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CMake: do not expand variables beforehand 

In **general**, variables in `if()` commands should not be expanded
"by hand" before use, because substitution occurs before the `if()`
command is parsed: in practice that means that a command like

	if(${A} STREQUAL "A")

can expand to (depending on the value of A being empty, "B" or "A")

	if( STREQUAL "A")
	if(B STREQUAL "A")
	if(A STREQUAL "A")

Then the `if()` command is processed, leading to:

 - a syntax error
 - comparing the value of variable B against string "A"
 - comparing the value of variable A (it's "A" because that
   is what `${A}` expanded to) against string "A"

This is explained in section *Variable Expansion* of the documentation
of the `if()` command, but keeps tripping people up.
This commit is contained in:
Adriaan de Groot 2021-06-02 10:53:58 +02:00
parent 06747e5924
commit a81a78becd
1 changed files with 1 additions and 1 deletions
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2
CMakeLists.txt
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@ -105,7 +105,7 @@ set_package_properties(OpenGL PROPERTIES DESCRIPTION "The OpenGL libraries"
)
add_feature_info(GLX ${OpenGL_GLX_FOUND} "OpenGL GLX libraries.")
if(OpenGL_GLX_FOUND AND X11_FOUND AND (${Qt5Gui_OPENGL_IMPLEMENTATION} STREQUAL "GL"))
if(OpenGL_GLX_FOUND AND X11_FOUND AND (Qt5Gui_OPENGL_IMPLEMENTATION STREQUAL "GL"))
set(HAVE_GLX 1)
else()
set(HAVE_GLX 0)