3 files changed, 51 insertions, 4 deletions
diff --git a/compiler/rustc_lint/src/internal.rs b/compiler/rustc_lint/src/internal.rs
index c2d98b8e4ad..af5972c6c81 100644
--- a/compiler/rustc_lint/src/internal.rs
+++ b/compiler/rustc_lint/src/internal.rs
@@ -10,7 +10,7 @@ use rustc_hir::{GenericArg, HirId, MutTy, Mutability, Path, PathSegment, QPath,
 use rustc_middle::ty;
 use rustc_session::{declare_lint_pass, declare_tool_lint, impl_lint_pass};
 use rustc_span::hygiene::{ExpnKind, MacroKind};
-use rustc_span::symbol::{sym, Ident, Symbol};
+use rustc_span::symbol::{kw, sym, Ident, Symbol};
 
 declare_tool_lint! {
     pub rustc::DEFAULT_HASH_TYPES,
@@ -267,3 +267,47 @@ impl EarlyLintPass for LintPassImpl {
         }
     }
 }
+
+declare_tool_lint! {
+    pub rustc::EXISTING_DOC_KEYWORD,
+    Allow,
+    "Check that documented keywords in std and core actually exist",
+    report_in_external_macro: true
+}
+
+declare_lint_pass!(ExistingDocKeyword => [EXISTING_DOC_KEYWORD]);
+
+fn is_doc_keyword(s: Symbol) -> bool {
+    s <= kw::Union
+}
+
+impl<'tcx> LateLintPass<'tcx> for ExistingDocKeyword {
+    fn check_item(&mut self, cx: &LateContext<'_>, item: &rustc_hir::Item<'_>) {
+        for attr in item.attrs {
+            if !attr.has_name(sym::doc) {
+                continue;
+            }
+            if let Some(list) = attr.meta_item_list() {
+                for nested in list {
+                    if nested.has_name(sym::keyword) {
+                        let v = nested
+                            .value_str()
+                            .expect("#[doc(keyword = \"...\")] expected a value!");
+                        if is_doc_keyword(v) {
+                            return;
+                        }
+                        cx.struct_span_lint(EXISTING_DOC_KEYWORD, attr.span, |lint| {
+                            lint.build(&format!(
+                                "Found non-existing keyword `{}` used in \
+                                     `#[doc(keyword = \"...\")]`",
+                                v,
+                            ))
+                            .help("only existing keywords are allowed in core/std")
+                            .emit();
+                        });
+                    }
+                }
+            }
+        }
+    }
+}
diff --git a/compiler/rustc_lint/src/lib.rs b/compiler/rustc_lint/src/lib.rs
index 81549be4b09..80ef855c385 100644
--- a/compiler/rustc_lint/src/lib.rs
+++ b/compiler/rustc_lint/src/lib.rs
@@ -463,6 +463,8 @@ fn register_internals(store: &mut LintStore) {
     store.register_early_pass(|| box DefaultHashTypes::new());
     store.register_lints(&LintPassImpl::get_lints());
     store.register_early_pass(|| box LintPassImpl);
+    store.register_lints(&ExistingDocKeyword::get_lints());
+    store.register_late_pass(|| box ExistingDocKeyword);
     store.register_lints(&TyTyKind::get_lints());
     store.register_late_pass(|| box TyTyKind);
     store.register_group(
@@ -475,6 +477,7 @@ fn register_internals(store: &mut LintStore) {
             LintId::of(LINT_PASS_IMPL_WITHOUT_MACRO),
             LintId::of(TY_PASS_BY_REFERENCE),
             LintId::of(USAGE_OF_QUALIFIED_TY),
+            LintId::of(EXISTING_DOC_KEYWORD),
         ],
     );
 }
diff --git a/compiler/rustc_lint/src/nonstandard_style.rs b/compiler/rustc_lint/src/nonstandard_style.rs
index 2720c376774..6d61b86f32e 100644
--- a/compiler/rustc_lint/src/nonstandard_style.rs
+++ b/compiler/rustc_lint/src/nonstandard_style.rs
@@ -131,7 +131,7 @@ impl NonCamelCaseTypes {
                 let cc = to_camel_case(name);
                 // We cannot provide meaningful suggestions
                 // if the characters are in the category of "Lowercase Letter".
-                if name.to_string() != cc {
+                if *name != cc {
                     err.span_suggestion(
                         ident.span,
                         "convert the identifier to upper camel case",
@@ -271,7 +271,7 @@ impl NonSnakeCase {
                 let mut err = lint.build(&msg);
                 // We cannot provide meaningful suggestions
                 // if the characters are in the category of "Uppercase Letter".
-                if name.to_string() != sc {
+                if *name != sc {
                     // We have a valid span in almost all cases, but we don't have one when linting a crate
                     // name provided via the command line.
                     if !ident.span.is_dummy() {
@@ -455,7 +455,7 @@ impl NonUpperCaseGlobals {
                     lint.build(&format!("{} `{}` should have an upper case name", sort, name));
                 // We cannot provide meaningful suggestions
                 // if the characters are in the category of "Lowercase Letter".
-                if name.to_string() != uc {
+                if *name != uc {
                     err.span_suggestion(
                         ident.span,
                         "convert the identifier to upper case",