mbe: Shorten `MetaVarExpr` -> `Mve` in structural diagnostics

More diagnostic structs related to metavariable expressions will be
introduced. Introduce the abbreviation "mve" which is reasonably
unambiguous (`rg Mve` and `rg '(\b|_|-)mve(\b|_|-)'` return no results
outside of a Thumb target feature) and use it for these diagnostic
types. A new module is also created.

1 files changed, 13 insertions, 8 deletions

diff --git a/compiler/rustc_expand/src/errors.rs b/compiler/rustc_expand/src/errors.rs
index 714ba3bf0f4..0d77916d4cf 100644
--- a/compiler/rustc_expand/src/errors.rs
+++ b/compiler/rustc_expand/src/errors.rs
@@ -28,14 +28,6 @@ pub(crate) struct CountRepetitionMisplaced {
 }
 
 #[derive(Diagnostic)]
-#[diag(expand_meta_var_expr_unrecognized_var)]
-pub(crate) struct MetaVarExprUnrecognizedVar {
-    #[primary_span]
-    pub span: Span,
-    pub key: MacroRulesNormalizedIdent,
-}
-
-#[derive(Diagnostic)]
 #[diag(expand_var_still_repeating)]
 pub(crate) struct VarStillRepeating {
     #[primary_span]
@@ -500,3 +492,16 @@ pub(crate) struct ProcMacroBackCompat {
     pub crate_name: String,
     pub fixed_version: String,
 }
+
+pub(crate) use metavar_exprs::*;
+mod metavar_exprs {
+    use super::*;
+
+    #[derive(Diagnostic)]
+    #[diag(expand_mve_unrecognized_var)]
+    pub(crate) struct MveUnrecognizedVar {
+        #[primary_span]
+        pub span: Span,
+        pub key: MacroRulesNormalizedIdent,
+    }
+}