mbe: Rework diagnostics for metavariable expressions.

compiler/rustc_expand/messages.ftl

@@ -109,9 +109,6 @@ expand_malformed_feature_attribute =
 
 expand_meta_var_dif_seq_matchers = {$msg}
 
-expand_meta_var_expr_unrecognized_var =
-    variable `{$key}` is not recognized in meta-variable expression
-
 expand_missing_fragment_specifier = missing fragment specifier
     .note = fragment specifiers must be provided
     .suggestion_add_fragspec = try adding a specifier here
@@ -136,6 +133,41 @@ expand_module_multiple_candidates =
 expand_must_repeat_once =
     this must repeat at least once
 
+expand_mve_expected_ident =
+    expected an identifier
+    .not_ident = not a valid identifier
+    .expr_name = expected a metavariable expression name: `{"${expr( /* ... */ )}"}`
+    .expr_name_note = valid metavariable expressions are {$valid_expr_list}
+    .ignore_expr_note = `ignore` takes a metavariable argument
+    .count_expr_note = `count` takes a metavariable argument
+
+expand_mve_extra_tokens_in_braces =
+    unexpected trailing tokens in metavariable expression braces
+    .suggestion = try removing these tokens
+
+expand_mve_extra_tokens_in_expr =
+    unexpected trailing tokens in metavariable expression
+    .label = for this metavariable expression
+    .note= the `{$name}` metavariable expression takes up to {$max} arguments
+    .suggestion = try removing {$count ->
+        [one] this token
+        *[other] these tokens
+    }
+
+expand_mve_missing_paren =
+    expected `(`
+    .label = for this this metavariable expression
+    .note = metavariable expressions use function-like parentheses syntax
+    .suggestion = try adding parentheses
+
+expand_mve_unrecognized_expr =
+    unrecognized metavariable expression
+    .label = not a valid metavariable expression
+    .note = valid metavariable expressions are {$valid_expr_list}
+
+expand_mve_unrecognized_var =
+    variable `{$key}` is not recognized in meta-variable expression
+
 expand_non_inline_modules_in_proc_macro_input_are_unstable =
     non-inline modules in proc macro input are unstable
 

compiler/rustc_expand/src/errors.rs

@@ -27,14 +27,6 @@ pub(crate) struct CountRepetitionMisplaced {
     pub span: Span,
 }
 
-#[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 {
@@ -500,3 +492,82 @@ 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_expected_ident)]
+    pub(crate) struct MveExpectedIdent {
+        #[primary_span]
+        pub span: Span,
+        #[label(expand_not_ident)]
+        pub not_ident_label: Option<Span>,
+        /// This error is reused a handful of places, the context here tells us how to customize
+        /// the message.
+        #[subdiagnostic]
+        pub context: MveExpectedIdentContext,
+    }
+
+    #[derive(Subdiagnostic)]
+    pub(crate) enum MveExpectedIdentContext {
+        #[note(expand_expr_name)]
+        #[note(expand_expr_name_note)]
+        ExprName { valid_expr_list: &'static str },
+        #[note(expand_ignore_expr_note)]
+        Ignore,
+        #[note(expand_count_expr_note)]
+        Count,
+    }
+
+    #[derive(Diagnostic)]
+    #[diag(expand_mve_extra_tokens_in_braces)]
+    pub(crate) struct MveExtraTokensInBraces {
+        #[primary_span]
+        #[suggestion(code = "", applicability = "machine-applicable")]
+        pub span: Span,
+    }
+
+    #[derive(Diagnostic)]
+    #[note]
+    #[diag(expand_mve_extra_tokens_in_expr)]
+    pub(crate) struct MveExtraTokensInExpr {
+        #[primary_span]
+        #[suggestion(code = "", applicability = "machine-applicable")]
+        pub span: Span,
+        #[label]
+        pub ident_span: Span,
+        pub count: usize,
+        pub max: usize,
+        pub name: &'static str,
+    }
+
+    #[derive(Diagnostic)]
+    #[note]
+    #[diag(expand_mve_missing_paren)]
+    pub(crate) struct MveMissingParen {
+        #[primary_span]
+        pub span: Span,
+        #[suggestion(code = "( /* ... */ )", applicability = "has-placeholders")]
+        pub insert_span: Option<Span>,
+    }
+
+    #[derive(Diagnostic)]
+    #[note]
+    #[diag(expand_mve_unrecognized_expr)]
+    pub(crate) struct MveUnrecognizedExpr {
+        #[primary_span]
+        #[label]
+        pub span: Span,
+        pub valid_expr_list: &'static str,
+    }
+
+    #[derive(Diagnostic)]
+    #[diag(expand_mve_unrecognized_var)]
+    pub(crate) struct MveUnrecognizedVar {
+        #[primary_span]
+        pub span: Span,
+        pub key: MacroRulesNormalizedIdent,
+    }
+}