[Issue 19777] New: [REG2.086a] SortedRange.opSlice is wrongly `@trusted`

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=19777

          Issue ID: 19777
           Summary: [REG2.086a] SortedRange.opSlice is wrongly `@trusted`
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Severity: regression
          Priority: P1
         Component: phobos
          Assignee: nobody at puremagic.com
          Reporter: ag0aep6g at gmail.com

The following code used to be rejected correctly (up to 2.085). It compiles
with git master (3b4ec9299). Introduced in
<https://github.com/dlang/phobos/pull/6866>.

----
import std.range: SortedRange;

struct R
{
    int[] a;

    @safe
    {
        @property bool empty() { return a.length == 0; }
        @property ref int front() { return a[0]; }
        @property ref int back() { return a[$ - 1]; }
        void popFront() { a = a[1 .. $]; }
        void popBack() { a = a[0 .. $ - 1]; }
        @property R save() { return this; }
        ref int opIndex(size_t i) { return a[i]; }
        size_t length() { return a.length; }
    }

    R opSlice(size_t x, size_t y) @system
    {
        import core.stdc.stdio;
        printf("This is @system code.\n");
        return R(a[x .. y]);
    }
}

void main() @safe
{
    SortedRange!R s;
    auto sliced = s[0 .. 0];
        /* Prints "This is @system code.". Should fail compilation. */
}
----

--