On Thu, Jun 18, 2015 at 12:57 PM, Patrick Palka <patr...@parcs.ath.cx> wrote: > On Thu, Jun 18, 2015 at 12:31 PM, David Malcolm <dmalc...@redhat.com> wrote: >> On Tue, 2015-06-09 at 13:31 -0400, Patrick Palka wrote: >>> This patch improves the heuristics of the warning in a number of ways. >>> The improvements are hopefully adequately documented in the code >>> comments. >>> >>> The additions to the test case also highlight the improvements. >>> >>> I tested an earlier version of this patch on more than a dozen C code >>> bases. I only found one class of bogus warnings yet emitted, in the >>> libpng and bdwgc projects. These projects have a coding style which >>> indents code inside #ifdefs as if this code was guarded by an if(), e.g. >>> >>> if (foo != 0) >>> x = 10; >>> else // GUARD >>> y = 100; // BODY >>> >>> #ifdef BAR >>> blah (); // NEXT >>> #endif >> >> We have detect_preprocessor_logic which suppresses warnings when there's >> preprocessor logic between BODY_EXPLOC and NEXT_STMT_EXPLOC, for cases >> like this: >> >> if (flagA) >> foo (); >> ^ BODY_EXPLOC >> #if SOME_CONDITION_THAT_DOES_NOT_HOLD >> if (flagB) >> #endif >> bar (); >> ^ NEXT_STMT_EXPLOC >> >> This currently requires that it be multiline preprocessor logic: there >> must be 3 or more lines between BODY_EXPLOC and NEXT_STMT_EXPLOC for >> this rejection heuristic to fire. > > Oh I now see why it requires 3 or more lines: one line each for the > #if, #endif and for the > >> >> Perhaps we could tweak or reuse that heuristic, perhaps if there's an >> entirely blank (or all whitespace) line separating them (given that this >> warning is all about the "look" of the code). > > That makes sense. What about just checking in > detect_preprocessor_logic() if there is > 1 line (instead of >= 3 > lines) between the body and the next statement? When that's the case, > then whatever is in between the start of the body must either be more > of the body (if it's a multi-line compound statement) or whitespace. > In either case we should not warn if the next statement is aligned > with the body.
Actually, the body cannot be a compound statement because (with this patch) we have already bailed out in that case. So if there is > 1 line between the body and the next statement then there must be whitespace... unless there are just more #ifdefs, e.g. if (foo) bar (); #ifdef A #ifdef B baz (); #endif #endif We would want to warn here even though there are 2 lines, not 1 line, in between the body and the next statement. So we still have to directly check for a whitespace line, I think. > Yet we will still rightfully warn on the following > code: > > if (foo) // GUARD > bar (); // BODY > #ifdef BAZ > baz (); // NEXT > #endif > > because there is just one line between the body and the next > statement. The user can add a line between the body and the next > statement to suppress the warning if it's bogus. I meant to say, a (empty) line between the body and the #ifdef. > >> >>> These bogus warnings are pre-existing, however (i.e. not caused by this >>> patch). >> >> (nods) Fixing the false positives from libpng/bdwgc sounds like a >> separate issue and thus a separate patch then. >> >> [...snip...] >> >>