Rollup merge of #121085 - davidtwco:always-eager-diagnostics, r=nnethercote

errors: only eagerly translate subdiagnostics

Subdiagnostics don't need to be lazily translated, they can always be eagerly translated. Eager translation is slightly more complex as we need to have a `DiagCtxt` available to perform the translation, which involves slightly more threading of that context.

This slight increase in complexity should enable later simplifications - like passing `DiagCtxt` into `AddToDiagnostic` and moving Fluent messages into the diagnostic structs rather than having them in separate files (working on that was what led to this change).

r? ```@nnethercote```

1 files changed, 1 insertions, 1 deletions

diff --git a/compiler/rustc_parse/src/parser/expr.rs b/compiler/rustc_parse/src/parser/expr.rs
index 2424b6c130d..20b9581f2ef 100644
--- a/compiler/rustc_parse/src/parser/expr.rs
+++ b/compiler/rustc_parse/src/parser/expr.rs
@@ -1433,7 +1433,7 @@ impl<'a> Parser<'a> {
                     // If the input is something like `if a { 1 } else { 2 } | if a { 3 } else { 4 }`
                     // then suggest parens around the lhs.
                     if let Some(sp) = this.sess.ambiguous_block_expr_parse.borrow().get(&lo) {
-                        err.subdiagnostic(ExprParenthesesNeeded::surrounding(*sp));
+                        err.subdiagnostic(this.dcx(), ExprParenthesesNeeded::surrounding(*sp));
                     }
                     err
                 })