Source files with .C not indexed.

[janagulo]

Even though the software allows one to add extra extensions manually, which true for above case(see below), source files with the extension(.C) -- note the case, are ignored and thus not indexed.
<source_extensions>
<source_extension>.cpp</source_extension>
<source_extension>.cxx</source_extension>
<source_extension>.cc</source_extension>
<source_extension>.C</source_extension>
</source_extensions>

[egraether]

Fixed with 2018.3.36
The casing is usually ignored, bu this got broken. The other direction still works, so as workaround you can define the extension lowercase .c and then .C file will also get indexed.