-Wfloat-equal produces compiler warning in Mapbox SDK

[leviathan]

Platform:

MacOS high sierra - 10.13.4 (17E202)
Xcode Version 9.3 (9E145)
Carthage 0.29.0

Mapbox SDK version:

Maps SDK for iOS v4.0.0

Steps to trigger behavior

1. Include Mapbox SDK via carthage into the project.
2. In Xcode build settings Treat Warnings as Errors = YES
3. In xcconfig set WARNING_CFLAGS = -Wfloat-equal

Expected behavior

No warning is produced, because float numbers are compared for equality as suggested by Apple (e.g. `fabs(...) & epsilon).

Actual behavior

Compiler warning is produced:

Mapbox.framework/Headers/MGLGeometry.h:33:33: Comparing floating point with == or != is unsafe

[friedbunny]

Thanks for the report — I’m unsure if this warning represents a practical issue, as there’s some dispute about this tricky topic.

As for how MGLCoordinateSpans are generated and used, I think manually input values could be problematic in terms of comparison:

- (void)testCoordinateSpan {
    MGLCoordinateBounds bounds = MGLCoordinateBoundsMake(CLLocationCoordinate2DMake(38.9131982, -77.0325453144239),
                                                         CLLocationCoordinate2DMake(37.7757368, -122.4135302));

    MGLCoordinateSpan span = MGLCoordinateBoundsGetCoordinateSpan(bounds);
    MGLCoordinateSpan expectedSpan = MGLCoordinateSpanMake(-1.1374614, -45.3809848856);

//    error: -[MGLGeometryTests testCoordinateSpan] : ((span.latitudeDelta) equal to (expectedSpan.latitudeDelta)) failed: ("-1.1374614") is not equal to ("-1.1374614")
//    error: -[MGLGeometryTests testCoordinateSpan] : ((span.longitudeDelta) equal to (expectedSpan.longitudeDelta)) failed: ("-45.3809848856") is not equal to ("-45.3809848856")

    expectedSpan = MGLCoordinateSpanMake(-1.1374613999999994, -45.380984885576098);

    XCTAssertEqual(span.latitudeDelta, expectedSpan.latitudeDelta);
    XCTAssertEqual(span.longitudeDelta, expectedSpan.longitudeDelta);

    XCTAssertTrue(MGLCoordinateSpanEqualToCoordinateSpan(span, expectedSpan));

    // ✅
}

... but I don’t think manual input is a use case we’ve ever seen — MGLCoordinateSpan is always generated by the SDK from existing bounds, where full precision is maintained. This isn’t a topic I’m particularly well versed in, though, so perhaps @1ec5 and @julianrex have thoughts.

[1ec5]

MGLCoordinateSpanEqualToCoordinateSpan() is a pretty obscure function provided for completeness rather than a concrete need in the SDK itself. MapKit apparently doesn’t have a corresponding MKCoordinateSpanEqualToCoordinateSpan() function, even though that library uses coordinate spans a lot more heavily than this SDK does.

Some options:

• Introduce an epsilon tolerance into the comparison. Does this change the expected semantics of an “is equal” function?
• Move the implementation of this function into MGLGeometry.mm so that the inlined code doesn’t pollute application targets’ build logs.
• Use a pragma to ignore the warning.

/ref #6060

[leviathan]

Regarding severity, for me this issue is rather low priority.
I did solve it on our end, by "just" removing the -Wfloat-equal warning flag.

For me it would have been helpful to find a hint about this (or other conflicting compiler flags) in the Mapbox docs. So, that I know that the Mapbox SDK is working properly and I don’t get the impression that the SDK version, I’m trying to build is "kaputt".

-Wundef does trigger a compiler error as well, e.g. "TARGET_INTERFACE_BUILDER" not defined".

[stale]

This issue has been automatically detected as stale because it has not had recent activity and will be archived. Thank you for your contributions.