Re: RFC: Named warnings

[DJ Delorie <dj at redhat dot com>]

Why not adopt what CSS and Xt do?  Have a mnemonic but heirarchical
system of naming and categorizing warnings, and let the user specify
any part of the warning to select it?  That automatically segregates
the language front ends, standards, and targets; and gives us grouping
functionality.  It also allows us to isolate the logic for selecting
warnings if we treat them as "just strings" (i.e. allows for future
creation of a ".gccrc").  Example:

Warnings:

	std.c99.proto.missing
	std.c99.proto.cast
	std.c99.proto.implicit
	std.c99.enum.foo
	lang.c++.proto.class
	lang.c.proto.implicit

Command line options (or pragmas):

	-Wproto
	-Wno-class  (no pun intended)
	-Wstd.c99
	-Wno-c.proto

GCC's code would go from this:

	if (warn_missing_protos)
	  warn ("missing prototype: %s", foo);

to this:

	warn ("std.c99.proto.missing", "missing prototype: %s", foo);

Or potentially (although I don't like this idea):

	warn (".proto.missing", "missing prototype: %s", foo);

(so one could say "this warning is independent of standards, langs,
 etc" but let the user use -Wstd.c99 to enable/disable it, if the
 warning is as listed above).

As for telling the user what the warnings are, perhaps a gcc option
"-fverbose-warnings" would add the warning spec to the warning
message?

	foo.c:45: Warning: missing prototype: foo
	foo.c:45: Warning[std.c99.proto.missing]: missing prototype: foo

Also, by specifying the warnings as a string in the warn() call, we
could write software to scan the sources and summarize all the
available warnings.  We could even specify a comment format, to
preceed the first (or main) occurrence of a warn() call, to document
them:

	/* warning[std.c99.proto.missing]
	   ...fill in docs...
	*/

We could also handle the "warning classes" (like -Wextra) in the
isolated logic for managing the warnings, perhaps
with some table like this (ignore the syntax):

	std.extra = {
	  std.c99.enum.foo
	  lang.c.proto.implicit
	}

So then -Wstd.extra (or just -Wextra) would enable those warnings as
if they user had listed them all.