mark ghc.cabal so that unsuspecting newbies don't try to edit it

[nr]

Please change the configure/build system so that (a) ghc.cabal is not writable and (b) it contains a comment at the top saying that people wishing to add source files to the compiler should extend file ghc.cabal.in and re-run ../configure; they should not edit ghc.cabal directly.

I know of two people who have fallen into this pit; let's not have any more.

[simonmar]

let's do this in the new build system.

[guest]

+ to informative comment

- to unwritable files, they're just annoying (eg: if you want to use rm -r rather than rm -rf because it has warning messages. Or if you know (for whatever reason) that you actually do want to edit ghc.cabal.) It doesn't seem to be the convention to make all generated files unwritable... But others could have a different opinion from me.

-Isaac Dupree

[simonmar]

In the new build system I did this (the patch isn't in HEAD, it came in as part of the "new build system megapatch"):

Fri Apr 24 14:42:07 BST 2009  Simon Marlow <marlowsd@gmail.com>
  * Add warnings to the top of pre-processed files (#3115)
  I tried adding a preamble to the generated versions of these files
  using autoconf, but that turns out not to work very well.  You have to
  generate an intermediate file with the preamble, and then the
  intermediate file doesn't get updated if the original file changes.