This issue was originally raised in Bug 1715475:
Based on some experiments, it looks like the extension comparison is case-insensitive (for all platforms), however at least some of the compilers I tested were case-sensitive in their handling of extensions (for example, the Forte compiler will accept a .cpp extension, but will reject a .CPP extension). Should CC-tasks file matching be case-sensitive or case-insensitive? Or should it be determined by the compiler (Windows compilers will probably be case-insensitive, while some Unix compilers will be case-sensitive).
Initial response from carnold:
Looks like a debatable decision down in compiler/AbstractProcessor. Definitely needs to be case-insensitive for the Windows compilers and gcc-like compilers on Windows. Is there a scenario you have where there is, for example, a compiler that handles ".C" and a different compiler that handles ".c" and the current behavior depends on the order of the bids? If there was a file that really wanted ".C" files, it could double its bid which would give it prescendence over a compiler that was just matching ".c". I'd be reluctant to change it until I knew of a harm.