Rollup merge of #155822 - mejrs:default_fmt_args, r=JonathanBrouwer

Add default field values to diagnostic FormatArgs

This type has a decent amount of unused fields (and I am planning to add more).

Author: JonathanBrouwer

compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs

@@ -156,14 +156,7 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
                     .collect();
                 generic_args.push((kw::SelfUpper, this.clone()));
 
-                let args = FormatArgs {
-                    this,
-                    // Unused
-                    this_sugared: String::new(),
-                    // Unused
-                    item_context: "",
-                    generic_args,
-                };
+                let args = FormatArgs { this, generic_args, .. };
                 let CustomDiagnostic { message, label, notes, parent_label: _ } =
                     directive.eval(None, &args);
 

compiler/rustc_expand/src/lib.rs

@@ -1,6 +1,7 @@
 // tidy-alphabetical-start
 #![allow(internal_features)]
 #![feature(associated_type_defaults)]
+#![feature(default_field_values)]
 #![feature(macro_metavar_expr)]
 #![feature(proc_macro_diagnostic)]
 #![feature(proc_macro_internals)]

compiler/rustc_expand/src/mbe/diagnostics.rs

@@ -77,19 +77,8 @@ pub(super) fn failed_to_match_macro(
     let CustomDiagnostic {
         message: custom_message, label: custom_label, notes: custom_notes, ..
     } = {
-        let macro_name = name.to_string();
         on_unmatch_args
-            .map(|directive| {
-                directive.eval(
-                    None,
-                    &FormatArgs {
-                        this: macro_name.clone(),
-                        this_sugared: macro_name,
-                        item_context: "macro invocation",
-                        generic_args: Vec::new(),
-                    },
-                )
-            })
+            .map(|directive| directive.eval(None, &FormatArgs { this: name.to_string(), .. }))
             .unwrap_or_default()
     };
 

compiler/rustc_hir/src/attrs/diagnostic.rs

@@ -218,10 +218,11 @@ impl FormatString {
 /// ```
 #[derive(Debug)]
 pub struct FormatArgs {
+    /// The name of the item the attribute is on.
     pub this: String,
-    pub this_sugared: String,
-    pub item_context: &'static str,
-    pub generic_args: Vec<(Symbol, String)>,
+    pub this_sugared: String = String::new(),
+    pub item_context: &'static str = "",
+    pub generic_args: Vec<(Symbol, String)> = Vec::new(),
 }
 
 #[derive(Clone, Debug, HashStable_Generic, Encodable, Decodable, PrintAttribute)]

compiler/rustc_hir/src/lib.rs

@@ -7,6 +7,7 @@
 #![feature(closure_track_caller)]
 #![feature(const_default)]
 #![feature(const_trait_impl)]
+#![feature(default_field_values)]
 #![feature(derive_const)]
 #![feature(exhaustive_patterns)]
 #![feature(never_type)]

compiler/rustc_resolve/src/imports.rs

@@ -886,12 +886,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
 
                 let args = FormatArgs {
                     this,
-                    // Unused
-                    this_sugared: String::new(),
-                    // Unused
-                    item_context: "",
-                    // Unused
-                    generic_args: Vec::new(),
+                    ..
                 };
                 let CustomDiagnostic { message, label, notes, .. } = directive.eval(None, &args);