunCMake)
 
 run_cmake(Created)
+run_cmake(PrefixInPATH)

Tests/RunCMake/find_path/CMakeLists.txt

@@ -0,0 +1,3 @@
+cmake_minimum_required(VERSION 3.1)
+project(${RunCMake_TEST} NONE)
+include(${RunCMake_TEST}.cmake)

Tests/RunCMake/find_path/PrefixInPATH-stdout.txt

@@ -0,0 +1,4 @@
+-- PrefixInPATH_INCLUDE_DIR='PrefixInPATH_INCLUDE_DIR-NOTFOUND'
+-- PrefixInPATH_INCLUDE_DIR='.*/Tests/RunCMake/find_path/include'
+-- PrefixInPATH_INCLUDE_DIR='.*/Tests/RunCMake/find_path/include'
+-- PrefixInPATH_INCLUDE_DIR='.*/Tests/RunCMake/find_path/include'

Tests/RunCMake/find_path/PrefixInPATH.cmake

@@ -0,0 +1,8 @@
+set(ENV_PATH "$ENV{PATH}")
+foreach(path "/does_not_exist" "" "/bin" "/sbin")
+  unset(PrefixInPATH_INCLUDE_DIR CACHE)
+  set(ENV{PATH} "${CMAKE_CURRENT_SOURCE_DIR}${path}")
+  find_path(PrefixInPATH_INCLUDE_DIR NAMES PrefixInPATH.h)
+  message(STATUS "PrefixInPATH_INCLUDE_DIR='${PrefixInPATH_INCLUDE_DIR}'")
+endforeach()
+set(ENV{PATH} "${ENV_PATH}")

Tests/RunCMake/find_path/RunCMakeTest.cmake

@@ -0,0 +1,3 @@
+include(RunCMake)
+
+run_cmake(PrefixInPATH)