[BUG] New terse function syntax requires adding a semicolon after expression

[gregmarr]

Describe the bug
A trailing semicolon is required when dropping the -> _ = from an inline lambda expression used inside a function call.

To Reproduce
Steps to reproduce the behavior:

1. Sample code - distilled down to minimal essentials please

    // okay
    std::transform(a.begin(), a.end(), b.begin(), :(x) -> _ = { return x + 1; });

    // remove "{ return" and "; }", okay
    std::transform(a.begin(), a.end(), b.begin(), :(x) -> _ = x + 1);

    // remove "-> _ =", error: invalid statement encountered inside a compound-statement (at 'x')
    std::transform(a.begin(), a.end(), b.begin(), :(x) x + 1);

    // put back the ";", okay
    std::transform(a.begin(), a.end(), b.begin(), :(x) x + 1;);

2. Command lines including which C++ compiler you are using
   https://www.godbolt.org/z/6T9z4nx88

3. Expected result - what you expected to happen
   Successful compilation.

4. Actual result/error
   error: invalid statement encountered inside a compound-statement (at 'x')

Additional context
#714

[hsutter]

How about that... somehow I had in my head that the ; was always required. I'm a little surprised that the second example works... perhaps it's looking for any valid expression (which would maximally grab as much as could be a valid expression, which could include an expression_statement) rather than specifically an expression-statement.

Well, for the terse syntax I just changed the check to see if there was a valid expression instead of expression-statement and all seems to be well. Let's try it. Saves another character on the tersest syntax...

Also, just to make sure it still works on a non-first argument, this is fine too now with the latest commit above:

main: () = {
    a: std::vector<int> = (1, 2, 3);
    b: std::vector<int> = (7, 8, 9);

    test( :(x) x+1, a, b );

    for b do (e) std::cout << e;
}

test: (c, a, inout b) =
    std::transform(a.begin(), a.end(), b.begin(), c);

Thanks!