# SE-0196 β€” Compiler Diagnostic Directives **URL:** \ **Category:** Proposal Reviews\ **Created:** [January 24, 2018, 7:40am UTC](https://forums.swift.org/t/se-0196-compiler-diagnostic-directives/8734 "2018-01-24T07:40:39Z")\ **Posts on this page:** 7\ **Page:** 3
**Author:** ![jarod](https://sea2.discourse-cdn.com/swift/user_avatar/forums.swift.org/jarod/32/364_2.png) [@jarod](https://forums.swift.org/u/jarod)\ **Post date:** [January 25, 2018, 8:33pm UTC](https://forums.swift.org/t/se-0196-compiler-diagnostic-directives/8734/41 "2018-01-25T20:33:55Z")
> What is your evaluation of the proposal? +1, I've always wanted a `#warning` directive in Swift. > Is the problem being addressed significant enough to warrant a change to Swift? Yes. There are workarounds, but imo they're cumbersome enough to make this feature important. The workaround I've used is to define a global `TODO` symbol that's flagged as deprecated, so you can reference that symbol to produce a warning. However, this can only be used on lines where a standalone expression is supported, i.e. inside a function body, which is quite limiting. Also, the deprecation warning is semantically incorrect as mentioned above, and you can't specify a message at the call site. `#warning` doesn't have any of these limitations. The other workaround I know of is to use a build script to surface TODO comments as warnings, but it's cumbersome to set this up in every project, and it feels like a hack. Having something standardized and built-in would be very helpful. > Does this proposal fit well with the feel and direction of Swift? I think it does. > If you have used other languages or libraries with a similar feature, how do you feel that this proposal compares to those? It's basically the same as `#warning` / `#error` in ObjC, which worked well imo. > How much effort did you put into your review? A glance, a quick reading, or an in-depth study? Read the full proposal and skimmed the discussion. ---
**Author:** ![Michael\_Ilseman](https://sea2.discourse-cdn.com/swift/user_avatar/forums.swift.org/michael_ilseman/32/44640_2.png) [@Michael\_Ilseman](https://forums.swift.org/u/Michael_Ilseman)\ **Post date:** [January 26, 2018, 1:08am UTC](https://forums.swift.org/t/se-0196-compiler-diagnostic-directives/8734/42 "2018-01-26T01:08:10Z")
Did you consider a #assert, which would be an equivalent of C++'s static\_assert? That could also tip the balance towards explicit parenthesis. ---
**Author:** ![harlanhaskins](https://sea2.discourse-cdn.com/swift/user_avatar/forums.swift.org/harlanhaskins/32/333_2.png) [@harlanhaskins](https://forums.swift.org/u/harlanhaskins)\ **Post date:** [January 26, 2018, 1:10am UTC](https://forums.swift.org/t/se-0196-compiler-diagnostic-directives/8734/43 "2018-01-26T01:10:36Z")
That could be cool for mutually exclusive build configurations, but if we added `#assert`, I’d want `constexpr` 😈 ---
**Author:** ![David\_Moore](https://sea2.discourse-cdn.com/swift/user_avatar/forums.swift.org/david_moore/32/7639_2.png) [@David\_Moore](https://forums.swift.org/u/David_Moore)\ **Post date:** [January 26, 2018, 2:27am UTC](https://forums.swift.org/t/se-0196-compiler-diagnostic-directives/8734/44 "2018-01-26T02:27:28Z")
## What is your evaluation of the proposal? Adding these directives to the Swift compiler will be an excellent addition that has a number of particularly handy use cases. Definitely +1 on this. ## Is the problem being addressed significant enough to warrant a change to Swift? Although this might not be a necessarily essential feature, it's definitely a helpful one that'll hopefully improve code readability and review. ## Does this proposal fit well with the feel and direction of Swift? Since this is a compiler directive there isn't necessarily a Swifty feel to it, but that is to be expected with such a feature. However, that being said, it _does_ fit in well with the feel and direction of existing Swift compiler directives. ## If you have used other languages or libraries with a similar feature, how do you feel that this proposal compares to those? This is very similar to `#pragma` when using Clang (i.e., Objective-C, C++, etc...), so it should be intuitive for developers coming from those languages. It also improves on that syntax by using appropriate language that explicitly describes the purpose of the directive. ## How much effort did you put into your review? I read the entire proposal, in addition to the evolution discussion, and was very excited as this is something that I've felt Swift was missing. ---
**Author:** ![Nathan\_Gray](https://sea2.discourse-cdn.com/swift/user_avatar/forums.swift.org/nathan_gray/32/1598_2.png) [@Nathan\_Gray](https://forums.swift.org/u/Nathan_Gray)\ **Post date:** [January 26, 2018, 8:03pm UTC](https://forums.swift.org/t/se-0196-compiler-diagnostic-directives/8734/45 "2018-01-26T20:03:32Z")
+1 This is a small but significant improvement that will be useful in a variety of contexts. The proposed syntax seems fine to me. ---
**Author:** ![pkirvan](https://avatars.discourse-cdn.com/v4/letter/p/8c91f0/32.png) [@pkirvan](https://forums.swift.org/u/pkirvan)\ **Post date:** [January 28, 2018, 8:42am UTC](https://forums.swift.org/t/se-0196-compiler-diagnostic-directives/8734/46 "2018-01-28T08:42:41Z")
> [@Nevin](#): > > Technically, you can already do that, since β€œ#error” does indeed produce a compiler error. :-) Oh we know. In Swift as it currently exists you can make an error just by typing ljkhhkljahlkh on the line you want the error to be. Sometimes out of desperation I do just that. However, that doesn't cover the usage case of wanting a warning, not an error, so that I can compile and test other things in the mean time. This proposal also offers a much more professional looking way to get the error. πŸ˜€ ---
**Author:** ![tkremenek](https://sea2.discourse-cdn.com/swift/user_avatar/forums.swift.org/tkremenek/32/9115_2.png) [@tkremenek](https://forums.swift.org/u/tkremenek)\ **Post date:** [February 2, 2018, 12:27am UTC](https://forums.swift.org/t/se-0196-compiler-diagnostic-directives/8734/47 "2018-02-02T00:27:13Z")
## Review accepted with slight revision On February 1, 2018 the Core Team decided to **accept** this proposal with slight revision over the [original proposal](https://github.com/apple/swiftevolution/blob/ab0c22a2340be9bfcb82e6f237752b4d959a93b7/proposals/0196-diagnostic-directives.md). The only revision over the original proposal is to change the syntax to use `#warning()` instead of `#warning `. This fits well with most of Swift's existing compiler directives, and was strongly supported in the review discussion. The review discussion also covered a variety of possible extensions or variants to this proposal, including support for using `#warning` [as an expression](https://forums.swift.org/t/se-0196-compiler-diagnostic-directives/8734/21) instead of a line directive and [support for runtime issues](https://forums.swift.org/t/se-0196-compiler-diagnostic-directives/8734/6). The Core Team decided that while these directions are interesting and worth exploring, they are complementary to the core functionality serviced by this proposal. Further, keeping `#warning` as a line directive allows it to be used in a wide variety of contexts, and serves a different need than using it as a placeholder expression. [Previous page](https://forums.swift.org/t/se-0196-compiler-diagnostic-directives/8734.md?page=2)