Rollup merge of #93926 - PatchMixolydic:bugfix/must_use-on-exprs, r=cjgillot

Lint against more useless `#[must_use]` attributes

This expands the existing `#[must_use]` check in `unused_attributes` to lint against pretty much everything `#[must_use]` doesn't support.
Fixes #93906.

4 files changed, 493 insertions, 162 deletions

diff --git a/src/test/ui/feature-gates/issue-43106-gating-of-builtin-attrs.rs b/src/test/ui/feature-gates/issue-43106-gating-of-builtin-attrs.rs
index ed382406efa..b0e295178c8 100644
--- a/src/test/ui/feature-gates/issue-43106-gating-of-builtin-attrs.rs
+++ b/src/test/ui/feature-gates/issue-43106-gating-of-builtin-attrs.rs
@@ -71,6 +71,7 @@
 //~^^ WARN this was previously accepted by the compiler
 // see issue-43106-gating-of-rustc_deprecated.rs
 #![must_use]
+//~^ WARN `#[must_use]` has no effect
 // see issue-43106-gating-of-stable.rs
 // see issue-43106-gating-of-unstable.rs
 // see issue-43106-gating-of-deprecated.rs
@@ -597,17 +598,17 @@ mod deprecated {
     #[deprecated] impl super::StructForDeprecated { }
 }
 
-#[must_use]
+#[must_use] //~ WARN `#[must_use]` has no effect
 mod must_use {
-    mod inner { #![must_use] }
+    mod inner { #![must_use] } //~ WARN `#[must_use]` has no effect
 
     #[must_use] fn f() { }
 
     #[must_use] struct S;
 
-    #[must_use] type T = S;
+    #[must_use] type T = S; //~ WARN `#[must_use]` has no effect
 
-    #[must_use] impl S { }
+    #[must_use] impl S { } //~ WARN `#[must_use]` has no effect
 }
 
 #[windows_subsystem = "windows"]
diff --git a/src/test/ui/feature-gates/issue-43106-gating-of-builtin-attrs.stderr b/src/test/ui/feature-gates/issue-43106-gating-of-builtin-attrs.stderr
index bd3e33320c3..2431957e539 100644
--- a/src/test/ui/feature-gates/issue-43106-gating-of-builtin-attrs.stderr
+++ b/src/test/ui/feature-gates/issue-43106-gating-of-builtin-attrs.stderr
@@ -29,151 +29,151 @@ LL | #![deny(x5100)]
    |         ^^^^^
 
 warning: unknown lint: `x5400`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:105:8
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:106:8
    |
 LL | #[warn(x5400)]
    |        ^^^^^
 
 warning: unknown lint: `x5400`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:108:25
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:109:25
    |
 LL |     mod inner { #![warn(x5400)] }
    |                         ^^^^^
 
 warning: unknown lint: `x5400`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:111:12
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:112:12
    |
 LL |     #[warn(x5400)] fn f() { }
    |            ^^^^^
 
 warning: unknown lint: `x5400`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:114:12
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:115:12
    |
 LL |     #[warn(x5400)] struct S;
    |            ^^^^^
 
 warning: unknown lint: `x5400`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:117:12
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:118:12
    |
 LL |     #[warn(x5400)] type T = S;
    |            ^^^^^
 
 warning: unknown lint: `x5400`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:120:12
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:121:12
    |
 LL |     #[warn(x5400)] impl S { }
    |            ^^^^^
 
 warning: unknown lint: `x5300`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:124:9
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:125:9
    |
 LL | #[allow(x5300)]
    |         ^^^^^
 
 warning: unknown lint: `x5300`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:127:26
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:128:26
    |
 LL |     mod inner { #![allow(x5300)] }
    |                          ^^^^^
 
 warning: unknown lint: `x5300`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:130:13
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:131:13
    |
 LL |     #[allow(x5300)] fn f() { }
    |             ^^^^^
 
 warning: unknown lint: `x5300`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:133:13
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:134:13
    |
 LL |     #[allow(x5300)] struct S;
    |             ^^^^^
 
 warning: unknown lint: `x5300`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:136:13
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:137:13
    |
 LL |     #[allow(x5300)] type T = S;
    |             ^^^^^
 
 warning: unknown lint: `x5300`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:139:13
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:140:13
    |
 LL |     #[allow(x5300)] impl S { }
    |             ^^^^^
 
 warning: unknown lint: `x5200`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:143:10
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:144:10
    |
 LL | #[forbid(x5200)]
    |          ^^^^^
 
 warning: unknown lint: `x5200`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:146:27
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:147:27
    |
 LL |     mod inner { #![forbid(x5200)] }
    |                           ^^^^^
 
 warning: unknown lint: `x5200`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:149:14
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:150:14
    |
 LL |     #[forbid(x5200)] fn f() { }
    |              ^^^^^
 
 warning: unknown lint: `x5200`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:152:14
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:153:14
    |
 LL |     #[forbid(x5200)] struct S;
    |              ^^^^^
 
 warning: unknown lint: `x5200`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:155:14
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:156:14
    |
 LL |     #[forbid(x5200)] type T = S;
    |              ^^^^^
 
 warning: unknown lint: `x5200`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:158:14
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:159:14
    |
 LL |     #[forbid(x5200)] impl S { }
    |              ^^^^^
 
 warning: unknown lint: `x5100`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:162:8
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:163:8
    |
 LL | #[deny(x5100)]
    |        ^^^^^
 
 warning: unknown lint: `x5100`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:165:25
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:166:25
    |
 LL |     mod inner { #![deny(x5100)] }
    |                         ^^^^^
 
 warning: unknown lint: `x5100`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:168:12
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:169:12
    |
 LL |     #[deny(x5100)] fn f() { }
    |            ^^^^^
 
 warning: unknown lint: `x5100`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:171:12
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:172:12
    |
 LL |     #[deny(x5100)] struct S;
    |            ^^^^^
 
 warning: unknown lint: `x5100`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:174:12
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:175:12
    |
 LL |     #[deny(x5100)] type T = S;
    |            ^^^^^
 
 warning: unknown lint: `x5100`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:177:12
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:178:12
    |
 LL |     #[deny(x5100)] impl S { }
    |            ^^^^^
 
 warning: `#[macro_escape]` is a deprecated synonym for `#[macro_use]`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:400:17
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:401:17
    |
 LL |     mod inner { #![macro_escape] }
    |                 ^^^^^^^^^^^^^^^^
@@ -181,13 +181,13 @@ LL |     mod inner { #![macro_escape] }
    = help: try an outer attribute: `#[macro_use]`
 
 warning: `#[macro_escape]` is a deprecated synonym for `#[macro_use]`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:397:1
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:398:1
    |
 LL | #[macro_escape]
    | ^^^^^^^^^^^^^^^
 
 warning: use of deprecated attribute `crate_id`: no longer used.
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:84:1
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:85:1
    |
 LL | #![crate_id = "10"]
    | ^^^^^^^^^^^^^^^^^^^ help: remove this attribute
@@ -195,13 +195,13 @@ LL | #![crate_id = "10"]
    = note: `#[warn(deprecated)]` on by default
 
 warning: use of deprecated attribute `no_start`: no longer used.
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:94:1
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:95:1
    |
 LL | #![no_start]
    | ^^^^^^^^^^^^ help: remove this attribute
 
 warning: `#[macro_export]` only has an effect on macro definitions
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:198:1
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:199:1
    |
 LL | #[macro_export]
    | ^^^^^^^^^^^^^^^
@@ -213,13 +213,13 @@ LL | #![warn(unused_attributes, unknown_lints)]
    |         ^^^^^^^^^^^^^^^^^
 
 warning: `#[automatically_derived]` only has an effect on items
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:266:1
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:267:1
    |
 LL | #[automatically_derived]
    | ^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: attribute should be applied to a free function, impl method or static
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:284:1
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:285:1
    |
 LL |   #[no_mangle]
    |   ^^^^^^^^^^^^
@@ -236,31 +236,31 @@ LL | | }
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
 
 warning: `#[should_panic]` only has an effect on functions
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:324:1
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:325:1
    |
 LL | #[should_panic]
    | ^^^^^^^^^^^^^^^
 
 warning: `#[ignore]` only has an effect on functions
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:342:1
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:343:1
    |
 LL | #[ignore]
    | ^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: `#![foo]`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:377:1
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:378:1
    |
 LL | #[reexport_test_harness_main = "2900"]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: `#![foo]`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:417:1
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:418:1
    |
 LL | #[no_std]
    | ^^^^^^^^^
 
 warning: attribute should be applied to a function
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:453:1
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:454:1
    |
 LL |   #[cold]
    |   ^^^^^^^
@@ -277,7 +277,7 @@ LL | | }
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
 
 warning: attribute should be applied to a foreign function or static
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:482:1
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:483:1
    |
 LL |   #[link_name = "1900"]
    |   ^^^^^^^^^^^^^^^^^^^^^
@@ -294,7 +294,7 @@ LL | | }
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
 
 warning: attribute should be applied to a function or static
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:521:1
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:522:1
    |
 LL |   #[link_section = "1800"]
    |   ^^^^^^^^^^^^^^^^^^^^^^^^
@@ -311,7 +311,7 @@ LL | | }
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
 
 warning: attribute should be applied to an `extern` block
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:553:1
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:554:1
    |
 LL |   #[link()]
    |   ^^^^^^^^^
@@ -327,50 +327,56 @@ LL | | }
    |
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
 
+warning: `#[must_use]` has no effect when applied to a module
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:601:1
+   |
+LL | #[must_use]
+   | ^^^^^^^^^^^
+
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: `#![foo]`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:613:1
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:614:1
    |
 LL | #[windows_subsystem = "windows"]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: `#![foo]`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:634:1
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:635:1
    |
 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:653:1
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:654:1
    |
 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:672:1
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:673:1
    |
 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:692:1
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:693:1
    |
 LL | #[no_main]
    | ^^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: `#![foo]`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:711:1
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:712:1
    |
 LL | #[no_builtins]
    | ^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: `#![foo]`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:730:1
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:731:1
    |
 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:749:1
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:750:1
    |
 LL | #[type_length_limit="0100"]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -425,110 +431,116 @@ LL | #![link_section = "1800"]
    |
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
 
+warning: `#[must_use]` has no effect when applied to a module
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:73:1
+   |
+LL | #![must_use]
+   | ^^^^^^^^^^^^
+
 warning: `#[macro_use]` only has an effect on `extern crate` and modules
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:185:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:186:5
    |
 LL |     #[macro_use] fn f() { }
    |     ^^^^^^^^^^^^
 
 warning: `#[macro_use]` only has an effect on `extern crate` and modules
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:188:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:189:5
    |
 LL |     #[macro_use] struct S;
    |     ^^^^^^^^^^^^
 
 warning: `#[macro_use]` only has an effect on `extern crate` and modules
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:191:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:192:5
    |
 LL |     #[macro_use] type T = S;
    |     ^^^^^^^^^^^^
 
 warning: `#[macro_use]` only has an effect on `extern crate` and modules
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:194:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:195:5
    |
 LL |     #[macro_use] impl S { }
    |     ^^^^^^^^^^^^
 
 warning: `#[macro_export]` only has an effect on macro definitions
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:201:17
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:202:17
    |
 LL |     mod inner { #![macro_export] }
    |                 ^^^^^^^^^^^^^^^^
 
 warning: `#[macro_export]` only has an effect on macro definitions
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:204:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:205:5
    |
 LL |     #[macro_export] fn f() { }
    |     ^^^^^^^^^^^^^^^
 
 warning: `#[macro_export]` only has an effect on macro definitions
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:207:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:208:5
    |
 LL |     #[macro_export] struct S;
    |     ^^^^^^^^^^^^^^^
 
 warning: `#[macro_export]` only has an effect on macro definitions
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:210:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:211:5
    |
 LL |     #[macro_export] type T = S;
    |     ^^^^^^^^^^^^^^^
 
 warning: `#[macro_export]` only has an effect on macro definitions
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:213:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:214:5
    |
 LL |     #[macro_export] impl S { }
    |     ^^^^^^^^^^^^^^^
 
 warning: `#[path]` only has an effect on modules
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:253:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:254:5
    |
 LL |     #[path = "3800"] fn f() { }
    |     ^^^^^^^^^^^^^^^^
 
 warning: `#[path]` only has an effect on modules
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:256:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:257:5
    |
 LL |     #[path = "3800"]  struct S;
    |     ^^^^^^^^^^^^^^^^
 
 warning: `#[path]` only has an effect on modules
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:259:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:260:5
    |
 LL |     #[path = "3800"] type T = S;
    |     ^^^^^^^^^^^^^^^^
 
 warning: `#[path]` only has an effect on modules
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:262:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:263:5
    |
 LL |     #[path = "3800"] impl S { }
    |     ^^^^^^^^^^^^^^^^
 
 warning: `#[automatically_derived]` only has an effect on items
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:269:17
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:270:17
    |
 LL |     mod inner { #![automatically_derived] }
    |                 ^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: `#[automatically_derived]` only has an effect on items
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:272:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:273:5
    |
 LL |     #[automatically_derived] fn f() { }
    |     ^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: `#[automatically_derived]` only has an effect on items
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:275:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:276:5
    |
 LL |     #[automatically_derived] struct S;
    |     ^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: `#[automatically_derived]` only has an effect on items
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:278:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:279:5
    |
 LL |     #[automatically_derived] type T = S;
    |     ^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: attribute should be applied to a free function, impl method or static
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:289:17
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:290:17
    |
 LL |     mod inner { #![no_mangle] }
    |     ------------^^^^^^^^^^^^^-- not a free function, impl method or static
@@ -536,7 +548,7 @@ LL |     mod inner { #![no_mangle] }
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
 
 warning: attribute should be applied to a free function, impl method or static
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:296:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:297:5
    |
 LL |     #[no_mangle] struct S;
    |     ^^^^^^^^^^^^ --------- not a free function, impl method or static
@@ -544,7 +556,7 @@ LL |     #[no_mangle] struct S;
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
 
 warning: attribute should be applied to a free function, impl method or static
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:301:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:302:5
    |
 LL |     #[no_mangle] type T = S;
    |     ^^^^^^^^^^^^ ----------- not a free function, impl method or static
@@ -552,7 +564,7 @@ LL |     #[no_mangle] type T = S;
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
 
 warning: attribute should be applied to a free function, impl method or static
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:306:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:307:5
    |
 LL |     #[no_mangle] impl S { }
    |     ^^^^^^^^^^^^ ---------- not a free function, impl method or static
@@ -560,7 +572,7 @@ LL |     #[no_mangle] impl S { }
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
 
 warning: attribute should be applied to a free function, impl method or static
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:312:9
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:313:9
    |
 LL |         #[no_mangle] fn foo();
    |         ^^^^^^^^^^^^ --------- not a free function, impl method or static
@@ -568,7 +580,7 @@ LL |         #[no_mangle] fn foo();
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
 
 warning: attribute should be applied to a free function, impl method or static
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:317:9
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:318:9
    |
 LL |         #[no_mangle] fn bar() {}
    |         ^^^^^^^^^^^^ ----------- not a free function, impl method or static
@@ -576,163 +588,163 @@ LL |         #[no_mangle] fn bar() {}
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
 
 warning: `#[should_panic]` only has an effect on functions
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:327:17
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:328:17
    |
 LL |     mod inner { #![should_panic] }
    |                 ^^^^^^^^^^^^^^^^
 
 warning: `#[should_panic]` only has an effect on functions
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:332:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:333:5
    |
 LL |     #[should_panic] struct S;
    |     ^^^^^^^^^^^^^^^
 
 warning: `#[should_panic]` only has an effect on functions
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:335:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:336:5
    |
 LL |     #[should_panic] type T = S;
    |     ^^^^^^^^^^^^^^^
 
 warning: `#[should_panic]` only has an effect on functions
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:338:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:339:5
    |
 LL |     #[should_panic] impl S { }
    |     ^^^^^^^^^^^^^^^
 
 warning: `#[ignore]` only has an effect on functions
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:345:17
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:346:17
    |
 LL |     mod inner { #![ignore] }
    |                 ^^^^^^^^^^
 
 warning: `#[ignore]` only has an effect on functions
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:350:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:351:5
    |
 LL |     #[ignore] struct S;
    |     ^^^^^^^^^
 
 warning: `#[ignore]` only has an effect on functions
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:353:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:354:5
    |
 LL |     #[ignore] type T = S;
    |     ^^^^^^^^^
 
 warning: `#[ignore]` only has an effect on functions
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:356:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:357:5
    |
 LL |     #[ignore] impl S { }
    |     ^^^^^^^^^
 
 warning: `#[no_implicit_prelude]` only has an effect on modules
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:364:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:365:5
    |
 LL |     #[no_implicit_prelude] fn f() { }
    |     ^^^^^^^^^^^^^^^^^^^^^^
 
 warning: `#[no_implicit_prelude]` only has an effect on modules
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:367:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:368:5
    |
 LL |     #[no_implicit_prelude] struct S;
    |     ^^^^^^^^^^^^^^^^^^^^^^
 
 warning: `#[no_implicit_prelude]` only has an effect on modules
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:370:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:371:5
    |
 LL |     #[no_implicit_prelude] type T = S;
    |     ^^^^^^^^^^^^^^^^^^^^^^
 
 warning: `#[no_implicit_prelude]` only has an effect on modules
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:373:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:374:5
    |
 LL |     #[no_implicit_prelude] impl S { }
    |     ^^^^^^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be in the root module
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:380:17
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:381:17
    |
 LL |     mod inner { #![reexport_test_harness_main="2900"] }
    |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: `#![foo]`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:383:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:384:5
    |
 LL |     #[reexport_test_harness_main = "2900"] fn f() { }
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: `#![foo]`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:386:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:387:5
    |
 LL |     #[reexport_test_harness_main = "2900"] struct S;
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: `#![foo]`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:389:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:390:5
    |
 LL |     #[reexport_test_harness_main = "2900"] 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:392:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:393:5
    |
 LL |     #[reexport_test_harness_main = "2900"] impl S { }
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: `#[macro_escape]` only has an effect on `extern crate` and modules
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:404:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:405:5
    |
 LL |     #[macro_escape] fn f() { }
    |     ^^^^^^^^^^^^^^^
 
 warning: `#[macro_escape]` only has an effect on `extern crate` and modules
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:407:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:408:5
    |
 LL |     #[macro_escape] struct S;
    |     ^^^^^^^^^^^^^^^
 
 warning: `#[macro_escape]` only has an effect on `extern crate` and modules
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:410:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:411:5
    |
 LL |     #[macro_escape] type T = S;
    |     ^^^^^^^^^^^^^^^
 
 warning: `#[macro_escape]` only has an effect on `extern crate` and modules
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:413:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:414:5
    |
 LL |     #[macro_escape] impl S { }
    |     ^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be in the root module
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:420:17
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:421:17
    |
 LL |     mod inner { #![no_std] }
    |                 ^^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: `#![foo]`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:423:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:424:5
    |
 LL |     #[no_std] fn f() { }
    |     ^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: `#![foo]`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:426:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:427:5
    |
 LL |     #[no_std] struct S;
    |     ^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: `#![foo]`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:429:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:430:5
    |
 LL |     #[no_std] 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:432:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:433:5
    |
 LL |     #[no_std] impl S { }
    |     ^^^^^^^^^
 
 warning: attribute should be applied to a function
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:459:17
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:460:17
    |
 LL |     mod inner { #![cold] }
    |     ------------^^^^^^^^-- not a function
@@ -740,7 +752,7 @@ LL |     mod inner { #![cold] }
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
 
 warning: attribute should be applied to a function
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:466:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:467:5
    |
 LL |     #[cold] struct S;
    |     ^^^^^^^ --------- not a function
@@ -748,7 +760,7 @@ LL |     #[cold] struct S;
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
 
 warning: attribute should be applied to a function
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:471:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:472:5
    |
 LL |     #[cold] type T = S;
    |     ^^^^^^^ ----------- not a function
@@ -756,7 +768,7 @@ LL |     #[cold] type T = S;
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
 
 warning: attribute should be applied to a function
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:476:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:477:5
    |
 LL |     #[cold] impl S { }
    |     ^^^^^^^ ---------- not a function
@@ -764,7 +776,7 @@ LL |     #[cold] impl S { }
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
 
 warning: attribute should be applied to a foreign function or static
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:488:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:489:5
    |
 LL |     #[link_name = "1900"]
    |     ^^^^^^^^^^^^^^^^^^^^^
@@ -774,13 +786,13 @@ LL |     extern "C" { }
    |
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
 help: try `#[link(name = "1900")]` instead
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:488:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:489:5
    |
 LL |     #[link_name = "1900"]
    |     ^^^^^^^^^^^^^^^^^^^^^
 
 warning: attribute should be applied to a foreign function or static
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:495:17
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:496:17
    |
 LL |     mod inner { #![link_name="1900"] }
    |     ------------^^^^^^^^^^^^^^^^^^^^-- not a foreign function or static
@@ -788,7 +800,7 @@ LL |     mod inner { #![link_name="1900"] }
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
 
 warning: attribute should be applied to a foreign function or static
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:500:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:501:5
    |
 LL |     #[link_name = "1900"] fn f() { }
    |     ^^^^^^^^^^^^^^^^^^^^^ ---------- not a foreign function or static
@@ -796,7 +808,7 @@ LL |     #[link_name = "1900"] fn f() { }
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
 
 warning: attribute should be applied to a foreign function or static
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:505:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:506:5
    |
 LL |     #[link_name = "1900"] struct S;
    |     ^^^^^^^^^^^^^^^^^^^^^ --------- not a foreign function or static
@@ -804,7 +816,7 @@ LL |     #[link_name = "1900"] struct S;
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
 
 warning: attribute should be applied to a foreign function or static
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:510:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:511:5
    |
 LL |     #[link_name = "1900"] type T = S;
    |     ^^^^^^^^^^^^^^^^^^^^^ ----------- not a foreign function or static
@@ -812,7 +824,7 @@ LL |     #[link_name = "1900"] type T = S;
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
 
 warning: attribute should be applied to a foreign function or static
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:515:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:516:5
    |
 LL |     #[link_name = "1900"] impl S { }
    |     ^^^^^^^^^^^^^^^^^^^^^ ---------- not a foreign function or static
@@ -820,7 +832,7 @@ LL |     #[link_name = "1900"] impl S { }
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
 
 warning: attribute should be applied to a function or static
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:527:17
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:528:17
    |
 LL |     mod inner { #![link_section="1800"] }
    |     ------------^^^^^^^^^^^^^^^^^^^^^^^-- not a function or static
@@ -828,7 +840,7 @@ LL |     mod inner { #![link_section="1800"] }
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
 
 warning: attribute should be applied to a function or static
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:534:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:535:5
    |
 LL |     #[link_section = "1800"] struct S;
    |     ^^^^^^^^^^^^^^^^^^^^^^^^ --------- not a function or static
@@ -836,7 +848,7 @@ LL |     #[link_section = "1800"] struct S;
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
 
 warning: attribute should be applied to a function or static
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:539:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:540:5
    |
 LL |     #[link_section = "1800"] type T = S;
    |     ^^^^^^^^^^^^^^^^^^^^^^^^ ----------- not a function or static
@@ -844,7 +856,7 @@ LL |     #[link_section = "1800"] type T = S;
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
 
 warning: attribute should be applied to a function or static
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:544:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:545:5
    |
 LL |     #[link_section = "1800"] impl S { }
    |     ^^^^^^^^^^^^^^^^^^^^^^^^ ---------- not a function or static
@@ -852,7 +864,7 @@ LL |     #[link_section = "1800"] impl S { }
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
 
 warning: attribute should be applied to an `extern` block
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:559:17
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:560:17
    |
 LL |     mod inner { #![link()] }
    |     ------------^^^^^^^^^^-- not an `extern` block
@@ -860,7 +872,7 @@ LL |     mod inner { #![link()] }
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
 
 warning: attribute should be applied to an `extern` block
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:564:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:565:5
    |
 LL |     #[link()] fn f() { }
    |     ^^^^^^^^^ ---------- not an `extern` block
@@ -868,7 +880,7 @@ LL |     #[link()] fn f() { }
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
 
 warning: attribute should be applied to an `extern` block
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:569:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:570:5
    |
 LL |     #[link()] struct S;
    |     ^^^^^^^^^ --------- not an `extern` block
@@ -876,7 +888,7 @@ LL |     #[link()] struct S;
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
 
 warning: attribute should be applied to an `extern` block
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:574:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:575:5
    |
 LL |     #[link()] type T = S;
    |     ^^^^^^^^^ ----------- not an `extern` block
@@ -884,260 +896,278 @@ LL |     #[link()] type T = S;
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
 
 warning: attribute should be applied to an `extern` block
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:579:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:580:5
    |
 LL |     #[link()] impl S { }
    |     ^^^^^^^^^ ---------- not an `extern` block
    |
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
 
+warning: `#[must_use]` has no effect when applied to a module
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:603:17
+   |
+LL |     mod inner { #![must_use] }
+   |                 ^^^^^^^^^^^^
+
+warning: `#[must_use]` has no effect when applied to a type alias
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:609:5
+   |
+LL |     #[must_use] type T = S;
+   |     ^^^^^^^^^^^
+
+warning: `#[must_use]` has no effect when applied to an item
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:611:5
+   |
+LL |     #[must_use] impl S { }
+   |     ^^^^^^^^^^^
+
 warning: crate-level attribute should be in the root module
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:616:17
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:617:17
    |
 LL |     mod inner { #![windows_subsystem="windows"] }
    |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: `#![foo]`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:619:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:620:5
    |
 LL |     #[windows_subsystem = "windows"] fn f() { }
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: `#![foo]`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:622:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:623:5
    |
 LL |     #[windows_subsystem = "windows"] struct S;
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: `#![foo]`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:625:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:626:5
    |
 LL |     #[windows_subsystem = "windows"] 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:628:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:629:5
    |
 LL |     #[windows_subsystem = "windows"] impl S { }
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be in the root module
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:637:17
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:638:17
    |
 LL |     mod inner { #![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:640:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:641:5
    |
 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:643:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:644:5
    |
 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:646:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:647:5
    |
 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:649:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:650:5
    |
 LL |     #[crate_name = "0900"] impl S { }
    |     ^^^^^^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be in the root module
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:656:17
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:657:17
    |
 LL |     mod inner { #![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:659:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:660:5
    |
 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:662:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:663:5
    |
 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:665:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:666:5
    |
 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:668:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:669:5
    |
 LL |     #[crate_type = "0800"] impl S { }
    |     ^^^^^^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be in the root module
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:675:17
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:676:17
    |
 LL |     mod inner { #![feature(x0600)] }
    |                 ^^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: `#![foo]`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:678:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:679:5
    |
 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:681:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:682:5
    |
 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:684:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:685:5
    |
 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:687:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:688:5
    |
 LL |     #[feature(x0600)] impl S { }
    |     ^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be in the root module
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:695:17
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:696:17
    |
 LL |     mod inner { #![no_main] }
    |                 ^^^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: `#![foo]`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:698:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:699:5
    |
 LL |     #[no_main] fn f() { }
    |     ^^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: `#![foo]`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:701:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:702:5
    |
 LL |     #[no_main] 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:705:5
    |
 LL |     #[no_main] 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:707:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:708:5
    |
 LL |     #[no_main] impl S { }
    |     ^^^^^^^^^^
 
 warning: crate-level attribute should be in the root module
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:714:17
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:715:17
    |
 LL |     mod inner { #![no_builtins] }
    |                 ^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: `#![foo]`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:717:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:718:5
    |
 LL |     #[no_builtins] fn f() { }
    |     ^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: `#![foo]`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:720:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:721:5
    |
 LL |     #[no_builtins] struct S;
    |     ^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be an inner attribute: add an exclamation mark: `#![foo]`
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:723:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:724:5
    |
 LL |     #[no_builtins] 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:726:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:727:5
    |
 LL |     #[no_builtins] impl S { }
    |     ^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be in the root module
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:733:17
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:734:17
    |
 LL |     mod inner { #![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:736:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:737:5
    |
 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:739:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:740:5
    |
 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:742:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:743:5
    |
 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:745:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:746:5
    |
 LL |     #[recursion_limit="0200"] impl S { }
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: crate-level attribute should be in the root module
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:752:17
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:753:17
    |
 LL |     mod inner { #![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:755:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:756:5
    |
 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:758:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:759:5
    |
 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:761:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:762:5
    |
 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:764:5
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:765:5
    |
 LL |     #[type_length_limit="0100"] impl S { }
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: the feature `rust1` has been stable since 1.0.0 and no longer requires an attribute to enable
-  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:90:12
+  --> $DIR/issue-43106-gating-of-builtin-attrs.rs:91:12
    |
 LL | #![feature(rust1)]
    |            ^^^^^
    |
    = note: `#[warn(stable_features)]` on by default
 
-warning: 167 warnings emitted
+warning: 172 warnings emitted
 
diff --git a/src/test/ui/lint/unused/unused_attributes-must_use.rs b/src/test/ui/lint/unused/unused_attributes-must_use.rs
new file mode 100644
index 00000000000..1c4abb9491e
--- /dev/null
+++ b/src/test/ui/lint/unused/unused_attributes-must_use.rs
@@ -0,0 +1,125 @@
+#![allow(dead_code, path_statements)]
+#![deny(unused_attributes, unused_must_use)]
+#![feature(asm_experimental_arch, stmt_expr_attributes, trait_alias)]
+
+#[must_use] //~ ERROR `#[must_use]` has no effect
+extern crate std as std2;
+
+#[must_use] //~ ERROR `#[must_use]` has no effect
+mod test_mod {}
+
+#[must_use] //~ ERROR `#[must_use]` has no effect
+use std::arch::global_asm;
+
+#[must_use] //~ ERROR `#[must_use]` has no effect
+const CONST: usize = 4;
+#[must_use] //~ ERROR `#[must_use]` has no effect
+#[no_mangle]
+static STATIC: usize = 4;
+
+#[must_use]
+struct X;
+
+#[must_use]
+enum Y {
+    Z,
+}
+
+#[must_use]
+union U {
+    unit: (),
+}
+
+#[must_use] //~ ERROR `#[must_use]` has no effect
+impl U {
+    #[must_use]
+    fn method() -> i32 {
+        4
+    }
+}
+
+#[must_use]
+#[no_mangle]
+fn foo() -> i64 {
+    4
+}
+
+#[must_use] //~ ERROR `#[must_use]` has no effect
+extern "Rust" {
+    #[link_name = "STATIC"]
+    #[must_use] //~ ERROR `#[must_use]` has no effect
+    static FOREIGN_STATIC: usize;
+
+    #[link_name = "foo"]
+    #[must_use]
+    fn foreign_foo() -> i64;
+}
+
+#[must_use] //~ ERROR unused attribute
+global_asm!("");
+
+#[must_use] //~ ERROR `#[must_use]` has no effect
+type UseMe = ();
+
+fn qux<#[must_use] T>(_: T) {} //~ ERROR `#[must_use]` has no effect
+
+#[must_use]
+trait Use {
+    #[must_use] //~ ERROR `#[must_use]` has no effect
+    const ASSOC_CONST: usize = 4;
+    #[must_use] //~ ERROR `#[must_use]` has no effect
+    type AssocTy;
+
+    #[must_use]
+    fn get_four(&self) -> usize {
+        4
+    }
+}
+
+#[must_use] //~ ERROR `#[must_use]` has no effect
+impl Use for () {
+    type AssocTy = ();
+}
+
+#[must_use] //~ ERROR `#[must_use]` has no effect
+trait Alias = Use;
+
+#[must_use] //~ ERROR `#[must_use]` has no effect
+macro_rules! cool_macro {
+    () => {
+        4
+    };
+}
+
+fn main() {
+    #[must_use] //~ ERROR `#[must_use]` has no effect
+    let x = || {};
+    x();
+
+    let x = #[must_use] //~ ERROR `#[must_use]` has no effect
+    || {};
+    x();
+
+    X; //~ ERROR that must be used
+    Y::Z; //~ ERROR that must be used
+    U { unit: () }; //~ ERROR that must be used
+    U::method(); //~ ERROR that must be used
+    foo(); //~ ERROR that must be used
+
+    unsafe {
+        foreign_foo(); //~ ERROR that must be used
+    };
+
+    CONST;
+    STATIC;
+    unsafe { FOREIGN_STATIC };
+    cool_macro!();
+    qux(4);
+    ().get_four(); //~ ERROR that must be used
+
+    match Some(4) {
+        #[must_use] //~ ERROR `#[must_use]` has no effect
+        Some(res) => res,
+        None => 0,
+    };
+}
diff --git a/src/test/ui/lint/unused/unused_attributes-must_use.stderr b/src/test/ui/lint/unused/unused_attributes-must_use.stderr
new file mode 100644
index 00000000000..27269580e52
--- /dev/null
+++ b/src/test/ui/lint/unused/unused_attributes-must_use.stderr
@@ -0,0 +1,175 @@
+error: unused attribute `must_use`
+  --> $DIR/unused_attributes-must_use.rs:58:1
+   |
+LL | #[must_use]
+   | ^^^^^^^^^^^
+   |
+note: the lint level is defined here
+  --> $DIR/unused_attributes-must_use.rs:2:9
+   |
+LL | #![deny(unused_attributes, unused_must_use)]
+   |         ^^^^^^^^^^^^^^^^^
+note: the built-in attribute `must_use` will be ignored, since it's applied to the macro invocation `global_asm`
+  --> $DIR/unused_attributes-must_use.rs:59:1
+   |
+LL | global_asm!("");
+   | ^^^^^^^^^^
+
+error: `#[must_use]` has no effect when applied to an extern crate
+  --> $DIR/unused_attributes-must_use.rs:5:1
+   |
+LL | #[must_use]
+   | ^^^^^^^^^^^
+
+error: `#[must_use]` has no effect when applied to a module
+  --> $DIR/unused_attributes-must_use.rs:8:1
+   |
+LL | #[must_use]
+   | ^^^^^^^^^^^
+
+error: `#[must_use]` has no effect when applied to a use
+  --> $DIR/unused_attributes-must_use.rs:11:1
+   |
+LL | #[must_use]
+   | ^^^^^^^^^^^
+
+error: `#[must_use]` has no effect when applied to a constant item
+  --> $DIR/unused_attributes-must_use.rs:14:1
+   |
+LL | #[must_use]
+   | ^^^^^^^^^^^
+
+error: `#[must_use]` has no effect when applied to a static item
+  --> $DIR/unused_attributes-must_use.rs:16:1
+   |
+LL | #[must_use]
+   | ^^^^^^^^^^^
+
+error: `#[must_use]` has no effect when applied to an item
+  --> $DIR/unused_attributes-must_use.rs:33:1
+   |
+LL | #[must_use]
+   | ^^^^^^^^^^^
+
+error: `#[must_use]` has no effect when applied to a foreign module
+  --> $DIR/unused_attributes-must_use.rs:47:1
+   |
+LL | #[must_use]
+   | ^^^^^^^^^^^
+
+error: `#[must_use]` has no effect when applied to a type alias
+  --> $DIR/unused_attributes-must_use.rs:61:1
+   |
+LL | #[must_use]
+   | ^^^^^^^^^^^
+
+error: `#[must_use]` has no effect when applied to a type parameter
+  --> $DIR/unused_attributes-must_use.rs:64:8
+   |
+LL | fn qux<#[must_use] T>(_: T) {}
+   |        ^^^^^^^^^^^
+
+error: `#[must_use]` has no effect when applied to an item
+  --> $DIR/unused_attributes-must_use.rs:79:1
+   |
+LL | #[must_use]
+   | ^^^^^^^^^^^
+
+error: `#[must_use]` has no effect when applied to a trait alias
+  --> $DIR/unused_attributes-must_use.rs:84:1
+   |
+LL | #[must_use]
+   | ^^^^^^^^^^^
+
+error: `#[must_use]` has no effect when applied to a macro def
+  --> $DIR/unused_attributes-must_use.rs:87:1
+   |
+LL | #[must_use]
+   | ^^^^^^^^^^^
+
+error: `#[must_use]` has no effect when applied to a statement
+  --> $DIR/unused_attributes-must_use.rs:95:5
+   |
+LL |     #[must_use]
+   |     ^^^^^^^^^^^
+
+error: `#[must_use]` has no effect when applied to a closure
+  --> $DIR/unused_attributes-must_use.rs:99:13
+   |
+LL |     let x = #[must_use]
+   |             ^^^^^^^^^^^
+
+error: `#[must_use]` has no effect when applied to an match arm
+  --> $DIR/unused_attributes-must_use.rs:121:9
+   |
+LL |         #[must_use]
+   |         ^^^^^^^^^^^
+
+error: `#[must_use]` has no effect when applied to an associated const
+  --> $DIR/unused_attributes-must_use.rs:68:5
+   |
+LL |     #[must_use]
+   |     ^^^^^^^^^^^
+
+error: `#[must_use]` has no effect when applied to an associated type
+  --> $DIR/unused_attributes-must_use.rs:70:5
+   |
+LL |     #[must_use]
+   |     ^^^^^^^^^^^
+
+error: `#[must_use]` has no effect when applied to a foreign static item
+  --> $DIR/unused_attributes-must_use.rs:50:5
+   |
+LL |     #[must_use]
+   |     ^^^^^^^^^^^
+
+error: unused `X` that must be used
+  --> $DIR/unused_attributes-must_use.rs:103:5
+   |
+LL |     X;
+   |     ^^
+   |
+note: the lint level is defined here
+  --> $DIR/unused_attributes-must_use.rs:2:28
+   |
+LL | #![deny(unused_attributes, unused_must_use)]
+   |                            ^^^^^^^^^^^^^^^
+
+error: unused `Y` that must be used
+  --> $DIR/unused_attributes-must_use.rs:104:5
+   |
+LL |     Y::Z;
+   |     ^^^^^
+
+error: unused `U` that must be used
+  --> $DIR/unused_attributes-must_use.rs:105:5
+   |
+LL |     U { unit: () };
+   |     ^^^^^^^^^^^^^^^
+
+error: unused return value of `U::method` that must be used
+  --> $DIR/unused_attributes-must_use.rs:106:5
+   |
+LL |     U::method();
+   |     ^^^^^^^^^^^^
+
+error: unused return value of `foo` that must be used
+  --> $DIR/unused_attributes-must_use.rs:107:5
+   |
+LL |     foo();
+   |     ^^^^^^
+
+error: unused return value of `foreign_foo` that must be used
+  --> $DIR/unused_attributes-must_use.rs:110:9
+   |
+LL |         foreign_foo();
+   |         ^^^^^^^^^^^^^^
+
+error: unused return value of `Use::get_four` that must be used
+  --> $DIR/unused_attributes-must_use.rs:118:5
+   |
+LL |     ().get_four();
+   |     ^^^^^^^^^^^^^^
+
+error: aborting due to 26 previous errors
+