https://issues.dlang.org/show_bug.cgi?id=22278

          Issue ID: 22278
           Summary: [Conditional Compilation] there should be in and out
                    flags
           Product: D
           Version: D2
          Hardware: x86_64
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P1
         Component: dmd
          Assignee: nobody@puremagic.com
          Reporter: jlourenco5691@gmail.com

Currently, there is no way within the language to check if contracts are being compiled or not. The only way is to use `version(assert)`, which accomplishes that in a way. The problem is if the user runs unit tests in release mode. The assertions are compiled but contracts are not, leading to the failure of all `assertThrown` checks.

There are ways to still compile without failures. DMD has the `check` flag that can override the build mode. To run unit tests in release with `in` contracts on, one can pass `-check=in=on` to the compiler. But this still isn't favorable because the flag isn't shared across compilers. LDC for example has `--enable-preconditions=1`.

Having a language version can standardize this and make it easier when working with this.

I propose implementing the version flags: D_PreConditions and D_PostConditions for `in` and `out` contracts respectively.

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