Incorrect handling of nested preprocessor if/else blocks

[albertziegenhagel]

Describe the bug
Given a nested pre-processor block like this:

#if 0
#if 1
#define FOO 1
#endif
#endif

FOO is incorrectly defined to 1. fortls seems to only take the innermost #if into account and ignores that the outer #if statement evaluates to false.

To Reproduce
Given the example above is written to a file pp-nested-if.F90. Executing

python -m fortls --debug_filepath=pp-nested-if.F90 --debug_parser

gives

=== PreProc Pass ===

#if 0 !!! Conditional FALSE(1)
#if 1 !!! Conditional TRUE(2)
#define FOO 1 !!! Define statement(3)
#endif !!! Conditional TRUE/END(4)
#endif !!! Conditional FALSE/END(5)

=== Parsing Pass ===

which shows that the line #define FOO 1 is evaluated.

Expected behavior
FOO should not be defined.

Setup information (please complete the following information):

• OS: Windows
• Python Version 3.11
• fortls Version 3.1.1.dev