Generate lint diagnostic message from BuiltinLintDiag

Translation of the lint message happens when the actual diagnostic is
created, not when the lint is buffered. Generating the message from
BuiltinLintDiag ensures that all required data to construct the message
is preserved in the LintBuffer, eventually allowing the messages to be
moved to fluent.

Remove the `msg` field from BufferedEarlyLint, it is either generated
from the data in the BuiltinLintDiag or stored inside
BuiltinLintDiag::Normal.

compiler/rustc_ast_passes/messages.ftl

@@ -55,9 +55,6 @@ ast_passes_const_without_body =
 ast_passes_constraint_on_negative_bound =
     associated type constraints not allowed on negative bounds
 
-ast_passes_deprecated_where_clause_location =
-    where clause not allowed here
-
 ast_passes_equality_in_where = equality constraints are not yet supported in `where` clauses
     .label = not supported
     .suggestion = if `{$ident}` is an associated type you're trying to set, use the associated type binding syntax
@@ -80,8 +77,6 @@ ast_passes_extern_types_cannot = `type`s inside `extern` blocks cannot have {$de
     .suggestion = remove the {$remove_descr}
     .label = `extern` block begins here
 
-ast_passes_extern_without_abi = extern declarations without an explicit ABI are deprecated
-
 ast_passes_feature_on_non_nightly = `#![feature]` may not be used on the {$channel} release channel
     .suggestion = remove the attribute
     .stable_since = the feature `{$name}` has been stable since `{$since}` and no longer requires an attribute to enable

compiler/rustc_ast_passes/src/ast_validation.rs

@@ -27,7 +27,6 @@ use std::ops::{Deref, DerefMut};
 use thin_vec::thin_vec;
 
 use crate::errors;
-use crate::fluent_generated as fluent;
 
 /// Is `self` allowed semantically as the first parameter in an `FnDecl`?
 enum SelfSemantic {
@@ -770,7 +769,6 @@ impl<'a> AstValidator<'a> {
                 MISSING_ABI,
                 id,
                 span,
-                fluent::ast_passes_extern_without_abi,
                 BuiltinLintDiag::MissingAbi(span, abi::Abi::FALLBACK),
             )
         }
@@ -1428,17 +1426,15 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
             Self::check_decl_no_pat(&sig.decl, |span, ident, mut_ident| {
                 if mut_ident && matches!(ctxt, FnCtxt::Assoc(_)) {
                     if let Some(ident) = ident {
-                        let msg = match ctxt {
-                            FnCtxt::Foreign => fluent::ast_passes_pattern_in_foreign,
-                            _ => fluent::ast_passes_pattern_in_bodiless,
-                        };
-                        let diag = BuiltinLintDiag::PatternsInFnsWithoutBody(span, ident);
                         self.lint_buffer.buffer_lint_with_diagnostic(
                             PATTERNS_IN_FNS_WITHOUT_BODY,
                             id,
                             span,
-                            msg,
+                            BuiltinLintDiag::PatternsInFnsWithoutBody {
-                            diag,
+                                span,
+                                ident,
+                                is_foreign: matches!(ctxt, FnCtxt::Foreign),
+                            },
                         )
                     }
                 } else {
@@ -1514,7 +1510,6 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
                 DEPRECATED_WHERE_CLAUSE_LOCATION,
                 item.id,
                 err.span,
-                fluent::ast_passes_deprecated_where_clause_location,
                 BuiltinLintDiag::DeprecatedWhereclauseLocation(sugg),
             );
         }

compiler/rustc_ast_passes/src/errors.rs

@@ -669,6 +669,7 @@ pub struct ConstAndCVariadic {
 
 #[derive(Diagnostic)]
 #[diag(ast_passes_pattern_in_foreign, code = E0130)]
+// FIXME: deduplicate with rustc_lint (`BuiltinLintDiag::PatternsInFnsWithoutBody`)
 pub struct PatternInForeign {
     #[primary_span]
     #[label]
@@ -677,6 +678,7 @@ pub struct PatternInForeign {
 
 #[derive(Diagnostic)]
 #[diag(ast_passes_pattern_in_bodiless, code = E0642)]
+// FIXME: deduplicate with rustc_lint (`BuiltinLintDiag::PatternsInFnsWithoutBody`)
 pub struct PatternInBodiless {
     #[primary_span]
     #[label]

compiler/rustc_attr/src/builtin.rs

@@ -532,11 +532,6 @@ pub fn cfg_matches(
                     UNEXPECTED_CFGS,
                     cfg.span,
                     lint_node_id,
-                    if let Some(value) = cfg.value {
-                        format!("unexpected `cfg` condition value: `{value}`")
-                    } else {
-                        format!("unexpected `cfg` condition value: (none)")
-                    },
                     BuiltinLintDiag::UnexpectedCfgValue(
                         (cfg.name, cfg.name_span),
                         cfg.value.map(|v| (v, cfg.value_span.unwrap())),
@@ -548,7 +543,6 @@ pub fn cfg_matches(
                     UNEXPECTED_CFGS,
                     cfg.span,
                     lint_node_id,
-                    format!("unexpected `cfg` condition name: `{}`", cfg.name),
                     BuiltinLintDiag::UnexpectedCfgName(
                         (cfg.name, cfg.name_span),
                         cfg.value.map(|v| (v, cfg.value_span.unwrap())),

compiler/rustc_builtin_macros/src/deriving/generic/mod.rs

@@ -1625,10 +1625,9 @@ impl<'a> TraitDef<'a> {
                                 BYTE_SLICE_IN_PACKED_STRUCT_WITH_DERIVE,
                                 sp,
                                 ast::CRATE_NODE_ID,
-                                format!(
+                                rustc_lint_defs::BuiltinLintDiag::ByteSliceInPackedStructWithDerive {
-                                    "{ty} slice in a packed struct that derives a built-in trait"
+                                    ty: ty.to_string(),
-                                ),
+                                },
-                                rustc_lint_defs::BuiltinLintDiag::ByteSliceInPackedStructWithDerive,
                             );
                         } else {
                             // Wrap the expression in `{...}`, causing a copy.

compiler/rustc_builtin_macros/src/format.rs

@@ -556,7 +556,6 @@ fn make_format_args(
             let arg_name = args.explicit_args()[index].kind.ident().unwrap();
             ecx.buffered_early_lint.push(BufferedEarlyLint {
                 span: arg_name.span.into(),
-                msg: format!("named argument `{}` is not used by name", arg_name.name).into(),
                 node_id: rustc_ast::CRATE_NODE_ID,
                 lint_id: LintId::of(NAMED_ARGUMENTS_USED_POSITIONALLY),
                 diagnostic: BuiltinLintDiag::NamedArgumentUsedPositionally {

compiler/rustc_expand/src/base.rs

@@ -1370,7 +1370,6 @@ fn pretty_printing_compatibility_hack(item: &Item, sess: &Session) -> bool {
                                         PROC_MACRO_BACK_COMPAT,
                                         item.ident.span,
                                         ast::CRATE_NODE_ID,
-                                        "using an old version of `rental`",
                                         BuiltinLintDiag::ProcMacroBackCompat(
                                         "older versions of the `rental` crate will stop compiling in future versions of Rust; \
                                         please update to `rental` v0.5.6, or switch to one of the `rental` alternatives".to_string()

compiler/rustc_expand/src/expand.rs

@@ -1803,7 +1803,6 @@ impl<'a, 'b> InvocationCollector<'a, 'b> {
                     UNUSED_DOC_COMMENTS,
                     current_span,
                     self.cx.current_expansion.lint_node_id,
-                    "unused doc comment",
                     BuiltinLintDiag::UnusedDocComment(attr.span),
                 );
             } else if rustc_attr::is_builtin_attr(attr) {
@@ -1815,7 +1814,6 @@ impl<'a, 'b> InvocationCollector<'a, 'b> {
                         UNUSED_ATTRIBUTES,
                         attr.span,
                         self.cx.current_expansion.lint_node_id,
-                        format!("unused attribute `{attr_name}`"),
                         BuiltinLintDiag::UnusedBuiltinAttribute {
                             attr_name,
                             macro_name: pprust::path_to_string(&call.path),

compiler/rustc_expand/src/mbe/macro_rules.rs

@@ -83,7 +83,6 @@ impl<'a> ParserAnyMacro<'a> {
                     SEMICOLON_IN_EXPRESSIONS_FROM_MACROS,
                     parser.token.span,
                     lint_node_id,
-                    "trailing semicolon in macro used in expression position",
                     BuiltinLintDiag::TrailingMacro(is_trailing_mac, macro_ident),
                 );
             }
@@ -1158,7 +1157,6 @@ fn check_matcher_core<'tt>(
                             RUST_2021_INCOMPATIBLE_OR_PATTERNS,
                             span,
                             ast::CRATE_NODE_ID,
-                            "the meaning of the `pat` fragment specifier is changing in Rust 2021, which may affect this macro",
                             BuiltinLintDiag::OrPatternsBackCompat(span, suggestion),
                         );
                     }

compiler/rustc_interface/src/util.rs

@@ -409,7 +409,6 @@ pub(crate) fn check_attr_crate_type(
                             lint::builtin::UNKNOWN_CRATE_TYPES,
                             ast::CRATE_NODE_ID,
                             span,
-                            "invalid `crate_type` value",
                             BuiltinLintDiag::UnknownCrateTypes(
                                 span,
                                 "did you mean".to_string(),

compiler/rustc_lint/messages.ftl

@@ -180,6 +180,9 @@ lint_deprecated_lint_name =
     .suggestion = change it to
     .help = change it to {$replace}
 
+lint_deprecated_where_clause_location =
+    where clause not allowed here
+
 lint_diag_out_of_impl =
     diagnostics should only be created in `Diagnostic`/`Subdiagnostic`/`LintDiagnostic` impls
 
@@ -209,6 +212,8 @@ lint_expectation = this lint expectation is unfulfilled
     .note = the `unfulfilled_lint_expectations` lint can't be expected and will always produce this message
     .rationale = {$rationale}
 
+lint_extern_without_abi = extern declarations without an explicit ABI are deprecated
+
 lint_for_loops_over_fallibles =
     for loop over {$article} `{$ty}`. This is more readably written as an `if let` statement
     .suggestion = consider using `if let` to clear intent
@@ -521,6 +526,12 @@ lint_path_statement_drop = path statement drops value
 
 lint_path_statement_no_effect = path statement with no effect
 
+lint_pattern_in_bodiless = patterns aren't allowed in functions without bodies
+    .label = pattern not allowed in function without body
+
+lint_pattern_in_foreign = patterns aren't allowed in foreign function declarations
+    .label = pattern not allowed in foreign function
+
 lint_ptr_null_checks_fn_ptr = function pointers are not nullable, so checking them for null will always return false
     .help = wrap the function pointer inside an `Option` and use `Option::is_none` to check for null pointer value
     .label = expression has type `{$orig_ty}`

compiler/rustc_lint/src/context.rs

@@ -539,12 +539,11 @@ pub trait LintContext {
         &self,
         lint: &'static Lint,
         span: Option<impl Into<MultiSpan>>,
-        msg: impl Into<DiagMessage>,
         decorate: impl for<'a, 'b> FnOnce(&'b mut Diag<'a, ()>),
         diagnostic: BuiltinLintDiag,
     ) {
         // We first generate a blank diagnostic.
-        self.opt_span_lint(lint, span, msg, |db| {
+        self.opt_span_lint(lint, span, diagnostics::builtin_message(&diagnostic), |db| {
             // Now, set up surrounding context.
             diagnostics::builtin(self.sess(), diagnostic, db);
             // Rewrap `db`, and pass control to the user.

compiler/rustc_lint/src/context/diagnostics.rs

@@ -2,7 +2,7 @@
 #![allow(rustc::untranslatable_diagnostic)]
 
 use rustc_ast::util::unicode::TEXT_FLOW_CONTROL_CHARS;
-use rustc_errors::{elided_lifetime_in_path_suggestion, Diag};
+use rustc_errors::{elided_lifetime_in_path_suggestion, pluralize, Diag, DiagMessage};
 use rustc_errors::{Applicability, SuggestionStyle};
 use rustc_middle::middle::stability;
 use rustc_session::lint::BuiltinLintDiag;
@@ -50,7 +50,7 @@ pub(super) fn builtin(sess: &Session, diagnostic: BuiltinLintDiag, diag: &mut Di
                 );
             }
         }
-        BuiltinLintDiag::Normal => (),
+        BuiltinLintDiag::Normal(_) => (),
         BuiltinLintDiag::AbsPathWithModule(span) => {
             let (sugg, app) = match sess.source_map().span_to_snippet(span) {
                 Ok(ref s) => {
@@ -64,7 +64,7 @@ pub(super) fn builtin(sess: &Session, diagnostic: BuiltinLintDiag, diag: &mut Di
             };
             diag.span_suggestion(span, "use `crate`", sugg, app);
         }
-        BuiltinLintDiag::ProcMacroDeriveResolutionFallback(span) => {
+        BuiltinLintDiag::ProcMacroDeriveResolutionFallback { span, .. } => {
             diag.span_label(
                 span,
                 "names from parent modules are not accessible without an explicit import",
@@ -88,16 +88,16 @@ pub(super) fn builtin(sess: &Session, diagnostic: BuiltinLintDiag, diag: &mut Di
         BuiltinLintDiag::UnknownCrateTypes(span, note, sugg) => {
             diag.span_suggestion(span, note, sugg, Applicability::MaybeIncorrect);
         }
-        BuiltinLintDiag::UnusedImports(message, replaces, in_test_module) => {
+        BuiltinLintDiag::UnusedImports { fix_msg, fixes, test_module_span, .. } => {
-            if !replaces.is_empty() {
+            if !fixes.is_empty() {
                 diag.tool_only_multipart_suggestion(
-                    message,
+                    fix_msg,
-                    replaces,
+                    fixes,
                     Applicability::MachineApplicable,
                 );
             }
 
-            if let Some(span) = in_test_module {
+            if let Some(span) = test_module_span {
                 diag.span_help(
                     sess.source_map().guess_head_span(span),
                     "if this is a test module, consider adding a `#[cfg(test)]` to the containing module",
@@ -114,7 +114,7 @@ pub(super) fn builtin(sess: &Session, diagnostic: BuiltinLintDiag, diag: &mut Di
                 );
             }
         }
-        BuiltinLintDiag::DeprecatedMacro(suggestion, span) => {
+        BuiltinLintDiag::DeprecatedMacro { suggestion, span, .. } => {
             stability::deprecation_suggestion(diag, "macro", suggestion, span)
         }
         BuiltinLintDiag::UnusedDocComment(span) => {
@@ -122,7 +122,7 @@ pub(super) fn builtin(sess: &Session, diagnostic: BuiltinLintDiag, diag: &mut Di
             diag.help("to document an item produced by a macro, \
                                   the macro must produce the documentation as part of its expansion");
         }
-        BuiltinLintDiag::PatternsInFnsWithoutBody(span, ident) => {
+        BuiltinLintDiag::PatternsInFnsWithoutBody { span, ident, .. } => {
             diag.span_suggestion(
                 span,
                 "remove `mut` from the parameter",
@@ -148,7 +148,7 @@ pub(super) fn builtin(sess: &Session, diagnostic: BuiltinLintDiag, diag: &mut Di
                 Applicability::MachineApplicable,
             );
         }
-        BuiltinLintDiag::ReservedPrefix(span) => {
+        BuiltinLintDiag::ReservedPrefix(span, _) => {
             diag.span_label(span, "unknown prefix");
             diag.span_suggestion_verbose(
                 span.shrink_to_hi(),
@@ -206,6 +206,7 @@ pub(super) fn builtin(sess: &Session, diagnostic: BuiltinLintDiag, diag: &mut Di
             param_span,
             use_span: Some((use_span, elide)),
             deletion_span,
+            ..
         } => {
             debug!(?param_span, ?use_span, ?deletion_span);
             diag.span_label(param_span, "this lifetime...");
@@ -230,7 +231,9 @@ pub(super) fn builtin(sess: &Session, diagnostic: BuiltinLintDiag, diag: &mut Di
                 diag.multipart_suggestion(msg, suggestions, Applicability::MachineApplicable);
             }
         }
-        BuiltinLintDiag::SingleUseLifetime { param_span: _, use_span: None, deletion_span } => {
+        BuiltinLintDiag::SingleUseLifetime {
+            param_span: _, use_span: None, deletion_span, ..
+        } => {
             debug!(?deletion_span);
             if let Some(deletion_span) = deletion_span {
                 diag.span_suggestion(
@@ -277,7 +280,7 @@ pub(super) fn builtin(sess: &Session, diagnostic: BuiltinLintDiag, diag: &mut Di
                 );
             }
         }
-        BuiltinLintDiag::ByteSliceInPackedStructWithDerive => {
+        BuiltinLintDiag::ByteSliceInPackedStructWithDerive { .. } => {
             diag.help("consider implementing the trait by hand, or remove the `packed` attribute");
         }
         BuiltinLintDiag::UnusedExternCrate { removal_span } => {
@@ -337,7 +340,7 @@ pub(super) fn builtin(sess: &Session, diagnostic: BuiltinLintDiag, diag: &mut Di
                 Applicability::MachineApplicable,
             );
         }
-        BuiltinLintDiag::RedundantImportVisibility { max_vis, span } => {
+        BuiltinLintDiag::RedundantImportVisibility { max_vis, span, .. } => {
             diag.span_note(span, format!("the most public imported item is `{max_vis}`"));
             diag.help(
                 "reduce the glob import's visibility or increase visibility of imported items",
@@ -353,3 +356,122 @@ pub(super) fn builtin(sess: &Session, diagnostic: BuiltinLintDiag, diag: &mut Di
         }
     }
 }
+
+pub(super) fn builtin_message(diagnostic: &BuiltinLintDiag) -> DiagMessage {
+    match diagnostic {
+        BuiltinLintDiag::Normal(msg) => msg.clone(),
+        BuiltinLintDiag::AbsPathWithModule(_) => {
+            "absolute paths must start with `self`, `super`, `crate`, or an \
+                external crate name in the 2018 edition"
+                .into()
+        }
+        BuiltinLintDiag::ProcMacroDeriveResolutionFallback { ns, ident, .. } => {
+            format!("cannot find {} `{}` in this scope", ns.descr(), ident).into()
+        }
+        BuiltinLintDiag::MacroExpandedMacroExportsAccessedByAbsolutePaths(_) => {
+            "macro-expanded `macro_export` macros from the current crate cannot \
+                be referred to by absolute paths"
+                .into()
+        }
+        BuiltinLintDiag::ElidedLifetimesInPaths(_, _, _, _) => {
+            "hidden lifetime parameters in types are deprecated".into()
+        }
+        BuiltinLintDiag::UnknownCrateTypes(_, _, _) => "invalid `crate_type` value".into(),
+        BuiltinLintDiag::UnusedImports { span_snippets, .. } => format!(
+            "unused import{}{}",
+            pluralize!(span_snippets.len()),
+            if !span_snippets.is_empty() {
+                format!(": {}", span_snippets.join(", "))
+            } else {
+                String::new()
+            }
+        )
+        .into(),
+        BuiltinLintDiag::RedundantImport(_, source) => {
+            format!("the item `{source}` is imported redundantly").into()
+        }
+        BuiltinLintDiag::DeprecatedMacro { message, .. } => message.clone().into(),
+        BuiltinLintDiag::MissingAbi(_, _) => crate::fluent_generated::lint_extern_without_abi,
+        BuiltinLintDiag::UnusedDocComment(_) => "unused doc comment".into(),
+        BuiltinLintDiag::UnusedBuiltinAttribute { attr_name, .. } => {
+            format!("unused attribute `{attr_name}`").into()
+        }
+        BuiltinLintDiag::PatternsInFnsWithoutBody { is_foreign, .. } => {
+            if *is_foreign {
+                crate::fluent_generated::lint_pattern_in_foreign
+            } else {
+                crate::fluent_generated::lint_pattern_in_bodiless
+            }
+        }
+        BuiltinLintDiag::LegacyDeriveHelpers(_) => {
+            "derive helper attribute is used before it is introduced".into()
+        }
+        BuiltinLintDiag::ProcMacroBackCompat(_) => "using an old version of `rental`".into(),
+        BuiltinLintDiag::OrPatternsBackCompat(_, _) => {
+            "the meaning of the `pat` fragment specifier is changing in Rust 2021, \
+            which may affect this macro"
+                .into()
+        }
+        BuiltinLintDiag::ReservedPrefix(_, prefix) => {
+            format!("prefix `{prefix}` is unknown").into()
+        }
+        BuiltinLintDiag::TrailingMacro(_, _) => {
+            "trailing semicolon in macro used in expression position".into()
+        }
+        BuiltinLintDiag::BreakWithLabelAndLoop(_) => {
+            "this labeled break expression is easy to confuse with an unlabeled break with a \
+            labeled value expression"
+                .into()
+        }
+        BuiltinLintDiag::UnicodeTextFlow(_, _) => {
+            "unicode codepoint changing visible direction of text present in comment".into()
+        }
+        BuiltinLintDiag::UnexpectedCfgName((name, _), _) => {
+            format!("unexpected `cfg` condition name: `{}`", name).into()
+        }
+        BuiltinLintDiag::UnexpectedCfgValue(_, v) => if let Some((value, _)) = v {
+            format!("unexpected `cfg` condition value: `{value}`")
+        } else {
+            format!("unexpected `cfg` condition value: (none)")
+        }
+        .into(),
+        BuiltinLintDiag::DeprecatedWhereclauseLocation(_) => {
+            crate::fluent_generated::lint_deprecated_where_clause_location
+        }
+        BuiltinLintDiag::SingleUseLifetime { use_span, ident, .. } => {
+            if use_span.is_some() {
+                format!("lifetime parameter `{}` only used once", ident).into()
+            } else {
+                format!("lifetime parameter `{}` never used", ident).into()
+            }
+        }
+        BuiltinLintDiag::NamedArgumentUsedPositionally { named_arg_name, .. } => {
+            format!("named argument `{}` is not used by name", named_arg_name).into()
+        }
+        BuiltinLintDiag::ByteSliceInPackedStructWithDerive { ty } => {
+            format!("{ty} slice in a packed struct that derives a built-in trait").into()
+        }
+        BuiltinLintDiag::UnusedExternCrate { .. } => "unused extern crate".into(),
+        BuiltinLintDiag::ExternCrateNotIdiomatic { .. } => {
+            "`extern crate` is not idiomatic in the new edition".into()
+        }
+        BuiltinLintDiag::AmbiguousGlobImports { diag } => diag.msg.clone().into(),
+        BuiltinLintDiag::AmbiguousGlobReexports { .. } => "ambiguous glob re-exports".into(),
+        BuiltinLintDiag::HiddenGlobReexports { .. } => {
+            "private item shadows public glob re-export".into()
+        }
+        BuiltinLintDiag::UnusedQualifications { .. } => "unnecessary qualification".into(),
+        BuiltinLintDiag::AssociatedConstElidedLifetime { elided, .. } => if *elided {
+            "`&` without an explicit lifetime name cannot be used here"
+        } else {
+            "`'_` cannot be used here"
+        }
+        .into(),
+        BuiltinLintDiag::RedundantImportVisibility { import_vis, .. } => format!(
+            "glob import doesn't reexport anything with visibility `{}` \
+            because no imported item is public enough",
+            import_vis
+        )
+        .into(),
+    }
+}

compiler/rustc_lint/src/early.rs

@@ -44,14 +44,8 @@ impl<'a, T: EarlyLintPass> EarlyContextAndPass<'a, T> {
     #[allow(rustc::diagnostic_outside_of_impl)]
     fn inlined_check_id(&mut self, id: ast::NodeId) {
         for early_lint in self.context.buffered.take(id) {
-            let BufferedEarlyLint { span, msg, node_id: _, lint_id, diagnostic } = early_lint;
+            let BufferedEarlyLint { span, node_id: _, lint_id, diagnostic } = early_lint;
-            self.context.span_lint_with_diagnostics(
+            self.context.span_lint_with_diagnostics(lint_id.lint, Some(span), |_| {}, diagnostic);
-                lint_id.lint,
-                Some(span),
-                msg,
-                |_| {},
-                diagnostic,
-            );
         }
     }
 

compiler/rustc_lint_defs/src/lib.rs

@@ -6,6 +6,7 @@ use rustc_data_structures::stable_hasher::{
     HashStable, StableCompare, StableHasher, ToStableHashKey,
 };
 use rustc_error_messages::{DiagMessage, MultiSpan};
+use rustc_hir::def::Namespace;
 use rustc_hir::HashStableContext;
 use rustc_hir::HirId;
 use rustc_macros::{Decodable, Encodable, HashStable_Generic};
@@ -569,15 +570,28 @@ pub struct AmbiguityErrorDiag {
 // becomes hacky (and it gets allocated).
 #[derive(Debug)]
 pub enum BuiltinLintDiag {
-    Normal,
+    Normal(DiagMessage),
     AbsPathWithModule(Span),
-    ProcMacroDeriveResolutionFallback(Span),
+    ProcMacroDeriveResolutionFallback {
+        span: Span,
+        ns: Namespace,
+        ident: Ident,
+    },
     MacroExpandedMacroExportsAccessedByAbsolutePaths(Span),
     ElidedLifetimesInPaths(usize, Span, bool, Span),
     UnknownCrateTypes(Span, String, String),
-    UnusedImports(String, Vec<(Span, String)>, Option<Span>),
+    UnusedImports {
+        fix_msg: String,
+        fixes: Vec<(Span, String)>,
+        test_module_span: Option<Span>,
+        span_snippets: Vec<String>,
+    },
     RedundantImport(Vec<(Span, bool)>, Ident),
-    DeprecatedMacro(Option<Symbol>, Span),
+    DeprecatedMacro {
+        suggestion: Option<Symbol>,
+        span: Span,
+        message: String,
+    },
     MissingAbi(Span, Abi),
     UnusedDocComment(Span),
     UnusedBuiltinAttribute {
@@ -585,11 +599,15 @@ pub enum BuiltinLintDiag {
         macro_name: String,
         invoc_span: Span,
     },
-    PatternsInFnsWithoutBody(Span, Ident),
+    PatternsInFnsWithoutBody {
+        span: Span,
+        ident: Ident,
+        is_foreign: bool,
+    },
     LegacyDeriveHelpers(Span),
     ProcMacroBackCompat(String),
     OrPatternsBackCompat(Span, String),
-    ReservedPrefix(Span),
+    ReservedPrefix(Span, String),
     TrailingMacro(bool, Ident),
     BreakWithLabelAndLoop(Span),
     UnicodeTextFlow(Span, String),
@@ -605,6 +623,7 @@ pub enum BuiltinLintDiag {
         /// Span of the single use, or None if the lifetime is never used.
         /// If true, the lifetime will be fully elided.
         use_span: Option<(Span, bool)>,
+        ident: Ident,
     },
     NamedArgumentUsedPositionally {
         /// Span where the named argument is used by position and will be replaced with the named
@@ -619,7 +638,10 @@ pub enum BuiltinLintDiag {
         /// Indicates if the named argument is used as a width/precision for formatting
         is_formatting_arg: bool,
     },
-    ByteSliceInPackedStructWithDerive,
+    ByteSliceInPackedStructWithDerive {
+        // FIXME: enum of byte/string
+        ty: String,
+    },
     UnusedExternCrate {
         removal_span: Span,
     },
@@ -661,6 +683,7 @@ pub enum BuiltinLintDiag {
     RedundantImportVisibility {
         span: Span,
         max_vis: String,
+        import_vis: String,
     },
     MaybeTypo {
         span: Span,
@@ -675,9 +698,6 @@ pub struct BufferedEarlyLint {
     /// The span of code that we are linting on.
     pub span: MultiSpan,
 
-    /// The lint message.
-    pub msg: DiagMessage,
-
     /// The `NodeId` of the AST node that generated the lint.
     pub node_id: NodeId,
 
@@ -705,12 +725,10 @@ impl LintBuffer {
         lint: &'static Lint,
         node_id: NodeId,
         span: MultiSpan,
-        msg: impl Into<DiagMessage>,
         diagnostic: BuiltinLintDiag,
     ) {
         let lint_id = LintId::of(lint);
-        let msg = msg.into();
+        self.add_early_lint(BufferedEarlyLint { lint_id, node_id, span, diagnostic });
-        self.add_early_lint(BufferedEarlyLint { lint_id, node_id, span, msg, diagnostic });
     }
 
     pub fn take(&mut self, id: NodeId) -> Vec<BufferedEarlyLint> {
@@ -725,7 +743,7 @@ impl LintBuffer {
         sp: impl Into<MultiSpan>,
         msg: impl Into<DiagMessage>,
     ) {
-        self.add_lint(lint, id, sp.into(), msg, BuiltinLintDiag::Normal)
+        self.add_lint(lint, id, sp.into(), BuiltinLintDiag::Normal(msg.into()))
     }
 
     pub fn buffer_lint_with_diagnostic(
@@ -733,10 +751,9 @@ impl LintBuffer {
         lint: &'static Lint,
         id: NodeId,
         sp: impl Into<MultiSpan>,
-        msg: impl Into<DiagMessage>,
         diagnostic: BuiltinLintDiag,
     ) {
-        self.add_lint(lint, id, sp.into(), msg, diagnostic)
+        self.add_lint(lint, id, sp.into(), diagnostic)
     }
 }
 

compiler/rustc_middle/src/middle/stability.rs

@@ -200,8 +200,8 @@ pub fn early_report_deprecation(
         return;
     }
 
-    let diag = BuiltinLintDiag::DeprecatedMacro(suggestion, span);
+    let diag = BuiltinLintDiag::DeprecatedMacro { suggestion, span, message };
-    lint_buffer.buffer_lint_with_diagnostic(lint, node_id, span, message, diag);
+    lint_buffer.buffer_lint_with_diagnostic(lint, node_id, span, diag);
 }
 
 fn late_report_deprecation(

compiler/rustc_parse/src/lexer/mod.rs

@@ -374,7 +374,6 @@ impl<'psess, 'src> StringReader<'psess, 'src> {
                 TEXT_DIRECTION_CODEPOINT_IN_COMMENT,
                 span,
                 ast::CRATE_NODE_ID,
-                "unicode codepoint changing visible direction of text present in comment",
                 BuiltinLintDiag::UnicodeTextFlow(span, content.to_string()),
             );
         }
@@ -727,8 +726,7 @@ impl<'psess, 'src> StringReader<'psess, 'src> {
                 RUST_2021_PREFIXES_INCOMPATIBLE_SYNTAX,
                 prefix_span,
                 ast::CRATE_NODE_ID,
-                format!("prefix `{prefix}` is unknown"),
+                BuiltinLintDiag::ReservedPrefix(prefix_span, prefix.to_string()),
-                BuiltinLintDiag::ReservedPrefix(prefix_span),
             );
         }
     }

compiler/rustc_parse/src/parser/expr.rs

@@ -1917,7 +1917,6 @@ impl<'a> Parser<'a> {
                         BREAK_WITH_LABEL_AND_LOOP,
                         lo.to(expr.span),
                         ast::CRATE_NODE_ID,
-                        "this labeled break expression is easy to confuse with an unlabeled break with a labeled value expression",
                         BuiltinLintDiag::BreakWithLabelAndLoop(expr.span),
                     );
                 }

compiler/rustc_resolve/src/check_unused.rs

@@ -32,7 +32,7 @@ use rustc_ast as ast;
 use rustc_ast::visit::{self, Visitor};
 use rustc_data_structures::fx::{FxHashMap, FxIndexMap, FxIndexSet};
 use rustc_data_structures::unord::UnordSet;
-use rustc_errors::{pluralize, MultiSpan};
+use rustc_errors::MultiSpan;
 use rustc_hir::def::{DefKind, Res};
 use rustc_session::lint::builtin::{MACRO_USE_EXTERN_CRATE, UNUSED_EXTERN_CRATES};
 use rustc_session::lint::builtin::{UNUSED_IMPORTS, UNUSED_QUALIFICATIONS};
@@ -155,7 +155,6 @@ impl<'a, 'b, 'tcx> UnusedImportCheckVisitor<'a, 'b, 'tcx> {
                         UNUSED_EXTERN_CRATES,
                         extern_crate.id,
                         span,
-                        "unused extern crate",
                         BuiltinLintDiag::UnusedExternCrate {
                             removal_span: extern_crate.span_with_attributes,
                         },
@@ -208,7 +207,6 @@ impl<'a, 'b, 'tcx> UnusedImportCheckVisitor<'a, 'b, 'tcx> {
                 UNUSED_EXTERN_CRATES,
                 extern_crate.id,
                 extern_crate.span,
-                "`extern crate` is not idiomatic in the new edition",
                 BuiltinLintDiag::ExternCrateNotIdiomatic { vis_span, ident_span },
             );
         }
@@ -459,16 +457,6 @@ impl Resolver<'_, '_> {
                 .collect::<Vec<String>>();
             span_snippets.sort();
 
-            let msg = format!(
-                "unused import{}{}",
-                pluralize!(ms.primary_spans().len()),
-                if !span_snippets.is_empty() {
-                    format!(": {}", span_snippets.join(", "))
-                } else {
-                    String::new()
-                }
-            );
-
             let fix_msg = if fixes.len() == 1 && fixes[0].0 == unused.item_span {
                 "remove the whole `use` item"
             } else if ms.primary_spans().len() > 1 {
@@ -505,8 +493,12 @@ impl Resolver<'_, '_> {
                 UNUSED_IMPORTS,
                 unused.use_tree_id,
                 ms,
-                msg,
+                BuiltinLintDiag::UnusedImports {
-                BuiltinLintDiag::UnusedImports(fix_msg.into(), fixes, test_module_span),
+                    fix_msg: fix_msg.into(),
+                    fixes,
+                    test_module_span,
+                    span_snippets,
+                },
             );
         }
 
@@ -556,7 +548,6 @@ impl Resolver<'_, '_> {
                 UNUSED_QUALIFICATIONS,
                 unn_qua.node_id,
                 unn_qua.path_span,
-                "unnecessary qualification",
                 BuiltinLintDiag::UnusedQualifications { removal_span: unn_qua.removal_span },
             );
         }

compiler/rustc_resolve/src/diagnostics.rs

@@ -128,13 +128,10 @@ impl<'a, 'tcx> Resolver<'a, 'tcx> {
         self.report_with_use_injections(krate);
 
         for &(span_use, span_def) in &self.macro_expanded_macro_export_errors {
-            let msg = "macro-expanded `macro_export` macros from the current crate \
-                       cannot be referred to by absolute paths";
             self.lint_buffer.buffer_lint_with_diagnostic(
                 MACRO_EXPANDED_MACRO_EXPORTS_ACCESSED_BY_ABSOLUTE_PATHS,
                 CRATE_NODE_ID,
                 span_use,
-                msg,
                 BuiltinLintDiag::MacroExpandedMacroExportsAccessedByAbsolutePaths(span_def),
             );
         }
@@ -149,7 +146,6 @@ impl<'a, 'tcx> Resolver<'a, 'tcx> {
                     AMBIGUOUS_GLOB_IMPORTS,
                     import.root_id,
                     ambiguity_error.ident.span,
-                    diag.msg.to_string(),
                     BuiltinLintDiag::AmbiguousGlobImports { diag },
                 );
             } else {
@@ -530,8 +526,6 @@ impl<'a, 'tcx> Resolver<'a, 'tcx> {
             ABSOLUTE_PATHS_NOT_STARTING_WITH_CRATE,
             node_id,
             root_span,
-            "absolute paths must start with `self`, `super`, \
-             `crate`, or an external crate name in the 2018 edition",
             diag,
         );
     }

compiler/rustc_resolve/src/ident.rs

@@ -528,14 +528,11 @@ impl<'a, 'tcx> Resolver<'a, 'tcx> {
                                         PROC_MACRO_DERIVE_RESOLUTION_FALLBACK,
                                         lint_id,
                                         orig_ident.span,
-                                        format!(
+                                        BuiltinLintDiag::ProcMacroDeriveResolutionFallback {
-                                            "cannot find {} `{}` in this scope",
+                                            span: orig_ident.span,
-                                            ns.descr(),
+                                            ns,
-                                            ident
+                                            ident,
-                                        ),
+                                        },
-                                        BuiltinLintDiag::ProcMacroDeriveResolutionFallback(
-                                            orig_ident.span,
-                                        ),
                                     );
                                 }
                                 let misc_flags = if module == this.graph_root {

compiler/rustc_resolve/src/imports.rs

@@ -623,7 +623,6 @@ impl<'a, 'tcx> Resolver<'a, 'tcx> {
                             AMBIGUOUS_GLOB_REEXPORTS,
                             import.root_id,
                             import.root_span,
-                            "ambiguous glob re-exports",
                             BuiltinLintDiag::AmbiguousGlobReexports {
                                 name: key.ident.to_string(),
                                 namespace: key.ns.descr().to_string(),
@@ -659,7 +658,6 @@ impl<'a, 'tcx> Resolver<'a, 'tcx> {
                                 HIDDEN_GLOB_REEXPORTS,
                                 binding_id,
                                 binding.span,
-                                "private item shadows public glob re-export",
                                 BuiltinLintDiag::HiddenGlobReexports {
                                     name: key.ident.name.to_string(),
                                     namespace: key.ns.descr().to_owned(),
@@ -1015,17 +1013,13 @@ impl<'a, 'tcx> Resolver<'a, 'tcx> {
                         && !max_vis.is_at_least(import_vis, self.tcx)
                     {
                         let def_id = self.local_def_id(id);
-                        let msg = format!(
-                            "glob import doesn't reexport anything with visibility `{}` because no imported item is public enough",
-                            import_vis.to_string(def_id, self.tcx)
-                        );
                         self.lint_buffer.buffer_lint_with_diagnostic(
                             UNUSED_IMPORTS,
                             id,
                             import.span,
-                            msg,
                             BuiltinLintDiag::RedundantImportVisibility {
                                 max_vis: max_vis.to_string(def_id, self.tcx),
+                                import_vis: import_vis.to_string(def_id, self.tcx),
                                 span: import.span,
                             },
                         );
@@ -1397,7 +1391,6 @@ impl<'a, 'tcx> Resolver<'a, 'tcx> {
                 UNUSED_IMPORTS,
                 id,
                 import.span,
-                format!("the item `{source}` is imported redundantly"),
                 BuiltinLintDiag::RedundantImport(redundant_spans, source),
             );
             */

compiler/rustc_resolve/src/late.rs

@@ -1675,16 +1675,10 @@ impl<'a: 'ast, 'b, 'ast, 'tcx> LateResolutionVisitor<'a, 'b, 'ast, 'tcx> {
                     return;
                 }
                 LifetimeRibKind::AnonymousWarn(node_id) => {
-                    let msg = if elided {
-                        "`&` without an explicit lifetime name cannot be used here"
-                    } else {
-                        "`'_` cannot be used here"
-                    };
                     self.r.lint_buffer.buffer_lint_with_diagnostic(
                         lint::builtin::ELIDED_LIFETIMES_IN_ASSOCIATED_CONSTANT,
                         node_id,
                         lifetime.ident.span,
-                        msg,
                         lint::BuiltinLintDiag::AssociatedConstElidedLifetime {
                             elided,
                             span: lifetime.ident.span,
@@ -1970,7 +1964,6 @@ impl<'a: 'ast, 'b, 'ast, 'tcx> LateResolutionVisitor<'a, 'b, 'ast, 'tcx> {
                     lint::builtin::ELIDED_LIFETIMES_IN_PATHS,
                     segment_id,
                     elided_lifetime_span,
-                    "hidden lifetime parameters in types are deprecated",
                     lint::BuiltinLintDiag::ElidedLifetimesInPaths(
                         expected_lifetimes,
                         path_span,

compiler/rustc_resolve/src/late/diagnostics.rs

@@ -2655,11 +2655,11 @@ impl<'a: 'ast, 'ast, 'tcx> LateResolutionVisitor<'a, '_, 'ast, 'tcx> {
                         lint::builtin::SINGLE_USE_LIFETIMES,
                         param.id,
                         param.ident.span,
-                        format!("lifetime parameter `{}` only used once", param.ident),
                         lint::BuiltinLintDiag::SingleUseLifetime {
                             param_span: param.ident.span,
                             use_span: Some((use_span, elidable)),
                             deletion_span,
+                            ident: param.ident,
                         },
                     );
                 }
@@ -2673,11 +2673,11 @@ impl<'a: 'ast, 'ast, 'tcx> LateResolutionVisitor<'a, '_, 'ast, 'tcx> {
                             lint::builtin::UNUSED_LIFETIMES,
                             param.id,
                             param.ident.span,
-                            format!("lifetime parameter `{}` never used", param.ident),
                             lint::BuiltinLintDiag::SingleUseLifetime {
                                 param_span: param.ident.span,
                                 use_span: None,
                                 deletion_span,
+                                ident: param.ident,
                             },
                         );
                     }

compiler/rustc_resolve/src/macros.rs

@@ -786,7 +786,6 @@ impl<'a, 'tcx> Resolver<'a, 'tcx> {
                             LEGACY_DERIVE_HELPERS,
                             node_id,
                             ident.span,
-                            "derive helper attribute is used before it is introduced",
                             BuiltinLintDiag::LegacyDeriveHelpers(binding.span),
                         );
                     }

compiler/rustc_session/src/parse.rs

@@ -311,9 +311,8 @@ impl ParseSess {
             buffered_lints.push(BufferedEarlyLint {
                 span: span.into(),
                 node_id,
-                msg: msg.into(),
                 lint_id: LintId::of(lint),
-                diagnostic: BuiltinLintDiag::Normal,
+                diagnostic: BuiltinLintDiag::Normal(msg.into()),
             });
         });
     }
@@ -323,14 +322,12 @@ impl ParseSess {
         lint: &'static Lint,
         span: impl Into<MultiSpan>,
         node_id: NodeId,
-        msg: impl Into<DiagMessage>,
         diagnostic: BuiltinLintDiag,
     ) {
         self.buffered_lints.with_lock(|buffered_lints| {
             buffered_lints.push(BufferedEarlyLint {
                 span: span.into(),
                 node_id,
-                msg: msg.into(),
                 lint_id: LintId::of(lint),
                 diagnostic,
             });