Add option to fully disable url output (for tests)

[CAD97]

As an example snapshot test:

---
source: tests/snapshots.rs
assertion_line: 30
expression: "crate::target=warn/[0-9]/"
---
tracing_filter::simple::Error::MultipleSlash (https://docs.rs/tracing-filter/0.0.0-dev/tracing-filter/enum.Error.html#variant.MultipleSlash)

  × logging spec has too many `/`s
   ╭────
 1 │ crate::target=warn/[0-9]/
   ·                    ───┬──
   ·                       │ ╰── this `/` is not allowed ...
   ·                       ╰── ... in this regex filter
   ╰────
  help: regex filters may not contain `/`

Because I've used #[diagnostic(url(docsrs))], the docsrs URL is embedded into the diagnostic, and the output is version-dependent. This means that bumping the version number will also require re-blessing all of the snapshot tests with the new version number.

I'm already directly using GraphicalReportHandler to get (hopefully) environment-independent formatting with no ANSI codes

impl fmt::Display for DisplayDiagnostic<'_> {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        miette::GraphicalReportHandler::new_themed(miette::GraphicalTheme::unicode_nocolor())
            .with_links(false)
            .render_report(f, self.0)
            .or_else(|_| write!(f, "failed to pretty-print {:#?}", self.0))
    }
}

but it'd be nice to be able to also completely remove the URL for test purposes.

This would add a new flag to GraphicalReportHandler, with_urls(urls: bool), which would fully disable reporting of Diagnostic::url.

[CAD97]

You can get partway there with a wrapper diagnostic to strip the URLs

#[derive(Debug, Error)]
#[error(transparent)]
struct StripDiagnosticUrl<T>(T);

impl<T: Diagnostic> Diagnostic for StripDiagnosticUrl<T> {
    fn code<'a>(&'a self) -> Option<Box<dyn fmt::Display + 'a>> {
        self.0.code()
    }

    fn severity(&self) -> Option<miette::Severity> {
        self.0.severity()
    }

    fn help<'a>(&'a self) -> Option<Box<dyn fmt::Display + 'a>> {
        self.0.help()
    }

    fn url<'a>(&'a self) -> Option<Box<dyn fmt::Display + 'a>> {
        None
    }

    fn source_code(&self) -> Option<&dyn miette::SourceCode> {
        self.0.source_code()
    }

    fn labels(&self) -> Option<Box<dyn Iterator<Item = miette::LabeledSpan> + '_>> {
        self.0.labels()
    }

    fn related<'a>(&'a self) -> Option<Box<dyn Iterator<Item = &'a dyn miette::Diagnostic> + 'a>> {
        self.0.related()
    }
}

but this doesn't strip the URLs from related diagnostics, and I don't think there's a way to transform Box<dyn Iterator<Item = &'a dyn miette::Diagnostic> + 'a> to strip the URLs from the iterated diagnostics. Specifically, there's no¹ way to produce fn(&dyn miette::Diagnostic) -> &dyn miette::Diagnostic that wraps the diagnostic with a modification.

Footnotes

1. other than Box::leak ↩

[CAD97]

For the purpose of tests, leaking is probably fine, so here's a full interim solution:

#[derive(Debug, Error)]
#[error(transparent)]
struct StripDiagnosticUrl<'a>(&'a dyn Diagnostic);

impl Diagnostic for StripDiagnosticUrl<'_> {
    fn code<'a>(&'a self) -> Option<Box<dyn fmt::Display + 'a>> {
        self.0.code()
    }

    fn severity(&self) -> Option<miette::Severity> {
        self.0.severity()
    }

    fn help<'a>(&'a self) -> Option<Box<dyn fmt::Display + 'a>> {
        self.0.help()
    }

    fn url<'a>(&'a self) -> Option<Box<dyn fmt::Display + 'a>> {
        None
    }

    fn source_code(&self) -> Option<&dyn miette::SourceCode> {
        self.0.source_code()
    }

    fn labels(&self) -> Option<Box<dyn Iterator<Item = miette::LabeledSpan> + '_>> {
        self.0.labels()
    }

    fn related<'a>(&'a self) -> Option<Box<dyn Iterator<Item = &'a dyn miette::Diagnostic> + 'a>> {
        self.0.related().map(
            |iter| -> Box<dyn Iterator<Item = &'a dyn miette::Diagnostic> + 'a> {
                Box::new(
                    // leakage is sad but required to strip URLs from the test output [zkat/miette#136]
                    iter.map(|d| -> &dyn Diagnostic { Box::leak(Box::new(StripDiagnosticUrl(d))) }),
                )
            },
        )
    }
}