Support eager subdiagnostics again

compiler/rustc_macros/src/diagnostics/diagnostic_builder.rs

@@ -382,10 +382,26 @@ impl<'a> DiagnosticDeriveVariantBuilder<'a> {
                     return Ok(quote! { #diag.subdiagnostic(#binding); });
                 }
             }
-            (Meta::List(_), "subdiagnostic") => {
-                throw_invalid_attr!(attr, &meta, |diag| {
-                    diag.help("`subdiagnostic` does not support nested attributes")
-                })
+            (Meta::List(MetaList { ref nested, .. }), "subdiagnostic") => {
+                if nested.len() == 1
+                    && let Some(NestedMeta::Meta(Meta::Path(path))) = nested.first()
+                    && path.is_ident("eager") {
+                        let handler = match &self.parent.kind {
+                            DiagnosticDeriveKind::Diagnostic { handler } => handler,
+                            DiagnosticDeriveKind::LintDiagnostic => {
+                                throw_invalid_attr!(attr, &meta, |diag| {
+                                    diag.help("eager subdiagnostics are not supported on lints")
+                                })
+                            }
+                        };
+                        return Ok(quote! { #diag.eager_subdiagnostic(#handler, #binding); });
+                } else {
+                    throw_invalid_attr!(attr, &meta, |diag| {
+                        diag.help(
+                            "`eager` is the only supported nested attribute for `subdiagnostic`",
+                        )
+                    })
+                }
             }
             _ => (),
         }

compiler/rustc_macros/src/lib.rs

@@ -1,5 +1,6 @@
 #![feature(allow_internal_unstable)]
 #![feature(if_let_guard)]
+#![feature(let_chains)]
 #![feature(never_type)]
 #![feature(proc_macro_diagnostic)]
 #![feature(proc_macro_span)]

tests/ui-fulldeps/session-diagnostic/diagnostic-derive.rs

@@ -723,7 +723,6 @@ struct SubdiagnosticEagerLint {
 #[diag(compiletest_example)]
 struct SubdiagnosticEagerCorrect {
     #[subdiagnostic(eager)]
-    //~^ ERROR `#[subdiagnostic(...)]` is not a valid attribute
     note: Note,
 }
 
@@ -744,7 +743,6 @@ pub(crate) struct SubdiagnosticWithSuggestion {
 #[diag(compiletest_example)]
 struct SubdiagnosticEagerSuggestion {
     #[subdiagnostic(eager)]
-    //~^ ERROR `#[subdiagnostic(...)]` is not a valid attribute
     sub: SubdiagnosticWithSuggestion,
 }
 

tests/ui-fulldeps/session-diagnostic/diagnostic-derive.stderr

@@ -539,7 +539,7 @@ error: `#[subdiagnostic(...)]` is not a valid attribute
 LL |     #[subdiagnostic(bad)]
    |     ^^^^^^^^^^^^^^^^^^^^^
    |
-   = help: `subdiagnostic` does not support nested attributes
+   = help: `eager` is the only supported nested attribute for `subdiagnostic`
 
 error: `#[subdiagnostic = ...]` is not a valid attribute
   --> $DIR/diagnostic-derive.rs:693:5
@@ -553,54 +553,38 @@ error: `#[subdiagnostic(...)]` is not a valid attribute
 LL |     #[subdiagnostic(bad, bad)]
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
-   = help: `subdiagnostic` does not support nested attributes
+   = help: `eager` is the only supported nested attribute for `subdiagnostic`
 
 error: `#[subdiagnostic(...)]` is not a valid attribute
   --> $DIR/diagnostic-derive.rs:709:5
    |
 LL |     #[subdiagnostic("bad")]
    |     ^^^^^^^^^^^^^^^^^^^^^^^
    |
-   = help: `subdiagnostic` does not support nested attributes
+   = help: `eager` is the only supported nested attribute for `subdiagnostic`
 
 error: `#[subdiagnostic(...)]` is not a valid attribute
   --> $DIR/diagnostic-derive.rs:717:5
    |
 LL |     #[subdiagnostic(eager)]
    |     ^^^^^^^^^^^^^^^^^^^^^^^
    |
-   = help: `subdiagnostic` does not support nested attributes
-
-error: `#[subdiagnostic(...)]` is not a valid attribute
-  --> $DIR/diagnostic-derive.rs:725:5
-   |
-LL |     #[subdiagnostic(eager)]
-   |     ^^^^^^^^^^^^^^^^^^^^^^^
-   |
-   = help: `subdiagnostic` does not support nested attributes
-
-error: `#[subdiagnostic(...)]` is not a valid attribute
-  --> $DIR/diagnostic-derive.rs:746:5
-   |
-LL |     #[subdiagnostic(eager)]
-   |     ^^^^^^^^^^^^^^^^^^^^^^^
-   |
-   = help: `subdiagnostic` does not support nested attributes
+   = help: eager subdiagnostics are not supported on lints
 
 error: expected at least one string literal for `code(...)`
-  --> $DIR/diagnostic-derive.rs:777:18
+  --> $DIR/diagnostic-derive.rs:775:18
    |
 LL |     #[suggestion(code())]
    |                  ^^^^^^
 
 error: `code(...)` must contain only string literals
-  --> $DIR/diagnostic-derive.rs:785:23
+  --> $DIR/diagnostic-derive.rs:783:23
    |
 LL |     #[suggestion(code(foo))]
    |                       ^^^
 
 error: `code = "..."`/`code(...)` must contain only string literals
-  --> $DIR/diagnostic-derive.rs:793:18
+  --> $DIR/diagnostic-derive.rs:791:18
    |
 LL |     #[suggestion(code = 3)]
    |                  ^^^^^^^^
@@ -676,7 +660,7 @@ note: required by a bound in `DiagnosticBuilder::<'a, G>::set_arg`
   --> $COMPILER_DIR/rustc_errors/src/diagnostic_builder.rs:LL:CC
    = note: this error originates in the derive macro `Diagnostic` which comes from the expansion of the macro `forward` (in Nightly builds, run with -Z macro-backtrace for more info)
 
-error: aborting due to 85 previous errors
+error: aborting due to 83 previous errors
 
 Some errors have detailed explanations: E0277, E0425.
 For more information about an error, try `rustc --explain E0277`.