Migrate parts of rustc_expand to session diagnostics

This migrates everything but the `mbe` and `proc_macro` modules. It also
contains a few cleanups and drive-by/accidental diagnostic improvements
which can be seen in the diff for the UI tests.

compiler/rustc_expand/src/errors.rs

@@ -1,6 +1,10 @@
+use rustc_ast::ast;
 use rustc_macros::Diagnostic;
-use rustc_span::symbol::MacroRulesNormalizedIdent;
-use rustc_span::Span;
+use rustc_session::Limit;
+use rustc_span::edition::Edition;
+use rustc_span::symbol::{Ident, MacroRulesNormalizedIdent};
+use rustc_span::{Span, Symbol};
+use std::borrow::Cow;
 
 #[derive(Diagnostic)]
 #[diag(expand_expr_repeat_no_syntax_vars)]
@@ -46,3 +50,321 @@ pub(crate) struct MetaVarsDifSeqMatchers {
     pub span: Span,
     pub msg: String,
 }
+
+#[derive(Diagnostic)]
+#[diag(expand_resolve_relative_path)]
+pub(crate) struct ResolveRelativePath {
+    #[primary_span]
+    pub span: Span,
+    pub path: String,
+}
+
+#[derive(Diagnostic)]
+#[diag(expand_macro_const_stability)]
+pub(crate) struct MacroConstStability {
+    #[primary_span]
+    #[label]
+    pub span: Span,
+    #[label(label2)]
+    pub head_span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(expand_macro_body_stability)]
+pub(crate) struct MacroBodyStability {
+    #[primary_span]
+    #[label]
+    pub span: Span,
+    #[label(label2)]
+    pub head_span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(expand_attr_no_arguments)]
+pub(crate) struct AttrNoArguments {
+    #[primary_span]
+    pub span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(expand_not_a_meta_item)]
+pub(crate) struct NotAMetaItem {
+    #[primary_span]
+    pub span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(expand_only_one_word)]
+pub(crate) struct OnlyOneWord {
+    #[primary_span]
+    pub span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(expand_cannot_be_name_of_macro)]
+pub(crate) struct CannotBeNameOfMacro<'a> {
+    #[primary_span]
+    pub span: Span,
+    pub trait_ident: Ident,
+    pub macro_type: &'a str,
+}
+
+#[derive(Diagnostic)]
+#[diag(expand_arg_not_attributes)]
+pub(crate) struct ArgumentNotAttributes {
+    #[primary_span]
+    pub span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(expand_attributes_wrong_form)]
+pub(crate) struct AttributesWrongForm {
+    #[primary_span]
+    pub span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(expand_attribute_meta_item)]
+pub(crate) struct AttributeMetaItem {
+    #[primary_span]
+    pub span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(expand_attribute_single_word)]
+pub(crate) struct AttributeSingleWord {
+    #[primary_span]
+    pub span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(expand_helper_attribute_name_invalid)]
+pub(crate) struct HelperAttributeNameInvalid {
+    #[primary_span]
+    pub span: Span,
+    pub name: Ident,
+}
+
+#[derive(Diagnostic)]
+#[diag(expand_expected_comma_in_list)]
+pub(crate) struct ExpectedCommaInList {
+    #[primary_span]
+    pub span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(expand_only_one_argument)]
+pub(crate) struct OnlyOneArgument<'a> {
+    #[primary_span]
+    pub span: Span,
+    pub name: &'a str,
+}
+
+#[derive(Diagnostic)]
+#[diag(expand_takes_no_arguments)]
+pub(crate) struct TakesNoArguments<'a> {
+    #[primary_span]
+    pub span: Span,
+    pub name: &'a str,
+}
+
+#[derive(Diagnostic)]
+#[diag(expand_feature_included_in_edition, code = "E0705")]
+pub(crate) struct FeatureIncludedInEdition {
+    #[primary_span]
+    pub span: Span,
+    pub feature: Symbol,
+    pub edition: Edition,
+}
+
+#[derive(Diagnostic)]
+#[diag(expand_feature_removed, code = "E0557")]
+pub(crate) struct FeatureRemoved<'a> {
+    #[primary_span]
+    #[label]
+    pub span: Span,
+    #[subdiagnostic]
+    pub reason: Option<FeatureRemovedReason<'a>>,
+}
+
+#[derive(Subdiagnostic)]
+#[note(reason)]
+pub(crate) struct FeatureRemovedReason<'a> {
+    pub reason: &'a str,
+}
+
+#[derive(Diagnostic)]
+#[diag(expand_feature_not_allowed, code = "E0725")]
+pub(crate) struct FeatureNotAllowed {
+    #[primary_span]
+    pub span: Span,
+    pub name: Symbol,
+}
+
+#[derive(Diagnostic)]
+#[diag(expand_recursion_limit_reached)]
+#[help]
+pub(crate) struct RecursionLimitReached<'a> {
+    #[primary_span]
+    pub span: Span,
+    pub descr: String,
+    pub suggested_limit: Limit,
+    pub crate_name: &'a str,
+}
+
+#[derive(Diagnostic)]
+#[diag(expand_malformed_feature_attribute, code = "E0556")]
+pub(crate) struct MalformedFeatureAttribute {
+    #[primary_span]
+    pub span: Span,
+    #[subdiagnostic]
+    pub help: MalformedFeatureAttributeHelp,
+}
+
+#[derive(Subdiagnostic)]
+pub(crate) enum MalformedFeatureAttributeHelp {
+    #[label(expected)]
+    Label {
+        #[primary_span]
+        span: Span,
+    },
+    #[suggestion(expected, code = "{suggestion}", applicability = "maybe-incorrect")]
+    Suggestion {
+        #[primary_span]
+        span: Span,
+        suggestion: Symbol,
+    },
+}
+
+#[derive(Diagnostic)]
+#[diag(expand_remove_expr_not_supported)]
+pub(crate) struct RemoveExprNotSupported {
+    #[primary_span]
+    pub span: Span,
+}
+
+#[derive(Diagnostic)]
+pub(crate) enum InvalidCfg {
+    #[diag(expand_invalid_cfg_no_parens)]
+    NotFollowedByParens {
+        #[primary_span]
+        #[suggestion(
+            expand_invalid_cfg_expected_syntax,
+            code = "cfg(/* predicate */)",
+            applicability = "has-placeholders"
+        )]
+        span: Span,
+    },
+    #[diag(expand_invalid_cfg_no_predicate)]
+    NoPredicate {
+        #[primary_span]
+        #[suggestion(
+            expand_invalid_cfg_expected_syntax,
+            code = "cfg(/* predicate */)",
+            applicability = "has-placeholders"
+        )]
+        span: Span,
+    },
+    #[diag(expand_invalid_cfg_multiple_predicates)]
+    MultiplePredicates {
+        #[primary_span]
+        span: Span,
+    },
+    #[diag(expand_invalid_cfg_predicate_literal)]
+    PredicateLiteral {
+        #[primary_span]
+        span: Span,
+    },
+}
+
+#[derive(Diagnostic)]
+#[diag(expand_wrong_fragment_kind)]
+pub(crate) struct WrongFragmentKind<'a> {
+    #[primary_span]
+    pub span: Span,
+    pub kind: &'a str,
+    pub name: &'a ast::Path,
+}
+
+#[derive(Diagnostic)]
+#[diag(expand_unsupported_key_value)]
+pub(crate) struct UnsupportedKeyValue {
+    #[primary_span]
+    pub span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(expand_incomplete_parse)]
+#[note]
+pub(crate) struct IncompleteParse<'a> {
+    #[primary_span]
+    pub span: Span,
+    pub token: Cow<'a, str>,
+    #[label]
+    pub label_span: Span,
+    pub macro_path: &'a ast::Path,
+    pub kind_name: &'a str,
+
+    #[suggestion(
+        suggestion_add_semi,
+        style = "verbose",
+        code = ";",
+        applicability = "maybe-incorrect"
+    )]
+    pub add_semicolon: Option<Span>,
+}
+
+#[derive(Diagnostic)]
+#[diag(expand_remove_node_not_supported)]
+pub(crate) struct RemoveNodeNotSupported {
+    #[primary_span]
+    pub span: Span,
+    pub descr: &'static str,
+}
+
+#[derive(Diagnostic)]
+#[diag(expand_module_circular)]
+pub(crate) struct ModuleCircular {
+    #[primary_span]
+    pub span: Span,
+    pub modules: String,
+}
+
+#[derive(Diagnostic)]
+#[diag(expand_module_in_block)]
+pub(crate) struct ModuleInBlock {
+    #[primary_span]
+    pub span: Span,
+    #[subdiagnostic]
+    pub name: Option<ModuleInBlockName>,
+}
+
+#[derive(Subdiagnostic)]
+#[note(note)]
+pub(crate) struct ModuleInBlockName {
+    #[primary_span]
+    pub span: Span,
+    pub name: Ident,
+}
+
+#[derive(Diagnostic)]
+#[diag(expand_module_file_not_found, code = "E0583")]
+#[help]
+pub(crate) struct ModuleFileNotFound {
+    #[primary_span]
+    pub span: Span,
+    pub name: Ident,
+    pub default_path: String,
+    pub secondary_path: String,
+}
+
+#[derive(Diagnostic)]
+#[diag(expand_module_multiple_candidates, code = "E0761")]
+#[help]
+pub(crate) struct ModuleMultipleCandidates {
+    #[primary_span]
+    pub span: Span,
+    pub name: Ident,
+    pub default_path: String,
+    pub secondary_path: String,
+}