diff --git a/compiler/rustc_lint_defs/src/builtin.rs b/compiler/rustc_lint_defs/src/builtin.rs
index 8f908cf96c8c1..80d8167765322 100644
--- a/compiler/rustc_lint_defs/src/builtin.rs
+++ b/compiler/rustc_lint_defs/src/builtin.rs
@@ -271,6 +271,30 @@ declare_lint! {
     };
 }
 
+declare_lint! {
+    /// The `repeated_reprs` lint detects when the same representation is
+    /// specified more than once in a `#[repr(..)]` attribute.
+    ///
+    /// ### Example
+    ///
+    /// ```rust
+    /// #[repr(C)]
+    /// #[repr(C)]
+    /// enum Foo { A }
+    /// ```
+    ///
+    /// {{produces}}
+    ///
+    /// ### Explanation
+    ///
+    /// While some representations may be specified more than once, the compiler
+    /// will reject repeated uses of some others. For consistency, prefer to
+    /// only specify the representation once.
+    pub REPEATED_REPRS,
+    Warn,
+    "detects repeated representations in `#[repr(..)]` attributes",
+}
+
 declare_lint! {
     /// The `meta_variable_misuse` lint detects possible meta-variable misuse
     /// in macro definitions.
diff --git a/compiler/rustc_passes/src/check_attr.rs b/compiler/rustc_passes/src/check_attr.rs
index d698a7ed4127a..2b2477df527c7 100644
--- a/compiler/rustc_passes/src/check_attr.rs
+++ b/compiler/rustc_passes/src/check_attr.rs
@@ -40,7 +40,7 @@ use rustc_session::errors::feature_err;
 use rustc_session::lint;
 use rustc_session::lint::builtin::{
     CONFLICTING_REPR_HINTS, INVALID_DOC_ATTRIBUTES, MALFORMED_DIAGNOSTIC_FORMAT_LITERALS,
-    MISPLACED_DIAGNOSTIC_ATTRIBUTES, UNUSED_ATTRIBUTES,
+    MISPLACED_DIAGNOSTIC_ATTRIBUTES, REPEATED_REPRS, UNUSED_ATTRIBUTES,
 };
 use rustc_span::edition::Edition;
 use rustc_span::{DUMMY_SP, Ident, Span, Symbol, sym};
@@ -1212,24 +1212,59 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
         let mut is_c = false;
         let mut is_simd = false;
         let mut is_transparent = false;
+        let mut is_align = false;
+        let mut is_packed = false;
+        let mut repeated_repr = false;
+        let mut maybe_last_int_type = None;
 
         for (repr, _repr_span) in reprs {
             match repr {
                 ReprAttr::ReprRust => {
+                    if is_explicit_rust {
+                        repeated_repr = true;
+                    }
                     is_explicit_rust = true;
                 }
                 ReprAttr::ReprC => {
+                    if is_c {
+                        repeated_repr = true;
+                    }
                     is_c = true;
                 }
-                ReprAttr::ReprAlign(..) => {}
-                ReprAttr::ReprPacked(_) => {}
+                ReprAttr::ReprAlign(..) => {
+                    if is_align {
+                        repeated_repr = true;
+                    }
+                    is_align = true;
+                }
+                ReprAttr::ReprPacked(..) => {
+                    if is_packed {
+                        repeated_repr = true;
+                    }
+                    is_packed = true;
+                }
                 ReprAttr::ReprSimd => {
+                    if is_simd {
+                        repeated_repr = true;
+                    }
                     is_simd = true;
                 }
                 ReprAttr::ReprTransparent => {
+                    // No need to check for repeated transparent because that is already checked
+                    // when checking for any other attribute together with transparent.
                     is_transparent = true;
                 }
-                ReprAttr::ReprInt(_) => {
+                ReprAttr::ReprInt(int_type) => {
+                    if let Some(last_int_type) = maybe_last_int_type
+                        && last_int_type == int_type
+                    {
+                        // We'll "miss" detecting repeated int reprs if the user specifies
+                        // #[repr(u8, u64, u8)] for example. But that's okay because we've got
+                        // conflicting reprs anyway so it's not worth the effort to do more precise
+                        // tracking.
+                        repeated_repr = true;
+                    }
+                    maybe_last_int_type = Some(int_type);
                     int_reprs += 1;
                 }
             };
@@ -1274,10 +1309,19 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
             self.tcx.emit_node_span_lint(
                 CONFLICTING_REPR_HINTS,
                 hir_id,
-                hint_spans.collect::<Vec<Span>>(),
+                hint_spans.clone().collect::<Vec<Span>>(),
                 errors::ReprConflictingLint,
             );
         }
+
+        if repeated_repr {
+            self.tcx.emit_node_span_lint(
+                REPEATED_REPRS,
+                hir_id,
+                hint_spans.collect::<Vec<Span>>(),
+                errors::RepeatedRepr,
+            );
+        }
     }
 
     /// Outputs an error for attributes that can only be applied to macros, such as
diff --git a/compiler/rustc_passes/src/errors.rs b/compiler/rustc_passes/src/errors.rs
index 97dd413e16cf6..3f9e4a16da9c3 100644
--- a/compiler/rustc_passes/src/errors.rs
+++ b/compiler/rustc_passes/src/errors.rs
@@ -703,6 +703,11 @@ pub(crate) struct TransparentIncompatible {
     pub target: String,
 }
 
+#[derive(Diagnostic)]
+#[diag("representation attribute is specified more than once")]
+#[note("for consistency, only specify the representation once")]
+pub(crate) struct RepeatedRepr;
+
 #[derive(Diagnostic)]
 #[diag("deprecated attribute must be paired with either stable or unstable attribute", code = E0549)]
 pub(crate) struct DeprecatedAttribute {
diff --git a/tests/ui/attributes/issue-100631.rs b/tests/ui/attributes/issue-100631.rs
index 0fefcf83fd516..d496231c73026 100644
--- a/tests/ui/attributes/issue-100631.rs
+++ b/tests/ui/attributes/issue-100631.rs
@@ -2,6 +2,7 @@
 // can reasonably deal with multiple attributes.
 // `repr` will use `TyCtxt::get_attrs` since it's `DuplicatesOk`.
 #[repr(C)] //~ ERROR: unsupported representation for zero-variant enum [E0084]
+//~^ WARN representation attribute is specified more than once
 #[repr(C)]
 enum Foo {}
 
diff --git a/tests/ui/attributes/issue-100631.stderr b/tests/ui/attributes/issue-100631.stderr
index b2bd0a9632513..66e08738eb02c 100644
--- a/tests/ui/attributes/issue-100631.stderr
+++ b/tests/ui/attributes/issue-100631.stderr
@@ -1,12 +1,24 @@
-error[E0084]: unsupported representation for zero-variant enum
+warning: representation attribute is specified more than once
   --> $DIR/issue-100631.rs:4:8
    |
 LL | #[repr(C)]
    |        ^
+LL |
 LL | #[repr(C)]
+   |        ^
+   |
+   = note: for consistency, only specify the representation once
+   = note: `#[warn(repeated_reprs)]` on by default
+
+error[E0084]: unsupported representation for zero-variant enum
+  --> $DIR/issue-100631.rs:4:8
+   |
+LL | #[repr(C)]
+   |        ^
+...
 LL | enum Foo {}
    | -------- zero-variant enum
 
-error: aborting due to 1 previous error
+error: aborting due to 1 previous error; 1 warning emitted
 
 For more information about this error, try `rustc --explain E0084`.
diff --git a/tests/ui/lint/unused/unused-attr-duplicate.rs b/tests/ui/lint/unused/unused-attr-duplicate.rs
index 54c040f4bcac4..348c9590e8b27 100644
--- a/tests/ui/lint/unused/unused-attr-duplicate.rs
+++ b/tests/ui/lint/unused/unused-attr-duplicate.rs
@@ -64,8 +64,7 @@ fn t1() {}
 #[must_use = "some message"]
 //~^ ERROR unused attribute
 //~| WARN this was previously accepted
-// No warnings for #[repr], would require more logic.
-#[repr(C)]
+#[repr(C)] //~ WARN representation attribute is specified more than once
 #[repr(C)]
 #[non_exhaustive]
 #[non_exhaustive] //~ ERROR unused attribute
diff --git a/tests/ui/lint/unused/unused-attr-duplicate.stderr b/tests/ui/lint/unused/unused-attr-duplicate.stderr
index f25263e9cef90..bf66392162878 100644
--- a/tests/ui/lint/unused/unused-attr-duplicate.stderr
+++ b/tests/ui/lint/unused/unused-attr-duplicate.stderr
@@ -16,6 +16,17 @@ note: the lint level is defined here
 LL | #![deny(unused_attributes)]
    |         ^^^^^^^^^^^^^^^^^
 
+warning: representation attribute is specified more than once
+  --> $DIR/unused-attr-duplicate.rs:67:8
+   |
+LL | #[repr(C)]
+   |        ^
+LL | #[repr(C)]
+   |        ^
+   |
+   = note: for consistency, only specify the representation once
+   = note: `#[warn(repeated_reprs)]` on by default
+
 error: unused attribute
   --> $DIR/unused-attr-duplicate.rs:37:1
    |
@@ -104,124 +115,124 @@ LL | #[must_use]
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
 
 error: unused attribute
-  --> $DIR/unused-attr-duplicate.rs:71:1
+  --> $DIR/unused-attr-duplicate.rs:70:1
    |
 LL | #[non_exhaustive]
    | ^^^^^^^^^^^^^^^^^ help: remove this attribute
    |
 note: attribute also specified here
-  --> $DIR/unused-attr-duplicate.rs:70:1
+  --> $DIR/unused-attr-duplicate.rs:69:1
    |
 LL | #[non_exhaustive]
    | ^^^^^^^^^^^^^^^^^
 
 error: unused attribute
-  --> $DIR/unused-attr-duplicate.rs:77:1
+  --> $DIR/unused-attr-duplicate.rs:76:1
    |
 LL | #[automatically_derived]
    | ^^^^^^^^^^^^^^^^^^^^^^^^ help: remove this attribute
    |
 note: attribute also specified here
-  --> $DIR/unused-attr-duplicate.rs:76:1
+  --> $DIR/unused-attr-duplicate.rs:75:1
    |
 LL | #[automatically_derived]
    | ^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: unused attribute
-  --> $DIR/unused-attr-duplicate.rs:81:1
+  --> $DIR/unused-attr-duplicate.rs:80:1
    |
 LL | #[inline(never)]
    | ^^^^^^^^^^^^^^^^ help: remove this attribute
    |
 note: attribute also specified here
-  --> $DIR/unused-attr-duplicate.rs:80:1
+  --> $DIR/unused-attr-duplicate.rs:79:1
    |
 LL | #[inline(always)]
    | ^^^^^^^^^^^^^^^^^
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
 
 error: unused attribute
-  --> $DIR/unused-attr-duplicate.rs:84:1
+  --> $DIR/unused-attr-duplicate.rs:83:1
    |
 LL | #[cold]
    | ^^^^^^^ help: remove this attribute
    |
 note: attribute also specified here
-  --> $DIR/unused-attr-duplicate.rs:83:1
+  --> $DIR/unused-attr-duplicate.rs:82:1
    |
 LL | #[cold]
    | ^^^^^^^
 
 error: unused attribute
-  --> $DIR/unused-attr-duplicate.rs:86:1
+  --> $DIR/unused-attr-duplicate.rs:85:1
    |
 LL | #[track_caller]
    | ^^^^^^^^^^^^^^^ help: remove this attribute
    |
 note: attribute also specified here
-  --> $DIR/unused-attr-duplicate.rs:85:1
+  --> $DIR/unused-attr-duplicate.rs:84:1
    |
 LL | #[track_caller]
    | ^^^^^^^^^^^^^^^
 
 error: unused attribute
-  --> $DIR/unused-attr-duplicate.rs:94:5
+  --> $DIR/unused-attr-duplicate.rs:93:5
    |
 LL |     #[link_name = "rust_dbg_extern_identity_u32"]
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: remove this attribute
    |
 note: attribute also specified here
-  --> $DIR/unused-attr-duplicate.rs:93:5
+  --> $DIR/unused-attr-duplicate.rs:92:5
    |
 LL |     #[link_name = "this_does_not_exist"]
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
 
 error: unused attribute
-  --> $DIR/unused-attr-duplicate.rs:100:1
+  --> $DIR/unused-attr-duplicate.rs:99:1
    |
 LL | #[export_name = "exported_symbol_name2"]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: remove this attribute
    |
 note: attribute also specified here
-  --> $DIR/unused-attr-duplicate.rs:99:1
+  --> $DIR/unused-attr-duplicate.rs:98:1
    |
 LL | #[export_name = "exported_symbol_name"]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
 
 error: unused attribute
-  --> $DIR/unused-attr-duplicate.rs:105:1
+  --> $DIR/unused-attr-duplicate.rs:104:1
    |
 LL | #[no_mangle]
    | ^^^^^^^^^^^^ help: remove this attribute
    |
 note: attribute also specified here
-  --> $DIR/unused-attr-duplicate.rs:104:1
+  --> $DIR/unused-attr-duplicate.rs:103:1
    |
 LL | #[no_mangle]
    | ^^^^^^^^^^^^
 
 error: unused attribute
-  --> $DIR/unused-attr-duplicate.rs:109:1
+  --> $DIR/unused-attr-duplicate.rs:108:1
    |
 LL | #[used]
    | ^^^^^^^ help: remove this attribute
    |
 note: attribute also specified here
-  --> $DIR/unused-attr-duplicate.rs:108:1
+  --> $DIR/unused-attr-duplicate.rs:107:1
    |
 LL | #[used]
    | ^^^^^^^
 
 error: unused attribute
-  --> $DIR/unused-attr-duplicate.rs:113:1
+  --> $DIR/unused-attr-duplicate.rs:112:1
    |
 LL | #[link_section = "__DATA,__mod_init_func"]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: remove this attribute
    |
 note: attribute also specified here
-  --> $DIR/unused-attr-duplicate.rs:112:1
+  --> $DIR/unused-attr-duplicate.rs:111:1
    |
 LL | #[link_section = "__TEXT,__text"]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -316,5 +327,5 @@ note: attribute also specified here
 LL | #![no_builtins]
    | ^^^^^^^^^^^^^^^
 
-error: aborting due to 25 previous errors
+error: aborting due to 25 previous errors; 1 warning emitted
 
diff --git a/tests/ui/repr/conflicting-repr-hints.rs b/tests/ui/repr/conflicting-repr-hints.rs
index ed82b6a742c8d..032f2b2e6c608 100644
--- a/tests/ui/repr/conflicting-repr-hints.rs
+++ b/tests/ui/repr/conflicting-repr-hints.rs
@@ -36,14 +36,14 @@ struct G(i32); //~ ERROR type has conflicting packed and align representation hi
 #[repr(packed)]
 struct H(i32); //~ ERROR type has conflicting packed and align representation hints
 
-#[repr(packed, packed(2))]
+#[repr(packed, packed(2))] //~ WARN representation attribute is specified more than once
 struct I(i32); //~ ERROR type has conflicting packed representation hints
 
-#[repr(packed(2))]
+#[repr(packed(2))] //~ WARN representation attribute is specified more than once
 #[repr(packed)]
 struct J(i32); //~ ERROR type has conflicting packed representation hints
 
-#[repr(packed, packed(1))]
+#[repr(packed, packed(1))] //~ WARN attribute is specified more than once
 struct K(i32);
 
 #[repr(packed, align(8))]
diff --git a/tests/ui/repr/conflicting-repr-hints.stderr b/tests/ui/repr/conflicting-repr-hints.stderr
index 4da3d454e037d..a99546b754785 100644
--- a/tests/ui/repr/conflicting-repr-hints.stderr
+++ b/tests/ui/repr/conflicting-repr-hints.stderr
@@ -17,6 +17,33 @@ LL | #[repr(u32, u64)]
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
    = note: for more information, see issue #68585 <https://github.com/rust-lang/rust/issues/68585>
 
+warning: representation attribute is specified more than once
+  --> $DIR/conflicting-repr-hints.rs:39:8
+   |
+LL | #[repr(packed, packed(2))]
+   |        ^^^^^^  ^^^^^^^^^
+   |
+   = note: for consistency, only specify the representation once
+   = note: `#[warn(repeated_reprs)]` on by default
+
+warning: representation attribute is specified more than once
+  --> $DIR/conflicting-repr-hints.rs:42:8
+   |
+LL | #[repr(packed(2))]
+   |        ^^^^^^^^^
+LL | #[repr(packed)]
+   |        ^^^^^^
+   |
+   = note: for consistency, only specify the representation once
+
+warning: representation attribute is specified more than once
+  --> $DIR/conflicting-repr-hints.rs:46:8
+   |
+LL | #[repr(packed, packed(1))]
+   |        ^^^^^^  ^^^^^^^^^
+   |
+   = note: for consistency, only specify the representation once
+
 error[E0587]: type has conflicting packed and align representation hints
   --> $DIR/conflicting-repr-hints.rs:29:1
    |
@@ -77,7 +104,7 @@ error[E0587]: type has conflicting packed and align representation hints
 LL | pub union U {
    | ^^^^^^^^^^^
 
-error: aborting due to 12 previous errors
+error: aborting due to 12 previous errors; 3 warnings emitted
 
 Some errors have detailed explanations: E0566, E0587, E0634.
 For more information about an error, try `rustc --explain E0566`.
diff --git a/tests/ui/repr/repr-repeated-attrs.rs b/tests/ui/repr/repr-repeated-attrs.rs
new file mode 100644
index 0000000000000..61e3ba05625d8
--- /dev/null
+++ b/tests/ui/repr/repr-repeated-attrs.rs
@@ -0,0 +1,69 @@
+// Tests to ensure we warn on repeated `#[repr(..)]` attributes.
+
+#[repr(transparent, transparent)]
+//~^ ERROR transparent struct cannot have other repr hints
+#[repr(transparent)]
+struct SeveralTransparentReprs(*mut u8);
+
+#[repr(transparent)]
+//~^ ERROR transparent struct cannot have other repr hints
+#[repr(transparent)]
+struct MultilineOnly(*mut u8);
+
+#[repr(Rust, Rust)]
+//~^ WARN representation attribute is specified more than once
+struct SeveralRustReprs(u8);
+
+#[repr(C, C)]
+//~^ WARN representation attribute is specified more than once
+#[repr(C, C, C)]
+struct SeveralC(u8);
+
+#[repr(u8, u8)] //~ WARN representation attribute is specified more than once
+//~^ ERROR conflicting representation hints
+//~| WARN this was previously accepted
+enum SeveralPrimitiveRerprs {
+    Variant,
+}
+
+#[repr(C, C, u8)] //~ WARN representation attribute is specified more than once
+//~^ ERROR conflicting representation hints
+//~| WARN this was previously accepted
+#[repr(C, u8, u8)]
+enum SeveralCAndPrims {
+    Variant(u8),
+}
+
+#[repr(Rust, u8, u8)] //~ WARN representation attribute is specified more than once
+//~^ ERROR conflicting representation hints
+//~^^ ERROR conflicting representation hints
+//~| WARN this was previously accepted
+enum RustAndPrimDisallowed {
+    Variant(u8),
+}
+
+#[repr(u8, u8)] //~ WARN representation attribute is specified more than once
+//~^ ERROR conflicting representation hints
+//~| WARN this was previously accepted
+#[repr(u16)]
+enum ConflictingPrimReprs {
+    Variant,
+}
+
+#[repr(C, u8)]
+//~^ ERROR conflicting representation hints
+//~| WARN this was previously accepted
+enum CWithIntsCausesFCW1 {
+    A,
+    B,
+}
+
+#[repr(C, C, u8, u8, u8)] //~ WARN representation attribute is specified more than once
+//~^ ERROR conflicting representation hints
+//~| WARN this was previously accepted
+enum CWithIntsCausesFCW2 {
+    A,
+    B,
+}
+
+fn main() {}
diff --git a/tests/ui/repr/repr-repeated-attrs.stderr b/tests/ui/repr/repr-repeated-attrs.stderr
new file mode 100644
index 0000000000000..57af8ec804d76
--- /dev/null
+++ b/tests/ui/repr/repr-repeated-attrs.stderr
@@ -0,0 +1,227 @@
+error[E0692]: transparent struct cannot have other repr hints
+  --> $DIR/repr-repeated-attrs.rs:3:8
+   |
+LL | #[repr(transparent, transparent)]
+   |        ^^^^^^^^^^^  ^^^^^^^^^^^
+LL |
+LL | #[repr(transparent)]
+   |        ^^^^^^^^^^^
+
+error[E0692]: transparent struct cannot have other repr hints
+  --> $DIR/repr-repeated-attrs.rs:8:8
+   |
+LL | #[repr(transparent)]
+   |        ^^^^^^^^^^^
+LL |
+LL | #[repr(transparent)]
+   |        ^^^^^^^^^^^
+
+warning: representation attribute is specified more than once
+  --> $DIR/repr-repeated-attrs.rs:13:8
+   |
+LL | #[repr(Rust, Rust)]
+   |        ^^^^  ^^^^
+   |
+   = note: for consistency, only specify the representation once
+   = note: `#[warn(repeated_reprs)]` on by default
+
+warning: representation attribute is specified more than once
+  --> $DIR/repr-repeated-attrs.rs:17:8
+   |
+LL | #[repr(C, C)]
+   |        ^  ^
+LL |
+LL | #[repr(C, C, C)]
+   |        ^  ^  ^
+   |
+   = note: for consistency, only specify the representation once
+
+error[E0566]: conflicting representation hints
+  --> $DIR/repr-repeated-attrs.rs:22:8
+   |
+LL | #[repr(u8, u8)]
+   |        ^^  ^^
+   |
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = note: for more information, see issue #68585 <https://github.com/rust-lang/rust/issues/68585>
+   = note: `#[deny(conflicting_repr_hints)]` (part of `#[deny(future_incompatible)]`) on by default
+
+warning: representation attribute is specified more than once
+  --> $DIR/repr-repeated-attrs.rs:22:8
+   |
+LL | #[repr(u8, u8)]
+   |        ^^  ^^
+   |
+   = note: for consistency, only specify the representation once
+
+error[E0566]: conflicting representation hints
+  --> $DIR/repr-repeated-attrs.rs:29:8
+   |
+LL | #[repr(C, C, u8)]
+   |        ^  ^  ^^
+...
+LL | #[repr(C, u8, u8)]
+   |        ^  ^^  ^^
+   |
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = note: for more information, see issue #68585 <https://github.com/rust-lang/rust/issues/68585>
+
+warning: representation attribute is specified more than once
+  --> $DIR/repr-repeated-attrs.rs:29:8
+   |
+LL | #[repr(C, C, u8)]
+   |        ^  ^  ^^
+...
+LL | #[repr(C, u8, u8)]
+   |        ^  ^^  ^^
+   |
+   = note: for consistency, only specify the representation once
+
+error[E0566]: conflicting representation hints
+  --> $DIR/repr-repeated-attrs.rs:37:8
+   |
+LL | #[repr(Rust, u8, u8)]
+   |        ^^^^  ^^  ^^
+
+error[E0566]: conflicting representation hints
+  --> $DIR/repr-repeated-attrs.rs:37:8
+   |
+LL | #[repr(Rust, u8, u8)]
+   |        ^^^^  ^^  ^^
+   |
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = note: for more information, see issue #68585 <https://github.com/rust-lang/rust/issues/68585>
+
+warning: representation attribute is specified more than once
+  --> $DIR/repr-repeated-attrs.rs:37:8
+   |
+LL | #[repr(Rust, u8, u8)]
+   |        ^^^^  ^^  ^^
+   |
+   = note: for consistency, only specify the representation once
+
+error[E0566]: conflicting representation hints
+  --> $DIR/repr-repeated-attrs.rs:45:8
+   |
+LL | #[repr(u8, u8)]
+   |        ^^  ^^
+...
+LL | #[repr(u16)]
+   |        ^^^
+   |
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = note: for more information, see issue #68585 <https://github.com/rust-lang/rust/issues/68585>
+
+warning: representation attribute is specified more than once
+  --> $DIR/repr-repeated-attrs.rs:45:8
+   |
+LL | #[repr(u8, u8)]
+   |        ^^  ^^
+...
+LL | #[repr(u16)]
+   |        ^^^
+   |
+   = note: for consistency, only specify the representation once
+
+error[E0566]: conflicting representation hints
+  --> $DIR/repr-repeated-attrs.rs:53:8
+   |
+LL | #[repr(C, u8)]
+   |        ^  ^^
+   |
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = note: for more information, see issue #68585 <https://github.com/rust-lang/rust/issues/68585>
+
+error[E0566]: conflicting representation hints
+  --> $DIR/repr-repeated-attrs.rs:61:8
+   |
+LL | #[repr(C, C, u8, u8, u8)]
+   |        ^  ^  ^^  ^^  ^^
+   |
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = note: for more information, see issue #68585 <https://github.com/rust-lang/rust/issues/68585>
+
+warning: representation attribute is specified more than once
+  --> $DIR/repr-repeated-attrs.rs:61:8
+   |
+LL | #[repr(C, C, u8, u8, u8)]
+   |        ^  ^  ^^  ^^  ^^
+   |
+   = note: for consistency, only specify the representation once
+
+error: aborting due to 9 previous errors; 7 warnings emitted
+
+Some errors have detailed explanations: E0566, E0692.
+For more information about an error, try `rustc --explain E0566`.
+Future incompatibility report: Future breakage diagnostic:
+error[E0566]: conflicting representation hints
+  --> $DIR/repr-repeated-attrs.rs:22:8
+   |
+LL | #[repr(u8, u8)]
+   |        ^^  ^^
+   |
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = note: for more information, see issue #68585 <https://github.com/rust-lang/rust/issues/68585>
+   = note: `#[deny(conflicting_repr_hints)]` (part of `#[deny(future_incompatible)]`) on by default
+
+Future breakage diagnostic:
+error[E0566]: conflicting representation hints
+  --> $DIR/repr-repeated-attrs.rs:29:8
+   |
+LL | #[repr(C, C, u8)]
+   |        ^  ^  ^^
+...
+LL | #[repr(C, u8, u8)]
+   |        ^  ^^  ^^
+   |
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = note: for more information, see issue #68585 <https://github.com/rust-lang/rust/issues/68585>
+   = note: `#[deny(conflicting_repr_hints)]` (part of `#[deny(future_incompatible)]`) on by default
+
+Future breakage diagnostic:
+error[E0566]: conflicting representation hints
+  --> $DIR/repr-repeated-attrs.rs:37:8
+   |
+LL | #[repr(Rust, u8, u8)]
+   |        ^^^^  ^^  ^^
+   |
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = note: for more information, see issue #68585 <https://github.com/rust-lang/rust/issues/68585>
+   = note: `#[deny(conflicting_repr_hints)]` (part of `#[deny(future_incompatible)]`) on by default
+
+Future breakage diagnostic:
+error[E0566]: conflicting representation hints
+  --> $DIR/repr-repeated-attrs.rs:45:8
+   |
+LL | #[repr(u8, u8)]
+   |        ^^  ^^
+...
+LL | #[repr(u16)]
+   |        ^^^
+   |
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = note: for more information, see issue #68585 <https://github.com/rust-lang/rust/issues/68585>
+   = note: `#[deny(conflicting_repr_hints)]` (part of `#[deny(future_incompatible)]`) on by default
+
+Future breakage diagnostic:
+error[E0566]: conflicting representation hints
+  --> $DIR/repr-repeated-attrs.rs:53:8
+   |
+LL | #[repr(C, u8)]
+   |        ^  ^^
+   |
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = note: for more information, see issue #68585 <https://github.com/rust-lang/rust/issues/68585>
+   = note: `#[deny(conflicting_repr_hints)]` (part of `#[deny(future_incompatible)]`) on by default
+
+Future breakage diagnostic:
+error[E0566]: conflicting representation hints
+  --> $DIR/repr-repeated-attrs.rs:61:8
+   |
+LL | #[repr(C, C, u8, u8, u8)]
+   |        ^  ^  ^^  ^^  ^^
+   |
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = note: for more information, see issue #68585 <https://github.com/rust-lang/rust/issues/68585>
+   = note: `#[deny(conflicting_repr_hints)]` (part of `#[deny(future_incompatible)]`) on by default
+
diff --git a/tests/ui/structs-enums/align-enum.rs b/tests/ui/structs-enums/align-enum.rs
index ff80a19211cda..a635af7352afe 100644
--- a/tests/ui/structs-enums/align-enum.rs
+++ b/tests/ui/structs-enums/align-enum.rs
@@ -11,7 +11,7 @@ enum Align16 {
 }
 
 // Raise alignment by maximum
-#[repr(align(1), align(16))]
+#[repr(align(1), align(16))] //~ WARN representation attribute is specified more than once
 #[repr(align(32))]
 #[repr(align(4))]
 enum Align32 {
diff --git a/tests/ui/structs-enums/align-enum.stderr b/tests/ui/structs-enums/align-enum.stderr
new file mode 100644
index 0000000000000..9b8c9842f81df
--- /dev/null
+++ b/tests/ui/structs-enums/align-enum.stderr
@@ -0,0 +1,15 @@
+warning: representation attribute is specified more than once
+  --> $DIR/align-enum.rs:14:8
+   |
+LL | #[repr(align(1), align(16))]
+   |        ^^^^^^^^  ^^^^^^^^^
+LL | #[repr(align(32))]
+   |        ^^^^^^^^^
+LL | #[repr(align(4))]
+   |        ^^^^^^^^
+   |
+   = note: for consistency, only specify the representation once
+   = note: `#[warn(repeated_reprs)]` on by default
+
+warning: 1 warning emitted
+
diff --git a/tests/ui/structs-enums/align-struct.rs b/tests/ui/structs-enums/align-struct.rs
index 3d8dad6e324e3..2d1ebf6731a62 100644
--- a/tests/ui/structs-enums/align-struct.rs
+++ b/tests/ui/structs-enums/align-struct.rs
@@ -13,7 +13,7 @@ struct Align16(i32);
 struct Align1(i32);
 
 // Multiple attributes take the max
-#[repr(align(4))]
+#[repr(align(4))] //~ WARN representation attribute is specified more than once
 #[repr(align(16))]
 #[repr(align(8))]
 struct AlignMany(i32);
diff --git a/tests/ui/structs-enums/align-struct.stderr b/tests/ui/structs-enums/align-struct.stderr
new file mode 100644
index 0000000000000..f54e9cd14cd8b
--- /dev/null
+++ b/tests/ui/structs-enums/align-struct.stderr
@@ -0,0 +1,15 @@
+warning: representation attribute is specified more than once
+  --> $DIR/align-struct.rs:16:8
+   |
+LL | #[repr(align(4))]
+   |        ^^^^^^^^
+LL | #[repr(align(16))]
+   |        ^^^^^^^^^
+LL | #[repr(align(8))]
+   |        ^^^^^^^^
+   |
+   = note: for consistency, only specify the representation once
+   = note: `#[warn(repeated_reprs)]` on by default
+
+warning: 1 warning emitted
+