diff --git a/compiler/rustc_codegen_gcc/example/mini_core.rs b/compiler/rustc_codegen_gcc/example/mini_core.rs
index 0576b64ef6fa5..580c4622e3dbd 100644
--- a/compiler/rustc_codegen_gcc/example/mini_core.rs
+++ b/compiler/rustc_codegen_gcc/example/mini_core.rs
@@ -639,7 +639,7 @@ impl<T> Index<usize> for [T] {
     }
 }
 
-extern {
+extern "C" {
     type VaListImpl;
 }
 
diff --git a/compiler/rustc_codegen_gcc/example/mini_core_hello_world.rs b/compiler/rustc_codegen_gcc/example/mini_core_hello_world.rs
index dcfa34cb729d8..1d51e0a1856ba 100644
--- a/compiler/rustc_codegen_gcc/example/mini_core_hello_world.rs
+++ b/compiler/rustc_codegen_gcc/example/mini_core_hello_world.rs
@@ -258,13 +258,13 @@ fn main() {
 
     assert_eq!(((|()| 42u8) as fn(()) -> u8)(()), 42);
 
-    extern {
+    extern "C" {
         #[linkage = "weak"]
         static ABC: *const u8;
     }
 
     {
-        extern {
+        extern "C" {
             #[linkage = "weak"]
             static ABC: *const u8;
         }
diff --git a/compiler/rustc_codegen_gcc/example/mod_bench.rs b/compiler/rustc_codegen_gcc/example/mod_bench.rs
index cae911c1073d5..e8a9cade74745 100644
--- a/compiler/rustc_codegen_gcc/example/mod_bench.rs
+++ b/compiler/rustc_codegen_gcc/example/mod_bench.rs
@@ -3,7 +3,7 @@
 #![allow(internal_features)]
 
 #[link(name = "c")]
-extern {}
+extern "C" {}
 
 #[panic_handler]
 fn panic_handler(_: &core::panic::PanicInfo<'_>) -> ! {
diff --git a/compiler/rustc_codegen_gcc/example/std_example.rs b/compiler/rustc_codegen_gcc/example/std_example.rs
index 9e43b4635f0d3..5fa1e0afb0603 100644
--- a/compiler/rustc_codegen_gcc/example/std_example.rs
+++ b/compiler/rustc_codegen_gcc/example/std_example.rs
@@ -7,7 +7,7 @@ use std::arch::x86_64::*;
 use std::io::Write;
 use std::ops::Coroutine;
 
-extern {
+extern "C" {
     pub fn printf(format: *const i8, ...) -> i32;
 }
 
diff --git a/src/tools/clippy/tests/ui/boxed_local.rs b/src/tools/clippy/tests/ui/boxed_local.rs
index e2c27e585fce8..4f361f5162be4 100644
--- a/src/tools/clippy/tests/ui/boxed_local.rs
+++ b/src/tools/clippy/tests/ui/boxed_local.rs
@@ -173,6 +173,7 @@ mod issue_3739 {
 /// This shouldn't warn for `boxed_local` as it is intended to called from non-Rust code.
 pub extern "C" fn do_not_warn_me(_c_pointer: Box<String>) -> () {}
 
+#[allow(missing_abi)]
 #[rustfmt::skip] // Forces rustfmt to not add ABI
 pub extern fn do_not_warn_me_no_abi(_c_pointer: Box<String>) -> () {}
 
diff --git a/src/tools/clippy/tests/ui/boxed_local.stderr b/src/tools/clippy/tests/ui/boxed_local.stderr
index d3156c820b2c5..08fe375afb235 100644
--- a/src/tools/clippy/tests/ui/boxed_local.stderr
+++ b/src/tools/clippy/tests/ui/boxed_local.stderr
@@ -14,13 +14,13 @@ LL | pub fn new(_needs_name: Box<PeekableSeekable<&()>>) -> () {}
    |            ^^^^^^^^^^^
 
 error: local variable doesn't need to be boxed here
-  --> tests/ui/boxed_local.rs:188:44
+  --> tests/ui/boxed_local.rs:189:44
    |
 LL |         fn default_impl_x(self: Box<Self>, x: Box<u32>) -> u32 {
    |                                            ^
 
 error: local variable doesn't need to be boxed here
-  --> tests/ui/boxed_local.rs:196:16
+  --> tests/ui/boxed_local.rs:197:16
    |
 LL |         fn foo(x: Box<u32>) {}
    |                ^
diff --git a/src/tools/clippy/tests/ui/doc/doc-fixable.fixed b/src/tools/clippy/tests/ui/doc/doc-fixable.fixed
index 355f2bc773611..03c092a470276 100644
--- a/src/tools/clippy/tests/ui/doc/doc-fixable.fixed
+++ b/src/tools/clippy/tests/ui/doc/doc-fixable.fixed
@@ -239,7 +239,7 @@ fn parenthesized_word() {}
 /// UXes
 fn plural_acronym_test() {}
 
-extern {
+extern "C" {
     /// `foo()`
     fn in_extern();
 }
diff --git a/src/tools/clippy/tests/ui/doc/doc-fixable.rs b/src/tools/clippy/tests/ui/doc/doc-fixable.rs
index 9ced267762210..224355868d031 100644
--- a/src/tools/clippy/tests/ui/doc/doc-fixable.rs
+++ b/src/tools/clippy/tests/ui/doc/doc-fixable.rs
@@ -239,7 +239,7 @@ fn parenthesized_word() {}
 /// UXes
 fn plural_acronym_test() {}
 
-extern {
+extern "C" {
     /// foo()
     fn in_extern();
 }
diff --git a/src/tools/clippy/tests/ui/missing_const_for_fn/could_be_const.fixed b/src/tools/clippy/tests/ui/missing_const_for_fn/could_be_const.fixed
index f7b6e1a186bbd..48e7b5cfc7c74 100644
--- a/src/tools/clippy/tests/ui/missing_const_for_fn/could_be_const.fixed
+++ b/src/tools/clippy/tests/ui/missing_const_for_fn/could_be_const.fixed
@@ -150,6 +150,7 @@ mod msrv {
         //~^ ERROR: this could be a `const fn`
 
         #[rustfmt::skip]
+        #[allow(missing_abi)]
         const extern fn implicit_c() {}
         //~^ ERROR: this could be a `const fn`
 
diff --git a/src/tools/clippy/tests/ui/missing_const_for_fn/could_be_const.rs b/src/tools/clippy/tests/ui/missing_const_for_fn/could_be_const.rs
index 4866e3210245e..f92e36a0f6312 100644
--- a/src/tools/clippy/tests/ui/missing_const_for_fn/could_be_const.rs
+++ b/src/tools/clippy/tests/ui/missing_const_for_fn/could_be_const.rs
@@ -150,6 +150,7 @@ mod msrv {
         //~^ ERROR: this could be a `const fn`
 
         #[rustfmt::skip]
+        #[allow(missing_abi)]
         extern fn implicit_c() {}
         //~^ ERROR: this could be a `const fn`
 
diff --git a/src/tools/clippy/tests/ui/missing_const_for_fn/could_be_const.stderr b/src/tools/clippy/tests/ui/missing_const_for_fn/could_be_const.stderr
index f28dec5c7f195..2691dc973ea10 100644
--- a/src/tools/clippy/tests/ui/missing_const_for_fn/could_be_const.stderr
+++ b/src/tools/clippy/tests/ui/missing_const_for_fn/could_be_const.stderr
@@ -222,7 +222,7 @@ LL |         const extern "C" fn c() {}
    |         +++++
 
 error: this could be a `const fn`
-  --> tests/ui/missing_const_for_fn/could_be_const.rs:153:9
+  --> tests/ui/missing_const_for_fn/could_be_const.rs:154:9
    |
 LL |         extern fn implicit_c() {}
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -233,7 +233,7 @@ LL |         const extern fn implicit_c() {}
    |         +++++
 
 error: this could be a `const fn`
-  --> tests/ui/missing_const_for_fn/could_be_const.rs:170:9
+  --> tests/ui/missing_const_for_fn/could_be_const.rs:171:9
    |
 LL | /         pub fn new(strings: Vec<String>) -> Self {
 LL | |             Self { strings }
@@ -246,7 +246,7 @@ LL |         pub const fn new(strings: Vec<String>) -> Self {
    |             +++++
 
 error: this could be a `const fn`
-  --> tests/ui/missing_const_for_fn/could_be_const.rs:175:9
+  --> tests/ui/missing_const_for_fn/could_be_const.rs:176:9
    |
 LL | /         pub fn empty() -> Self {
 LL | |             Self { strings: Vec::new() }
@@ -259,7 +259,7 @@ LL |         pub const fn empty() -> Self {
    |             +++++
 
 error: this could be a `const fn`
-  --> tests/ui/missing_const_for_fn/could_be_const.rs:186:9
+  --> tests/ui/missing_const_for_fn/could_be_const.rs:187:9
    |
 LL | /         pub fn new(text: String) -> Self {
 LL | |             let vec = Vec::new();
@@ -273,7 +273,7 @@ LL |         pub const fn new(text: String) -> Self {
    |             +++++
 
 error: this could be a `const fn`
-  --> tests/ui/missing_const_for_fn/could_be_const.rs:205:5
+  --> tests/ui/missing_const_for_fn/could_be_const.rs:206:5
    |
 LL |     fn alias_ty_is_projection(bar: <() as FooTrait>::Foo) {}
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -284,7 +284,7 @@ LL |     const fn alias_ty_is_projection(bar: <() as FooTrait>::Foo) {}
    |     +++++
 
 error: this could be a `const fn`
-  --> tests/ui/missing_const_for_fn/could_be_const.rs:209:5
+  --> tests/ui/missing_const_for_fn/could_be_const.rs:210:5
    |
 LL |     extern "C-unwind" fn c_unwind() {}
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -295,7 +295,7 @@ LL |     const extern "C-unwind" fn c_unwind() {}
    |     +++++
 
 error: this could be a `const fn`
-  --> tests/ui/missing_const_for_fn/could_be_const.rs:211:5
+  --> tests/ui/missing_const_for_fn/could_be_const.rs:212:5
    |
 LL |     extern "system" fn system() {}
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -306,7 +306,7 @@ LL |     const extern "system" fn system() {}
    |     +++++
 
 error: this could be a `const fn`
-  --> tests/ui/missing_const_for_fn/could_be_const.rs:213:5
+  --> tests/ui/missing_const_for_fn/could_be_const.rs:214:5
    |
 LL |     extern "system-unwind" fn system_unwind() {}
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -317,7 +317,7 @@ LL |     const extern "system-unwind" fn system_unwind() {}
    |     +++++
 
 error: this could be a `const fn`
-  --> tests/ui/missing_const_for_fn/could_be_const.rs:215:5
+  --> tests/ui/missing_const_for_fn/could_be_const.rs:216:5
    |
 LL |     pub extern "vectorcall" fn std_call() {}
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -328,7 +328,7 @@ LL |     pub const extern "vectorcall" fn std_call() {}
    |         +++++
 
 error: this could be a `const fn`
-  --> tests/ui/missing_const_for_fn/could_be_const.rs:217:5
+  --> tests/ui/missing_const_for_fn/could_be_const.rs:218:5
    |
 LL |     pub extern "vectorcall-unwind" fn std_call_unwind() {}
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
diff --git a/tests/ui/associated-types/issue-91231.rs b/tests/ui/associated-types/issue-91231.rs
index d1c99fd44fa02..a04ab60a7fcdb 100644
--- a/tests/ui/associated-types/issue-91231.rs
+++ b/tests/ui/associated-types/issue-91231.rs
@@ -3,7 +3,7 @@
 #![feature(extern_types)]
 #![allow(dead_code)]
 
-extern {
+extern "C" {
     type Extern;
 }
 
diff --git a/tests/ui/attributes/key-value-expansion.rs b/tests/ui/attributes/key-value-expansion.rs
index dd408ebb77e4c..5a90efe88fb09 100644
--- a/tests/ui/attributes/key-value-expansion.rs
+++ b/tests/ui/attributes/key-value-expansion.rs
@@ -39,7 +39,7 @@ bug!();
 macro_rules! doc_comment {
     ($x:expr) => {
         #[doc = $x]
-        extern {}
+        extern "C" {}
     };
 }
 
diff --git a/tests/ui/borrowck/issue-92157.rs b/tests/ui/borrowck/issue-92157.rs
index 3a6f8908b219f..a2b685cdf6ede 100644
--- a/tests/ui/borrowck/issue-92157.rs
+++ b/tests/ui/borrowck/issue-92157.rs
@@ -5,7 +5,7 @@
 
 #[cfg(target_os = "linux")]
 #[link(name = "c")]
-extern {}
+extern "C" {}
 
 #[lang = "start"]
 fn start<T>(_main: fn() -> T, _argc: isize, _argv: *const *const u8) -> isize {
diff --git a/tests/ui/coherence/coherence-negative-impls-copy.rs b/tests/ui/coherence/coherence-negative-impls-copy.rs
index 377d750f8baa4..c0d852180a518 100644
--- a/tests/ui/coherence/coherence-negative-impls-copy.rs
+++ b/tests/ui/coherence/coherence-negative-impls-copy.rs
@@ -18,7 +18,7 @@ impl !Copy for WithDrop {}
 
 struct Type;
 trait Trait {}
-extern {
+extern "C" {
     type ExternType;
 }
 
diff --git a/tests/ui/conditional-compilation/cfg_accessible-not_sure.rs b/tests/ui/conditional-compilation/cfg_accessible-not_sure.rs
index e357d3c6cb56f..2ac57f356740f 100644
--- a/tests/ui/conditional-compilation/cfg_accessible-not_sure.rs
+++ b/tests/ui/conditional-compilation/cfg_accessible-not_sure.rs
@@ -63,7 +63,7 @@ const B: bool = true;
 
 // ForeignType::unresolved - error
 
-extern {
+extern "C" {
     type ForeignType;
 }
 
diff --git a/tests/ui/consts/const-eval/validation-ice-extern-type-field.rs b/tests/ui/consts/const-eval/validation-ice-extern-type-field.rs
index 3502409d576c2..8a32b170c40a4 100644
--- a/tests/ui/consts/const-eval/validation-ice-extern-type-field.rs
+++ b/tests/ui/consts/const-eval/validation-ice-extern-type-field.rs
@@ -1,6 +1,6 @@
 #![feature(extern_types)]
 
-extern {
+extern "C" {
     type Opaque;
 }
 
diff --git a/tests/ui/delegation/glob-non-impl.rs b/tests/ui/delegation/glob-non-impl.rs
index d523731eeb35f..e3a4061fb15a6 100644
--- a/tests/ui/delegation/glob-non-impl.rs
+++ b/tests/ui/delegation/glob-non-impl.rs
@@ -11,7 +11,7 @@ trait OtherTrait {
     reuse Trait::*; //~ ERROR glob delegation is only supported in impls
 }
 
-extern {
+extern "C" {
     reuse Trait::*; //~ ERROR delegation is not supported in `extern` blocks
 }
 
diff --git a/tests/ui/extern/extern-type-diag-not-similar.rs b/tests/ui/extern/extern-type-diag-not-similar.rs
index 39d00a6c1bc31..cd3eec9f1f7b8 100644
--- a/tests/ui/extern/extern-type-diag-not-similar.rs
+++ b/tests/ui/extern/extern-type-diag-not-similar.rs
@@ -4,11 +4,11 @@
 // because they are both extern types.
 
 #![feature(extern_types)]
-extern {
+extern "C" {
     type ShouldNotBeMentioned;
 }
 
-extern {
+extern "C" {
     type Foo;
 }
 
diff --git a/tests/ui/extern/issue-10025.rs b/tests/ui/extern/issue-10025.rs
index 0bdcf7c5c5875..0eec924290841 100644
--- a/tests/ui/extern/issue-10025.rs
+++ b/tests/ui/extern/issue-10025.rs
@@ -1,6 +1,6 @@
 //@ run-pass
 //@ pretty-expanded FIXME #23616
-#![allow(dead_code)]
+#![allow(dead_code, missing_abi)]
 
 unsafe extern fn foo() {}
 unsafe extern "C" fn bar() {}
diff --git a/tests/ui/extern/issue-95829.rs b/tests/ui/extern/issue-95829.rs
index c5ae4c6826597..493d53d2532f2 100644
--- a/tests/ui/extern/issue-95829.rs
+++ b/tests/ui/extern/issue-95829.rs
@@ -1,6 +1,6 @@
 //@ edition:2018
 
-extern {
+extern "C" {
     async fn L() { //~ ERROR: incorrect function inside `extern` block
         //~^ ERROR: functions in `extern` blocks cannot have `async` qualifier
         async fn M() {}
diff --git a/tests/ui/extern/issue-95829.stderr b/tests/ui/extern/issue-95829.stderr
index 2f396b8cc0415..2acd0fa3a2650 100644
--- a/tests/ui/extern/issue-95829.stderr
+++ b/tests/ui/extern/issue-95829.stderr
@@ -1,8 +1,8 @@
 error: incorrect function inside `extern` block
   --> $DIR/issue-95829.rs:4:14
    |
-LL |   extern {
-   |   ------ `extern` blocks define existing foreign functions and functions inside of them cannot have a body
+LL |   extern "C" {
+   |   ---------- `extern` blocks define existing foreign functions and functions inside of them cannot have a body
 LL |       async fn L() {
    |  ______________^___-
    | |              |
@@ -18,8 +18,8 @@ LL | |     }
 error: functions in `extern` blocks cannot have `async` qualifier
   --> $DIR/issue-95829.rs:4:5
    |
-LL | extern {
-   | ------ in this `extern` block
+LL | extern "C" {
+   | ---------- in this `extern` block
 LL |     async fn L() {
    |     ^^^^^ help: remove the `async` qualifier
 
diff --git a/tests/ui/extern/not-in-block.rs b/tests/ui/extern/not-in-block.rs
index d3bcafdef7b3c..c21616350902e 100644
--- a/tests/ui/extern/not-in-block.rs
+++ b/tests/ui/extern/not-in-block.rs
@@ -1,4 +1,5 @@
 #![crate_type = "lib"]
+#![allow(missing_abi)]
 
 extern fn none_fn(x: bool) -> i32;
 //~^ ERROR free function without a body
diff --git a/tests/ui/extern/not-in-block.stderr b/tests/ui/extern/not-in-block.stderr
index 2544949ab17a8..f86c279a23424 100644
--- a/tests/ui/extern/not-in-block.stderr
+++ b/tests/ui/extern/not-in-block.stderr
@@ -1,5 +1,5 @@
 error: free function without a body
-  --> $DIR/not-in-block.rs:3:1
+  --> $DIR/not-in-block.rs:4:1
    |
 LL | extern fn none_fn(x: bool) -> i32;
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -14,7 +14,7 @@ LL | extern { fn none_fn(x: bool) -> i32; }
    | ~~~~~~~~                             +
 
 error: free function without a body
-  --> $DIR/not-in-block.rs:5:1
+  --> $DIR/not-in-block.rs:6:1
    |
 LL | extern "C" fn c_fn(x: bool) -> i32;
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
diff --git a/tests/ui/foreign/issue-91370-foreign-fn-block-impl.rs b/tests/ui/foreign/issue-91370-foreign-fn-block-impl.rs
index 2ac3ca29355d8..e8634de86ea49 100644
--- a/tests/ui/foreign/issue-91370-foreign-fn-block-impl.rs
+++ b/tests/ui/foreign/issue-91370-foreign-fn-block-impl.rs
@@ -1,6 +1,6 @@
 // Regression test for issue #91370.
 
-extern {
+extern "C" {
     //~^ `extern` blocks define existing foreign functions
     fn f() {
         //~^ incorrect function inside `extern` block
diff --git a/tests/ui/foreign/issue-91370-foreign-fn-block-impl.stderr b/tests/ui/foreign/issue-91370-foreign-fn-block-impl.stderr
index fea2ab61e929f..155fdf9d09ab0 100644
--- a/tests/ui/foreign/issue-91370-foreign-fn-block-impl.stderr
+++ b/tests/ui/foreign/issue-91370-foreign-fn-block-impl.stderr
@@ -1,8 +1,8 @@
 error: incorrect function inside `extern` block
   --> $DIR/issue-91370-foreign-fn-block-impl.rs:5:8
    |
-LL |   extern {
-   |   ------ `extern` blocks define existing foreign functions and functions inside of them cannot have a body
+LL |   extern "C" {
+   |   ---------- `extern` blocks define existing foreign functions and functions inside of them cannot have a body
 LL |
 LL |       fn f() {
    |  ________^___-
diff --git a/tests/ui/invalid/invalid-rustc_legacy_const_generics-arguments.rs b/tests/ui/invalid/invalid-rustc_legacy_const_generics-arguments.rs
index 6eabd9b1015b7..73a0363904aeb 100644
--- a/tests/ui/invalid/invalid-rustc_legacy_const_generics-arguments.rs
+++ b/tests/ui/invalid/invalid-rustc_legacy_const_generics-arguments.rs
@@ -21,7 +21,7 @@ struct S;
 #[rustc_legacy_const_generics(0usize)] //~ ERROR suffixed literals are not allowed in attributes
 fn foo6<const X: usize>() {}
 
-extern {
+extern "C" {
     #[rustc_legacy_const_generics(1)] //~ ERROR attribute should be applied to a function
     fn foo7<const X: usize>(); //~ ERROR foreign items may not have const parameters
 }
diff --git a/tests/ui/linkage-attr/issue-109144.rs b/tests/ui/linkage-attr/issue-109144.rs
index 2f740e5538973..6970a4989bb53 100644
--- a/tests/ui/linkage-attr/issue-109144.rs
+++ b/tests/ui/linkage-attr/issue-109144.rs
@@ -1,4 +1,4 @@
 #![crate_type = "lib"]
 #[link(kind = "static", modifiers = "+whole-archive,+bundle")]
 //~^ ERROR `#[link]` attribute requires a `name = "string"` argument
-extern  {}
+extern "C" {}
diff --git a/tests/ui/lint/function-item-references.rs b/tests/ui/lint/function-item-references.rs
index 918d72e28a918..4f2fc4de8632e 100644
--- a/tests/ui/lint/function-item-references.rs
+++ b/tests/ui/lint/function-item-references.rs
@@ -11,7 +11,7 @@ fn baz(x: u32, y: u32) -> u32 { x + y }
 unsafe fn unsafe_fn() { }
 extern "C" fn c_fn() { }
 unsafe extern "C" fn unsafe_c_fn() { }
-unsafe extern fn variadic(_x: u32, _args: ...) { }
+unsafe extern "C" fn variadic(_x: u32, _args: ...) { }
 fn take_generic_ref<'a, T>(_x: &'a T) { }
 fn take_generic_array<T, const N: usize>(_x: [T; N]) { }
 fn multiple_generic<T, U>(_x: T, _y: U) { }
diff --git a/tests/ui/lint/lint-ctypes.rs b/tests/ui/lint/lint-ctypes.rs
index dae07930aba60..6dd9be10a48f8 100644
--- a/tests/ui/lint/lint-ctypes.rs
+++ b/tests/ui/lint/lint-ctypes.rs
@@ -72,7 +72,7 @@ extern "C" {
     pub fn transparent_fn(p: TransparentBadFn); //~ ERROR: uses type `Box<u32>`
     pub fn raw_array(arr: [u8; 8]); //~ ERROR: uses type `[u8; 8]`
 
-    pub fn no_niche_a(a: Option<UnsafeCell<extern fn()>>);
+    pub fn no_niche_a(a: Option<UnsafeCell<extern "C" fn()>>);
     //~^ ERROR: uses type `Option<UnsafeCell<extern "C" fn()>>`
     pub fn no_niche_b(b: Option<UnsafeCell<&i32>>);
     //~^ ERROR: uses type `Option<UnsafeCell<&i32>>`
diff --git a/tests/ui/lint/lint-ctypes.stderr b/tests/ui/lint/lint-ctypes.stderr
index 2c81c7b8e4b67..8137ae868d356 100644
--- a/tests/ui/lint/lint-ctypes.stderr
+++ b/tests/ui/lint/lint-ctypes.stderr
@@ -227,8 +227,8 @@ LL |     pub fn raw_array(arr: [u8; 8]);
 error: `extern` block uses type `Option<UnsafeCell<extern "C" fn()>>`, which is not FFI-safe
   --> $DIR/lint-ctypes.rs:75:26
    |
-LL |     pub fn no_niche_a(a: Option<UnsafeCell<extern fn()>>);
-   |                          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ not FFI-safe
+LL |     pub fn no_niche_a(a: Option<UnsafeCell<extern "C" fn()>>);
+   |                          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ not FFI-safe
    |
    = help: consider adding a `#[repr(C)]`, `#[repr(transparent)]`, or integer `#[repr(...)]` attribute to this enum
    = note: enum has no representation hint
diff --git a/tests/ui/native-library-link-flags/suggest-libname-only-1.stderr b/tests/ui/native-library-link-flags/suggest-libname-only-1.stderr
index e142835a9d64c..aae8f7de966a0 100644
--- a/tests/ui/native-library-link-flags/suggest-libname-only-1.stderr
+++ b/tests/ui/native-library-link-flags/suggest-libname-only-1.stderr
@@ -1,6 +1,14 @@
+warning: extern declarations without an explicit ABI are deprecated
+  --> $DIR/suggest-libname-only-1.rs:7:1
+   |
+LL | extern { }
+   | ^^^^^^ help: explicitly specify the C ABI: `extern "C"`
+   |
+   = note: `#[warn(missing_abi)]` on by default
+
 error: could not find native static library `libfoo.a`, perhaps an -L flag is missing?
    |
    = help: only provide the library name `foo`, not the full filename
 
-error: aborting due to 1 previous error
+error: aborting due to 1 previous error; 1 warning emitted
 
diff --git a/tests/ui/native-library-link-flags/suggest-libname-only-2.stderr b/tests/ui/native-library-link-flags/suggest-libname-only-2.stderr
index 392d2f01f619b..a2adaee3f97f5 100644
--- a/tests/ui/native-library-link-flags/suggest-libname-only-2.stderr
+++ b/tests/ui/native-library-link-flags/suggest-libname-only-2.stderr
@@ -1,6 +1,14 @@
+warning: extern declarations without an explicit ABI are deprecated
+  --> $DIR/suggest-libname-only-2.rs:7:1
+   |
+LL | extern { }
+   | ^^^^^^ help: explicitly specify the C ABI: `extern "C"`
+   |
+   = note: `#[warn(missing_abi)]` on by default
+
 error: could not find native static library `bar.lib`, perhaps an -L flag is missing?
    |
    = help: only provide the library name `bar`, not the full filename
 
-error: aborting due to 1 previous error
+error: aborting due to 1 previous error; 1 warning emitted
 
diff --git a/tests/ui/offset-of/offset-of-dst-field.rs b/tests/ui/offset-of/offset-of-dst-field.rs
index 5ae15f323577f..2e0bdb151e180 100644
--- a/tests/ui/offset-of/offset-of-dst-field.rs
+++ b/tests/ui/offset-of/offset-of-dst-field.rs
@@ -16,7 +16,7 @@ struct Beta {
     z: dyn Trait,
 }
 
-extern {
+extern "C" {
     type Extern;
 }
 
diff --git a/tests/ui/parser/bad-fn-ptr-qualifier.fixed b/tests/ui/parser/bad-fn-ptr-qualifier.fixed
index 558a27cd4562d..e2a2f9486b785 100644
--- a/tests/ui/parser/bad-fn-ptr-qualifier.fixed
+++ b/tests/ui/parser/bad-fn-ptr-qualifier.fixed
@@ -4,9 +4,9 @@
 
 pub type T0 =  fn(); //~ ERROR an `fn` pointer type cannot be `const`
 pub type T1 =  extern "C" fn(); //~ ERROR an `fn` pointer type cannot be `const`
-pub type T2 =  unsafe extern fn(); //~ ERROR an `fn` pointer type cannot be `const`
+pub type T2 =  unsafe extern "C" fn(); //~ ERROR an `fn` pointer type cannot be `const`
 pub type T3 =  fn(); //~ ERROR an `fn` pointer type cannot be `async`
-pub type T4 =  extern fn(); //~ ERROR an `fn` pointer type cannot be `async`
+pub type T4 =  extern "C" fn(); //~ ERROR an `fn` pointer type cannot be `async`
 pub type T5 =  unsafe extern "C" fn(); //~ ERROR an `fn` pointer type cannot be `async`
 pub type T6 =   unsafe extern "C" fn();
 //~^ ERROR an `fn` pointer type cannot be `const`
@@ -14,9 +14,9 @@ pub type T6 =   unsafe extern "C" fn();
 
 pub type FTT0 = for<'a>  fn(); //~ ERROR an `fn` pointer type cannot be `const`
 pub type FTT1 = for<'a>  extern "C" fn(); //~ ERROR an `fn` pointer type cannot be `const`
-pub type FTT2 = for<'a>  unsafe extern fn(); //~ ERROR an `fn` pointer type cannot be `const`
+pub type FTT2 = for<'a>  unsafe extern "C" fn(); //~ ERROR an `fn` pointer type cannot be `const`
 pub type FTT3 = for<'a>  fn(); //~ ERROR an `fn` pointer type cannot be `async`
-pub type FTT4 = for<'a>  extern fn(); //~ ERROR an `fn` pointer type cannot be `async`
+pub type FTT4 = for<'a>  extern "C" fn(); //~ ERROR an `fn` pointer type cannot be `async`
 pub type FTT5 = for<'a>  unsafe extern "C" fn();
 //~^ ERROR an `fn` pointer type cannot be `async`
 pub type FTT6 = for<'a>   unsafe extern "C" fn();
diff --git a/tests/ui/parser/bad-fn-ptr-qualifier.rs b/tests/ui/parser/bad-fn-ptr-qualifier.rs
index 9750f480935f2..f2611c93b1763 100644
--- a/tests/ui/parser/bad-fn-ptr-qualifier.rs
+++ b/tests/ui/parser/bad-fn-ptr-qualifier.rs
@@ -4,9 +4,9 @@
 
 pub type T0 = const fn(); //~ ERROR an `fn` pointer type cannot be `const`
 pub type T1 = const extern "C" fn(); //~ ERROR an `fn` pointer type cannot be `const`
-pub type T2 = const unsafe extern fn(); //~ ERROR an `fn` pointer type cannot be `const`
+pub type T2 = const unsafe extern "C" fn(); //~ ERROR an `fn` pointer type cannot be `const`
 pub type T3 = async fn(); //~ ERROR an `fn` pointer type cannot be `async`
-pub type T4 = async extern fn(); //~ ERROR an `fn` pointer type cannot be `async`
+pub type T4 = async extern "C" fn(); //~ ERROR an `fn` pointer type cannot be `async`
 pub type T5 = async unsafe extern "C" fn(); //~ ERROR an `fn` pointer type cannot be `async`
 pub type T6 = const async unsafe extern "C" fn();
 //~^ ERROR an `fn` pointer type cannot be `const`
@@ -14,9 +14,9 @@ pub type T6 = const async unsafe extern "C" fn();
 
 pub type FTT0 = for<'a> const fn(); //~ ERROR an `fn` pointer type cannot be `const`
 pub type FTT1 = for<'a> const extern "C" fn(); //~ ERROR an `fn` pointer type cannot be `const`
-pub type FTT2 = for<'a> const unsafe extern fn(); //~ ERROR an `fn` pointer type cannot be `const`
+pub type FTT2 = for<'a> const unsafe extern "C" fn(); //~ ERROR an `fn` pointer type cannot be `const`
 pub type FTT3 = for<'a> async fn(); //~ ERROR an `fn` pointer type cannot be `async`
-pub type FTT4 = for<'a> async extern fn(); //~ ERROR an `fn` pointer type cannot be `async`
+pub type FTT4 = for<'a> async extern "C" fn(); //~ ERROR an `fn` pointer type cannot be `async`
 pub type FTT5 = for<'a> async unsafe extern "C" fn();
 //~^ ERROR an `fn` pointer type cannot be `async`
 pub type FTT6 = for<'a> const async unsafe extern "C" fn();
diff --git a/tests/ui/parser/bad-fn-ptr-qualifier.stderr b/tests/ui/parser/bad-fn-ptr-qualifier.stderr
index 523ee47b0c942..ddc8bac678cfb 100644
--- a/tests/ui/parser/bad-fn-ptr-qualifier.stderr
+++ b/tests/ui/parser/bad-fn-ptr-qualifier.stderr
@@ -29,15 +29,15 @@ LL + pub type T1 =  extern "C" fn();
 error: an `fn` pointer type cannot be `const`
   --> $DIR/bad-fn-ptr-qualifier.rs:7:15
    |
-LL | pub type T2 = const unsafe extern fn();
-   |               -----^^^^^^^^^^^^^^^^^^^
+LL | pub type T2 = const unsafe extern "C" fn();
+   |               -----^^^^^^^^^^^^^^^^^^^^^^^
    |               |
    |               `const` because of this
    |
 help: remove the `const` qualifier
    |
-LL - pub type T2 = const unsafe extern fn();
-LL + pub type T2 =  unsafe extern fn();
+LL - pub type T2 = const unsafe extern "C" fn();
+LL + pub type T2 =  unsafe extern "C" fn();
    |
 
 error: an `fn` pointer type cannot be `async`
@@ -57,15 +57,15 @@ LL + pub type T3 =  fn();
 error: an `fn` pointer type cannot be `async`
   --> $DIR/bad-fn-ptr-qualifier.rs:9:15
    |
-LL | pub type T4 = async extern fn();
-   |               -----^^^^^^^^^^^^
+LL | pub type T4 = async extern "C" fn();
+   |               -----^^^^^^^^^^^^^^^^
    |               |
    |               `async` because of this
    |
 help: remove the `async` qualifier
    |
-LL - pub type T4 = async extern fn();
-LL + pub type T4 =  extern fn();
+LL - pub type T4 = async extern "C" fn();
+LL + pub type T4 =  extern "C" fn();
    |
 
 error: an `fn` pointer type cannot be `async`
@@ -141,15 +141,15 @@ LL + pub type FTT1 = for<'a>  extern "C" fn();
 error: an `fn` pointer type cannot be `const`
   --> $DIR/bad-fn-ptr-qualifier.rs:17:17
    |
-LL | pub type FTT2 = for<'a> const unsafe extern fn();
-   |                 ^^^^^^^^-----^^^^^^^^^^^^^^^^^^^
+LL | pub type FTT2 = for<'a> const unsafe extern "C" fn();
+   |                 ^^^^^^^^-----^^^^^^^^^^^^^^^^^^^^^^^
    |                         |
    |                         `const` because of this
    |
 help: remove the `const` qualifier
    |
-LL - pub type FTT2 = for<'a> const unsafe extern fn();
-LL + pub type FTT2 = for<'a>  unsafe extern fn();
+LL - pub type FTT2 = for<'a> const unsafe extern "C" fn();
+LL + pub type FTT2 = for<'a>  unsafe extern "C" fn();
    |
 
 error: an `fn` pointer type cannot be `async`
@@ -169,15 +169,15 @@ LL + pub type FTT3 = for<'a>  fn();
 error: an `fn` pointer type cannot be `async`
   --> $DIR/bad-fn-ptr-qualifier.rs:19:17
    |
-LL | pub type FTT4 = for<'a> async extern fn();
-   |                 ^^^^^^^^-----^^^^^^^^^^^^
+LL | pub type FTT4 = for<'a> async extern "C" fn();
+   |                 ^^^^^^^^-----^^^^^^^^^^^^^^^^
    |                         |
    |                         `async` because of this
    |
 help: remove the `async` qualifier
    |
-LL - pub type FTT4 = for<'a> async extern fn();
-LL + pub type FTT4 = for<'a>  extern fn();
+LL - pub type FTT4 = for<'a> async extern "C" fn();
+LL + pub type FTT4 = for<'a>  extern "C" fn();
    |
 
 error: an `fn` pointer type cannot be `async`
diff --git a/tests/ui/parser/bad-lit-suffixes.rs b/tests/ui/parser/bad-lit-suffixes.rs
index c614f49388574..f29dc53d322b9 100644
--- a/tests/ui/parser/bad-lit-suffixes.rs
+++ b/tests/ui/parser/bad-lit-suffixes.rs
@@ -1,10 +1,10 @@
 #![feature(rustc_attrs)]
 
-extern
+extern //~ WARN missing_abi
     "C"suffix //~ ERROR suffixes on string literals are invalid
     fn foo() {}
 
-extern
+extern //~ WARN missing_abi
     "C"suffix //~ ERROR suffixes on string literals are invalid
 {}
 
diff --git a/tests/ui/parser/bad-lit-suffixes.stderr b/tests/ui/parser/bad-lit-suffixes.stderr
index b5dacdf7d0d3d..121db2058f109 100644
--- a/tests/ui/parser/bad-lit-suffixes.stderr
+++ b/tests/ui/parser/bad-lit-suffixes.stderr
@@ -49,6 +49,20 @@ LL | #[rustc_layout_scalar_valid_range_start(0suffix)]
    |
    = help: the suffix must be one of the numeric types (`u32`, `isize`, `f32`, etc.)
 
+warning: extern declarations without an explicit ABI are deprecated
+  --> $DIR/bad-lit-suffixes.rs:3:1
+   |
+LL | extern
+   | ^^^^^^ help: explicitly specify the C ABI: `extern "C"`
+   |
+   = note: `#[warn(missing_abi)]` on by default
+
+warning: extern declarations without an explicit ABI are deprecated
+  --> $DIR/bad-lit-suffixes.rs:7:1
+   |
+LL | extern
+   | ^^^^^^ help: explicitly specify the C ABI: `extern "C"`
+
 error: suffixes on string literals are invalid
   --> $DIR/bad-lit-suffixes.rs:12:5
    |
@@ -149,5 +163,5 @@ LL |     1.0e10suffix;
    |
    = help: valid suffixes are `f32` and `f64`
 
-error: aborting due to 21 previous errors
+error: aborting due to 21 previous errors; 2 warnings emitted
 
diff --git a/tests/ui/parser/issues/issue-87217-keyword-order/wrong-unsafe.rs b/tests/ui/parser/issues/issue-87217-keyword-order/wrong-unsafe.rs
index 34b687a0f5261..5ecf804de09fe 100644
--- a/tests/ui/parser/issues/issue-87217-keyword-order/wrong-unsafe.rs
+++ b/tests/ui/parser/issues/issue-87217-keyword-order/wrong-unsafe.rs
@@ -1,4 +1,5 @@
 //@ edition:2018
+#![allow(missing_abi)]
 
 // There is an order to respect for keywords before a function:
 // `<visibility>, const, async, unsafe, extern, "<ABI>"`
diff --git a/tests/ui/parser/issues/issue-87217-keyword-order/wrong-unsafe.stderr b/tests/ui/parser/issues/issue-87217-keyword-order/wrong-unsafe.stderr
index 0e9f7c51e1a45..232da9acef309 100644
--- a/tests/ui/parser/issues/issue-87217-keyword-order/wrong-unsafe.stderr
+++ b/tests/ui/parser/issues/issue-87217-keyword-order/wrong-unsafe.stderr
@@ -1,5 +1,5 @@
 error: expected `fn`, found keyword `unsafe`
-  --> $DIR/wrong-unsafe.rs:9:8
+  --> $DIR/wrong-unsafe.rs:10:8
    |
 LL | extern unsafe fn test() {}
    | -------^^^^^^
diff --git a/tests/ui/parser/item-kw-case-mismatch.fixed b/tests/ui/parser/item-kw-case-mismatch.fixed
index f5afa482712f6..4ee8f9c19dc27 100644
--- a/tests/ui/parser/item-kw-case-mismatch.fixed
+++ b/tests/ui/parser/item-kw-case-mismatch.fixed
@@ -25,7 +25,7 @@ const unsafe fn _e() {}
 //~| ERROR keyword `unsafe` is written in the wrong case
 //~| ERROR keyword `fn` is written in the wrong case
 
-unsafe extern fn _f() {}
+unsafe extern "C" fn _f() {}
 //~^ ERROR keyword `unsafe` is written in the wrong case
 //~| ERROR keyword `extern` is written in the wrong case
 
diff --git a/tests/ui/parser/item-kw-case-mismatch.rs b/tests/ui/parser/item-kw-case-mismatch.rs
index ea224e08a0085..6c858b848cf2c 100644
--- a/tests/ui/parser/item-kw-case-mismatch.rs
+++ b/tests/ui/parser/item-kw-case-mismatch.rs
@@ -25,7 +25,7 @@ CONST UNSAFE FN _e() {}
 //~| ERROR keyword `unsafe` is written in the wrong case
 //~| ERROR keyword `fn` is written in the wrong case
 
-unSAFE EXTern fn _f() {}
+unSAFE EXTern "C" fn _f() {}
 //~^ ERROR keyword `unsafe` is written in the wrong case
 //~| ERROR keyword `extern` is written in the wrong case
 
diff --git a/tests/ui/parser/item-kw-case-mismatch.stderr b/tests/ui/parser/item-kw-case-mismatch.stderr
index 0abc59e064a00..36df72b5cad1c 100644
--- a/tests/ui/parser/item-kw-case-mismatch.stderr
+++ b/tests/ui/parser/item-kw-case-mismatch.stderr
@@ -111,23 +111,23 @@ LL | CONST UNSAFE fn _e() {}
 error: keyword `unsafe` is written in the wrong case
   --> $DIR/item-kw-case-mismatch.rs:28:1
    |
-LL | unSAFE EXTern fn _f() {}
+LL | unSAFE EXTern "C" fn _f() {}
    | ^^^^^^
    |
 help: write it in the correct case
    |
-LL | unsafe EXTern fn _f() {}
+LL | unsafe EXTern "C" fn _f() {}
    | ~~~~~~
 
 error: keyword `extern` is written in the wrong case
   --> $DIR/item-kw-case-mismatch.rs:28:8
    |
-LL | unSAFE EXTern fn _f() {}
+LL | unSAFE EXTern "C" fn _f() {}
    |        ^^^^^^
    |
 help: write it in the correct case
    |
-LL | unSAFE extern fn _f() {}
+LL | unSAFE extern "C" fn _f() {}
    |        ~~~~~~
 
 error: keyword `extern` is written in the wrong case
diff --git a/tests/ui/parser/lit-err-in-macro.rs b/tests/ui/parser/lit-err-in-macro.rs
index cff8ee6b40ca6..ca117ac4a15d4 100644
--- a/tests/ui/parser/lit-err-in-macro.rs
+++ b/tests/ui/parser/lit-err-in-macro.rs
@@ -1,6 +1,6 @@
 macro_rules! f {
     ($abi:literal) => {
-        extern $abi fn f() {}
+        extern $abi fn f() {} //~ WARN missing_abi
     }
 }
 
diff --git a/tests/ui/parser/lit-err-in-macro.stderr b/tests/ui/parser/lit-err-in-macro.stderr
index 12e6d51906030..fc2603d0b104c 100644
--- a/tests/ui/parser/lit-err-in-macro.stderr
+++ b/tests/ui/parser/lit-err-in-macro.stderr
@@ -4,5 +4,17 @@ error: suffixes on string literals are invalid
 LL | f!("Foo"__);
    |    ^^^^^^^ invalid suffix `__`
 
-error: aborting due to 1 previous error
+warning: extern declarations without an explicit ABI are deprecated
+  --> $DIR/lit-err-in-macro.rs:3:9
+   |
+LL |         extern $abi fn f() {}
+   |         ^^^^^^ help: explicitly specify the C ABI: `extern "C"`
+...
+LL | f!("Foo"__);
+   | ----------- in this macro invocation
+   |
+   = note: `#[warn(missing_abi)]` on by default
+   = note: this warning originates in the macro `f` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: aborting due to 1 previous error; 1 warning emitted
 
diff --git a/tests/ui/parser/recover/recover-const-async-fn-ptr.rs b/tests/ui/parser/recover/recover-const-async-fn-ptr.rs
index 2d8a3858aa603..45d753495999b 100644
--- a/tests/ui/parser/recover/recover-const-async-fn-ptr.rs
+++ b/tests/ui/parser/recover/recover-const-async-fn-ptr.rs
@@ -2,9 +2,9 @@
 
 type T0 = const fn(); //~ ERROR an `fn` pointer type cannot be `const`
 type T1 = const extern "C" fn(); //~ ERROR an `fn` pointer type cannot be `const`
-type T2 = const unsafe extern fn(); //~ ERROR an `fn` pointer type cannot be `const`
+type T2 = const unsafe extern "C" fn(); //~ ERROR an `fn` pointer type cannot be `const`
 type T3 = async fn(); //~ ERROR an `fn` pointer type cannot be `async`
-type T4 = async extern fn(); //~ ERROR an `fn` pointer type cannot be `async`
+type T4 = async extern "C" fn(); //~ ERROR an `fn` pointer type cannot be `async`
 type T5 = async unsafe extern "C" fn(); //~ ERROR an `fn` pointer type cannot be `async`
 type T6 = const async unsafe extern "C" fn();
 //~^ ERROR an `fn` pointer type cannot be `const`
@@ -12,9 +12,9 @@ type T6 = const async unsafe extern "C" fn();
 
 type FT0 = for<'a> const fn(); //~ ERROR an `fn` pointer type cannot be `const`
 type FT1 = for<'a> const extern "C" fn(); //~ ERROR an `fn` pointer type cannot be `const`
-type FT2 = for<'a> const unsafe extern fn(); //~ ERROR an `fn` pointer type cannot be `const`
+type FT2 = for<'a> const unsafe extern "C" fn(); //~ ERROR an `fn` pointer type cannot be `const`
 type FT3 = for<'a> async fn(); //~ ERROR an `fn` pointer type cannot be `async`
-type FT4 = for<'a> async extern fn(); //~ ERROR an `fn` pointer type cannot be `async`
+type FT4 = for<'a> async extern "C" fn(); //~ ERROR an `fn` pointer type cannot be `async`
 type FT5 = for<'a> async unsafe extern "C" fn(); //~ ERROR an `fn` pointer type cannot be `async`
 type FT6 = for<'a> const async unsafe extern "C" fn();
 //~^ ERROR an `fn` pointer type cannot be `const`
diff --git a/tests/ui/parser/recover/recover-const-async-fn-ptr.stderr b/tests/ui/parser/recover/recover-const-async-fn-ptr.stderr
index 8e5b76163ade1..9112a0e135a50 100644
--- a/tests/ui/parser/recover/recover-const-async-fn-ptr.stderr
+++ b/tests/ui/parser/recover/recover-const-async-fn-ptr.stderr
@@ -29,15 +29,15 @@ LL + type T1 =  extern "C" fn();
 error: an `fn` pointer type cannot be `const`
   --> $DIR/recover-const-async-fn-ptr.rs:5:11
    |
-LL | type T2 = const unsafe extern fn();
-   |           -----^^^^^^^^^^^^^^^^^^^
+LL | type T2 = const unsafe extern "C" fn();
+   |           -----^^^^^^^^^^^^^^^^^^^^^^^
    |           |
    |           `const` because of this
    |
 help: remove the `const` qualifier
    |
-LL - type T2 = const unsafe extern fn();
-LL + type T2 =  unsafe extern fn();
+LL - type T2 = const unsafe extern "C" fn();
+LL + type T2 =  unsafe extern "C" fn();
    |
 
 error: an `fn` pointer type cannot be `async`
@@ -57,15 +57,15 @@ LL + type T3 =  fn();
 error: an `fn` pointer type cannot be `async`
   --> $DIR/recover-const-async-fn-ptr.rs:7:11
    |
-LL | type T4 = async extern fn();
-   |           -----^^^^^^^^^^^^
+LL | type T4 = async extern "C" fn();
+   |           -----^^^^^^^^^^^^^^^^
    |           |
    |           `async` because of this
    |
 help: remove the `async` qualifier
    |
-LL - type T4 = async extern fn();
-LL + type T4 =  extern fn();
+LL - type T4 = async extern "C" fn();
+LL + type T4 =  extern "C" fn();
    |
 
 error: an `fn` pointer type cannot be `async`
@@ -141,15 +141,15 @@ LL + type FT1 = for<'a>  extern "C" fn();
 error: an `fn` pointer type cannot be `const`
   --> $DIR/recover-const-async-fn-ptr.rs:15:12
    |
-LL | type FT2 = for<'a> const unsafe extern fn();
-   |            ^^^^^^^^-----^^^^^^^^^^^^^^^^^^^
+LL | type FT2 = for<'a> const unsafe extern "C" fn();
+   |            ^^^^^^^^-----^^^^^^^^^^^^^^^^^^^^^^^
    |                    |
    |                    `const` because of this
    |
 help: remove the `const` qualifier
    |
-LL - type FT2 = for<'a> const unsafe extern fn();
-LL + type FT2 = for<'a>  unsafe extern fn();
+LL - type FT2 = for<'a> const unsafe extern "C" fn();
+LL + type FT2 = for<'a>  unsafe extern "C" fn();
    |
 
 error: an `fn` pointer type cannot be `async`
@@ -169,15 +169,15 @@ LL + type FT3 = for<'a>  fn();
 error: an `fn` pointer type cannot be `async`
   --> $DIR/recover-const-async-fn-ptr.rs:17:12
    |
-LL | type FT4 = for<'a> async extern fn();
-   |            ^^^^^^^^-----^^^^^^^^^^^^
+LL | type FT4 = for<'a> async extern "C" fn();
+   |            ^^^^^^^^-----^^^^^^^^^^^^^^^^
    |                    |
    |                    `async` because of this
    |
 help: remove the `async` qualifier
    |
-LL - type FT4 = for<'a> async extern fn();
-LL + type FT4 = for<'a>  extern fn();
+LL - type FT4 = for<'a> async extern "C" fn();
+LL + type FT4 = for<'a>  extern "C" fn();
    |
 
 error: an `fn` pointer type cannot be `async`
diff --git a/tests/ui/parser/recover/recover-fn-ptr-with-generics.rs b/tests/ui/parser/recover/recover-fn-ptr-with-generics.rs
index 76c56a715d2a4..ab2cfc961dff1 100644
--- a/tests/ui/parser/recover/recover-fn-ptr-with-generics.rs
+++ b/tests/ui/parser/recover/recover-fn-ptr-with-generics.rs
@@ -19,7 +19,7 @@ fn main() {
     type Hmm = fn<>();
     //~^ ERROR function pointer types may not have generic parameters
 
-    let _: extern fn<'a: 'static>();
+    let _: extern "C" fn<'a: 'static>();
     //~^ ERROR function pointer types may not have generic parameters
     //~| ERROR bounds cannot be used in this context
 
diff --git a/tests/ui/parser/recover/recover-fn-ptr-with-generics.stderr b/tests/ui/parser/recover/recover-fn-ptr-with-generics.stderr
index 6b6cb2d6bdde7..9023856ef2486 100644
--- a/tests/ui/parser/recover/recover-fn-ptr-with-generics.stderr
+++ b/tests/ui/parser/recover/recover-fn-ptr-with-generics.stderr
@@ -59,15 +59,15 @@ LL |     type Hmm = fn<>();
    |                  ^^
 
 error: function pointer types may not have generic parameters
-  --> $DIR/recover-fn-ptr-with-generics.rs:22:21
+  --> $DIR/recover-fn-ptr-with-generics.rs:22:25
    |
-LL |     let _: extern fn<'a: 'static>();
-   |                     ^^^^^^^^^^^^^
+LL |     let _: extern "C" fn<'a: 'static>();
+   |                         ^^^^^^^^^^^^^
    |
 help: consider moving the lifetime parameter to a `for` parameter list
    |
-LL -     let _: extern fn<'a: 'static>();
-LL +     let _: for<'a> extern fn();
+LL -     let _: extern "C" fn<'a: 'static>();
+LL +     let _: for<'a> extern "C" fn();
    |
 
 error: function pointer types may not have generic parameters
@@ -101,10 +101,10 @@ LL |     type Identity = fn<T>(T) -> T;
    |                                 ^ not found in this scope
 
 error: bounds cannot be used in this context
-  --> $DIR/recover-fn-ptr-with-generics.rs:22:26
+  --> $DIR/recover-fn-ptr-with-generics.rs:22:30
    |
-LL |     let _: extern fn<'a: 'static>();
-   |                          ^^^^^^^
+LL |     let _: extern "C" fn<'a: 'static>();
+   |                              ^^^^^^^
 
 error: aborting due to 12 previous errors
 
diff --git a/tests/ui/parser/recover/recover-missing-semi-before-item.fixed b/tests/ui/parser/recover/recover-missing-semi-before-item.fixed
index 6f85452c6fb96..871fa0d24eca7 100644
--- a/tests/ui/parser/recover/recover-missing-semi-before-item.fixed
+++ b/tests/ui/parser/recover/recover-missing-semi-before-item.fixed
@@ -28,7 +28,7 @@ fn for_fn() {
 
 fn for_extern() {
     let foo = 3; //~ ERROR expected `;`, found keyword `extern`
-    extern fn foo() {}
+    extern "C" fn foo() {}
 }
 
 fn for_impl() {
diff --git a/tests/ui/parser/recover/recover-missing-semi-before-item.rs b/tests/ui/parser/recover/recover-missing-semi-before-item.rs
index f75945b55c2b0..de92603a74c68 100644
--- a/tests/ui/parser/recover/recover-missing-semi-before-item.rs
+++ b/tests/ui/parser/recover/recover-missing-semi-before-item.rs
@@ -28,7 +28,7 @@ fn for_fn() {
 
 fn for_extern() {
     let foo = 3 //~ ERROR expected `;`, found keyword `extern`
-    extern fn foo() {}
+    extern "C" fn foo() {}
 }
 
 fn for_impl() {
diff --git a/tests/ui/parser/recover/recover-missing-semi-before-item.stderr b/tests/ui/parser/recover/recover-missing-semi-before-item.stderr
index 61c43f2f18998..3b55cd9ddd086 100644
--- a/tests/ui/parser/recover/recover-missing-semi-before-item.stderr
+++ b/tests/ui/parser/recover/recover-missing-semi-before-item.stderr
@@ -35,7 +35,7 @@ error: expected `;`, found keyword `extern`
    |
 LL |     let foo = 3
    |                ^ help: add `;` here
-LL |     extern fn foo() {}
+LL |     extern "C" fn foo() {}
    |     ------ unexpected token
 
 error: expected `;`, found keyword `impl`
diff --git a/tests/ui/proc-macro/inner-attrs.stderr b/tests/ui/proc-macro/inner-attrs.stderr
index ee8732c650dc9..3ab180be821a9 100644
--- a/tests/ui/proc-macro/inner-attrs.stderr
+++ b/tests/ui/proc-macro/inner-attrs.stderr
@@ -22,5 +22,13 @@ error: expected non-macro inner attribute, found attribute macro `print_attr`
 LL |         #![print_attr]
    |            ^^^^^^^^^^ not a non-macro inner attribute
 
-error: aborting due to 4 previous errors
+warning: extern declarations without an explicit ABI are deprecated
+  --> $DIR/inner-attrs.rs:82:1
+   |
+LL | extern {
+   | ^^^^^^ help: explicitly specify the C ABI: `extern "C"`
+   |
+   = note: `#[warn(missing_abi)]` on by default
+
+error: aborting due to 4 previous errors; 1 warning emitted
 
diff --git a/tests/ui/proc-macro/issue-66286.rs b/tests/ui/proc-macro/issue-66286.rs
index 3ca064768b2d6..9e7719c98367f 100644
--- a/tests/ui/proc-macro/issue-66286.rs
+++ b/tests/ui/proc-macro/issue-66286.rs
@@ -5,7 +5,7 @@
 extern crate issue_66286;
 
 #[issue_66286::vec_ice]
-pub extern fn foo(_: Vec(u32)) -> u32 {
+pub extern "C" fn foo(_: Vec(u32)) -> u32 {
     //~^ ERROR: parenthesized type parameters may only be used with a `Fn` trait
     0
 }
diff --git a/tests/ui/proc-macro/issue-66286.stderr b/tests/ui/proc-macro/issue-66286.stderr
index fc4c2062fd7bc..c92bed1b56344 100644
--- a/tests/ui/proc-macro/issue-66286.stderr
+++ b/tests/ui/proc-macro/issue-66286.stderr
@@ -1,13 +1,13 @@
 error[E0214]: parenthesized type parameters may only be used with a `Fn` trait
-  --> $DIR/issue-66286.rs:8:22
+  --> $DIR/issue-66286.rs:8:26
    |
-LL | pub extern fn foo(_: Vec(u32)) -> u32 {
-   |                      ^^^^^^^^ only `Fn` traits may use parentheses
+LL | pub extern "C" fn foo(_: Vec(u32)) -> u32 {
+   |                          ^^^^^^^^ only `Fn` traits may use parentheses
    |
 help: use angle brackets instead
    |
-LL | pub extern fn foo(_: Vec<u32>) -> u32 {
-   |                         ~   ~
+LL | pub extern "C" fn foo(_: Vec<u32>) -> u32 {
+   |                             ~   ~
 
 error: aborting due to 1 previous error
 
diff --git a/tests/ui/rfcs/rfc-2627-raw-dylib/link-ordinal-not-foreign-fn.rs b/tests/ui/rfcs/rfc-2627-raw-dylib/link-ordinal-not-foreign-fn.rs
index f33a3d62e2688..5982c771033d0 100644
--- a/tests/ui/rfcs/rfc-2627-raw-dylib/link-ordinal-not-foreign-fn.rs
+++ b/tests/ui/rfcs/rfc-2627-raw-dylib/link-ordinal-not-foreign-fn.rs
@@ -11,7 +11,7 @@ fn test() {}
 static mut imported_val: i32 = 123;
 
 #[link(name = "exporter", kind = "raw-dylib")]
-extern {
+extern "C" {
     #[link_ordinal(13)]
     fn imported_function();
 
diff --git a/tests/ui/rust-2024/unsafe-attributes/unsafe-attributes-fix.fixed b/tests/ui/rust-2024/unsafe-attributes/unsafe-attributes-fix.fixed
index 586881d180767..8b179f7ef933e 100644
--- a/tests/ui/rust-2024/unsafe-attributes/unsafe-attributes-fix.fixed
+++ b/tests/ui/rust-2024/unsafe-attributes/unsafe-attributes-fix.fixed
@@ -4,7 +4,7 @@
 macro_rules! tt {
     ($e:tt) => {
         #$e
-        extern fn foo() {}
+        extern "C" fn foo() {}
     }
 }
 
@@ -13,7 +13,7 @@ macro_rules! ident {
         #[unsafe($e)]
         //~^ ERROR: unsafe attribute used without unsafe
         //~| WARN this is accepted in the current edition
-        extern fn bar() {}
+        extern "C" fn bar() {}
     }
 }
 
@@ -22,21 +22,21 @@ macro_rules! ident2 {
         #[unsafe($e = $l)]
         //~^ ERROR: unsafe attribute used without unsafe
         //~| WARN this is accepted in the current edition
-        extern fn bars() {}
+        extern "C" fn bars() {}
     }
 }
 
 macro_rules! meta {
     ($m:meta) => {
         #[$m]
-        extern fn baz() {}
+        extern "C" fn baz() {}
     }
 }
 
 macro_rules! meta2 {
     ($m:meta) => {
         #[$m]
-        extern fn baw() {}
+        extern "C" fn baw() {}
     }
 }
 
diff --git a/tests/ui/rust-2024/unsafe-attributes/unsafe-attributes-fix.rs b/tests/ui/rust-2024/unsafe-attributes/unsafe-attributes-fix.rs
index 03e122c7d57e7..34e5a6b96e389 100644
--- a/tests/ui/rust-2024/unsafe-attributes/unsafe-attributes-fix.rs
+++ b/tests/ui/rust-2024/unsafe-attributes/unsafe-attributes-fix.rs
@@ -4,7 +4,7 @@
 macro_rules! tt {
     ($e:tt) => {
         #$e
-        extern fn foo() {}
+        extern "C" fn foo() {}
     }
 }
 
@@ -13,7 +13,7 @@ macro_rules! ident {
         #[$e]
         //~^ ERROR: unsafe attribute used without unsafe
         //~| WARN this is accepted in the current edition
-        extern fn bar() {}
+        extern "C" fn bar() {}
     }
 }
 
@@ -22,21 +22,21 @@ macro_rules! ident2 {
         #[$e = $l]
         //~^ ERROR: unsafe attribute used without unsafe
         //~| WARN this is accepted in the current edition
-        extern fn bars() {}
+        extern "C" fn bars() {}
     }
 }
 
 macro_rules! meta {
     ($m:meta) => {
         #[$m]
-        extern fn baz() {}
+        extern "C" fn baz() {}
     }
 }
 
 macro_rules! meta2 {
     ($m:meta) => {
         #[$m]
-        extern fn baw() {}
+        extern "C" fn baw() {}
     }
 }
 
diff --git a/tests/ui/simd/type-generic-monomorphisation-extern-nonnull-ptr.rs b/tests/ui/simd/type-generic-monomorphisation-extern-nonnull-ptr.rs
index a969295c9f9cd..65c57c42530a1 100644
--- a/tests/ui/simd/type-generic-monomorphisation-extern-nonnull-ptr.rs
+++ b/tests/ui/simd/type-generic-monomorphisation-extern-nonnull-ptr.rs
@@ -6,7 +6,7 @@
 
 use std::ptr::NonNull;
 
-extern {
+extern "C" {
     type Extern;
 }
 
diff --git a/tests/ui/statics/uninhabited-static.rs b/tests/ui/statics/uninhabited-static.rs
index a0f83f450792a..0f7c5ae6ef4a3 100644
--- a/tests/ui/statics/uninhabited-static.rs
+++ b/tests/ui/statics/uninhabited-static.rs
@@ -2,7 +2,7 @@
 #![deny(uninhabited_static)]
 
 enum Void {}
-extern {
+extern "C" {
     static VOID: Void; //~ ERROR static of uninhabited type
     //~| WARN: previously accepted
     static NEVER: !; //~ ERROR static of uninhabited type
diff --git a/tests/ui/unpretty/expanded-exhaustive.rs b/tests/ui/unpretty/expanded-exhaustive.rs
index 799e8071d028a..39ee25934c99e 100644
--- a/tests/ui/unpretty/expanded-exhaustive.rs
+++ b/tests/ui/unpretty/expanded-exhaustive.rs
@@ -452,15 +452,15 @@ mod items {
     /// ItemKind::Fn
     mod item_fn {
         pub const unsafe extern "C" fn f() {}
-        pub async unsafe extern fn g() {}
+        pub async unsafe extern "C" fn g() {}
         fn h<'a, T>() where T: 'a {}
 
         trait TraitItems {
-            unsafe extern fn f();
+            unsafe extern "C" fn f();
         }
 
         impl TraitItems for _ {
-            default unsafe extern fn f() {}
+            default unsafe extern "C" fn f() {}
         }
     }
 
@@ -472,7 +472,7 @@ mod items {
     /// ItemKind::ForeignMod
     mod item_foreign_mod {
         unsafe extern "C++" {}
-        unsafe extern {}
+        unsafe extern "C" {}
     }
 
     /// ItemKind::GlobalAsm
diff --git a/tests/ui/unpretty/expanded-exhaustive.stdout b/tests/ui/unpretty/expanded-exhaustive.stdout
index d8384951e12f0..34b55368fbdef 100644
--- a/tests/ui/unpretty/expanded-exhaustive.stdout
+++ b/tests/ui/unpretty/expanded-exhaustive.stdout
@@ -433,13 +433,13 @@ mod items {
     /// ItemKind::Fn
     mod item_fn {
         pub const unsafe extern "C" fn f() {}
-        pub async unsafe extern fn g() {}
+        pub async unsafe extern "C" fn g() {}
         fn h<'a, T>() where T: 'a {}
         trait TraitItems {
-            unsafe extern fn f();
+            unsafe extern "C" fn f();
         }
         impl TraitItems for _ {
-            default unsafe extern fn f() {}
+            default unsafe extern "C" fn f() {}
         }
     }
     /// ItemKind::Mod
@@ -447,7 +447,7 @@ mod items {
     /// ItemKind::ForeignMod
     mod item_foreign_mod {
         unsafe extern "C++" {}
-        unsafe extern {}
+        unsafe extern "C" {}
     }
     /// ItemKind::GlobalAsm
     mod item_global_asm {