diagnostics: translation infrastructure by davidtwco · Pull Request #95512 · rus...

An implementation of the infrastructure required to have translatable diagnostic messages.

• Introduces a DiagnosticMessage type which can represent both the current non-translatable messages and identifiers for Fluent.
• Modifies current diagnostic API so that existing calls still work but DiagnosticMessages can be provided too.
• Adds support for always loading a "fallback bundle" containing the English diagnostic messages, which are used when a DiagnosticMessage::FluentIdentifier is used in a diagnostic being emitted.
• Adds support for loading a "primary bundle" which contains the user's preferred language translation, and is used preferentially when it contains a diagnostic message being emitted. Primary bundles are loaded either from the path provided to -Ztranslate-alternate-ftl (for testing), or from the sysroot at $sysroot/locale/$locale/*.ftl given a locale with -Ztranslate-lang (which is parsed as a language identifier).
• Adds "diagnostic args" which enable normally-interpolated variables to be made available as variables for Fluent messages to use.
• Updates #[derive(SessionDiagnostic)] so that it can only be used for translatable diagnostics and update the handful of diagnostics which used the derive to be translatable.

For example, the following diagnostic...

#[derive(SessionDiagnostic)]
#[error = "E0195"]
pub struct LifetimesOrBoundsMismatchOnTrait {
    #[message = "lifetime parameters or bounds on {item_kind} `{ident}` do not match the trait declaration"]
    #[label = "lifetimes do not match {item_kind} in trait"]
    pub span: Span,
    #[label = "lifetimes in impl do not match this {item_kind} in trait"]
    pub generics_span: Option<Span>,
    pub item_kind: &'static str,
    pub ident: Ident,
}

...becomes...

#[derive(SessionDiagnostic)]
#[error(code = "E0195", slug = "typeck-lifetimes-or-bounds-mismatch-on-trait")]
pub struct LifetimesOrBoundsMismatchOnTrait {
    #[primary_span]
    #[label]
    pub span: Span,
    #[label = "generics-label"]
    pub generics_span: Option<Span>,
    pub item_kind: &'static str,
    pub ident: Ident,
}

typeck-lifetimes-or-bounds-mismatch-on-trait =
    lifetime parameters or bounds on {$item_kind} `{$ident}` do not match the trait declaration
    .label = lifetimes do not match {$item_kind} in trait
    .generics-label = lifetimes in impl do not match this {$item_kind} in trait

r? @estebank
cc @oli-obk @Manishearth