From 44ece2e9cef484368cfef98f0e287e5a6d1011dd Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Esteban=20K=C3=BCber?= <esteban@kuber.com.ar>
Date: Sat, 1 Nov 2025 19:21:27 +0000
Subject: [PATCH] Point at inner item when using outer const param

```
error[E0401]: can't use generic parameters from outer item
  --> $DIR/const-param-from-outer-fn.rs:3:9
   |
LL | fn foo<const X: u32>() {
   |              - const parameter from outer item
LL |     fn bar() -> u32 {
   |        --- generic parameter used in this inner function
LL |         X
   |         ^ use of generic parameter from outer item
   |
help: try introducing a local generic parameter here
   |
LL |     fn bar<X>() -> u32 {
   |           +++
```
---
 compiler/rustc_resolve/src/ident.rs           | 14 ++++++++++++-
 .../early/const-param-from-outer-fn.stderr    |  1 +
 ...e-65035-static-with-parent-generics.stderr | 21 ++++++++++++-------
 3 files changed, 28 insertions(+), 8 deletions(-)

diff --git a/compiler/rustc_resolve/src/ident.rs b/compiler/rustc_resolve/src/ident.rs
index 4856b1e7cf97..2abf129e9456 100644
--- a/compiler/rustc_resolve/src/ident.rs
+++ b/compiler/rustc_resolve/src/ident.rs
@@ -1484,13 +1484,25 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
 
                     // This was an attempt to use a const parameter outside its scope.
                     if let Some(span) = finalize {
+                        let item = if let Some(diag_metadata) = diag_metadata
+                            && let Some(current_item) = diag_metadata.current_item
+                        {
+                            let span = current_item
+                                .kind
+                                .ident()
+                                .map(|i| i.span)
+                                .unwrap_or(current_item.span);
+                            Some((span, current_item.kind.descr().to_string()))
+                        } else {
+                            None
+                        };
                         self.report_error(
                             span,
                             ResolutionError::GenericParamsFromOuterItem(
                                 res,
                                 has_generic_params,
                                 def_kind,
-                                None,
+                                item,
                             ),
                         );
                     }
diff --git a/tests/ui/const-generics/early/const-param-from-outer-fn.stderr b/tests/ui/const-generics/early/const-param-from-outer-fn.stderr
index 0f7c7fbc6be0..3c25dff41aa2 100644
--- a/tests/ui/const-generics/early/const-param-from-outer-fn.stderr
+++ b/tests/ui/const-generics/early/const-param-from-outer-fn.stderr
@@ -4,6 +4,7 @@ error[E0401]: can't use generic parameters from outer item
 LL | fn foo<const X: u32>() {
    |              - const parameter from outer item
 LL |     fn bar() -> u32 {
+   |        --- generic parameter used in this inner function
 LL |         X
    |         ^ use of generic parameter from outer item
    |
diff --git a/tests/ui/resolve/issue-65035-static-with-parent-generics.stderr b/tests/ui/resolve/issue-65035-static-with-parent-generics.stderr
index 869e1729cb85..b22bfb719bd5 100644
--- a/tests/ui/resolve/issue-65035-static-with-parent-generics.stderr
+++ b/tests/ui/resolve/issue-65035-static-with-parent-generics.stderr
@@ -27,11 +27,14 @@ LL |     static a: *const T = Default::default();
 error[E0401]: can't use generic parameters from outer item
   --> $DIR/issue-65035-static-with-parent-generics.rs:15:24
    |
-LL | fn h<const N: usize>() {
-   |            - const parameter from outer item
-LL |     extern "C" {
-LL |         static a: [u8; N];
-   |                        ^ use of generic parameter from outer item
+LL |   fn h<const N: usize>() {
+   |              - const parameter from outer item
+LL | /     extern "C" {
+LL | |         static a: [u8; N];
+   | |                        ^ use of generic parameter from outer item
+LL | |
+LL | |     }
+   | |_____- generic parameter used in this inner extern block
    |
    = note: a `static` is a separate item from the item that contains it
 
@@ -41,7 +44,9 @@ error[E0401]: can't use generic parameters from outer item
 LL | fn i<const N: usize>() {
    |            - const parameter from outer item
 LL |     static a: [u8; N] = [0; N];
-   |                    ^ use of generic parameter from outer item
+   |            -       ^ use of generic parameter from outer item
+   |            |
+   |            generic parameter used in this inner static item
    |
    = note: a `static` is a separate item from the item that contains it
 
@@ -51,7 +56,9 @@ error[E0401]: can't use generic parameters from outer item
 LL | fn i<const N: usize>() {
    |            - const parameter from outer item
 LL |     static a: [u8; N] = [0; N];
-   |                             ^ use of generic parameter from outer item
+   |            -                ^ use of generic parameter from outer item
+   |            |
+   |            generic parameter used in this inner static item
    |
    = note: a `static` is a separate item from the item that contains it