Moved structs to rustc_expand::errors, added several more migrations, fixed slug name

compiler/rustc_expand/src/errors.rs

@@ -0,0 +1,50 @@
+use rustc_macros::SessionDiagnostic;
+use rustc_span::Span;
+use rustc_span::symbol::{MacroRulesNormalizedIdent};
+
+#[derive(SessionDiagnostic)]
+#[error(expand::expr_repeat_no_syntax_vars)]
+pub(crate) struct NoSyntaxVarsExprRepeat {
+    #[primary_span]
+    pub span: Span,
+}
+
+#[derive(SessionDiagnostic)]
+#[error(expand::must_repeat_once)]
+pub(crate) struct MustRepeatOnce {
+    #[primary_span]
+    pub span: Span,
+}
+
+#[derive(SessionDiagnostic)]
+#[error(expand::count_repetition_misplaced)]
+pub(crate) struct CountRepetitionMisplaced {
+    #[primary_span]
+    pub span: Span,
+}
+
+#[derive(SessionDiagnostic)]
+#[error(expand::meta_var_expr_unrecognized_var)]
+pub(crate) struct MetaVarExprUnrecognizedVar {
+    #[primary_span]
+    pub span: Span,
+    pub key: MacroRulesNormalizedIdent,
+}
+
+#[derive(SessionDiagnostic)]
+#[error(expand::var_still_repeating)]
+pub(crate) struct VarStillRepeating {
+    #[primary_span]
+    pub span: Span,
+    pub ident: MacroRulesNormalizedIdent,
+}
+
+#[derive(SessionDiagnostic)]
+#[error(expand::var_still_repeating)]
+pub(crate) struct MetaVarsDifSeqMatchers {
+    #[primary_span]
+    pub span: Span,
+    pub msg: String,
+}
+
+