Bug 22184 – Template instantiation in static ifs in mutual recursion classes fail

The following code works with dmd 2.096.1 (uses sumtype via dub) but does not work since dmd 2.097.0 (uses sumtype or std.sumtype). I'm not sure it is a regression of std.sumtype or dmd. I tentatively set the `Component` field to `phobos`. run.dang.io - (sumtype): https://run.dlang.io/is/IiGESU - (std.sumtype): https://run.dlang.io/is/j8rqve ```dlang import std.sumtype; class A { SumType!B type; } class B { SumType!C fields; } class C { SumType!(B, int) type; } ``` Error message: ```console /dlang/dmd/linux/bin64/../../src/druntime/import/core/internal/traits.d(191): Error: forward reference of variable `isHashable` /dlang/dmd/linux/bin64/../../src/phobos/std/meta.d(842): Error: template instance `core.internal.traits.allSat!(isHashable, const(B), const(int))` error instantiating /dlang/dmd/linux/bin64/../../src/phobos/std/sumtype.d(771): instantiated from here: `allSatisfy!(isHashable, const(B), const(int))` onlineapp.d(15): instantiated from here: `SumType!(B, int)` /dlang/dmd/linux/bin64/../../src/druntime/import/core/internal/traits.d(191): Error: template instance `std.sumtype.pred!(const(C))` error instantiating /dlang/dmd/linux/bin64/../../src/phobos/std/meta.d(842): instantiated from here: `allSat!(isHashable, const(C))` /dlang/dmd/linux/bin64/../../src/phobos/std/sumtype.d(771): instantiated from here: `allSatisfy!(isHashable, const(C))` onlineapp.d(10): instantiated from here: `SumType!(C)` /dlang/dmd/linux/bin64/../../src/druntime/import/core/internal/traits.d(191): Error: template instance `std.sumtype.pred!(const(B))` error instantiating /dlang/dmd/linux/bin64/../../src/phobos/std/meta.d(842): instantiated from here: `allSat!(isHashable, const(B))` /dlang/dmd/linux/bin64/../../src/phobos/std/sumtype.d(771): instantiated from here: `allSatisfy!(isHashable, const(B))` onlineapp.d(5): instantiated from here: `SumType!(B)` ``` Notes: - It works if `A` is not available - It works if `C` has a field whose type is `SumType!B` rather than `SumType!(B, int)`

It works if we declare the classes in the following order: C, A and B. run.dlang.io: https://run.dlang.io/is/qRsc7e

I reduced the above code as follows: run.dlang.io: https://run.dlang.io/is/VZtiPO ```dlang class A { static if (isHashable!B) {} } class B { static if (isHashable!C) {} } class C { static if (isHashable!B && isHashable!int) {} } enum isHashable(T) = __traits(compiles, () { T.init; } ); void main(){} ``` - It compiles successfully if `isHashable` checks `T t;` rather than `T.init;`

I fixed the issue title and the `Component` section because it is a issue of dmd rather than std.sumtype.

Sorry, I found that I made an inappropriate reproducible code for the issue. The first example fails both of dmd 2.096.1 and dmd 2.097.0. Please close this issue as invalid.

Even if it's not a regression, it's still a valid issue. I'll change the category to "normal" and leave it open for now. Possibly related to issue 20443.

I close this issue because the first example now works with dmd 2.100.2. However, the reduced example still does not work. I will make a comment about the reduced case to the issue 20443 instead of keep open this issue.