Question

I want to modify csharp-mode.el so that it includes the appropriate error regex’s (regexi?) for the .NET csc.exe compiler.

How should a well-behaved progmode do this?

Answer 1

A well-behaved Emacs user should probably add the regexp to compilation-error-regexp-alist-alist and provide the patch to Emacs so it’ll get used by all in subsequent releases.

The variable defined in compile.el and can be found via

M-x find-variable compilation-error-regexp-alist-alist RET

I don’t think it makes sense for the csharp-mode major mode change the regexp. If anything, it should set the local value of compilation-error-regexp-alist to contain the new symbol you added in the ...-alist-alist variable.

That said, it could modify the ...-alist-alist variable by just checking to see if the symbol c# (or whatever you add) is a part of the list already, and add it if not. Note: the compilation-error-regexp-alist is defined apriori, so you’ll want to double check that variable’s contents to ensure it also contains the c# symbol.