Do not initialize non-mocked Dispatchers.Main unnecessarily #4301
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Before this change, the following could happen on the JVM: * `kotlinx.coroutines.test` accesses `Dispatchers.Main` before `setMain` is called. * `Dispatchers.Main` attempts to initialize *some other* Main dispatcher in addition to the `kotlinx-coroutines-test` Main dispatcher, if there is one. * If the `kotlinx-coroutines-android` artifact is present + its R8 rules are used to minify the tests, it's illegal to attempt to fail to create a `Main` dispatcher. `SUPPORT_MISSING = false` ensures that attempting to create a Main dispatcher fails immediately, in the call frame that attempts the creation, not waiting for `Dispatchers.Main` to be meaningfully used. In total, `kotlinx-coroutines-test` + `kotlinx-coroutines-android` + R8 minification of tests leads to some patterns of `kotlinx-coroutines-test` usage to crash. Fixes #4297
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Before this change, the following could happen on the JVM:
kotlinx.coroutines.testaccessesDispatchers.MainbeforesetMainis called.Dispatchers.Mainattempts to initialize some other Main dispatcher in addition to thekotlinx-coroutines-testMain dispatcher, if there is one.kotlinx-coroutines-androidartifact is present + its R8 rules are used to minify the tests, it's illegal to attempt to fail to create aMaindispatcher.SUPPORT_MISSING = falseensures that attempting to create a Main dispatcher fails immediately, in the call frame that attempts the creation, not waiting forDispatchers.Mainto be meaningfully used.In total,
kotlinx-coroutines-test+kotlinx-coroutines-android+ R8 minification of tests leads to some patterns ofkotlinx-coroutines-testusage to crash.Fixes #4297