Only the first macro expansion of an `include!`d file is expanded.

[emilio]

If you have a file that invokes a macro and you include! it, the following happens:

main.rs

fn main() {
    macro_rules! my_macro {
        ($name:expr) => {{
            printn!("{}", $name);
        }}
    }

    include!("helper.rs");
}

helper.rs

my_macro!("foo");
my_macro!("bar");

STR

$ rustc main.rs
$ ./main
foo

Expected output

Should print foo and bar, just as if the code would have been inlined.

Tested with latest nightly and stable:

rustc 1.12.0-nightly (080e0e072 2016-08-08)
rustc 1.10.0 (cfcb716cf 2016-07-03)

[TimNN]

This is unrelated to the macros used in the included file, the following exhibits the same problem:

main.rs:

fn print(s: &str) { println!("{}", s); }

fn main() {
    include!("helper.rs");
}

helper.rs:

print("foo");
print("bar");
print("foobar");

It looks like the issue is rather that include! inside of a function expands to the first statement only.

Wrapping the contents of helper.rs in braces prints all three lines.

Also note that the documentation of include! says:

Parse the current given file as an expression.

Thus the current behaviour is probably as documented.

[jonas-schievink]

But the contents of helper.rs aren't a valid expression, it's only valid as a list of statements. Maybe it's parsed as an expression and the remainder is thrown away (like macros used to do)?

[emilio]

Oh I see. If file contents are thrown away though, I think at least a warning would come handy, but yeah, I see now, thanks!

[ExpHP]

Someone reported a similar experience on users, trying to use [include!("path")] to populate an array.

While it doesn't surprise me that the result is limited to a single expression or statement, it seems like there ought to be an error message?

[est31]

Still happens, just ran into this today. Braces can be used as a workaround.

{
print("foo");
print("bar");
print("foobar");
}

cc @jseyfried @nrc