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Remove SubdiagMessage in favour of the identical DiagMessage #152351

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Merged
rust-bors merged 1 commit into from
Feb 10, 2026
Merged

Remove SubdiagMessage in favour of the identical DiagMessage #152351

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58 changes: 0 additions & 58 deletions compiler/rustc_error_messages/src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -230,38 +230,6 @@ pub fn fallback_fluent_bundle(
})))
}

/// Abstraction over a message in a subdiagnostic (i.e. label, note, help, etc) to support both
/// translatable and non-translatable diagnostic messages.
///
/// Translatable messages for subdiagnostics are typically attributes attached to a larger Fluent
/// message so messages of this type must be combined with a `DiagMessage` (using
/// `DiagMessage::with_subdiagnostic_message`) before rendering. However, subdiagnostics from
/// the `Subdiagnostic` derive refer to Fluent identifiers directly.
#[rustc_diagnostic_item = "SubdiagMessage"]
pub enum SubdiagMessage {
/// Non-translatable diagnostic message.
Str(Cow<'static, str>),
/// An inline Fluent message. Instances of this variant are generated by the
/// `Subdiagnostic` derive.
Inline(Cow<'static, str>),
}

impl From<String> for SubdiagMessage {
fn from(s: String) -> Self {
SubdiagMessage::Str(Cow::Owned(s))
}
}
impl From<&'static str> for SubdiagMessage {
fn from(s: &'static str) -> Self {
SubdiagMessage::Str(Cow::Borrowed(s))
}
}
impl From<Cow<'static, str>> for SubdiagMessage {
fn from(s: Cow<'static, str>) -> Self {
SubdiagMessage::Str(s)
}
}

/// Abstraction over a message in a diagnostic to support both translatable and non-translatable
/// diagnostic messages.
///
Expand All @@ -281,18 +249,6 @@ pub enum DiagMessage {
}

impl DiagMessage {
/// Given a `SubdiagMessage` which may contain a Fluent attribute, create a new
/// `DiagMessage` that combines that attribute with the Fluent identifier of `self`.
///
/// - If the `SubdiagMessage` is non-translatable then return the message as a `DiagMessage`.
/// - If `self` is non-translatable then return `self`'s message.
pub fn with_subdiagnostic_message(&self, sub: SubdiagMessage) -> Self {
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@nnethercote nnethercote Feb 10, 2026

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This is the heart of the change, right? I.e. this was the main thing that distinguished DiagMessage and SubdiagMessage... I assume the .ftl removal eliminated uses of this method?

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@JonathanBrouwer JonathanBrouwer Feb 10, 2026 •
edited
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Indeed, previously sub-diags like #[help] were allowed to have no slug, and would automatically take the parent DiagMessage's slug and add _help. There was an extra variant for this in SubdiagMessage which was already removed.

After the removal of .ftl files, all sub-diags need to have their own message so this distinction no longer exists

match sub {
SubdiagMessage::Str(s) => DiagMessage::Str(s),
SubdiagMessage::Inline(s) => DiagMessage::Inline(s),
}
}

pub fn as_str(&self) -> Option<&str> {
match self {
DiagMessage::Str(s) => Some(s),
Expand All @@ -317,20 +273,6 @@ impl From<Cow<'static, str>> for DiagMessage {
}
}

/// Translating *into* a subdiagnostic message from a diagnostic message is a little strange - but
/// the subdiagnostic functions (e.g. `span_label`) take a `SubdiagMessage` and the
/// subdiagnostic derive refers to typed identifiers that are `DiagMessage`s, so need to be
/// able to convert between these, as much as they'll be converted back into `DiagMessage`
/// using `with_subdiagnostic_message` eventually. Don't use this other than for the derive.
impl From<DiagMessage> for SubdiagMessage {
fn from(val: DiagMessage) -> Self {
match val {
DiagMessage::Str(s) => SubdiagMessage::Str(s),
DiagMessage::Inline(s) => SubdiagMessage::Inline(s),
}
}
}

/// A span together with some additional data.
#[derive(Clone, Debug)]
pub struct SpanLabel {
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