Geany (v1.38 here) already opens the Compiler tab if a build command fails. It is also aware of the lines that denote errors. However, it does not scroll to the first error but simply opens the tab if it's not open and that means that usually(?) it's at the very bottom of the output showing the return value and "Compilation failed." When using the build commands to actually compile something I am almost always interested in seeing the first problem that occurred. So I kept scrolling up which depending on the verbosity of the output is quite ineffective and stupid and I think that is a quite typical task. In some situations, when "misusing" Geany's build system, it might not be the best option but I could not come up with one so far. Therefore, I propose that Geany should jump to the first error when opening the Compiler tab due to a build error.
Thanks to another issue on github I have discovered the `Build/Next Error` functions that can be bound to hotkeys and that's kind of good enough for me but if you don't see any good reasons why it would be unwanted I could take a look into making a PR. It might actually be so trivial for anybody with a prepared build environment for Geany that I wouldn't feel sorry if somebody beat me to it ;)