[Issue 24637] New: [REG 2.104] Cannot insert const/immutable elements into DList

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=24637

          Issue ID: 24637
           Summary: [REG 2.104] Cannot insert const/immutable elements
                    into DList
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Severity: regression
          Priority: P1
         Component: dmd
          Assignee: nobody at puremagic.com
          Reporter: hos at hos.ac

The following code does not compile with DMD >=2.104.2:

```
import std.container : DList;

void main() {
  DList!int D;

  D.insert(1);  // OK

  int i = 2;
  D.insert(i);  // OK

  const c = 3;
  D.insert(c);  // error
  D.insert(c + 1);  // OK
  D.insert(c + c);  // error
}
```

with errors:

```
/usr/include/dmd/phobos/std/algorithm/mutation.d(1469): Error: cannot modify
`const` expression `target`
/usr/include/dmd/phobos/std/algorithm/mutation.d(1265): Error: template
instance `std.algorithm.mutation.moveEmplaceImpl!(const(int))` error
instantiating
/usr/include/dmd/phobos/std/algorithm/mutation.d(1190):        instantiated
from here: `moveImpl!(const(int))`
/usr/include/dmd/phobos/std/container/dlist.d(223):        instantiated from
here: `move!(const(int))`
/usr/include/dmd/phobos/std/container/dlist.d(761):        instantiated from
here: `createNode!(const(int))`
/usr/include/dmd/phobos/std/container/dlist.d(461):        instantiated from
here: `insertBeforeNode!(const(int))`
list_const.d(12):        instantiated from here: `insertBack!(const(int))`
/usr/include/dmd/phobos/std/algorithm/mutation.d(1267): Error: template
instance `std.algorithm.mutation.trustedMoveImpl!(const(int))` error
instantiating
/usr/include/dmd/phobos/std/algorithm/mutation.d(1190):        instantiated
from here: `moveImpl!(const(int))`
/usr/include/dmd/phobos/std/container/dlist.d(223):        instantiated from
here: `move!(const(int))`
/usr/include/dmd/phobos/std/container/dlist.d(761):        instantiated from
here: `createNode!(const(int))`
/usr/include/dmd/phobos/std/container/dlist.d(461):        instantiated from
here: `insertBeforeNode!(const(int))`
list_const.d(12):        instantiated from here: `insertBack!(const(int))`
```

for `D.insert(c);`, or for `D.insert(c + c);` if we comment out the former.

The expected behavior is that the code compiles.

If we replace `DList` with `SList`, it compiles.
If we replace `const` with `immutable`, it gives the same error.
According to run.dlang.io, the code passes with DMD <=2.103.1.

--