Auto merge of #119286 - jyn514:linker-output, r=bjorn3

show linker output even if the linker succeeds

Show stderr and stderr by default, controlled by a new `linker_messages` lint.

fixes https://github.com/rust-lang/rust/issues/83436. fixes https://github.com/rust-lang/rust/issues/38206. cc https://rust-lang.zulipchat.com/#narrow/stream/233931-t-compiler.2Fmajor-changes/topic/uplift.20some.20-Zverbose.20calls.20and.20rename.20to.E2.80.A6.20compiler-team.23706/near/408986134

<!-- try-job: dist-x86_64-msvc -->
try-job: aarch64-apple

r? `@bjorn3`

compiler/rustc_passes/messages.ftl

@@ -812,6 +812,9 @@ passes_unused_duplicate =
 passes_unused_empty_lints_note =
     attribute `{$name}` with an empty list has no effect
 
+passes_unused_linker_warnings_note =
+    the `linker_warnings` lint can only be controlled at the root of a crate that needs to be linked
+
 passes_unused_multiple =
     multiple `{$name}` attributes
     .suggestion = remove this attribute

compiler/rustc_passes/src/check_attr.rs

@@ -25,6 +25,7 @@ use rustc_middle::traits::ObligationCause;
 use rustc_middle::ty::error::{ExpectedFound, TypeError};
 use rustc_middle::ty::{self, TyCtxt, TypingMode};
 use rustc_middle::{bug, span_bug};
+use rustc_session::config::CrateType;
 use rustc_session::lint::builtin::{
     CONFLICTING_REPR_HINTS, INVALID_DOC_ATTRIBUTES, INVALID_MACRO_EXPORT_ARGUMENTS,
     UNKNOWN_OR_MALFORMED_DIAGNOSTIC_ATTRIBUTES, UNUSED_ATTRIBUTES,
@@ -2327,6 +2328,42 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
             && item.path == sym::reason
         {
             errors::UnusedNote::NoLints { name: attr.name_or_empty() }
+        } else if matches!(
+            attr.name_or_empty(),
+            sym::allow | sym::warn | sym::deny | sym::forbid | sym::expect
+        ) && let Some(meta) = attr.meta_item_list()
+            && meta.iter().any(|meta| {
+                meta.meta_item().map_or(false, |item| item.path == sym::linker_messages)
+            })
+        {
+            if hir_id != CRATE_HIR_ID {
+                match attr.style {
+                    ast::AttrStyle::Outer => self.tcx.emit_node_span_lint(
+                        UNUSED_ATTRIBUTES,
+                        hir_id,
+                        attr.span,
+                        errors::OuterCrateLevelAttr,
+                    ),
+                    ast::AttrStyle::Inner => self.tcx.emit_node_span_lint(
+                        UNUSED_ATTRIBUTES,
+                        hir_id,
+                        attr.span,
+                        errors::InnerCrateLevelAttr,
+                    ),
+                };
+                return;
+            } else {
+                let never_needs_link = self
+                    .tcx
+                    .crate_types()
+                    .iter()
+                    .all(|kind| matches!(kind, CrateType::Rlib | CrateType::Staticlib));
+                if never_needs_link {
+                    errors::UnusedNote::LinkerWarningsBinaryCrateOnly
+                } else {
+                    return;
+                }
+            }
         } else if attr.name_or_empty() == sym::default_method_body_is_const {
             errors::UnusedNote::DefaultMethodBodyConst
         } else {

compiler/rustc_passes/src/errors.rs

@@ -802,6 +802,8 @@ pub(crate) enum UnusedNote {
     NoLints { name: Symbol },
     #[note(passes_unused_default_method_body_const_note)]
     DefaultMethodBodyConst,
+    #[note(passes_unused_linker_warnings_note)]
+    LinkerWarningsBinaryCrateOnly,
 }
 
 #[derive(LintDiagnostic)]