Rollup merge of #103397 - crlf0710:port_dead_code_lint, r=davidtwco

Port `dead_code` lints to be translatable.

This adds an additional comma to lists with three or more items, to be consistent with list formatters like `icu4x`.

r? `@davidtwco`

compiler/rustc_errors/src/diagnostic_impls.rs

@@ -11,6 +11,7 @@ use rustc_target::abi::TargetDataLayoutErrors;
 use rustc_target::spec::{PanicStrategy, SplitDebuginfo, StackProtector, TargetTriple};
 use std::borrow::Cow;
 use std::fmt;
+use std::fmt::Write;
 use std::num::ParseIntError;
 use std::path::{Path, PathBuf};
 
@@ -170,6 +171,37 @@ impl IntoDiagnosticArg for Level {
     }
 }
 
+#[derive(Clone)]
+pub struct DiagnosticSymbolList(Vec<Symbol>);
+
+impl From<Vec<Symbol>> for DiagnosticSymbolList {
+    fn from(v: Vec<Symbol>) -> Self {
+        DiagnosticSymbolList(v)
+    }
+}
+
+impl IntoDiagnosticArg for DiagnosticSymbolList {
+    fn into_diagnostic_arg(self) -> DiagnosticArgValue<'static> {
+        // FIXME: replace the logic here with a real list formatter
+        let symbols = match &self.0[..] {
+            [symbol] => format!("`{symbol}`"),
+            [symbol, last] => {
+                format!("`{symbol}` and `{last}`",)
+            }
+            [symbols @ .., last] => {
+                let mut result = String::new();
+                for symbol in symbols {
+                    write!(result, "`{symbol}`, ").unwrap();
+                }
+                write!(result, "and `{last}`").unwrap();
+                result
+            }
+            [] => unreachable!(),
+        };
+        DiagnosticArgValue::Str(Cow::Owned(symbols))
+    }
+}
+
 impl IntoDiagnostic<'_, !> for TargetDataLayoutErrors<'_> {
     fn into_diagnostic(self, handler: &Handler) -> DiagnosticBuilder<'_, !> {
         let mut diag;

compiler/rustc_errors/src/lib.rs

@@ -376,7 +376,7 @@ pub use diagnostic::{
     DiagnosticStyledString, IntoDiagnosticArg, SubDiagnostic,
 };
 pub use diagnostic_builder::{DiagnosticBuilder, EmissionGuarantee, Noted};
-pub use diagnostic_impls::DiagnosticArgFromDisplay;
+pub use diagnostic_impls::{DiagnosticArgFromDisplay, DiagnosticSymbolList};
 use std::backtrace::Backtrace;
 
 /// A handler deals with errors and other compiler output.