diff --git a/src/librustc_macros/src/symbols.rs b/src/librustc_macros/src/symbols.rs
index 0f8bc4323070b..2e9b3a2a2562f 100644
--- a/src/librustc_macros/src/symbols.rs
+++ b/src/librustc_macros/src/symbols.rs
@@ -87,18 +87,29 @@ pub fn symbols(input: TokenStream) -> TokenStream {
     let mut prefill_stream = quote! {};
     let mut counter = 0u32;
     let mut keys = HashSet::<String>::new();
+    let mut prev_key: Option<String> = None;
+    let mut errors = Vec::<String>::new();
 
-    let mut check_dup = |str: &str| {
+    let mut check_dup = |str: &str, errors: &mut Vec<String>| {
         if !keys.insert(str.to_string()) {
-            panic!("Symbol `{}` is duplicated", str);
+            errors.push(format!("Symbol `{}` is duplicated", str));
         }
     };
 
+    let mut check_order = |str: &str, errors: &mut Vec<String>| {
+        if let Some(ref prev_str) = prev_key {
+            if str < prev_str {
+                errors.push(format!("Symbol `{}` must precede `{}`", str, prev_str));
+            }
+        }
+        prev_key = Some(str.to_string());
+    };
+
     // Generate the listed keywords.
     for keyword in &input.keywords.0 {
         let name = &keyword.name;
         let value = &keyword.value;
-        check_dup(&value.value());
+        check_dup(&value.value(), &mut errors);
         prefill_stream.extend(quote! {
             #value,
         });
@@ -116,7 +127,8 @@ pub fn symbols(input: TokenStream) -> TokenStream {
             Some(value) => value.value(),
             None => name.to_string(),
         };
-        check_dup(&value);
+        check_dup(&value, &mut errors);
+        check_order(&name.to_string(), &mut errors);
         prefill_stream.extend(quote! {
             #value,
         });
@@ -131,7 +143,7 @@ pub fn symbols(input: TokenStream) -> TokenStream {
     // Generate symbols for the strings "0", "1", ..., "9".
     for n in 0..10 {
         let n = n.to_string();
-        check_dup(&n);
+        check_dup(&n, &mut errors);
         prefill_stream.extend(quote! {
             #n,
         });
@@ -141,6 +153,13 @@ pub fn symbols(input: TokenStream) -> TokenStream {
         counter += 1;
     }
 
+    if !errors.is_empty() {
+        for error in errors.into_iter() {
+            eprintln!("error: {}", error)
+        }
+        panic!("errors in `Keywords` and/or `Symbols`");
+    }
+
     let tt = TokenStream::from(quote! {
         macro_rules! keywords {
             () => {
diff --git a/src/librustc_span/symbol.rs b/src/librustc_span/symbol.rs
index 86b770104ea8e..75f588918a020 100644
--- a/src/librustc_span/symbol.rs
+++ b/src/librustc_span/symbol.rs
@@ -19,6 +19,7 @@ use crate::{Span, DUMMY_SP, SESSION_GLOBALS};
 #[cfg(test)]
 mod tests;
 
+// The proc macro code for this is in `src/librustc_macros/src/symbols.rs`.
 symbols! {
     // After modifying this list adjust `is_special`, `is_used_keyword`/`is_unused_keyword`,
     // this should be rarely necessary though if the keywords are kept in alphabetic order.
@@ -113,8 +114,79 @@ symbols! {
     // As well as the symbols listed, there are symbols for the the strings
     // "0", "1", ..., "9", which are accessible via `sym::integer`.
     //
-    // Keep this list in sorted order, as defined by the Unix `sort` utility.
+    // The proc macro will abort if symbols are not in alphabetical order (as
+    // defined by `impl Ord for str`) or if any symbols are duplicated. Vim
+    // users can sort the list by selecting it and executing the command
+    // `:'<,'>!LC_ALL=C sort`.
+    //
+    // There is currently no checking that all symbols are used; that would be
+    // nice to have.
     Symbols {
+        Arc,
+        ArgumentV1,
+        Arguments,
+        C,
+        Clone,
+        Copy,
+        Debug,
+        Decodable,
+        Default,
+        Encodable,
+        Eq,
+        Equal,
+        Err,
+        From,
+        Future,
+        FxHashMap,
+        FxHashSet,
+        GlobalAlloc,
+        Hash,
+        HashMap,
+        HashSet,
+        Input,
+        IntoIterator,
+        ItemContext,
+        Iterator,
+        Layout,
+        LintPass,
+        None,
+        Ok,
+        Option,
+        Ord,
+        Ordering,
+        Output,
+        PartialEq,
+        PartialOrd,
+        Pending,
+        Pin,
+        Poll,
+        ProcMacroHack,
+        ProceduralMasqueradeDummyType,
+        Range,
+        RangeFrom,
+        RangeFull,
+        RangeInclusive,
+        RangeTo,
+        RangeToInclusive,
+        Rc,
+        Ready,
+        Result,
+        Return,
+        RustcDecodable,
+        RustcEncodable,
+        Send,
+        Some,
+        Sync,
+        Target,
+        Try,
+        Ty,
+        TyCtxt,
+        TyKind,
+        Vec,
+        Yield,
+        _Self,
+        __next,
+        _task_context,
         aarch64_target_feature,
         abi,
         abi_amdgpu_kernel,
@@ -131,8 +203,8 @@ symbols! {
         aborts,
         add,
         add_assign,
-        address,
         add_with_overflow,
+        address,
         advanced_slice_patterns,
         adx_target_feature,
         alias,
@@ -141,28 +213,26 @@ symbols! {
         alignstack,
         all,
         alloc,
-        allocator,
-        allocator_internals,
         alloc_error_handler,
         alloc_layout,
         alloc_zeroed,
+        allocator,
+        allocator_internals,
         allow,
-        allowed,
         allow_fail,
         allow_internal_unsafe,
         allow_internal_unstable,
         allow_internal_unstable_backcompat_hack,
+        allowed,
         always,
         and,
         any,
         arbitrary_enum_discriminant,
         arbitrary_self_types,
-        Arc,
-        Arguments,
-        ArgumentV1,
         arith_offset,
         arm_target_feature,
         array,
+        as_str,
         asm,
         assert,
         assert_inhabited,
@@ -173,16 +243,15 @@ symbols! {
         associated_type_bounds,
         associated_type_defaults,
         associated_types,
-        as_str,
         assume,
         assume_init,
         async_await,
         async_closure,
         atomics,
+        att_syntax,
         attr,
-        attributes,
         attr_literals,
-        att_syntax,
+        attributes,
         augmented_assignments,
         automatically_derived,
         avx512_target_feature,
@@ -210,11 +279,11 @@ symbols! {
         braced_empty_structs,
         breakpoint,
         bswap,
-        C,
+        c_variadic,
         call,
-        caller_location,
         call_mut,
         call_once,
+        caller_location,
         cdylib,
         ceilf32,
         ceilf64,
@@ -232,7 +301,6 @@ symbols! {
         char,
         clippy,
         clone,
-        Clone,
         clone_closures,
         clone_from,
         closure_to_fn_coercion,
@@ -274,7 +342,6 @@ symbols! {
         context,
         convert,
         copy,
-        Copy,
         copy_closures,
         copy_nonoverlapping,
         copysignf32,
@@ -303,18 +370,14 @@ symbols! {
         custom_derive,
         custom_inner_attributes,
         custom_test_frameworks,
-        c_variadic,
         dead_code,
         dealloc,
         debug,
-        Debug,
         debug_assertions,
         debug_trait,
-        declare_lint_pass,
         decl_macro,
-        Decodable,
+        declare_lint_pass,
         decode,
-        Default,
         default_lib_allocator,
         default_type_parameter_fallback,
         default_type_params,
@@ -339,8 +402,8 @@ symbols! {
         doc_masked,
         doctest,
         document_private_items,
-        dotdoteq_in_patterns,
         dotdot_in_tuple_patterns,
+        dotdoteq_in_patterns,
         double_braced_closure: "{{closure}}",
         double_braced_constant: "{{constant}}",
         double_braced_constructor: "{{constructor}}",
@@ -349,24 +412,20 @@ symbols! {
         double_braced_misc: "{{misc}}",
         double_braced_opaque: "{{opaque}}",
         drop,
-        dropck_eyepatch,
-        dropck_parametricity,
         drop_in_place,
         drop_types_in_const,
+        dropck_eyepatch,
+        dropck_parametricity,
         dylib,
         dyn_trait,
         eh_catch_typeinfo,
         eh_personality,
         enable,
         enclosing_scope,
-        Encodable,
         encode,
         env,
         eq,
-        Eq,
-        Equal,
         err,
-        Err,
         exact_div,
         except,
         exchange_malloc,
@@ -382,12 +441,12 @@ symbols! {
         export_name,
         expr,
         extern_absolute_paths,
-        external_doc,
         extern_crate_item_prelude,
         extern_crate_self,
         extern_in_paths,
         extern_prelude,
         extern_types,
+        external_doc,
         f16c_target_feature,
         f32,
         f32_runtime,
@@ -424,7 +483,6 @@ symbols! {
         freeze,
         frem_fast,
         from,
-        From,
         from_desugaring,
         from_error,
         from_generator,
@@ -436,29 +494,22 @@ symbols! {
         fsub_fast,
         fundamental,
         future,
-        Future,
         future_trait,
-        FxHashMap,
-        FxHashSet,
         ge,
+        gen_future,
+        gen_kill,
         generator,
-        generators,
         generator_state,
+        generators,
         generic_associated_types,
         generic_param_attrs,
-        gen_future,
-        gen_kill,
         get_context,
-        GlobalAlloc,
         global_allocator,
         global_asm,
         globs,
         gt,
         half_open_range_patterns,
         hash,
-        Hash,
-        HashMap,
-        HashSet,
         hexagon_target_feature,
         hidden,
         homogeneous_aggregate,
@@ -493,10 +544,8 @@ symbols! {
         inlateout,
         inline,
         inout,
-        Input,
         intel,
         into_iter,
-        IntoIterator,
         into_result,
         intrinsics,
         irrefutable_let_patterns,
@@ -505,10 +554,8 @@ symbols! {
         issue_5723_bootstrap,
         issue_tracker_base_url,
         item,
-        item_context: "ItemContext",
         item_like_imports,
         iter,
-        Iterator,
         keyword,
         kind,
         label,
@@ -516,7 +563,6 @@ symbols! {
         lang,
         lang_items,
         lateout,
-        Layout,
         lazy_normalization_consts,
         le,
         let_chains,
@@ -527,14 +573,13 @@ symbols! {
         likely,
         line,
         link,
-        linkage,
         link_args,
         link_cfg,
         link_llvm_intrinsics,
         link_name,
         link_ordinal,
         link_section,
-        LintPass,
+        linkage,
         lint_reasons,
         literal,
         llvm_asm,
@@ -543,9 +588,9 @@ symbols! {
         log10f64,
         log2f32,
         log2f64,
+        log_syntax,
         logf32,
         logf64,
-        log_syntax,
         loop_break_value,
         lt,
         macro_at_most_once_rep,
@@ -554,9 +599,9 @@ symbols! {
         macro_lifetime_matcher,
         macro_literal_matcher,
         macro_reexport,
-        macros_in_extern,
         macro_use,
         macro_vis_matcher,
+        macros_in_extern,
         main,
         managed_boxes,
         manually_drop,
@@ -567,23 +612,23 @@ symbols! {
         match_default_bindings,
         maxnumf32,
         maxnumf64,
+        may_dangle,
         maybe_uninit,
         maybe_uninit_uninit,
         maybe_uninit_zeroed,
-        may_dangle,
-        member_constraints,
-        memory,
         mem_uninitialized,
         mem_zeroed,
+        member_constraints,
+        memory,
         message,
         meta,
         min_align_of,
         min_align_of_val,
         min_const_fn,
         min_const_unsafe_fn,
+        min_specialization,
         minnumf32,
         minnumf64,
-        min_specialization,
         mips_target_feature,
         miri_start_panic,
         mmx_target_feature,
@@ -615,7 +660,6 @@ symbols! {
         never_type,
         never_type_fallback,
         new,
-        __next,
         next,
         nll,
         no,
@@ -629,47 +673,41 @@ symbols! {
         no_link,
         no_main,
         no_mangle,
+        no_niche,
+        no_sanitize,
+        no_stack_check,
+        no_start,
+        no_std,
         nomem,
         non_ascii_idents,
-        None,
-        none_error,
         non_exhaustive,
-        no_niche,
         non_modrs_mods,
+        none_error,
         nontemporal_store,
         nontrapping_dash_fptoint: "nontrapping-fptoint",
         noreturn,
-        no_sanitize,
         nostack,
-        no_stack_check,
-        no_start,
-        no_std,
         not,
         note,
         object_safe_for_dispatch,
         offset,
-        Ok,
         omit_gdb_pretty_printer_section,
         on,
         on_unimplemented,
         oom,
         opaque,
         ops,
+        opt_out_copy,
         optimize,
         optimize_attribute,
         optin_builtin_traits,
         option,
-        Option,
         option_env,
-        options,
         option_type,
-        opt_out_copy,
+        options,
         or,
-        Ord,
-        Ordering,
         or_patterns,
         out,
-        Output,
         overlapping_marker_traits,
         owned_box,
         packed,
@@ -686,17 +724,13 @@ symbols! {
         param_attrs,
         parent_trait,
         partial_cmp,
-        PartialEq,
         partial_ord,
-        PartialOrd,
         passes,
         pat,
         path,
         pattern_parentheses,
-        Pending,
         phantom_data,
         pin,
-        Pin,
         pinned,
         platform_intrinsics,
         plugin,
@@ -704,15 +738,14 @@ symbols! {
         plugins,
         pointer,
         poll,
-        Poll,
         post_dash_lto: "post-lto",
         powerpc_target_feature,
         powf32,
         powf64,
         powif32,
         powif64,
-        precise_pointer_size_matching,
         pre_dash_lto: "pre-lto",
+        precise_pointer_size_matching,
         pref_align_of,
         prefetch_read_data,
         prefetch_read_instruction,
@@ -723,14 +756,12 @@ symbols! {
         preserves_flags,
         primitive,
         proc_dash_macro: "proc-macro",
-        ProceduralMasqueradeDummyType,
         proc_macro,
         proc_macro_attribute,
         proc_macro_def_site,
         proc_macro_derive,
         proc_macro_expr,
         proc_macro_gen,
-        ProcMacroHack,
         proc_macro_hygiene,
         proc_macro_internals,
         proc_macro_mod,
@@ -747,18 +778,11 @@ symbols! {
         quad_precision_float,
         question_mark,
         quote,
-        Range,
-        RangeFrom,
-        RangeFull,
-        RangeInclusive,
-        RangeTo,
-        RangeToInclusive,
         raw_dylib,
         raw_identifiers,
         raw_ref_op,
-        Rc,
+        re_rebalance_coherence,
         readonly,
-        Ready,
         realloc,
         reason,
         receiver,
@@ -779,11 +803,8 @@ symbols! {
         repr_packed,
         repr_simd,
         repr_transparent,
-        re_rebalance_coherence,
         result,
-        Result,
         result_type,
-        Return,
         rhs,
         rintf32,
         rintf64,
@@ -799,6 +820,10 @@ symbols! {
         rust_2015_preview,
         rust_2018_preview,
         rust_begin_unwind,
+        rust_eh_personality,
+        rust_eh_register_frames,
+        rust_eh_unregister_frames,
+        rust_oom,
         rustc,
         rustc_allocator,
         rustc_allocator_nounwind,
@@ -810,7 +835,6 @@ symbols! {
         rustc_const_stable,
         rustc_const_unstable,
         rustc_conversion_suggestion,
-        RustcDecodable,
         rustc_def_path,
         rustc_deprecated,
         rustc_diagnostic_item,
@@ -820,7 +844,6 @@ symbols! {
         rustc_dump_env_program_clauses,
         rustc_dump_program_clauses,
         rustc_dump_user_substs,
-        RustcEncodable,
         rustc_error,
         rustc_expected_cgu_reuse,
         rustc_if_this_changed,
@@ -857,19 +880,15 @@ symbols! {
         rustc_then_this_would_need,
         rustc_unsafe_specialization_marker,
         rustc_variance,
-        rust_eh_personality,
         rustfmt,
-        rust_oom,
         rvalue_static_promotion,
         sanitize,
         sanitizer_runtime,
         saturating_add,
         saturating_sub,
-        _Self,
         self_in_typedefs,
         self_struct_ctor,
         semitransparent,
-        Send,
         send_trait,
         shl,
         shl_assign,
@@ -937,9 +956,9 @@ symbols! {
         sinf32,
         sinf64,
         size,
-        sized,
         size_of,
         size_of_val,
+        sized,
         slice,
         slice_alloc,
         slice_patterns,
@@ -947,7 +966,6 @@ symbols! {
         slice_u8_alloc,
         slicing_syntax,
         soft,
-        Some,
         specialization,
         speed,
         sqrtf32,
@@ -957,9 +975,9 @@ symbols! {
         staged_api,
         start,
         static_in_const,
-        staticlib,
         static_nobundle,
         static_recursion,
+        staticlib,
         std,
         std_inject,
         stmt,
@@ -970,10 +988,10 @@ symbols! {
         stringify,
         struct_field_attributes,
         struct_inherit,
+        struct_variant,
         structural_match,
         structural_peq,
         structural_teq,
-        struct_variant,
         sty,
         sub,
         sub_assign,
@@ -981,9 +999,7 @@ symbols! {
         suggestion,
         sym,
         sync,
-        Sync,
         sync_trait,
-        Target,
         target_arch,
         target_endian,
         target_env,
@@ -998,7 +1014,6 @@ symbols! {
         target_thread_local,
         target_vendor,
         task,
-        _task_context,
         tbm_target_feature,
         termination,
         termination_trait,
@@ -1024,7 +1039,6 @@ symbols! {
         trivial_bounds,
         truncf32,
         truncf64,
-        Try,
         try_blocks,
         try_trait,
         tt,
@@ -1032,9 +1046,6 @@ symbols! {
         tuple_indexing,
         two_phase,
         ty,
-        Ty,
-        TyCtxt,
-        TyKind,
         type_alias_enum_variants,
         type_alias_impl_trait,
         type_ascription,
@@ -1082,21 +1093,20 @@ symbols! {
         unwind,
         unwind_attributes,
         unwrap_or,
-        used,
         use_extern_macros,
         use_nested_groups,
+        used,
         usize,
         v1,
         va_arg,
         va_copy,
         va_end,
-        val,
         va_list,
+        va_start,
+        val,
         var,
         variant_count,
-        va_start,
         vec,
-        Vec,
         vec_type,
         version,
         vis,
@@ -1117,7 +1127,6 @@ symbols! {
         wrapping_mul,
         wrapping_sub,
         write_bytes,
-        Yield,
     }
 }
 
diff --git a/src/librustc_trait_selection/traits/error_reporting/on_unimplemented.rs b/src/librustc_trait_selection/traits/error_reporting/on_unimplemented.rs
index ec51dddc2c810..d2b9f84af33ae 100644
--- a/src/librustc_trait_selection/traits/error_reporting/on_unimplemented.rs
+++ b/src/librustc_trait_selection/traits/error_reporting/on_unimplemented.rs
@@ -126,7 +126,7 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
 
         let mut flags = vec![];
         flags.push((
-            sym::item_context,
+            sym::ItemContext,
             self.describe_enclosure(obligation.cause.body_id).map(|s| s.to_owned()),
         ));
 
diff --git a/src/librustc_trait_selection/traits/on_unimplemented.rs b/src/librustc_trait_selection/traits/on_unimplemented.rs
index a1dfa838e7af3..deb33708681fa 100644
--- a/src/librustc_trait_selection/traits/on_unimplemented.rs
+++ b/src/librustc_trait_selection/traits/on_unimplemented.rs
@@ -286,7 +286,7 @@ impl<'tcx> OnUnimplementedFormatString {
                     // `{from_desugaring}` is allowed
                     Position::ArgumentNamed(s) if s == sym::from_desugaring => (),
                     // `{ItemContext}` is allowed
-                    Position::ArgumentNamed(s) if s == sym::item_context => (),
+                    Position::ArgumentNamed(s) if s == sym::ItemContext => (),
                     // So is `{A}` if A is a type parameter
                     Position::ArgumentNamed(s) => {
                         match generics.params.iter().find(|param| param.name == s) {
@@ -350,7 +350,7 @@ impl<'tcx> OnUnimplementedFormatString {
 
         let s = self.0.as_str();
         let parser = Parser::new(&s, None, None, false, ParseMode::Format);
-        let item_context = (options.get(&sym::item_context)).unwrap_or(&empty_string);
+        let item_context = (options.get(&sym::ItemContext)).unwrap_or(&empty_string);
         parser
             .map(|p| match p {
                 Piece::String(s) => s,
@@ -364,7 +364,7 @@ impl<'tcx> OnUnimplementedFormatString {
                             } else if s == sym::from_desugaring || s == sym::from_method {
                                 // don't break messages using these two arguments incorrectly
                                 &empty_string
-                            } else if s == sym::item_context {
+                            } else if s == sym::ItemContext {
                                 &item_context
                             } else {
                                 bug!(