[Bug analyzer/94371] New: Macro-printing within diagnostic paths can be very verbose.

[dmalcolm at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94371

            Bug ID: 94371
           Summary: Macro-printing within diagnostic paths can be very
                    verbose.
           Product: gcc
           Version: 10.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: analyzer
          Assignee: dmalcolm at gcc dot gnu.org
          Reporter: dmalcolm at gcc dot gnu.org
  Target Milestone: ---

The default -fdiagnostics-path-format=inline-events prints each macro expansion
for every event in the path that's from a macro expansion.  This can be very
verbose; consider e.g. the krb5 example here:
  https://dmalcolm.fedorapeople.org/gcc/2020-02-28/recvauth.c.html
where there's a:
 #define krb5_xfree(val) free((char *)(val))
The expansion is printed many times:
* for the primary location of each of the two diagnostics
* for events 9, 10, and 11 of the first diagnostic
* for events 9, 10, 12 and 13 of the second diagnostic
i.e. it's printed 4 times for the first diagnostic, and 5 times for the second
diagnostic.

Ideas for making it less verbose:
* only print macro expansions with paths once per path (so in the example it
would print the expansions per primary loc, and once per path)
* only print macro expansions within paths once per diagnostic_group (and not
printing it if the primary location showed it, so in the example it would only
print it per primary loc)
* only once within paths per diagnostic_context (so it the example it would
only print it once)
* or some other kind of consolidation

However, this is a simple macro; it's not clear what we should do with more
complicated macros.  Perhaps do it per token of the macro, so that if we're
exploring control flow within a macro, we show that.