Rollup merge of rust-lang#125913 - fmease:early-lints-spruce-up-some-diags, r=Nadrieril

Spruce up the diagnostics of some early lints

Implement the various "*(note to myself) in a follow-up PR we should turn parts of this message into a subdiagnostic (help msg or even struct sugg)*" drive-by comments I left in rust-lang#124417 during my review.

For context, before rust-lang#124417, only a few early lints touched/decorated/customized their diagnostic because the former API made it a bit awkward. Likely because of that, things that should've been subdiagnostics were just crammed into the primary message. This PR rectifies this.

Author: jieyouxu

compiler/rustc_expand/messages.ftl

@@ -157,7 +157,7 @@ expand_unsupported_key_value =
     key-value macro attributes are not supported
 
 expand_var_still_repeating =
-    variable '{$ident}' is still repeating at this depth
+    variable `{$ident}` is still repeating at this depth
 
 expand_wrong_fragment_kind =
     non-{$kind} macro in {$kind} position: {$name}

compiler/rustc_lint/messages.ftl

@@ -445,7 +445,8 @@ lint_macro_is_private = macro `{$ident}` is private
 lint_macro_rule_never_used = rule #{$n} of macro `{$name}` is never used
 
 lint_macro_use_deprecated =
-    deprecated `#[macro_use]` attribute used to import macros should be replaced at use sites with a `use` item to import the macro instead
+    applying the `#[macro_use]` attribute to an `extern crate` item is deprecated
+    .help = remove it and import macros at use sites with a `use` item instead
 
 lint_malformed_attribute = malformed lint attribute input
 
@@ -456,7 +457,7 @@ lint_map_unit_fn = `Iterator::map` call that discard the iterator's values
     .map_label = after this call to map, the resulting iterator is `impl Iterator<Item = ()>`, which means the only information carried by the iterator is the number of items
     .suggestion = you might have meant to use `Iterator::for_each`
 
-lint_metavariable_still_repeating = variable '{$name}' is still repeating at this depth
+lint_metavariable_still_repeating = variable `{$name}` is still repeating at this depth
 
 lint_metavariable_wrong_operator = meta-variable repeats with different Kleene operator
 
@@ -635,8 +636,8 @@ lint_pattern_in_bodiless = patterns aren't allowed in functions without bodies
 lint_pattern_in_foreign = patterns aren't allowed in foreign function declarations
     .label = pattern not allowed in foreign function
 
-lint_private_extern_crate_reexport =
-    extern crate `{$ident}` is private, and cannot be re-exported, consider declaring with `pub`
+lint_private_extern_crate_reexport = extern crate `{$ident}` is private and cannot be re-exported
+    .suggestion = consider making the `extern crate` item publicly accessible
 
 lint_proc_macro_derive_resolution_fallback = cannot find {$ns} `{$ident}` in this scope
     .label = names from parent modules are not accessible without an explicit import
@@ -847,7 +848,8 @@ lint_unused_coroutine =
     }{$post} that must be used
     .note = coroutines are lazy and do nothing unless resumed
 
-lint_unused_crate_dependency = external crate `{$extern_crate}` unused in `{$local_crate}`: remove the dependency or add `use {$extern_crate} as _;`
+lint_unused_crate_dependency = extern crate `{$extern_crate}` is unused in crate `{$local_crate}`
+    .help = remove the dependency or add `use {$extern_crate} as _;` to the crate root
 
 lint_unused_def = unused {$pre}`{$def}`{$post} that must be used
     .suggestion = use `let _ = ...` to ignore the resulting value

compiler/rustc_lint/src/context/diagnostics.rs

@@ -340,8 +340,9 @@ pub(super) fn decorate_lint(sess: &Session, diagnostic: BuiltinLintDiag, diag: &
             lints::MacroUseDeprecated.decorate_lint(diag);
         }
         BuiltinLintDiag::UnusedMacroUse => lints::UnusedMacroUse.decorate_lint(diag),
-        BuiltinLintDiag::PrivateExternCrateReexport(ident) => {
-            lints::PrivateExternCrateReexport { ident }.decorate_lint(diag);
+        BuiltinLintDiag::PrivateExternCrateReexport { source: ident, extern_crate_span } => {
+            lints::PrivateExternCrateReexport { ident, sugg: extern_crate_span.shrink_to_lo() }
+                .decorate_lint(diag);
         }
         BuiltinLintDiag::UnusedLabel => lints::UnusedLabel.decorate_lint(diag),
         BuiltinLintDiag::MacroIsPrivate(ident) => {

compiler/rustc_lint/src/lints.rs

@@ -2313,6 +2313,7 @@ pub mod unexpected_cfg_value {
 
 #[derive(LintDiagnostic)]
 #[diag(lint_macro_use_deprecated)]
+#[help]
 pub struct MacroUseDeprecated;
 
 #[derive(LintDiagnostic)]
@@ -2323,6 +2324,8 @@ pub struct UnusedMacroUse;
 #[diag(lint_private_extern_crate_reexport, code = E0365)]
 pub struct PrivateExternCrateReexport {
     pub ident: Ident,
+    #[suggestion(code = "pub ", style = "verbose", applicability = "maybe-incorrect")]
+    pub sugg: Span,
 }
 
 #[derive(LintDiagnostic)]
@@ -2416,6 +2419,7 @@ pub struct UnknownMacroVariable {
 
 #[derive(LintDiagnostic)]
 #[diag(lint_unused_crate_dependency)]
+#[help]
 pub struct UnusedCrateDependency {
     pub extern_crate: Symbol,
     pub local_crate: Symbol,

compiler/rustc_lint_defs/src/builtin.rs

@@ -511,8 +511,9 @@ declare_lint! {
     /// This will produce:
     ///
     /// ```text
-    /// error: external crate `regex` unused in `lint_example`: remove the dependency or add `use regex as _;`
+    /// error: extern crate `regex` is unused in crate `lint_example`
     ///   |
+    ///   = help: remove the dependency or add `use regex as _;` to the crate root
     /// note: the lint level is defined here
     ///  --> src/lib.rs:1:9
     ///   |
@@ -2160,8 +2161,7 @@ declare_lint! {
 }
 
 declare_lint! {
-    /// The `macro_use_extern_crate` lint detects the use of the
-    /// [`macro_use` attribute].
+    /// The `macro_use_extern_crate` lint detects the use of the [`macro_use` attribute].
     ///
     /// ### Example
     ///
@@ -2179,12 +2179,13 @@ declare_lint! {
     /// This will produce:
     ///
     /// ```text
-    /// error: deprecated `#[macro_use]` attribute used to import macros should be replaced at use sites with a `use` item to import the macro instead
+    /// error: applying the `#[macro_use]` attribute to an `extern crate` item is deprecated
     ///  --> src/main.rs:3:1
     ///   |
     /// 3 | #[macro_use]
     ///   | ^^^^^^^^^^^^
     ///   |
+    ///   = help: remove it and import macros at use sites with a `use` item instead
     /// note: the lint level is defined here
     ///  --> src/main.rs:1:9
     ///   |

compiler/rustc_lint_defs/src/lib.rs

@@ -706,7 +706,10 @@ pub enum BuiltinLintDiag {
     },
     MacroUseDeprecated,
     UnusedMacroUse,
-    PrivateExternCrateReexport(Ident),
+    PrivateExternCrateReexport {
+        source: Ident,
+        extern_crate_span: Span,
+    },
     UnusedLabel,
     MacroIsPrivate(Ident),
     UnusedMacroDefinition(Symbol),

compiler/rustc_resolve/src/imports.rs

@@ -259,13 +259,18 @@ struct UnresolvedImportError {
 
 // Reexports of the form `pub use foo as bar;` where `foo` is `extern crate foo;`
 // are permitted for backward-compatibility under a deprecation lint.
-fn pub_use_of_private_extern_crate_hack(import: Import<'_>, binding: NameBinding<'_>) -> bool {
+fn pub_use_of_private_extern_crate_hack(
+    import: Import<'_>,
+    binding: NameBinding<'_>,
+) -> Option<NodeId> {
     match (&import.kind, &binding.kind) {
-        (ImportKind::Single { .. }, NameBindingKind::Import { import: binding_import, .. }) => {
-            matches!(binding_import.kind, ImportKind::ExternCrate { .. })
-                && import.expect_vis().is_public()
+        (ImportKind::Single { .. }, NameBindingKind::Import { import: binding_import, .. })
+            if let ImportKind::ExternCrate { id, .. } = binding_import.kind
+                && import.expect_vis().is_public() =>
+        {
+            Some(id)
         }
-        _ => false,
+        _ => None,
     }
 }
 
@@ -275,7 +280,7 @@ impl<'a, 'tcx> Resolver<'a, 'tcx> {
     pub(crate) fn import(&self, binding: NameBinding<'a>, import: Import<'a>) -> NameBinding<'a> {
         let import_vis = import.expect_vis().to_def_id();
         let vis = if binding.vis.is_at_least(import_vis, self.tcx)
-            || pub_use_of_private_extern_crate_hack(import, binding)
+            || pub_use_of_private_extern_crate_hack(import, binding).is_some()
         {
             import_vis
         } else {
@@ -1253,12 +1258,15 @@ impl<'a, 'tcx> Resolver<'a, 'tcx> {
         // All namespaces must be re-exported with extra visibility for an error to occur.
         if !any_successful_reexport {
             let (ns, binding) = reexport_error.unwrap();
-            if pub_use_of_private_extern_crate_hack(import, binding) {
+            if let Some(extern_crate_id) = pub_use_of_private_extern_crate_hack(import, binding) {
                 self.lint_buffer.buffer_lint(
                     PUB_USE_OF_PRIVATE_EXTERN_CRATE,
                     import_id,
                     import.span,
-                    BuiltinLintDiag::PrivateExternCrateReexport(ident),
+                    BuiltinLintDiag::PrivateExternCrateReexport {
+                        source: ident,
+                        extern_crate_span: self.tcx.source_span(self.local_def_id(extern_crate_id)),
+                    },
                 );
             } else {
                 if ns == TypeNS {

tests/ui/extern-flag/no-nounused.rs

@@ -2,5 +2,5 @@
 //@ compile-flags: -Zunstable-options -Dunused-crate-dependencies
 //@ edition:2018
 
-fn main() { //~ ERROR external crate `somedep` unused in `no_nounused`
+fn main() { //~ ERROR extern crate `somedep` is unused in crate `no_nounused`
 }

tests/ui/extern-flag/no-nounused.stderr

@@ -1,9 +1,10 @@
-error: external crate `somedep` unused in `no_nounused`: remove the dependency or add `use somedep as _;`
+error: extern crate `somedep` is unused in crate `no_nounused`
   --> $DIR/no-nounused.rs:5:1
    |
 LL | fn main() {
    | ^
    |
+   = help: remove the dependency or add `use somedep as _;` to the crate root
    = note: requested on the command line with `-D unused-crate-dependencies`
 
 error: aborting due to 1 previous error

tests/ui/macros/issue-61053-missing-repetition.rs

@@ -3,7 +3,7 @@
 macro_rules! foo {
     () => {};
     ($( $i:ident = $($j:ident),+ );*) => { $( $i = $j; )* };
-    //~^ ERROR variable 'j' is still repeating
+    //~^ ERROR variable `j` is still repeating
 }
 
 macro_rules! bar {
@@ -12,12 +12,12 @@ macro_rules! bar {
         macro_rules! nested {
             () => {};
             ($( $i:ident = $($j:ident),+ );*) => { $( $i = $j; )* };
-            //~^ ERROR variable 'j' is still repeating
+            //~^ ERROR variable `j` is still repeating
         }
     };
     ( $( $i:ident = $($j:ident),+ );* ) => {
         $(macro_rules! $i {
-            () => { $j }; //~ ERROR variable 'j' is still repeating
+            () => { $j }; //~ ERROR variable `j` is still repeating
         })*
     };
 }