[Issue 24582] New: Detect unsafe casting to bool

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=24582

          Issue ID: 24582
           Summary: Detect unsafe casting to bool
           Product: D
           Version: D2
          Hardware: x86_64
                OS: Linux
            Status: NEW
          Severity: major
          Priority: P1
         Component: dmd
          Assignee: nobody at puremagic.com
          Reporter: nick at geany.org

Given that only 0 and 1 are safe values:
https://dlang.org/spec/function.html#safe-values

Each of the casts below should fail.

void main() @safe
{
    bool v = cast(bool) 2;

    ubyte[] a = [2, 4];
    auto b = cast(bool[]) a;
    auto c = cast(bool[]) [2, 4]; // literal cast
}

PR incoming.

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