static if (condition) pragma(msg, "Look, Ma!");

Or static assert().

Note that the compiler already...

...such as `pragma(msg)` and `enum`,
  but not others, such as `static assert`, hence why...

...such as `pragma(msg)` and `enum`,
  but not others, such as `static assert`, hence why...

...mod1;
    pragma(msg, "C");

    static assert(a == "foo");
    static assert(b == "");      // Error: static assert:  "foo...

...3.0f)); // 1077936128u
pragma (msg, bitRepresentation(3.0));  // 4613937818241073152LU

void main()
{
    static assert(bitRepresentation(3...

...Foo : string { bar = "baz" }

pragma(msg, ReplaceType!(char...Enum : string { foo = "Bar" }
    assert(is(ReplaceType!(char...

...pragma Assume has a clear meaning and works fine.

Given that we already have assert...

...string));
    assert(r);
    assert(r.pre == "a*");
    assert...private size_t _offset;

    pragma(inline, true):

        inout...

...string));
    assert(r);
    assert(r.pre == "a*");
    assert...offset;

        auto pre() @trusted
        {
            pragma(inline, true);
            if...

...contracts, out contracts, and assert statements, e.g...end of the message.

pragma(msg) get's...