doxygen -x_noenv option to not expand environment variables

[ferdymercury]

Describe the bug
doxygen -x expands environment variables before doing the 'diff'.

Expected behavior
It would be interesting to have a "-x2" option that does not substitute the environment variables but rather treats them as plain text so that the 'real diff' is shown.

Screenshots
Let's assume an external user is inspecting a 'foreign Doxyfile' and does not have info about whether there are environmental variables defined within (thus, they are undefined in the shell). He gets:

doxygen -x Doxyfile
# Difference with default Doxyfile 1.9.4 (70d1c6baf5107dcfaae6fee02ea6b3ef93cea61c*)

So it's empty, no differences. Versus the manual diff I do normally:

diff Doxyfile Doxyfile.orig
41c41
< PROJECT_NUMBER         = $(SOME_VARIABLE)
---
> PROJECT_NUMBER         =

which shows the difference.

To Reproduce

• doxygen -g
• cp Doxyfile Doxyfile.orig
• Open the generated file and set PROJECT_NUMBER = $(SOME_VARIABLE)
• doxygen -x Doxyfile
• diff Doxyfile Doxyfile.orig

Version
Doxyfile 1.9.4 (70d1c6b*)

[albert-github]

The idea behind doxygen -x is that it gives the differences between the Doxyfile that will be used when running doxygen and the default doxygen settings.
The mentioned idea / use case of having the possibility to retain the original environment settings is not a bad idea, though -x2 probably would be better as -x_noenv.

[albert-github]

I've just pushed a proposed patch, pull request #9189

[ferdymercury]

Thanks for the fix!

[albert-github]

Code has been integrated in master on GitHub (please don't close the issue as this will be done at the moment of an official release).

[doxygen]

This issue was previously marked 'fixed but not released',
which means it should be fixed in doxygen version 1.9.4.
Please verify if this is indeed the case. Reopen the
issue if you think it is not fixed and please include any additional information
that you think can be relevant (preferably in the form of a self-contained example).