From 26dccadb476aaafa0930e6036c5583eea2c052e1 Mon Sep 17 00:00:00 2001
From: Jubilee Young <workingjubilee@gmail.com>
Date: Sat, 22 Jun 2024 14:42:26 -0700
Subject: [PATCH 1/2] Allow "C-unwind" fn to have C variadics

---
 compiler/rustc_ast_passes/src/ast_validation.rs | 1 +
 compiler/rustc_span/src/symbol.rs               | 1 +
 tests/ui/abi/variadic-ffi.rs                    | 8 ++++++++
 3 files changed, 10 insertions(+)

diff --git a/compiler/rustc_ast_passes/src/ast_validation.rs b/compiler/rustc_ast_passes/src/ast_validation.rs
index e89b412687d96..79717c969d79a 100644
--- a/compiler/rustc_ast_passes/src/ast_validation.rs
+++ b/compiler/rustc_ast_passes/src/ast_validation.rs
@@ -637,6 +637,7 @@ impl<'a> AstValidator<'a> {
             (Some(FnCtxt::Foreign), _) => return,
             (Some(FnCtxt::Free), Some(header)) => match header.ext {
                 Extern::Explicit(StrLit { symbol_unescaped: sym::C, .. }, _)
+                | Extern::Explicit(StrLit { symbol_unescaped: sym::C_dash_unwind, .. }, _)
                 | Extern::Implicit(_)
                     if matches!(header.safety, Safety::Unsafe(_)) =>
                 {
diff --git a/compiler/rustc_span/src/symbol.rs b/compiler/rustc_span/src/symbol.rs
index a8123fe994c34..8d8f4927e99cb 100644
--- a/compiler/rustc_span/src/symbol.rs
+++ b/compiler/rustc_span/src/symbol.rs
@@ -167,6 +167,7 @@ symbols! {
         Break,
         C,
         CStr,
+        C_dash_unwind: "C-unwind",
         CallOnceFuture,
         CallRefFuture,
         Capture,
diff --git a/tests/ui/abi/variadic-ffi.rs b/tests/ui/abi/variadic-ffi.rs
index de4844ac86057..6cfae0f2a320f 100644
--- a/tests/ui/abi/variadic-ffi.rs
+++ b/tests/ui/abi/variadic-ffi.rs
@@ -14,6 +14,10 @@ pub unsafe extern "C" fn test_valist_forward(n: u64, mut ap: ...) -> f64 {
     rust_valist_interesting_average(n, ap.as_va_list())
 }
 
+pub unsafe extern "C-unwind" fn c_unwind_can_forward(n: u64, mut ap: ...) -> f64 {
+    rust_valist_interesting_average(n, ap.as_va_list())
+}
+
 pub unsafe extern "C" fn test_va_copy(_: u64, mut ap: ...) {
     let mut ap2 = ap.clone();
     assert_eq!(rust_valist_interesting_average(2, ap2.as_va_list()) as i64, 30);
@@ -72,6 +76,10 @@ pub fn main() {
         assert_eq!(test_valist_forward(2, 10i64, 10f64, 20i64, 20f64) as i64, 30);
     }
 
+    unsafe {
+        assert_eq!(c_unwind_can_forward(2, 10i64, 10f64, 20i64, 20f64) as i64, 30);
+    }
+
     unsafe {
         test_va_copy(4, 10i64, 10f64, 20i64, 20f64, 30i64, 30f64, 40i64, 40f64);
     }

From 43a6b018a2a7a68686adda1220ebf07194ed11fc Mon Sep 17 00:00:00 2001
From: Jubilee Young <workingjubilee@gmail.com>
Date: Sat, 22 Jun 2024 23:19:19 -0700
Subject: [PATCH 2/2] compiler: Mention C-unwind in C-variadic error

---
 compiler/rustc_ast_passes/messages.ftl        |  2 +-
 tests/ui/c-variadic/issue-86053-1.stderr      |  2 +-
 .../issue-83499-input-output-iteration-ice.rs |  2 +-
 ...ue-83499-input-output-iteration-ice.stderr |  2 +-
 .../variadic-ffi-semantic-restrictions.rs     | 42 +++++++++----------
 .../variadic-ffi-semantic-restrictions.stderr | 42 +++++++++----------
 6 files changed, 46 insertions(+), 46 deletions(-)

diff --git a/compiler/rustc_ast_passes/messages.ftl b/compiler/rustc_ast_passes/messages.ftl
index fff1bcd72bcef..7da726ef40868 100644
--- a/compiler/rustc_ast_passes/messages.ftl
+++ b/compiler/rustc_ast_passes/messages.ftl
@@ -28,7 +28,7 @@ ast_passes_auto_super_lifetime = auto traits cannot have super traits or lifetim
     .label = {ast_passes_auto_super_lifetime}
     .suggestion = remove the super traits or lifetime bounds
 
-ast_passes_bad_c_variadic = only foreign or `unsafe extern "C"` functions may be C-variadic
+ast_passes_bad_c_variadic = only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
 
 ast_passes_bare_fn_invalid_safety = function pointers cannot be declared with `safe` safety qualifier
     .suggestion = remove safe from this item
diff --git a/tests/ui/c-variadic/issue-86053-1.stderr b/tests/ui/c-variadic/issue-86053-1.stderr
index 69e19e1d4d26b..67a619e46d57d 100644
--- a/tests/ui/c-variadic/issue-86053-1.stderr
+++ b/tests/ui/c-variadic/issue-86053-1.stderr
@@ -46,7 +46,7 @@ error: `...` must be the last argument of a C-variadic function
 LL |     self , ... ,   self ,   self , ... ) where F : FnOnce ( & 'a & 'b usize ) {
    |            ^^^
 
-error: only foreign or `unsafe extern "C"` functions may be C-variadic
+error: only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
   --> $DIR/issue-86053-1.rs:11:12
    |
 LL |     self , ... ,   self ,   self , ... ) where F : FnOnce ( & 'a & 'b usize ) {
diff --git a/tests/ui/mir/issue-83499-input-output-iteration-ice.rs b/tests/ui/mir/issue-83499-input-output-iteration-ice.rs
index 0086d2ec18cfa..78e5c96180285 100644
--- a/tests/ui/mir/issue-83499-input-output-iteration-ice.rs
+++ b/tests/ui/mir/issue-83499-input-output-iteration-ice.rs
@@ -5,6 +5,6 @@
 fn main() {}
 
 fn foo(_: Bar, ...) -> impl {}
-//~^ ERROR only foreign or `unsafe extern "C"` functions may be C-variadic
+//~^ ERROR only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
 //~| ERROR cannot find type `Bar` in this scope
 //~| ERROR at least one trait must be specified
diff --git a/tests/ui/mir/issue-83499-input-output-iteration-ice.stderr b/tests/ui/mir/issue-83499-input-output-iteration-ice.stderr
index 4eb3adc8b4f1c..80a8a94aea400 100644
--- a/tests/ui/mir/issue-83499-input-output-iteration-ice.stderr
+++ b/tests/ui/mir/issue-83499-input-output-iteration-ice.stderr
@@ -1,4 +1,4 @@
-error: only foreign or `unsafe extern "C"` functions may be C-variadic
+error: only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
   --> $DIR/issue-83499-input-output-iteration-ice.rs:7:16
    |
 LL | fn foo(_: Bar, ...) -> impl {}
diff --git a/tests/ui/parser/variadic-ffi-semantic-restrictions.rs b/tests/ui/parser/variadic-ffi-semantic-restrictions.rs
index 11126dbc65d25..1cd6d13d56b6b 100644
--- a/tests/ui/parser/variadic-ffi-semantic-restrictions.rs
+++ b/tests/ui/parser/variadic-ffi-semantic-restrictions.rs
@@ -4,29 +4,29 @@
 fn main() {}
 
 fn f1_1(x: isize, ...) {}
-//~^ ERROR only foreign or `unsafe extern "C"` functions may be C-variadic
+//~^ ERROR only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
 
 fn f1_2(...) {}
-//~^ ERROR only foreign or `unsafe extern "C"` functions may be C-variadic
+//~^ ERROR only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
 
 extern "C" fn f2_1(x: isize, ...) {}
-//~^ ERROR only foreign or `unsafe extern "C"` functions may be C-variadic
+//~^ ERROR only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
 
 extern "C" fn f2_2(...) {}
-//~^ ERROR only foreign or `unsafe extern "C"` functions may be C-variadic
+//~^ ERROR only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
 
 extern "C" fn f2_3(..., x: isize) {}
-//~^ ERROR only foreign or `unsafe extern "C"` functions may be C-variadic
+//~^ ERROR only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
 //~| ERROR `...` must be the last argument of a C-variadic function
 
 extern "C" fn f3_1(x: isize, ...) {}
-//~^ ERROR only foreign or `unsafe extern "C"` functions may be C-variadic
+//~^ ERROR only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
 
 extern "C" fn f3_2(...) {}
-//~^ ERROR only foreign or `unsafe extern "C"` functions may be C-variadic
+//~^ ERROR only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
 
 extern "C" fn f3_3(..., x: isize) {}
-//~^ ERROR only foreign or `unsafe extern "C"` functions may be C-variadic
+//~^ ERROR only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
 //~| ERROR `...` must be the last argument of a C-variadic function
 
 const unsafe extern "C" fn f4_1(x: isize, ...) {}
@@ -35,12 +35,12 @@ const unsafe extern "C" fn f4_1(x: isize, ...) {}
 
 const extern "C" fn f4_2(x: isize, ...) {}
 //~^ ERROR functions cannot be both `const` and C-variadic
-//~| ERROR only foreign or `unsafe extern "C"` functions may be C-variadic
+//~| ERROR only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
 //~| ERROR destructor of `VaListImpl<'_>` cannot be evaluated at compile-time
 
 const extern "C" fn f4_3(..., x: isize, ...) {}
 //~^ ERROR functions cannot be both `const` and C-variadic
-//~| ERROR only foreign or `unsafe extern "C"` functions may be C-variadic
+//~| ERROR only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
 //~| ERROR `...` must be the last argument of a C-variadic function
 
 extern "C" {
@@ -52,34 +52,34 @@ struct X;
 
 impl X {
     fn i_f1(x: isize, ...) {}
-    //~^ ERROR only foreign or `unsafe extern "C"` functions may be C-variadic
+    //~^ ERROR only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
     fn i_f2(...) {}
-    //~^ ERROR only foreign or `unsafe extern "C"` functions may be C-variadic
+    //~^ ERROR only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
     fn i_f3(..., x: isize, ...) {}
-    //~^ ERROR only foreign or `unsafe extern "C"` functions may be C-variadic
+    //~^ ERROR only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
     //~| ERROR `...` must be the last argument of a C-variadic function
     fn i_f4(..., x: isize, ...) {}
-    //~^ ERROR only foreign or `unsafe extern "C"` functions may be C-variadic
+    //~^ ERROR only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
     //~| ERROR `...` must be the last argument of a C-variadic function
     const fn i_f5(x: isize, ...) {}
-    //~^ ERROR only foreign or `unsafe extern "C"` functions may be C-variadic
+    //~^ ERROR only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
     //~| ERROR functions cannot be both `const` and C-variadic
     //~| ERROR destructor of `VaListImpl<'_>` cannot be evaluated at compile-time
 }
 
 trait T {
     fn t_f1(x: isize, ...) {}
-    //~^ ERROR only foreign or `unsafe extern "C"` functions may be C-variadic
+    //~^ ERROR only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
     fn t_f2(x: isize, ...);
-    //~^ ERROR only foreign or `unsafe extern "C"` functions may be C-variadic
+    //~^ ERROR only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
     fn t_f3(...) {}
-    //~^ ERROR only foreign or `unsafe extern "C"` functions may be C-variadic
+    //~^ ERROR only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
     fn t_f4(...);
-    //~^ ERROR only foreign or `unsafe extern "C"` functions may be C-variadic
+    //~^ ERROR only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
     fn t_f5(..., x: isize) {}
-    //~^ ERROR only foreign or `unsafe extern "C"` functions may be C-variadic
+    //~^ ERROR only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
     //~| ERROR `...` must be the last argument of a C-variadic function
     fn t_f6(..., x: isize);
-    //~^ ERROR only foreign or `unsafe extern "C"` functions may be C-variadic
+    //~^ ERROR only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
     //~| ERROR `...` must be the last argument of a C-variadic function
 }
diff --git a/tests/ui/parser/variadic-ffi-semantic-restrictions.stderr b/tests/ui/parser/variadic-ffi-semantic-restrictions.stderr
index f71e3863440f5..b740cef020055 100644
--- a/tests/ui/parser/variadic-ffi-semantic-restrictions.stderr
+++ b/tests/ui/parser/variadic-ffi-semantic-restrictions.stderr
@@ -1,22 +1,22 @@
-error: only foreign or `unsafe extern "C"` functions may be C-variadic
+error: only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
   --> $DIR/variadic-ffi-semantic-restrictions.rs:6:19
    |
 LL | fn f1_1(x: isize, ...) {}
    |                   ^^^
 
-error: only foreign or `unsafe extern "C"` functions may be C-variadic
+error: only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
   --> $DIR/variadic-ffi-semantic-restrictions.rs:9:9
    |
 LL | fn f1_2(...) {}
    |         ^^^
 
-error: only foreign or `unsafe extern "C"` functions may be C-variadic
+error: only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
   --> $DIR/variadic-ffi-semantic-restrictions.rs:12:30
    |
 LL | extern "C" fn f2_1(x: isize, ...) {}
    |                              ^^^
 
-error: only foreign or `unsafe extern "C"` functions may be C-variadic
+error: only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
   --> $DIR/variadic-ffi-semantic-restrictions.rs:15:20
    |
 LL | extern "C" fn f2_2(...) {}
@@ -28,19 +28,19 @@ error: `...` must be the last argument of a C-variadic function
 LL | extern "C" fn f2_3(..., x: isize) {}
    |                    ^^^
 
-error: only foreign or `unsafe extern "C"` functions may be C-variadic
+error: only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
   --> $DIR/variadic-ffi-semantic-restrictions.rs:18:20
    |
 LL | extern "C" fn f2_3(..., x: isize) {}
    |                    ^^^
 
-error: only foreign or `unsafe extern "C"` functions may be C-variadic
+error: only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
   --> $DIR/variadic-ffi-semantic-restrictions.rs:22:30
    |
 LL | extern "C" fn f3_1(x: isize, ...) {}
    |                              ^^^
 
-error: only foreign or `unsafe extern "C"` functions may be C-variadic
+error: only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
   --> $DIR/variadic-ffi-semantic-restrictions.rs:25:20
    |
 LL | extern "C" fn f3_2(...) {}
@@ -52,7 +52,7 @@ error: `...` must be the last argument of a C-variadic function
 LL | extern "C" fn f3_3(..., x: isize) {}
    |                    ^^^
 
-error: only foreign or `unsafe extern "C"` functions may be C-variadic
+error: only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
   --> $DIR/variadic-ffi-semantic-restrictions.rs:28:20
    |
 LL | extern "C" fn f3_3(..., x: isize) {}
@@ -70,7 +70,7 @@ error: functions cannot be both `const` and C-variadic
 LL | const extern "C" fn f4_2(x: isize, ...) {}
    | ^^^^^ `const` because of this      ^^^ C-variadic because of this
 
-error: only foreign or `unsafe extern "C"` functions may be C-variadic
+error: only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
   --> $DIR/variadic-ffi-semantic-restrictions.rs:36:36
    |
 LL | const extern "C" fn f4_2(x: isize, ...) {}
@@ -91,7 +91,7 @@ LL | const extern "C" fn f4_3(..., x: isize, ...) {}
    | |                        C-variadic because of this
    | `const` because of this
 
-error: only foreign or `unsafe extern "C"` functions may be C-variadic
+error: only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
   --> $DIR/variadic-ffi-semantic-restrictions.rs:41:26
    |
 LL | const extern "C" fn f4_3(..., x: isize, ...) {}
@@ -103,13 +103,13 @@ error: `...` must be the last argument of a C-variadic function
 LL |     fn e_f2(..., x: isize);
    |             ^^^
 
-error: only foreign or `unsafe extern "C"` functions may be C-variadic
+error: only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
   --> $DIR/variadic-ffi-semantic-restrictions.rs:54:23
    |
 LL |     fn i_f1(x: isize, ...) {}
    |                       ^^^
 
-error: only foreign or `unsafe extern "C"` functions may be C-variadic
+error: only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
   --> $DIR/variadic-ffi-semantic-restrictions.rs:56:13
    |
 LL |     fn i_f2(...) {}
@@ -121,7 +121,7 @@ error: `...` must be the last argument of a C-variadic function
 LL |     fn i_f3(..., x: isize, ...) {}
    |             ^^^
 
-error: only foreign or `unsafe extern "C"` functions may be C-variadic
+error: only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
   --> $DIR/variadic-ffi-semantic-restrictions.rs:58:13
    |
 LL |     fn i_f3(..., x: isize, ...) {}
@@ -133,7 +133,7 @@ error: `...` must be the last argument of a C-variadic function
 LL |     fn i_f4(..., x: isize, ...) {}
    |             ^^^
 
-error: only foreign or `unsafe extern "C"` functions may be C-variadic
+error: only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
   --> $DIR/variadic-ffi-semantic-restrictions.rs:61:13
    |
 LL |     fn i_f4(..., x: isize, ...) {}
@@ -147,31 +147,31 @@ LL |     const fn i_f5(x: isize, ...) {}
    |     |
    |     `const` because of this
 
-error: only foreign or `unsafe extern "C"` functions may be C-variadic
+error: only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
   --> $DIR/variadic-ffi-semantic-restrictions.rs:64:29
    |
 LL |     const fn i_f5(x: isize, ...) {}
    |                             ^^^
 
-error: only foreign or `unsafe extern "C"` functions may be C-variadic
+error: only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
   --> $DIR/variadic-ffi-semantic-restrictions.rs:71:23
    |
 LL |     fn t_f1(x: isize, ...) {}
    |                       ^^^
 
-error: only foreign or `unsafe extern "C"` functions may be C-variadic
+error: only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
   --> $DIR/variadic-ffi-semantic-restrictions.rs:73:23
    |
 LL |     fn t_f2(x: isize, ...);
    |                       ^^^
 
-error: only foreign or `unsafe extern "C"` functions may be C-variadic
+error: only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
   --> $DIR/variadic-ffi-semantic-restrictions.rs:75:13
    |
 LL |     fn t_f3(...) {}
    |             ^^^
 
-error: only foreign or `unsafe extern "C"` functions may be C-variadic
+error: only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
   --> $DIR/variadic-ffi-semantic-restrictions.rs:77:13
    |
 LL |     fn t_f4(...);
@@ -183,7 +183,7 @@ error: `...` must be the last argument of a C-variadic function
 LL |     fn t_f5(..., x: isize) {}
    |             ^^^
 
-error: only foreign or `unsafe extern "C"` functions may be C-variadic
+error: only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
   --> $DIR/variadic-ffi-semantic-restrictions.rs:79:13
    |
 LL |     fn t_f5(..., x: isize) {}
@@ -195,7 +195,7 @@ error: `...` must be the last argument of a C-variadic function
 LL |     fn t_f6(..., x: isize);
    |             ^^^
 
-error: only foreign or `unsafe extern "C"` functions may be C-variadic
+error: only foreign, `unsafe extern "C"`, or `unsafe extern "C-unwind"` functions may have a C-variadic arg
   --> $DIR/variadic-ffi-semantic-restrictions.rs:82:13
    |
 LL |     fn t_f6(..., x: isize);