Rollup merge of #138924 - nnethercote:less-kw-Empty-3, r=compiler-errors

Reduce `kw::Empty` usage, part 3

Remove some more `kw::Empty` uses, in support of #137978.

r? `@davidtwco`

13 files changed, 66 insertions, 46 deletions

diff --git a/compiler/rustc_attr_parsing/src/attributes/stability.rs b/compiler/rustc_attr_parsing/src/attributes/stability.rs
index 6d76456e83c..bdad6b50186 100644
--- a/compiler/rustc_attr_parsing/src/attributes/stability.rs
+++ b/compiler/rustc_attr_parsing/src/attributes/stability.rs
@@ -5,7 +5,7 @@ use rustc_attr_data_structures::{
     StableSince, UnstableReason, VERSION_PLACEHOLDER,
 };
 use rustc_errors::ErrorGuaranteed;
-use rustc_span::{Span, Symbol, kw, sym};
+use rustc_span::{Span, Symbol, sym};
 
 use super::util::parse_version;
 use super::{AcceptMapping, AttributeParser, SingleAttributeParser};
@@ -61,11 +61,7 @@ impl AttributeParser for StabilityParser {
         }),
         (&[sym::rustc_allowed_through_unstable_modules], |this, cx, args| {
             reject_outside_std!(cx);
-            this.allowed_through_unstable_modules =
-                Some(match args.name_value().and_then(|i| i.value_as_str()) {
-                    Some(msg) => msg,
-                    None => kw::Empty,
-                });
+            this.allowed_through_unstable_modules = args.name_value().and_then(|i| i.value_as_str())
         }),
     ];
 
diff --git a/compiler/rustc_builtin_macros/src/derive.rs b/compiler/rustc_builtin_macros/src/derive.rs
index 2653a9f48b9..e259f5b3955 100644
--- a/compiler/rustc_builtin_macros/src/derive.rs
+++ b/compiler/rustc_builtin_macros/src/derive.rs
@@ -103,7 +103,7 @@ impl MultiItemModifier for Expander {
 fn dummy_annotatable() -> Annotatable {
     Annotatable::GenericParam(ast::GenericParam {
         id: ast::DUMMY_NODE_ID,
-        ident: Ident::empty(),
+        ident: Ident::dummy(),
         attrs: Default::default(),
         bounds: Default::default(),
         is_placeholder: false,
diff --git a/compiler/rustc_error_codes/src/error_codes/E0789.md b/compiler/rustc_error_codes/src/error_codes/E0789.md
index 2c0018cc799..c7bc6cfde51 100644
--- a/compiler/rustc_error_codes/src/error_codes/E0789.md
+++ b/compiler/rustc_error_codes/src/error_codes/E0789.md
@@ -14,7 +14,7 @@ Erroneous code example:
 
 #![unstable(feature = "foo_module", reason = "...", issue = "123")]
 
-#[rustc_allowed_through_unstable_modules]
+#[rustc_allowed_through_unstable_modules = "deprecation message"]
 // #[stable(feature = "foo", since = "1.0")]
 struct Foo;
 // ^^^ error: `rustc_allowed_through_unstable_modules` attribute must be
diff --git a/compiler/rustc_lint/src/non_fmt_panic.rs b/compiler/rustc_lint/src/non_fmt_panic.rs
index ac9f8d92dac..16c06100808 100644
--- a/compiler/rustc_lint/src/non_fmt_panic.rs
+++ b/compiler/rustc_lint/src/non_fmt_panic.rs
@@ -7,7 +7,7 @@ use rustc_parse_format::{ParseMode, Parser, Piece};
 use rustc_session::lint::FutureIncompatibilityReason;
 use rustc_session::{declare_lint, declare_lint_pass};
 use rustc_span::edition::Edition;
-use rustc_span::{InnerSpan, Span, Symbol, hygiene, kw, sym};
+use rustc_span::{InnerSpan, Span, Symbol, hygiene, sym};
 use rustc_trait_selection::infer::InferCtxtExt;
 
 use crate::lints::{NonFmtPanicBraces, NonFmtPanicUnused};
@@ -167,7 +167,7 @@ fn check_panic<'tcx>(cx: &LateContext<'tcx>, f: &'tcx hir::Expr<'tcx>, arg: &'tc
                     .get_diagnostic_item(sym::Debug)
                     .is_some_and(|t| infcx.type_implements_trait(t, [ty], param_env).may_apply());
 
-            let suggest_panic_any = !is_str && panic == sym::std_panic_macro;
+            let suggest_panic_any = !is_str && panic == Some(sym::std_panic_macro);
 
             let fmt_applicability = if suggest_panic_any {
                 // If we can use panic_any, use that as the MachineApplicable suggestion.
@@ -297,10 +297,13 @@ fn find_delimiters(cx: &LateContext<'_>, span: Span) -> Option<(Span, Span, char
     ))
 }
 
-fn panic_call<'tcx>(cx: &LateContext<'tcx>, f: &'tcx hir::Expr<'tcx>) -> (Span, Symbol, Symbol) {
+fn panic_call<'tcx>(
+    cx: &LateContext<'tcx>,
+    f: &'tcx hir::Expr<'tcx>,
+) -> (Span, Option<Symbol>, Symbol) {
     let mut expn = f.span.ctxt().outer_expn_data();
 
-    let mut panic_macro = kw::Empty;
+    let mut panic_macro = None;
 
     // Unwrap more levels of macro expansion, as panic_2015!()
     // was likely expanded from panic!() and possibly from
@@ -320,7 +323,7 @@ fn panic_call<'tcx>(cx: &LateContext<'tcx>, f: &'tcx hir::Expr<'tcx>) -> (Span,
             break;
         }
         expn = parent;
-        panic_macro = name;
+        panic_macro = Some(name);
     }
 
     let macro_symbol =
diff --git a/compiler/rustc_parse/src/parser/item.rs b/compiler/rustc_parse/src/parser/item.rs
index f4df4044dd2..123234fedce 100644
--- a/compiler/rustc_parse/src/parser/item.rs
+++ b/compiler/rustc_parse/src/parser/item.rs
@@ -2871,7 +2871,7 @@ impl<'a> Parser<'a> {
                 // Skip every token until next possible arg or end.
                 p.eat_to_tokens(&[exp!(Comma), exp!(CloseParen)]);
                 // Create a placeholder argument for proper arg count (issue #34264).
-                Ok(dummy_arg(Ident::new(kw::Empty, lo.to(p.prev_token.span)), guar))
+                Ok(dummy_arg(Ident::new(sym::dummy, lo.to(p.prev_token.span)), guar))
             });
             // ...now that we've parsed the first argument, `self` is no longer allowed.
             first_param = false;
diff --git a/compiler/rustc_passes/src/errors.rs b/compiler/rustc_passes/src/errors.rs
index a72f40cd843..0ee17430aab 100644
--- a/compiler/rustc_passes/src/errors.rs
+++ b/compiler/rustc_passes/src/errors.rs
@@ -1348,12 +1348,12 @@ pub(crate) struct DuplicateLangItem {
     pub local_span: Option<Span>,
     pub lang_item_name: Symbol,
     pub crate_name: Symbol,
-    pub dependency_of: Symbol,
+    pub dependency_of: Option<Symbol>,
     pub is_local: bool,
     pub path: String,
     pub first_defined_span: Option<Span>,
-    pub orig_crate_name: Symbol,
-    pub orig_dependency_of: Symbol,
+    pub orig_crate_name: Option<Symbol>,
+    pub orig_dependency_of: Option<Symbol>,
     pub orig_is_local: bool,
     pub orig_path: String,
     pub(crate) duplicate: Duplicate,
@@ -1374,10 +1374,16 @@ impl<G: EmissionGuarantee> Diagnostic<'_, G> for DuplicateLangItem {
         diag.code(E0152);
         diag.arg("lang_item_name", self.lang_item_name);
         diag.arg("crate_name", self.crate_name);
-        diag.arg("dependency_of", self.dependency_of);
+        if let Some(dependency_of) = self.dependency_of {
+            diag.arg("dependency_of", dependency_of);
+        }
         diag.arg("path", self.path);
-        diag.arg("orig_crate_name", self.orig_crate_name);
-        diag.arg("orig_dependency_of", self.orig_dependency_of);
+        if let Some(orig_crate_name) = self.orig_crate_name {
+            diag.arg("orig_crate_name", orig_crate_name);
+        }
+        if let Some(orig_dependency_of) = self.orig_dependency_of {
+            diag.arg("orig_dependency_of", orig_dependency_of);
+        }
         diag.arg("orig_path", self.orig_path);
         if let Some(span) = self.local_span {
             diag.span(span);
@@ -1385,7 +1391,7 @@ impl<G: EmissionGuarantee> Diagnostic<'_, G> for DuplicateLangItem {
         if let Some(span) = self.first_defined_span {
             diag.span_note(span, fluent::passes_first_defined_span);
         } else {
-            if self.orig_dependency_of.is_empty() {
+            if self.orig_dependency_of.is_none() {
                 diag.note(fluent::passes_first_defined_crate);
             } else {
                 diag.note(fluent::passes_first_defined_crate_depends);
diff --git a/compiler/rustc_passes/src/lang_items.rs b/compiler/rustc_passes/src/lang_items.rs
index fe1140d893e..9d4b46cd306 100644
--- a/compiler/rustc_passes/src/lang_items.rs
+++ b/compiler/rustc_passes/src/lang_items.rs
@@ -16,7 +16,7 @@ use rustc_hir::{LangItem, LanguageItems, MethodKind, Target};
 use rustc_middle::query::Providers;
 use rustc_middle::ty::{ResolverAstLowering, TyCtxt};
 use rustc_session::cstore::ExternCrate;
-use rustc_span::{Span, kw};
+use rustc_span::Span;
 
 use crate::errors::{
     DuplicateLangItem, IncorrectTarget, LangItemOnIncorrectTarget, UnknownLangItem,
@@ -98,7 +98,7 @@ impl<'ast, 'tcx> LanguageItemCollector<'ast, 'tcx> {
         {
             let lang_item_name = lang_item.name();
             let crate_name = self.tcx.crate_name(item_def_id.krate);
-            let mut dependency_of = kw::Empty;
+            let mut dependency_of = None;
             let is_local = item_def_id.is_local();
             let path = if is_local {
                 String::new()
@@ -112,8 +112,8 @@ impl<'ast, 'tcx> LanguageItemCollector<'ast, 'tcx> {
             };
 
             let first_defined_span = self.item_spans.get(&original_def_id).copied();
-            let mut orig_crate_name = kw::Empty;
-            let mut orig_dependency_of = kw::Empty;
+            let mut orig_crate_name = None;
+            let mut orig_dependency_of = None;
             let orig_is_local = original_def_id.is_local();
             let orig_path = if orig_is_local {
                 String::new()
@@ -127,11 +127,11 @@ impl<'ast, 'tcx> LanguageItemCollector<'ast, 'tcx> {
             };
 
             if first_defined_span.is_none() {
-                orig_crate_name = self.tcx.crate_name(original_def_id.krate);
+                orig_crate_name = Some(self.tcx.crate_name(original_def_id.krate));
                 if let Some(ExternCrate { dependency_of: inner_dependency_of, .. }) =
                     self.tcx.extern_crate(original_def_id.krate)
                 {
-                    orig_dependency_of = self.tcx.crate_name(*inner_dependency_of);
+                    orig_dependency_of = Some(self.tcx.crate_name(*inner_dependency_of));
                 }
             }
 
@@ -140,7 +140,7 @@ impl<'ast, 'tcx> LanguageItemCollector<'ast, 'tcx> {
             } else {
                 match self.tcx.extern_crate(item_def_id.krate) {
                     Some(ExternCrate { dependency_of: inner_dependency_of, .. }) => {
-                        dependency_of = self.tcx.crate_name(*inner_dependency_of);
+                        dependency_of = Some(self.tcx.crate_name(*inner_dependency_of));
                         Duplicate::CrateDepends
                     }
                     _ => Duplicate::Crate,
diff --git a/compiler/rustc_resolve/src/build_reduced_graph.rs b/compiler/rustc_resolve/src/build_reduced_graph.rs
index 42fe01b1c84..90cb0817644 100644
--- a/compiler/rustc_resolve/src/build_reduced_graph.rs
+++ b/compiler/rustc_resolve/src/build_reduced_graph.rs
@@ -131,7 +131,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                 let expn_id = self.cstore().expn_that_defined_untracked(def_id, self.tcx.sess);
                 return Some(self.new_module(
                     parent,
-                    ModuleKind::Def(def_kind, def_id, self.tcx.item_name(def_id)),
+                    ModuleKind::Def(def_kind, def_id, Some(self.tcx.item_name(def_id))),
                     expn_id,
                     self.def_span(def_id),
                     // FIXME: Account for `#[no_implicit_prelude]` attributes.
@@ -594,7 +594,7 @@ impl<'a, 'ra, 'tcx> BuildReducedGraphVisitor<'a, 'ra, 'tcx> {
                         // HACK(eddyb) unclear how good this is, but keeping `$crate`
                         // in `source` breaks `tests/ui/imports/import-crate-var.rs`,
                         // while the current crate doesn't have a valid `crate_name`.
-                        if crate_name != kw::Empty {
+                        if let Some(crate_name) = crate_name {
                             // `crate_name` should not be interpreted as relative.
                             module_path.push(Segment::from_ident_and_id(
                                 Ident { name: kw::PathRoot, span: source.ident.span },
@@ -603,7 +603,7 @@ impl<'a, 'ra, 'tcx> BuildReducedGraphVisitor<'a, 'ra, 'tcx> {
                             source.ident.name = crate_name;
                         }
                         if rename.is_none() {
-                            ident.name = crate_name;
+                            ident.name = sym::dummy;
                         }
 
                         self.r.dcx().emit_err(errors::CrateImported { span: item.span });
@@ -775,7 +775,7 @@ impl<'a, 'ra, 'tcx> BuildReducedGraphVisitor<'a, 'ra, 'tcx> {
             ItemKind::Mod(.., ref mod_kind) => {
                 let module = self.r.new_module(
                     Some(parent),
-                    ModuleKind::Def(def_kind, def_id, ident.name),
+                    ModuleKind::Def(def_kind, def_id, Some(ident.name)),
                     expansion.to_expn_id(),
                     item.span,
                     parent.no_implicit_prelude
@@ -811,7 +811,7 @@ impl<'a, 'ra, 'tcx> BuildReducedGraphVisitor<'a, 'ra, 'tcx> {
             ItemKind::Enum(_, _) | ItemKind::Trait(..) => {
                 let module = self.r.new_module(
                     Some(parent),
-                    ModuleKind::Def(def_kind, def_id, ident.name),
+                    ModuleKind::Def(def_kind, def_id, Some(ident.name)),
                     expansion.to_expn_id(),
                     item.span,
                     parent.no_implicit_prelude,
diff --git a/compiler/rustc_resolve/src/diagnostics.rs b/compiler/rustc_resolve/src/diagnostics.rs
index 7decc2a0972..63ea8c4ced1 100644
--- a/compiler/rustc_resolve/src/diagnostics.rs
+++ b/compiler/rustc_resolve/src/diagnostics.rs
@@ -2438,7 +2438,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
         let Res::Def(DefKind::Macro(MacroKind::Bang), _) = binding.res() else {
             return None;
         };
-        let module_name = crate_module.kind.name().unwrap();
+        let module_name = crate_module.kind.name().unwrap_or(kw::Empty);
         let import_snippet = match import.kind {
             ImportKind::Single { source, target, .. } if source != target => {
                 format!("{source} as {target}")
diff --git a/compiler/rustc_resolve/src/lib.rs b/compiler/rustc_resolve/src/lib.rs
index 78153fd4174..f0ea8cb89cb 100644
--- a/compiler/rustc_resolve/src/lib.rs
+++ b/compiler/rustc_resolve/src/lib.rs
@@ -503,18 +503,18 @@ enum ModuleKind {
     ///
     /// * A normal module – either `mod from_file;` or `mod from_block { }` –
     ///   or the crate root (which is conceptually a top-level module).
-    ///   Note that the crate root's [name][Self::name] will be [`kw::Empty`].
+    ///   The crate root will have `None` for the symbol.
     /// * A trait or an enum (it implicitly contains associated types, methods and variant
     ///   constructors).
-    Def(DefKind, DefId, Symbol),
+    Def(DefKind, DefId, Option<Symbol>),
 }
 
 impl ModuleKind {
     /// Get name of the module.
     fn name(&self) -> Option<Symbol> {
-        match self {
+        match *self {
             ModuleKind::Block => None,
-            ModuleKind::Def(.., name) => Some(*name),
+            ModuleKind::Def(.., name) => name,
         }
     }
 }
@@ -1402,7 +1402,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
         let mut module_self_bindings = FxHashMap::default();
         let graph_root = arenas.new_module(
             None,
-            ModuleKind::Def(DefKind::Mod, root_def_id, kw::Empty),
+            ModuleKind::Def(DefKind::Mod, root_def_id, None),
             ExpnId::root(),
             crate_span,
             attr::contains_name(attrs, sym::no_implicit_prelude),
@@ -1411,7 +1411,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
         );
         let empty_module = arenas.new_module(
             None,
-            ModuleKind::Def(DefKind::Mod, root_def_id, kw::Empty),
+            ModuleKind::Def(DefKind::Mod, root_def_id, None),
             ExpnId::root(),
             DUMMY_SP,
             true,
@@ -2286,7 +2286,8 @@ fn module_to_string(mut module: Module<'_>) -> Option<String> {
     loop {
         if let ModuleKind::Def(.., name) = module.kind {
             if let Some(parent) = module.parent {
-                names.push(name);
+                // `unwrap` is safe: the presence of a parent means it's not the crate root.
+                names.push(name.unwrap());
                 module = parent
             } else {
                 break;
diff --git a/compiler/rustc_resolve/src/macros.rs b/compiler/rustc_resolve/src/macros.rs
index 3637854f120..12ceaee722f 100644
--- a/compiler/rustc_resolve/src/macros.rs
+++ b/compiler/rustc_resolve/src/macros.rs
@@ -168,7 +168,7 @@ impl<'ra, 'tcx> ResolverExpand for Resolver<'ra, 'tcx> {
         hygiene::update_dollar_crate_names(|ctxt| {
             let ident = Ident::new(kw::DollarCrate, DUMMY_SP.with_ctxt(ctxt));
             match self.resolve_crate_root(ident).kind {
-                ModuleKind::Def(.., name) if name != kw::Empty => name,
+                ModuleKind::Def(.., name) if let Some(name) = name => name,
                 _ => kw::Crate,
             }
         });
@@ -1067,11 +1067,12 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
             );
             if fallback_binding.ok().and_then(|b| b.res().opt_def_id()) != Some(def_id) {
                 let location = match parent_scope.module.kind {
-                    ModuleKind::Def(_, _, name) if name == kw::Empty => {
-                        "the crate root".to_string()
-                    }
                     ModuleKind::Def(kind, def_id, name) => {
-                        format!("{} `{name}`", kind.descr(def_id))
+                        if let Some(name) = name {
+                            format!("{} `{name}`", kind.descr(def_id))
+                        } else {
+                            "the crate root".to_string()
+                        }
                     }
                     ModuleKind::Block => "this scope".to_string(),
                 };
diff --git a/tests/ui/attributes/crate-name-empty.rs b/tests/ui/attributes/crate-name-empty.rs
new file mode 100644
index 00000000000..dfba77a52de
--- /dev/null
+++ b/tests/ui/attributes/crate-name-empty.rs
@@ -0,0 +1,5 @@
+// Ensure we reject `#![crate_name = ""]`.
+
+#![crate_name = ""] //~ ERROR crate name must not be empty
+
+fn main() {}
diff --git a/tests/ui/attributes/crate-name-empty.stderr b/tests/ui/attributes/crate-name-empty.stderr
new file mode 100644
index 00000000000..509a42d05f7
--- /dev/null
+++ b/tests/ui/attributes/crate-name-empty.stderr
@@ -0,0 +1,8 @@
+error: crate name must not be empty
+  --> $DIR/crate-name-empty.rs:3:1
+   |
+LL | #![crate_name = ""]
+   | ^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 1 previous error
+