From 734fb2c811cdb0c26153c2bd5b62e458343963e7 Mon Sep 17 00:00:00 2001
From: sfan5 <sfan5@live.de>
Date: Wed, 28 Apr 2021 08:38:18 +0200
Subject: Add helpful error messages if Irrlicht library / include dir are set
 incorrectly (#11232)

---
 cmake/Modules/FindIrrlicht.cmake | 20 +++++++++++++++++---
 1 file changed, 17 insertions(+), 3 deletions(-)

diff --git a/cmake/Modules/FindIrrlicht.cmake b/cmake/Modules/FindIrrlicht.cmake
index bb501b3b4..058e93878 100644
--- a/cmake/Modules/FindIrrlicht.cmake
+++ b/cmake/Modules/FindIrrlicht.cmake
@@ -1,5 +1,5 @@
 
-mark_as_advanced(IRRLICHT_LIBRARY IRRLICHT_INCLUDE_DIR IRRLICHT_DLL)
+mark_as_advanced(IRRLICHT_DLL)
 
 # Find include directory and libraries
 
@@ -29,8 +29,22 @@ foreach(libname IN ITEMS IrrlichtMt Irrlicht)
 	endif()
 endforeach()
 
-# Users will likely need to edit these
-mark_as_advanced(CLEAR IRRLICHT_LIBRARY IRRLICHT_INCLUDE_DIR)
+# Handholding for users
+if(IRRLICHT_INCLUDE_DIR AND (NOT IS_DIRECTORY "${IRRLICHT_INCLUDE_DIR}" OR
+	NOT EXISTS "${IRRLICHT_INCLUDE_DIR}/irrlicht.h"))
+	message(WARNING "IRRLICHT_INCLUDE_DIR was set to ${IRRLICHT_INCLUDE_DIR} "
+		"but irrlicht.h does not exist inside. The path will not be used.")
+	unset(IRRLICHT_INCLUDE_DIR CACHE)
+endif()
+if(WIN32 OR CMAKE_SYSTEM_NAME STREQUAL "Linux" OR APPLE)
+	# (only on systems where we're sure how a valid library looks like)
+	if(IRRLICHT_LIBRARY AND (IS_DIRECTORY "${IRRLICHT_LIBRARY}" OR
+		NOT IRRLICHT_LIBRARY MATCHES "\\.(a|so|dylib|lib)([.0-9]+)?$"))
+		message(WARNING "IRRLICHT_LIBRARY was set to ${IRRLICHT_LIBRARY} "
+			"but is not a valid library file. The path will not be used.")
+		unset(IRRLICHT_LIBRARY CACHE)
+	endif()
+endif()
 
 # On Windows, find the DLL for installation
 if(WIN32)
-- 
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