Macro include_optional::include_str_optional

include_str_optional!() { /* proc-macro */ }

Wraps include_str! inside Option.

You should call this macro as include_str_optional!("./path/to/file.txt") (with either an absolute or a relative path).

The macro checks whether a file exists under the given path:

• If the file does exist, the macro emits Some(include_str!("./path/to/file.txt")).
• If the file does not exist, the macro emits None.
• If trying to check the existence of the file resulted in an error (for example, because it is in a directory that the current user does not have read permissions for or because of hardware failure), compilation fails.

Examples

You can use this macro to include metadata from a file, falling back to some default value if the file does not exist.

Consider a file ./metadata_files/file_exists.txt with the content metadata string from file. The file ./metadata_files/file_missing.txt does not exist.

use include_optional::include_str_optional;

static DEFAULT_METADATA: &'static str = "default metadata string";

fn main() {
    let metadata_file_exists: &'static str =
        include_str_optional!("./metadata_files/file_exists.txt").unwrap_or(DEFAULT_METADATA);
    let metadata_file_missing: &'static str =
        include_str_optional!("./metadata_files/file_missing.txt").unwrap_or(DEFAULT_METADATA);

    assert_eq!(metadata_file_exists, "metadata string from file");
    assert_eq!(metadata_file_missing, DEFAULT_METADATA);
}