diff --git a/src/librustc/lint/builtin.rs b/src/librustc/lint/builtin.rs
index de583e81ca831..9fa6230670b67 100644
--- a/src/librustc/lint/builtin.rs
+++ b/src/librustc/lint/builtin.rs
@@ -206,6 +206,12 @@ declare_lint! {
     "potentially-conflicting impls were erroneously allowed"
 }
 
+declare_lint! {
+    pub BAD_REPR,
+    Warn,
+    "detects incorrect use of `repr` attribute"
+}
+
 declare_lint! {
     pub DEPRECATED,
     Warn,
diff --git a/src/librustc_lint/builtin.rs b/src/librustc_lint/builtin.rs
index 79c7a79114761..b3b737ab28329 100644
--- a/src/librustc_lint/builtin.rs
+++ b/src/librustc_lint/builtin.rs
@@ -673,6 +673,79 @@ impl EarlyLintPass for AnonymousParameters {
     }
 }
 
+/// Checks for incorrect use use of `repr` attributes.
+#[derive(Clone)]
+pub struct BadRepr;
+
+impl LintPass for BadRepr {
+    fn get_lints(&self) -> LintArray {
+        lint_array!()
+    }
+}
+
+impl EarlyLintPass for BadRepr {
+    fn check_attribute(&mut self, cx: &EarlyContext, attr: &ast::Attribute) {
+        if attr.name() == "repr" {
+            let list = attr.meta_item_list();
+
+            let repr_str = |lit: &str| { format!("#[repr({})]", lit) };
+
+            // Emit warnings with `repr` either has a literal assignment (`#[repr = "C"]`) or
+            // no hints (``#[repr]`)
+            let has_hints = list.as_ref().map(|ref list| !list.is_empty()).unwrap_or(false);
+            if !has_hints {
+                let mut suggested = false;
+                let mut warn = if let Some(ref lit) = attr.value_str() {
+                    // avoid warning about empty `repr` on `#[repr = "foo"]`
+                    let mut warn = cx.struct_span_lint(
+                        BAD_REPR,
+                        attr.span,
+                        "`repr` attribute isn't configurable with a literal",
+                    );
+                    match format!("{}", lit).as_ref() {
+                        | "C" | "packed" | "rust" | "transparent"
+                        | "u8" | "u16" | "u32" | "u64" | "u128" | "usize"
+                        | "i8" | "i16" | "i32" | "i64" | "i128" | "isize" => {
+                            // if the literal could have been a valid `repr` arg,
+                            // suggest the correct syntax
+                            warn.span_suggestion(
+                                attr.span,
+                                "give `repr` a hint",
+                                repr_str(&lit.as_str()),
+                            );
+                            suggested = true;
+                        }
+                        _ => {  // the literal wasn't a valid `repr` arg
+                            warn.span_label(attr.span, "needs a hint");
+                        }
+                    };
+                    warn
+                } else {
+                    let mut warn = cx.struct_span_lint(
+                        BAD_REPR,
+                        attr.span,
+                        "`repr` attribute must have a hint",
+                    );
+                    warn.span_label(attr.span, "needs a hint");
+                    warn
+                };
+                if !suggested {
+                    warn.help(&format!(
+                        "valid hints include `{}`, `{}`, `{}` and `{}`",
+                        repr_str("C"),
+                        repr_str("packed"),
+                        repr_str("rust"),
+                        repr_str("transparent"),
+                    ));
+                    warn.note("for more information, visit \
+                               <https://doc.rust-lang.org/reference/type-layout.html>");
+                }
+                warn.emit();
+            }
+        }
+    }
+}
+
 /// Checks for use of attributes which have been deprecated.
 #[derive(Clone)]
 pub struct DeprecatedAttr {
diff --git a/src/librustc_lint/lib.rs b/src/librustc_lint/lib.rs
index d6ce5b2ea57fe..e1106281f4523 100644
--- a/src/librustc_lint/lib.rs
+++ b/src/librustc_lint/lib.rs
@@ -107,6 +107,7 @@ pub fn register_builtins(store: &mut lint::LintStore, sess: Option<&Session>) {
                        UnusedImportBraces,
                        AnonymousParameters,
                        UnusedDocComment,
+                       BadRepr,
                        );
 
     add_early_builtin_with_new!(sess,
diff --git a/src/test/compile-fail/issue-43988.rs b/src/test/compile-fail/issue-43988.rs
index 0dfa9f6f0d341..6361af7648258 100644
--- a/src/test/compile-fail/issue-43988.rs
+++ b/src/test/compile-fail/issue-43988.rs
@@ -34,6 +34,7 @@ fn main() {
     #[repr]
     let _y = "123";
     //~^^ ERROR attribute should not be applied to a statement
+    //~| WARN `repr` attribute must have a hint
 
 
     fn foo() {}
@@ -44,5 +45,5 @@ fn main() {
 
     let _z = #[repr] 1;
     //~^ ERROR attribute should not be applied to an expression
-
+    //~| WARN `repr` attribute must have a hint
 }
diff --git a/src/test/ui/feature-gate/issue-43106-gating-of-builtin-attrs.rs b/src/test/ui/feature-gate/issue-43106-gating-of-builtin-attrs.rs
index 76fb09f27bedf..db50b9514430c 100644
--- a/src/test/ui/feature-gate/issue-43106-gating-of-builtin-attrs.rs
+++ b/src/test/ui/feature-gate/issue-43106-gating-of-builtin-attrs.rs
@@ -59,7 +59,9 @@
 #![start                     = "x4300"] //~ WARN unused attribute
 // see issue-43106-gating-of-test.rs for crate-level; but non crate-level is below at "4200"
 // see issue-43106-gating-of-bench.rs for crate-level; but non crate-level is below at "4100"
-#![repr                       = "3900"] //~ WARN unused attribute
+#![repr                       = "3900"]
+//~^ WARN unused attribute
+//~| WARN `repr` attribute isn't configurable with a literal
 #![path                       = "3800"] //~ WARN unused attribute
 #![abi                        = "3700"] //~ WARN unused attribute
 #![automatically_derived      = "3600"] //~ WARN unused attribute
@@ -309,20 +311,25 @@ mod bench {
 
 #[repr = "3900"]
 //~^ WARN unused attribute
+//~| WARN `repr` attribute isn't configurable with a literal
 mod repr {
     mod inner { #![repr="3900"] }
     //~^ WARN unused attribute
+    //~| WARN `repr` attribute isn't configurable with a literal
 
     #[repr = "3900"] fn f() { }
     //~^ WARN unused attribute
+    //~| WARN `repr` attribute isn't configurable with a literal
 
     struct S;
 
     #[repr = "3900"] type T = S;
     //~^ WARN unused attribute
+    //~| WARN `repr` attribute isn't configurable with a literal
 
     #[repr = "3900"] impl S { }
     //~^ WARN unused attribute
+    //~| WARN `repr` attribute isn't configurable with a literal
 }
 
 #[path = "3800"]
diff --git a/src/test/ui/feature-gate/issue-43106-gating-of-builtin-attrs.stderr b/src/test/ui/feature-gate/issue-43106-gating-of-builtin-attrs.stderr
index f8e5f58ca0e89..f351a9e69d011 100644
--- a/src/test/ui/feature-gate/issue-43106-gating-of-builtin-attrs.stderr
+++ b/src/test/ui/feature-gate/issue-43106-gating-of-builtin-attrs.stderr
@@ -1,11 +1,11 @@
 warning: macro_escape is a deprecated synonym for macro_use
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:493:1
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:500:1
    |
 LL | #[macro_escape]
    | ^^^^^^^^^^^^^^^
 
 warning: macro_escape is a deprecated synonym for macro_use
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:496:17
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:503:17
    |
 LL |     mod inner { #![macro_escape] }
    |                 ^^^^^^^^^^^^^^^^
@@ -43,151 +43,206 @@ LL | #![deny                        (x5100)] //~ WARN unknown lint: `x5100`
    |                                 ^^^^^
 
 warning: unknown lint: `x5400`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:112:8
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:114:8
    |
 LL | #[warn(x5400)]
    |        ^^^^^
 
 warning: unknown lint: `x5400`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:115:25
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:117:25
    |
 LL |     mod inner { #![warn(x5400)] }
    |                         ^^^^^
 
 warning: unknown lint: `x5400`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:118:12
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:120:12
    |
 LL |     #[warn(x5400)] fn f() { }
    |            ^^^^^
 
 warning: unknown lint: `x5400`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:121:12
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:123:12
    |
 LL |     #[warn(x5400)] struct S;
    |            ^^^^^
 
 warning: unknown lint: `x5400`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:124:12
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:126:12
    |
 LL |     #[warn(x5400)] type T = S;
    |            ^^^^^
 
 warning: unknown lint: `x5400`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:127:12
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:129:12
    |
 LL |     #[warn(x5400)] impl S { }
    |            ^^^^^
 
 warning: unknown lint: `x5300`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:131:9
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:133:9
    |
 LL | #[allow(x5300)]
    |         ^^^^^
 
 warning: unknown lint: `x5300`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:134:26
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:136:26
    |
 LL |     mod inner { #![allow(x5300)] }
    |                          ^^^^^
 
 warning: unknown lint: `x5300`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:137:13
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:139:13
    |
 LL |     #[allow(x5300)] fn f() { }
    |             ^^^^^
 
 warning: unknown lint: `x5300`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:140:13
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:142:13
    |
 LL |     #[allow(x5300)] struct S;
    |             ^^^^^
 
 warning: unknown lint: `x5300`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:143:13
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:145:13
    |
 LL |     #[allow(x5300)] type T = S;
    |             ^^^^^
 
 warning: unknown lint: `x5300`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:146:13
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:148:13
    |
 LL |     #[allow(x5300)] impl S { }
    |             ^^^^^
 
 warning: unknown lint: `x5200`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:150:10
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:152:10
    |
 LL | #[forbid(x5200)]
    |          ^^^^^
 
 warning: unknown lint: `x5200`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:153:27
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:155:27
    |
 LL |     mod inner { #![forbid(x5200)] }
    |                           ^^^^^
 
 warning: unknown lint: `x5200`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:156:14
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:158:14
    |
 LL |     #[forbid(x5200)] fn f() { }
    |              ^^^^^
 
 warning: unknown lint: `x5200`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:159:14
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:161:14
    |
 LL |     #[forbid(x5200)] struct S;
    |              ^^^^^
 
 warning: unknown lint: `x5200`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:162:14
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:164:14
    |
 LL |     #[forbid(x5200)] type T = S;
    |              ^^^^^
 
 warning: unknown lint: `x5200`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:165:14
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:167:14
    |
 LL |     #[forbid(x5200)] impl S { }
    |              ^^^^^
 
 warning: unknown lint: `x5100`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:169:8
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:171:8
    |
 LL | #[deny(x5100)]
    |        ^^^^^
 
 warning: unknown lint: `x5100`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:172:25
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:174:25
    |
 LL |     mod inner { #![deny(x5100)] }
    |                         ^^^^^
 
 warning: unknown lint: `x5100`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:175:12
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:177:12
    |
 LL |     #[deny(x5100)] fn f() { }
    |            ^^^^^
 
 warning: unknown lint: `x5100`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:178:12
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:180:12
    |
 LL |     #[deny(x5100)] struct S;
    |            ^^^^^
 
 warning: unknown lint: `x5100`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:181:12
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:183:12
    |
 LL |     #[deny(x5100)] type T = S;
    |            ^^^^^
 
 warning: unknown lint: `x5100`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:184:12
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:186:12
    |
 LL |     #[deny(x5100)] impl S { }
    |            ^^^^^
 
+warning: `repr` attribute isn't configurable with a literal
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:316:17
+   |
+LL |     mod inner { #![repr="3900"] }
+   |                 ^^^^^^^^^^^^^^^ needs a hint
+   |
+   = note: #[warn(bad_repr)] on by default
+   = help: valid hints include `#[repr(C)]`, `#[repr(packed)]`, `#[repr(rust)]` and `#[repr(transparent)]`
+   = note: for more information, visit <https://doc.rust-lang.org/reference/type-layout.html>
+
+warning: `repr` attribute isn't configurable with a literal
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:320:5
+   |
+LL |     #[repr = "3900"] fn f() { }
+   |     ^^^^^^^^^^^^^^^^ needs a hint
+   |
+   = help: valid hints include `#[repr(C)]`, `#[repr(packed)]`, `#[repr(rust)]` and `#[repr(transparent)]`
+   = note: for more information, visit <https://doc.rust-lang.org/reference/type-layout.html>
+
+warning: `repr` attribute isn't configurable with a literal
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:326:5
+   |
+LL |     #[repr = "3900"] type T = S;
+   |     ^^^^^^^^^^^^^^^^ needs a hint
+   |
+   = help: valid hints include `#[repr(C)]`, `#[repr(packed)]`, `#[repr(rust)]` and `#[repr(transparent)]`
+   = note: for more information, visit <https://doc.rust-lang.org/reference/type-layout.html>
+
+warning: `repr` attribute isn't configurable with a literal
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:330:5
+   |
+LL |     #[repr = "3900"] impl S { }
+   |     ^^^^^^^^^^^^^^^^ needs a hint
+   |
+   = help: valid hints include `#[repr(C)]`, `#[repr(packed)]`, `#[repr(rust)]` and `#[repr(transparent)]`
+   = note: for more information, visit <https://doc.rust-lang.org/reference/type-layout.html>
+
+warning: `repr` attribute isn't configurable with a literal
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:312:1
+   |
+LL | #[repr = "3900"]
+   | ^^^^^^^^^^^^^^^^ needs a hint
+   |
+   = help: valid hints include `#[repr(C)]`, `#[repr(packed)]`, `#[repr(rust)]` and `#[repr(transparent)]`
+   = note: for more information, visit <https://doc.rust-lang.org/reference/type-layout.html>
+
+warning: `repr` attribute isn't configurable with a literal
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:62:1
+   |
+LL | #![repr                       = "3900"]
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ needs a hint
+   |
+   = help: valid hints include `#[repr(C)]`, `#[repr(packed)]`, `#[repr(rust)]` and `#[repr(transparent)]`
+   = note: for more information, visit <https://doc.rust-lang.org/reference/type-layout.html>
+
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:192:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:194:5
    |
 LL |     #[macro_use] fn f() { }
    |     ^^^^^^^^^^^^
@@ -199,277 +254,277 @@ LL | #![warn(unused_attributes, unknown_lints)]
    |         ^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:195:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:197:5
    |
 LL |     #[macro_use] struct S;
    |     ^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:198:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:200:5
    |
 LL |     #[macro_use] type T = S;
    |     ^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:201:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:203:5
    |
 LL |     #[macro_use] impl S { }
    |     ^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:208:17
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:210:17
    |
 LL |     mod inner { #![macro_export="4800"] }
    |                 ^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:211:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:213:5
    |
 LL |     #[macro_export = "4800"] fn f() { }
    |     ^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:214:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:216:5
    |
 LL |     #[macro_export = "4800"] struct S;
    |     ^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:217:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:219:5
    |
 LL |     #[macro_export = "4800"] type T = S;
    |     ^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:220:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:222:5
    |
 LL |     #[macro_export = "4800"] impl S { }
    |     ^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:205:1
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:207:1
    |
 LL | #[macro_export = "4800"]
    | ^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:227:17
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:229:17
    |
 LL |     mod inner { #![plugin_registrar="4700"] }
    |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:232:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:234:5
    |
 LL |     #[plugin_registrar = "4700"] struct S;
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:235:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:237:5
    |
 LL |     #[plugin_registrar = "4700"] type T = S;
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:238:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:240:5
    |
 LL |     #[plugin_registrar = "4700"] impl S { }
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:224:1
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:226:1
    |
 LL | #[plugin_registrar = "4700"]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:245:17
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:247:17
    |
 LL |     mod inner { #![main="4300"] }
    |                 ^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:250:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:252:5
    |
 LL |     #[main = "4400"] struct S;
    |     ^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:253:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:255:5
    |
 LL |     #[main = "4400"] type T = S;
    |     ^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:256:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:258:5
    |
 LL |     #[main = "4400"] impl S { }
    |     ^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:242:1
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:244:1
    |
 LL | #[main = "4400"]
    | ^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:263:17
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:265:17
    |
 LL |     mod inner { #![start="4300"] }
    |                 ^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:268:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:270:5
    |
 LL |     #[start = "4300"] struct S;
    |     ^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:271:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:273:5
    |
 LL |     #[start = "4300"] type T = S;
    |     ^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:274:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:276:5
    |
 LL |     #[start = "4300"] impl S { }
    |     ^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:260:1
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:262:1
    |
 LL | #[start = "4300"]
    | ^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:313:17
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:316:17
    |
 LL |     mod inner { #![repr="3900"] }
    |                 ^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:316:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:320:5
    |
 LL |     #[repr = "3900"] fn f() { }
    |     ^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:321:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:326:5
    |
 LL |     #[repr = "3900"] type T = S;
    |     ^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:324:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:330:5
    |
 LL |     #[repr = "3900"] impl S { }
    |     ^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:310:1
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:312:1
    |
 LL | #[repr = "3900"]
    | ^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:332:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:339:5
    |
 LL |     #[path = "3800"] fn f() { }
    |     ^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:335:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:342:5
    |
 LL |     #[path = "3800"]  struct S;
    |     ^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:338:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:345:5
    |
 LL |     #[path = "3800"] type T = S;
    |     ^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:341:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:348:5
    |
 LL |     #[path = "3800"] impl S { }
    |     ^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:348:17
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:355:17
    |
 LL |     mod inner { #![abi="3700"] }
    |                 ^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:351:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:358:5
    |
 LL |     #[abi = "3700"] fn f() { }
    |     ^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:354:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:361:5
    |
 LL |     #[abi = "3700"] struct S;
    |     ^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:357:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:364:5
    |
 LL |     #[abi = "3700"] type T = S;
    |     ^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:360:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:367:5
    |
 LL |     #[abi = "3700"] impl S { }
    |     ^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:345:1
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:352:1
    |
 LL | #[abi = "3700"]
    | ^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:367:17
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:374:17
    |
 LL |     mod inner { #![automatically_derived="3600"] }
    |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:370:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:377:5
    |
 LL |     #[automatically_derived = "3600"] fn f() { }
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:373:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:380:5
    |
 LL |     #[automatically_derived = "3600"] struct S;
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:376:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:383:5
    |
 LL |     #[automatically_derived = "3600"] type T = S;
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:379:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:386:5
    |
 LL |     #[automatically_derived = "3600"] impl S { }
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:364:1
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:371:1
    |
 LL | #[automatically_derived = "3600"]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: function is marked #[no_mangle], but not exported
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:387:27
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:394:27
    |
 LL |     #[no_mangle = "3500"] fn f() { }
    |                           -^^^^^^^^^
@@ -479,709 +534,709 @@ LL |     #[no_mangle = "3500"] fn f() { }
    = note: #[warn(private_no_mangle_fns)] on by default
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:400:17
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:407:17
    |
 LL |     mod inner { #![no_link="3400"] }
    |                 ^^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:403:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:410:5
    |
 LL |     #[no_link = "3400"] fn f() { }
    |     ^^^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:406:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:413:5
    |
 LL |     #[no_link = "3400"] struct S;
    |     ^^^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:409:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:416:5
    |
 LL |     #[no_link = "3400"]type T = S;
    |     ^^^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:412:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:419:5
    |
 LL |     #[no_link = "3400"] impl S { }
    |     ^^^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:397:1
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:404:1
    |
 LL | #[no_link = "3400"]
    | ^^^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:419:17
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:426:17
    |
 LL |     mod inner { #![should_panic="3200"] }
    |                 ^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:422:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:429:5
    |
 LL |     #[should_panic = "3200"] fn f() { }
    |     ^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:425:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:432:5
    |
 LL |     #[should_panic = "3200"] struct S;
    |     ^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:428:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:435:5
    |
 LL |     #[should_panic = "3200"] type T = S;
    |     ^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:431:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:438:5
    |
 LL |     #[should_panic = "3200"] impl S { }
    |     ^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:416:1
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:423:1
    |
 LL | #[should_panic = "3200"]
    | ^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:438:17
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:445:17
    |
 LL |     mod inner { #![ignore="3100"] }
    |                 ^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:441:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:448:5
    |
 LL |     #[ignore = "3100"] fn f() { }
    |     ^^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:444:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:451:5
    |
 LL |     #[ignore = "3100"] struct S;
    |     ^^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:447:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:454:5
    |
 LL |     #[ignore = "3100"] type T = S;
    |     ^^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:450:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:457:5
    |
 LL |     #[ignore = "3100"] impl S { }
    |     ^^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:435:1
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:442:1
    |
 LL | #[ignore = "3100"]
    | ^^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:457:17
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:464:17
    |
 LL |     mod inner { #![no_implicit_prelude="3000"] }
    |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:460:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:467:5
    |
 LL |     #[no_implicit_prelude = "3000"] fn f() { }
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:463:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:470:5
    |
 LL |     #[no_implicit_prelude = "3000"] struct S;
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:466:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:473:5
    |
 LL |     #[no_implicit_prelude = "3000"] type T = S;
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:469:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:476:5
    |
 LL |     #[no_implicit_prelude = "3000"] impl S { }
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:454:1
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:461:1
    |
 LL | #[no_implicit_prelude = "3000"]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:476:17
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:483:17
    |
 LL |     mod inner { #![reexport_test_harness_main="2900"] }
    |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:479:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:486:5
    |
 LL |     #[reexport_test_harness_main = "2900"] fn f() { }
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:482:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:489:5
    |
 LL |     #[reexport_test_harness_main = "2900"] struct S;
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:485:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:492:5
    |
 LL |     #[reexport_test_harness_main = "2900"] type T = S;
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:488:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:495:5
    |
 LL |     #[reexport_test_harness_main = "2900"] impl S { }
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:473:1
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:480:1
    |
 LL | #[reexport_test_harness_main = "2900"]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:499:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:506:5
    |
 LL |     #[macro_escape] fn f() { }
    |     ^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:502:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:509:5
    |
 LL |     #[macro_escape] struct S;
    |     ^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:505:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:512:5
    |
 LL |     #[macro_escape] type T = S;
    |     ^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:508:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:515:5
    |
 LL |     #[macro_escape] impl S { }
    |     ^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:516:17
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:523:17
    |
 LL |     mod inner { #![no_std="2600"] }
    |                 ^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be in the root module
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:516:17
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:523:17
    |
 LL |     mod inner { #![no_std="2600"] }
    |                 ^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:520:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:527:5
    |
 LL |     #[no_std = "2600"] fn f() { }
    |     ^^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: #![foo]
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:520:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:527:5
    |
 LL |     #[no_std = "2600"] fn f() { }
    |     ^^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:524:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:531:5
    |
 LL |     #[no_std = "2600"] struct S;
    |     ^^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: #![foo]
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:524:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:531:5
    |
 LL |     #[no_std = "2600"] struct S;
    |     ^^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:528:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:535:5
    |
 LL |     #[no_std = "2600"] type T = S;
    |     ^^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: #![foo]
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:528:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:535:5
    |
 LL |     #[no_std = "2600"] type T = S;
    |     ^^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:532:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:539:5
    |
 LL |     #[no_std = "2600"] impl S { }
    |     ^^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: #![foo]
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:532:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:539:5
    |
 LL |     #[no_std = "2600"] impl S { }
    |     ^^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:512:1
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:519:1
    |
 LL | #[no_std = "2600"]
    | ^^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: #![foo]
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:512:1
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:519:1
    |
 LL | #[no_std = "2600"]
    | ^^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:671:17
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:678:17
    |
 LL |     mod inner { #![crate_name="0900"] }
    |                 ^^^^^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be in the root module
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:671:17
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:678:17
    |
 LL |     mod inner { #![crate_name="0900"] }
    |                 ^^^^^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:675:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:682:5
    |
 LL |     #[crate_name = "0900"] fn f() { }
    |     ^^^^^^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: #![foo]
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:675:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:682:5
    |
 LL |     #[crate_name = "0900"] fn f() { }
    |     ^^^^^^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:679:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:686:5
    |
 LL |     #[crate_name = "0900"] struct S;
    |     ^^^^^^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: #![foo]
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:679:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:686:5
    |
 LL |     #[crate_name = "0900"] struct S;
    |     ^^^^^^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:683:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:690:5
    |
 LL |     #[crate_name = "0900"] type T = S;
    |     ^^^^^^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: #![foo]
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:683:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:690:5
    |
 LL |     #[crate_name = "0900"] type T = S;
    |     ^^^^^^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:687:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:694:5
    |
 LL |     #[crate_name = "0900"] impl S { }
    |     ^^^^^^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: #![foo]
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:687:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:694:5
    |
 LL |     #[crate_name = "0900"] impl S { }
    |     ^^^^^^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:667:1
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:674:1
    |
 LL | #[crate_name = "0900"]
    | ^^^^^^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: #![foo]
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:667:1
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:674:1
    |
 LL | #[crate_name = "0900"]
    | ^^^^^^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:696:17
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:703:17
    |
 LL |     mod inner { #![crate_type="0800"] }
    |                 ^^^^^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be in the root module
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:696:17
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:703:17
    |
 LL |     mod inner { #![crate_type="0800"] }
    |                 ^^^^^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:700:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:707:5
    |
 LL |     #[crate_type = "0800"] fn f() { }
    |     ^^^^^^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: #![foo]
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:700:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:707:5
    |
 LL |     #[crate_type = "0800"] fn f() { }
    |     ^^^^^^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:704:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:711:5
    |
 LL |     #[crate_type = "0800"] struct S;
    |     ^^^^^^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: #![foo]
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:704:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:711:5
    |
 LL |     #[crate_type = "0800"] struct S;
    |     ^^^^^^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:708:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:715:5
    |
 LL |     #[crate_type = "0800"] type T = S;
    |     ^^^^^^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: #![foo]
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:708:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:715:5
    |
 LL |     #[crate_type = "0800"] type T = S;
    |     ^^^^^^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:712:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:719:5
    |
 LL |     #[crate_type = "0800"] impl S { }
    |     ^^^^^^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: #![foo]
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:712:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:719:5
    |
 LL |     #[crate_type = "0800"] impl S { }
    |     ^^^^^^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:692:1
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:699:1
    |
 LL | #[crate_type = "0800"]
    | ^^^^^^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: #![foo]
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:692:1
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:699:1
    |
 LL | #[crate_type = "0800"]
    | ^^^^^^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:721:17
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:728:17
    |
 LL |     mod inner { #![feature(x0600)] }
    |                 ^^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be in the root module
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:721:17
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:728:17
    |
 LL |     mod inner { #![feature(x0600)] }
    |                 ^^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:725:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:732:5
    |
 LL |     #[feature(x0600)] fn f() { }
    |     ^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: #![foo]
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:725:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:732:5
    |
 LL |     #[feature(x0600)] fn f() { }
    |     ^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:729:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:736:5
    |
 LL |     #[feature(x0600)] struct S;
    |     ^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: #![foo]
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:729:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:736:5
    |
 LL |     #[feature(x0600)] struct S;
    |     ^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:733:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:740:5
    |
 LL |     #[feature(x0600)] type T = S;
    |     ^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: #![foo]
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:733:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:740:5
    |
 LL |     #[feature(x0600)] type T = S;
    |     ^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:737:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:744:5
    |
 LL |     #[feature(x0600)] impl S { }
    |     ^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: #![foo]
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:737:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:744:5
    |
 LL |     #[feature(x0600)] impl S { }
    |     ^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:717:1
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:724:1
    |
 LL | #[feature(x0600)]
    | ^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: #![foo]
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:717:1
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:724:1
    |
 LL | #[feature(x0600)]
    | ^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:747:17
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:754:17
    |
 LL |     mod inner { #![no_main="0400"] }
    |                 ^^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be in the root module
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:747:17
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:754:17
    |
 LL |     mod inner { #![no_main="0400"] }
    |                 ^^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:751:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:758:5
    |
 LL |     #[no_main = "0400"] fn f() { }
    |     ^^^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: #![foo]
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:751:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:758:5
    |
 LL |     #[no_main = "0400"] fn f() { }
    |     ^^^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:755:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:762:5
    |
 LL |     #[no_main = "0400"] struct S;
    |     ^^^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: #![foo]
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:755:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:762:5
    |
 LL |     #[no_main = "0400"] struct S;
    |     ^^^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:759:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:766:5
    |
 LL |     #[no_main = "0400"] type T = S;
    |     ^^^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: #![foo]
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:759:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:766:5
    |
 LL |     #[no_main = "0400"] type T = S;
    |     ^^^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:763:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:770:5
    |
 LL |     #[no_main = "0400"] impl S { }
    |     ^^^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: #![foo]
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:763:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:770:5
    |
 LL |     #[no_main = "0400"] impl S { }
    |     ^^^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:743:1
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:750:1
    |
 LL | #[no_main = "0400"]
    | ^^^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: #![foo]
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:743:1
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:750:1
    |
 LL | #[no_main = "0400"]
    | ^^^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:785:17
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:792:17
    |
 LL |     mod inner { #![recursion_limit="0200"] }
    |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be in the root module
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:785:17
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:792:17
    |
 LL |     mod inner { #![recursion_limit="0200"] }
    |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:789:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:796:5
    |
 LL |     #[recursion_limit="0200"] fn f() { }
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: #![foo]
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:789:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:796:5
    |
 LL |     #[recursion_limit="0200"] fn f() { }
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:793:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:800:5
    |
 LL |     #[recursion_limit="0200"] struct S;
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: #![foo]
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:793:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:800:5
    |
 LL |     #[recursion_limit="0200"] struct S;
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:797:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:804:5
    |
 LL |     #[recursion_limit="0200"] type T = S;
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: #![foo]
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:797:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:804:5
    |
 LL |     #[recursion_limit="0200"] type T = S;
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:801:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:808:5
    |
 LL |     #[recursion_limit="0200"] impl S { }
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: #![foo]
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:801:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:808:5
    |
 LL |     #[recursion_limit="0200"] impl S { }
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:781:1
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:788:1
    |
 LL | #[recursion_limit="0200"]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: #![foo]
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:781:1
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:788:1
    |
 LL | #[recursion_limit="0200"]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:810:17
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:817:17
    |
 LL |     mod inner { #![type_length_limit="0100"] }
    |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be in the root module
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:810:17
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:817:17
    |
 LL |     mod inner { #![type_length_limit="0100"] }
    |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:814:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:821:5
    |
 LL |     #[type_length_limit="0100"] fn f() { }
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: #![foo]
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:814:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:821:5
    |
 LL |     #[type_length_limit="0100"] fn f() { }
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:818:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:825:5
    |
 LL |     #[type_length_limit="0100"] struct S;
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: #![foo]
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:818:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:825:5
    |
 LL |     #[type_length_limit="0100"] struct S;
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:822:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:829:5
    |
 LL |     #[type_length_limit="0100"] type T = S;
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: #![foo]
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:822:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:829:5
    |
 LL |     #[type_length_limit="0100"] type T = S;
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:826:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:833:5
    |
 LL |     #[type_length_limit="0100"] impl S { }
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: #![foo]
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:826:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:833:5
    |
 LL |     #[type_length_limit="0100"] impl S { }
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:806:1
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:813:1
    |
 LL | #[type_length_limit="0100"]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: #![foo]
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:806:1
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:813:1
    |
 LL | #[type_length_limit="0100"]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -1213,53 +1268,53 @@ LL | #![start                     = "x4300"] //~ WARN unused attribute
 warning: unused attribute
   --> $DIR/issue-43106-gating-of-builtin-attrs.rs:62:1
    |
-LL | #![repr                       = "3900"] //~ WARN unused attribute
+LL | #![repr                       = "3900"]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:63:1
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:65:1
    |
 LL | #![path                       = "3800"] //~ WARN unused attribute
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:64:1
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:66:1
    |
 LL | #![abi                        = "3700"] //~ WARN unused attribute
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:65:1
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:67:1
    |
 LL | #![automatically_derived      = "3600"] //~ WARN unused attribute
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:67:1
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:69:1
    |
 LL | #![no_link                    = "3400"] //~ WARN unused attribute
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:69:1
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:71:1
    |
 LL | #![should_panic               = "3200"] //~ WARN unused attribute
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:70:1
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:72:1
    |
 LL | #![ignore                     = "3100"] //~ WARN unused attribute
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: unused attribute
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:76:1
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:78:1
    |
 LL | #![proc_macro_derive          = "2500"] //~ WARN unused attribute
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: compilation successful
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:837:1
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:844:1
    |
 LL | / fn main() { //~ ERROR compilation successful
 LL | |     println!("Hello World");
diff --git a/src/test/ui/suggestions/repr.rs b/src/test/ui/suggestions/repr.rs
new file mode 100644
index 0000000000000..312f60202c6c2
--- /dev/null
+++ b/src/test/ui/suggestions/repr.rs
@@ -0,0 +1,28 @@
+// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// compile-pass
+
+#[repr]
+//^ WARN `repr` attribute must have a hint
+struct _A {}
+
+#[repr = "B"]
+//^ WARN `repr` attribute isn't configurable with a literal
+struct _B {}
+
+#[repr = "C"]
+//^ WARN `repr` attribute isn't configurable with a literal
+struct _C {}
+
+#[repr(C)]
+struct _D {}
+
+fn main() {}
diff --git a/src/test/ui/suggestions/repr.stderr b/src/test/ui/suggestions/repr.stderr
new file mode 100644
index 0000000000000..7a99d8c04488f
--- /dev/null
+++ b/src/test/ui/suggestions/repr.stderr
@@ -0,0 +1,25 @@
+warning: `repr` attribute must have a hint
+  --> $DIR/repr.rs:13:1
+   |
+LL | #[repr]
+   | ^^^^^^^ needs a hint
+   |
+   = note: #[warn(bad_repr)] on by default
+   = help: valid hints include `#[repr(C)]`, `#[repr(packed)]`, `#[repr(rust)]` and `#[repr(transparent)]`
+   = note: for more information, visit <https://doc.rust-lang.org/reference/type-layout.html>
+
+warning: `repr` attribute isn't configurable with a literal
+  --> $DIR/repr.rs:17:1
+   |
+LL | #[repr = "B"]
+   | ^^^^^^^^^^^^^ needs a hint
+   |
+   = help: valid hints include `#[repr(C)]`, `#[repr(packed)]`, `#[repr(rust)]` and `#[repr(transparent)]`
+   = note: for more information, visit <https://doc.rust-lang.org/reference/type-layout.html>
+
+warning: `repr` attribute isn't configurable with a literal
+  --> $DIR/repr.rs:21:1
+   |
+LL | #[repr = "C"]
+   | ^^^^^^^^^^^^^ help: give `repr` a hint: `#[repr(C)]`
+