Auto merge of #86164 - FabianWolff:issue-86053, r=davidtwco

Handle C-variadic arguments properly when reporting region errors

This pull request fixes #86053. The issue is that for a C-variadic function
```rust
#![feature(c_variadic)]
unsafe extern "C" fn foo(_: (), ...) {}
```
`foo`'s signature will contain only the first parameter (and have `c_variadic` set to `true`), whereas its body has a second argument (a `hir::Pat` for the `...`).

The code for reporting region errors iterates over the body's parameters and tries to fetch the corresponding parameter from the signature; this causes an out-of-bounds ICE for the `...` (though not in the example above, because there are no region errors to report).

I have simply restricted the iteration over the body parameters to exclude `...`, which is fine because `...` cannot cause a region error.

compiler/rustc_ast_passes/src/ast_validation.rs

@@ -652,7 +652,7 @@ impl<'a> AstValidator<'a> {
                 self.err_handler()
                     .struct_span_err(
                         *span,
-                        "only foreign or `unsafe extern \"C\" functions may be C-variadic",
+                        "only foreign or `unsafe extern \"C\"` functions may be C-variadic",
                     )
                     .emit();
             }

compiler/rustc_infer/src/infer/error_reporting/nice_region_error/util.rs

@@ -56,33 +56,42 @@ impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
         let fn_decl = hir.fn_decl_by_hir_id(owner_id).unwrap();
         let poly_fn_sig = self.tcx().fn_sig(id);
         let fn_sig = self.tcx().liberate_late_bound_regions(id, poly_fn_sig);
-        body.params.iter().enumerate().find_map(|(index, param)| {
-            // May return None; sometimes the tables are not yet populated.
-            let ty = fn_sig.inputs()[index];
-            let mut found_anon_region = false;
-            let new_param_ty = self.tcx().fold_regions(ty, &mut false, |r, _| {
-                if *r == *anon_region {
-                    found_anon_region = true;
-                    replace_region
+        body.params
+            .iter()
+            .take(if fn_sig.c_variadic {
+                fn_sig.inputs().len()
+            } else {
+                assert_eq!(fn_sig.inputs().len(), body.params.len());
+                body.params.len()
+            })
+            .enumerate()
+            .find_map(|(index, param)| {
+                // May return None; sometimes the tables are not yet populated.
+                let ty = fn_sig.inputs()[index];
+                let mut found_anon_region = false;
+                let new_param_ty = self.tcx().fold_regions(ty, &mut false, |r, _| {
+                    if *r == *anon_region {
+                        found_anon_region = true;
+                        replace_region
+                    } else {
+                        r
+                    }
+                });
+                if found_anon_region {
+                    let ty_hir_id = fn_decl.inputs[index].hir_id;
+                    let param_ty_span = hir.span(ty_hir_id);
+                    let is_first = index == 0;
+                    Some(AnonymousParamInfo {
+                        param,
+                        param_ty: new_param_ty,
+                        param_ty_span,
+                        bound_region,
+                        is_first,
+                    })
                 } else {
-                    r
+                    None
                 }
-            });
-            if found_anon_region {
-                let ty_hir_id = fn_decl.inputs[index].hir_id;
-                let param_ty_span = hir.span(ty_hir_id);
-                let is_first = index == 0;
-                Some(AnonymousParamInfo {
-                    param,
-                    param_ty: new_param_ty,
-                    param_ty_span,
-                    bound_region,
-                    is_first,
-                })
-            } else {
-                None
-            }
-        })
+            })
     }
 
     pub(super) fn future_return_type(

src/test/ui/c-variadic/issue-86053-1.rs

@@ -0,0 +1,12 @@
+// Regression test for the ICE described in issue #86053.
+// error-pattern:unexpected `self` parameter in function
+// error-pattern:`...` must be the last argument of a C-variadic function
+// error-pattern:cannot find type `F` in this scope
+// error-pattern:in type `&'a &'b usize`, reference has a longer lifetime than the data it references
+
+#![feature(c_variadic)]
+#![crate_type="lib"]
+
+fn ordering4 < 'a , 'b     > ( a :            ,   self , self ,   self ,
+    self , ... ,   self ,   self , ... ) where F : FnOnce ( & 'a & 'b usize ) {
+}

src/test/ui/c-variadic/issue-86053-1.stderr

@@ -0,0 +1,101 @@
+error: expected type, found `,`
+  --> $DIR/issue-86053-1.rs:10:47
+   |
+LL | fn ordering4 < 'a , 'b     > ( a :            ,   self , self ,   self ,
+   |                                               ^ expected type
+
+error: unexpected `self` parameter in function
+  --> $DIR/issue-86053-1.rs:10:51
+   |
+LL | fn ordering4 < 'a , 'b     > ( a :            ,   self , self ,   self ,
+   |                                                   ^^^^ must be the first parameter of an associated function
+
+error: unexpected `self` parameter in function
+  --> $DIR/issue-86053-1.rs:10:58
+   |
+LL | fn ordering4 < 'a , 'b     > ( a :            ,   self , self ,   self ,
+   |                                                          ^^^^ must be the first parameter of an associated function
+
+error: unexpected `self` parameter in function
+  --> $DIR/issue-86053-1.rs:10:67
+   |
+LL | fn ordering4 < 'a , 'b     > ( a :            ,   self , self ,   self ,
+   |                                                                   ^^^^ must be the first parameter of an associated function
+
+error: unexpected `self` parameter in function
+  --> $DIR/issue-86053-1.rs:11:5
+   |
+LL |     self , ... ,   self ,   self , ... ) where F : FnOnce ( & 'a & 'b usize ) {
+   |     ^^^^ must be the first parameter of an associated function
+
+error: unexpected `self` parameter in function
+  --> $DIR/issue-86053-1.rs:11:20
+   |
+LL |     self , ... ,   self ,   self , ... ) where F : FnOnce ( & 'a & 'b usize ) {
+   |                    ^^^^ must be the first parameter of an associated function
+
+error: unexpected `self` parameter in function
+  --> $DIR/issue-86053-1.rs:11:29
+   |
+LL |     self , ... ,   self ,   self , ... ) where F : FnOnce ( & 'a & 'b usize ) {
+   |                             ^^^^ must be the first parameter of an associated function
+
+error: `...` must be the last argument of a C-variadic function
+  --> $DIR/issue-86053-1.rs:11:12
+   |
+LL |     self , ... ,   self ,   self , ... ) where F : FnOnce ( & 'a & 'b usize ) {
+   |            ^^^^
+
+error: only foreign or `unsafe extern "C"` functions may be C-variadic
+  --> $DIR/issue-86053-1.rs:11:12
+   |
+LL |     self , ... ,   self ,   self , ... ) where F : FnOnce ( & 'a & 'b usize ) {
+   |            ^^^^
+
+error: only foreign or `unsafe extern "C"` functions may be C-variadic
+  --> $DIR/issue-86053-1.rs:11:36
+   |
+LL |     self , ... ,   self ,   self , ... ) where F : FnOnce ( & 'a & 'b usize ) {
+   |                                    ^^^^
+
+error[E0412]: cannot find type `F` in this scope
+  --> $DIR/issue-86053-1.rs:11:48
+   |
+LL |     self , ... ,   self ,   self , ... ) where F : FnOnce ( & 'a & 'b usize ) {
+   |                                                ^
+   | 
+  ::: $SRC_DIR/core/src/ops/function.rs:LL:COL
+   |
+LL | pub trait Fn<Args>: FnMut<Args> {
+   | ------------------------------- similarly named trait `Fn` defined here
+   |
+help: a trait with a similar name exists
+   |
+LL |     self , ... ,   self ,   self , ... ) where Fn : FnOnce ( & 'a & 'b usize ) {
+   |                                                ^^
+help: you might be missing a type parameter
+   |
+LL | fn ordering4 < 'a , 'b, F     > ( a :            ,   self , self ,   self ,
+   |                       ^^^
+
+error[E0491]: in type `&'a &'b usize`, reference has a longer lifetime than the data it references
+  --> $DIR/issue-86053-1.rs:11:52
+   |
+LL |     self , ... ,   self ,   self , ... ) where F : FnOnce ( & 'a & 'b usize ) {
+   |                                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+note: the pointer is valid for the lifetime `'a` as defined on the function body at 10:16
+  --> $DIR/issue-86053-1.rs:10:16
+   |
+LL | fn ordering4 < 'a , 'b     > ( a :            ,   self , self ,   self ,
+   |                ^^
+note: but the referenced data is only valid for the lifetime `'b` as defined on the function body at 10:21
+  --> $DIR/issue-86053-1.rs:10:21
+   |
+LL | fn ordering4 < 'a , 'b     > ( a :            ,   self , self ,   self ,
+   |                     ^^
+
+error: aborting due to 12 previous errors
+
+Some errors have detailed explanations: E0412, E0491.
+For more information about an error, try `rustc --explain E0412`.

src/test/ui/c-variadic/issue-86053-2.rs

@@ -0,0 +1,11 @@
+// Regression test for the ICE caused by the example in
+// https://github.com/rust-lang/rust/issues/86053#issuecomment-855672258
+
+#![feature(c_variadic)]
+
+trait H<T> {}
+
+unsafe extern "C" fn ordering4<'a, F: H<&'static &'a ()>>(_: (), ...) {}
+//~^ ERROR: in type `&'static &'a ()`, reference has a longer lifetime than the data it references [E0491]
+
+fn main() {}

src/test/ui/c-variadic/issue-86053-2.stderr

@@ -0,0 +1,16 @@
+error[E0491]: in type `&'static &'a ()`, reference has a longer lifetime than the data it references
+  --> $DIR/issue-86053-2.rs:8:39
+   |
+LL | unsafe extern "C" fn ordering4<'a, F: H<&'static &'a ()>>(_: (), ...) {}
+   |                                       ^^^^^^^^^^^^^^^^^^
+   |
+   = note: the pointer is valid for the static lifetime
+note: but the referenced data is only valid for the lifetime `'a` as defined on the function body at 8:32
+  --> $DIR/issue-86053-2.rs:8:32
+   |
+LL | unsafe extern "C" fn ordering4<'a, F: H<&'static &'a ()>>(_: (), ...) {}
+   |                                ^^
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0491`.

src/test/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 or `unsafe extern "C"` functions may be C-variadic
 //~| ERROR cannot find type `Bar` in this scope
 //~| ERROR at least one trait must be specified

src/test/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 or `unsafe extern "C"` functions may be C-variadic
   --> $DIR/issue-83499-input-output-iteration-ice.rs:7:16
    |
 LL | fn foo(_: Bar, ...) -> impl {}

src/test/ui/parser/variadic-ffi-semantic-restrictions.rs

@@ -4,32 +4,32 @@
 fn main() {}
 
 fn f1_1(x: isize, ...) {}
-//~^ ERROR only foreign or `unsafe extern "C" functions may be C-variadic
+//~^ ERROR only foreign or `unsafe extern "C"` functions may be C-variadic
 
 fn f1_2(...) {}
-//~^ ERROR only foreign or `unsafe extern "C" functions may be C-variadic
+//~^ ERROR only foreign or `unsafe extern "C"` functions may be C-variadic
 //~| ERROR C-variadic function must be declared with at least one named argument
 
 extern "C" fn f2_1(x: isize, ...) {}
-//~^ ERROR only foreign or `unsafe extern "C" functions may be C-variadic
+//~^ ERROR only foreign or `unsafe extern "C"` functions may be C-variadic
 
 extern "C" fn f2_2(...) {}
-//~^ ERROR only foreign or `unsafe extern "C" functions may be C-variadic
+//~^ ERROR only foreign or `unsafe extern "C"` functions may be C-variadic
 //~| ERROR C-variadic function must be declared with at least one named argument
 
 extern "C" fn f2_3(..., x: isize) {}
-//~^ ERROR only foreign or `unsafe extern "C" functions may be C-variadic
+//~^ ERROR only foreign or `unsafe extern "C"` functions may be C-variadic
 //~| 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 or `unsafe extern "C"` functions may be C-variadic
 
 extern "C" fn f3_2(...) {}
-//~^ ERROR only foreign or `unsafe extern "C" functions may be C-variadic
+//~^ ERROR only foreign or `unsafe extern "C"` functions may be C-variadic
 //~| ERROR C-variadic function must be declared with at least one named argument
 
 extern "C" fn f3_3(..., x: isize) {}
-//~^ ERROR only foreign or `unsafe extern "C" functions may be C-variadic
+//~^ ERROR only foreign or `unsafe extern "C"` functions may be C-variadic
 //~| ERROR `...` must be the last argument of a C-variadic function
 
 extern "C" {
@@ -43,35 +43,35 @@ struct X;
 
 impl X {
     fn i_f1(x: isize, ...) {}
-    //~^ ERROR only foreign or `unsafe extern "C" functions may be C-variadic
+    //~^ ERROR only foreign or `unsafe extern "C"` functions may be C-variadic
     fn i_f2(...) {}
-    //~^ ERROR only foreign or `unsafe extern "C" functions may be C-variadic
+    //~^ ERROR only foreign or `unsafe extern "C"` functions may be C-variadic
     //~| ERROR C-variadic function must be declared with at least one named argument
     fn i_f3(..., x: isize, ...) {}
-    //~^ ERROR only foreign or `unsafe extern "C" functions may be C-variadic
-    //~| ERROR only foreign or `unsafe extern "C" functions may be C-variadic
+    //~^ ERROR only foreign or `unsafe extern "C"` functions may be C-variadic
+    //~| ERROR only foreign or `unsafe extern "C"` functions may be C-variadic
     //~| 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 or `unsafe extern "C" functions may be C-variadic
+    //~^ ERROR only foreign or `unsafe extern "C"` functions may be C-variadic
+    //~| ERROR only foreign or `unsafe extern "C"` functions may be C-variadic
     //~| ERROR `...` must be the last argument of a C-variadic function
 }
 
 trait T {
     fn t_f1(x: isize, ...) {}
-    //~^ ERROR only foreign or `unsafe extern "C" functions may be C-variadic
+    //~^ ERROR only foreign or `unsafe extern "C"` functions may be C-variadic
     fn t_f2(x: isize, ...);
-    //~^ ERROR only foreign or `unsafe extern "C" functions may be C-variadic
+    //~^ ERROR only foreign or `unsafe extern "C"` functions may be C-variadic
     fn t_f3(...) {}
-    //~^ ERROR only foreign or `unsafe extern "C" functions may be C-variadic
+    //~^ ERROR only foreign or `unsafe extern "C"` functions may be C-variadic
     //~| ERROR C-variadic function must be declared with at least one named argument
     fn t_f4(...);
-    //~^ ERROR only foreign or `unsafe extern "C" functions may be C-variadic
+    //~^ ERROR only foreign or `unsafe extern "C"` functions may be C-variadic
     //~| ERROR C-variadic function must be declared with at least one named argument
     fn t_f5(..., x: isize) {}
-    //~^ ERROR only foreign or `unsafe extern "C" functions may be C-variadic
+    //~^ ERROR only foreign or `unsafe extern "C"` functions may be C-variadic
     //~| 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 or `unsafe extern "C"` functions may be C-variadic
     //~| ERROR `...` must be the last argument of a C-variadic function
 }