Summary

With this feature, proc macros (like askama::Template) could parse external files and then emit diagnostics with appropriate spans.

Proposed API

Other APIs are possible, but I was thinking of something like this:

impl SourceFile {
    pub fn span(&self) -> Span { ... }
    pub fn contents(&self) -> &str { ... }
    pub fn load(path: &Path) -> Self { ... }
}

I'm not super familiar with the proc_macro API, so feel free to suggest better API designs.

See also

See this discussion on Zulip and this discussion on GitHub for why I think this feature would be useful.