[Issue 15550] New: [Reg 2.070.0-b1] compile error while testing template constraint

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=15550

          Issue ID: 15550
           Summary: [Reg 2.070.0-b1] compile error while testing template
                    constraint
           Product: D
           Version: D2
          Hardware: x86_64
                OS: All
            Status: NEW
          Severity: regression
          Priority: P1
         Component: dmd
          Assignee: nobody at puremagic.com
          Reporter: code at dawg.eu

cat > bug.d << CODE
struct Vector(T, int N)
{
    void opDispatch(string, U)(U)
    {
    }

}

struct Matrix(T, int R, int C)
{
    Matrix!(T, R, U._C) opBinary(string op, U)(U)
        // this constraint causes a compile error (even though the first test
already fails)
        if (is(typeof(U._isMatrix)) && (U._R == C) && (op == "*"))
    {
        return Matrix!(T, R, U._C)();
    }

    Vector!(T, R) opBinary(string op)(Vector!(T, C) x)
    {
        return Vector!(T, R)();
    }

    enum _R = R;
    enum _C = C;
    enum bool _isMatrix = true;
}

unittest
{
    Matrix!(int, 2, 2) z;
    auto z2 = z * z; // works
    static assert(!is(typeof(Vector!(int, 2)._isMatrix)));
    z * Vector!(int, 2)(); // errors on template constraint
}
CODE

dmd -c -unittest bug
----
math/gfm/math/matrix.d(11): Error: void has no value
math/gfm/math/matrix.d(11): Error: incompatible types for ((opDispatch!"_R") ==
(2)): 'void' and 'int'
----

There is something broken w/ the evaluation of template constraints.
  if (is(typeof(U._isMatrix)) && (U._R == C) && (op == "*"))
In here the IsExp is already false, so the rest shouldn't get evaluated.

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