• d-bugmail puremagic.com (58/58) Jun 24 2018 https://issues.dlang.org/show_bug.cgi?id=19021

d-bugmail puremagic.com writes:

https://issues.dlang.org/show_bug.cgi?id=19021

          Issue ID: 19021
           Summary: [REG 2.077] Type merging immutable -> mutable broken
                    in AST
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Severity: regression
          Priority: P1
         Component: dmd
          Assignee: nobody puremagic.com
          Reporter: ibuclaw gdcproject.org

Commit that caused regression.

https://github.com/dlang/dmd/pull/6998/commits/46b0f6b9a2a089ed6dcd106ca03fc7b2e040385d#diff-33cd340a268c63317687a0a372cd3d94L403


It happen that there are two mutable types T that have different deco, but
point to the same immutable!T because of failure to recognize that T and T are
the same type.

---
struct MultiwayMerge()
{ 
    bool compFront()
    {
        return true;
    }

    struct BinaryHeap(alias less)
    {
        struct Impl
        {
            int _payload;
        }

        void initialize()
        {
            immutable Impl init;
            checkTypes(init);
        }

        void checkTypes(T)(immutable T init)
        {
            alias IT = typeof(init);    // immutable(Impl)
            alias MT = T;               // Impl
            static assert(MT.mangleof ==
"S6setops__T13MultiwayMergeZQq__T10BinaryHeapS_DQBu__TQBqZQBu9compFrontMFNaNbNiNfZbZQBz4Impl");
            static assert(IT.mangleof ==
"yS6setops__T13MultiwayMergeZQq__T10BinaryHeapS_DQBu__TQBqZQBu9compFrontMFNaNbNiNfZbZQBz4Impl");
        }

        // Should be same as MT
        static assert(Impl.mangleof ==
"S6setops__T13MultiwayMergeZQq__T10BinaryHeapS_DQBu__TQBqZQBu9compFrontMFNaNbNiNfZbZQBz4Impl");
    }

    BinaryHeap!(compFront) _heap;
}

MultiwayMerge!() multiwayMerge;

---


What looks to be the case is that mangleToBuffer is called before compFront has
finished its semantic, so the first mutable T does not have pure nothrow  nogc
encoded into its symbol.

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