Label mismatched parameters at the def site for foreign functions.

compiler/rustc_hir_typeck/src/fn_ctxt/checks.rs

@@ -2641,8 +2641,9 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
     }
 
     /// Returns the parameters of a function, with their generic parameters if those are the full
-    /// type of that parameter. Returns `None` if the function has no generics or the body is
-    /// unavailable (eg is an instrinsic).
+    /// type of that parameter.
+    ///
+    /// Returns `None` if the body is not a named function (e.g. a closure).
     fn get_hir_param_info(
         &self,
         def_id: DefId,
@@ -2667,6 +2668,10 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 kind: hir::ItemKind::Fn { sig, generics, body, .. },
                 ..
             }) => (sig, generics, Some(body), None),
+            hir::Node::ForeignItem(&hir::ForeignItem {
+                kind: hir::ForeignItemKind::Fn(sig, params, generics),
+                ..
+            }) => (sig, generics, None, Some(params)),
             _ => return None,
         };
 
@@ -2700,7 +2705,8 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 ))
             }
             (None, Some(params)) => {
-                let params = params.get(is_method as usize..)?;
+                let params =
+                    params.get(is_method as usize..params.len() - sig.decl.c_variadic as usize)?;
                 debug_assert_eq!(params.len(), fn_inputs.len());
                 Some((
                     fn_inputs.zip(params.iter().map(|param| FnParam::Name(param))).collect(),

tests/ui/argument-suggestions/extern-fn-arg-names.stderr

@@ -14,7 +14,7 @@ note: function defined here
   --> $DIR/extern-fn-arg-names.rs:2:8
    |
 LL |     fn dstfn(src: i32, dst: err);
-   |        ^^^^^
+   |        ^^^^^           ---
 help: provide the argument
    |
 LL |     dstfn(1, /* dst */);

tests/ui/c-variadic/variadic-ffi-1.stderr

@@ -14,7 +14,7 @@ note: function defined here
   --> $DIR/variadic-ffi-1.rs:15:8
    |
 LL |     fn foo(f: isize, x: u8, ...);
-   |        ^^^
+   |        ^^^ -         -
 help: provide the arguments
    |
 LL |         foo(/* isize */, /* u8 */);
@@ -30,7 +30,7 @@ note: function defined here
   --> $DIR/variadic-ffi-1.rs:15:8
    |
 LL |     fn foo(f: isize, x: u8, ...);
-   |        ^^^
+   |        ^^^           -
 help: provide the argument
    |
 LL |         foo(1, /* u8 */);

tests/ui/error-codes/E0060.stderr

@@ -8,7 +8,7 @@ note: function defined here
   --> $DIR/E0060.rs:2:8
    |
 LL |     fn printf(_: *const u8, ...) -> u32;
-   |        ^^^^^^
+   |        ^^^^^^ -
 help: provide the argument
    |
 LL |     unsafe { printf(/* *const u8 */); }

tests/ui/fn/param-mismatch-foreign.rs

@@ -0,0 +1,11 @@
+extern "C" {
+    fn foo(x: i32, y: u32, z: i32);
+    //~^ NOTE function defined here
+}
+
+fn main() {
+    foo(1i32, 2i32);
+    //~^ ERROR this function takes 3 arguments but 2 arguments were supplied
+    //~| NOTE argument #2 of type `u32` is missing
+    //~| HELP provide the argument
+}

tests/ui/fn/param-mismatch-foreign.stderr

@@ -0,0 +1,19 @@
+error[E0061]: this function takes 3 arguments but 2 arguments were supplied
+  --> $DIR/param-mismatch-foreign.rs:7:5
+   |
+LL |     foo(1i32, 2i32);
+   |     ^^^       ---- argument #2 of type `u32` is missing
+   |
+note: function defined here
+  --> $DIR/param-mismatch-foreign.rs:2:8
+   |
+LL |     fn foo(x: i32, y: u32, z: i32);
+   |        ^^^         -
+help: provide the argument
+   |
+LL |     foo(1i32, /* u32 */, 2i32);
+   |        ~~~~~~~~~~~~~~~~~~~~~~~
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0061`.

tests/ui/mismatched_types/issue-26480.stderr

@@ -13,7 +13,7 @@ note: function defined here
   --> $DIR/issue-26480.rs:2:8
    |
 LL |     fn write(fildes: i32, buf: *const i8, nbyte: u64) -> i64;
-   |        ^^^^^
+   |        ^^^^^                              -----
    = note: this error originates in the macro `write` (in Nightly builds, run with -Z macro-backtrace for more info)
 help: you can convert a `usize` to a `u64` and panic if the converted value doesn't fit
    |

tests/ui/suggestions/suggest-null-ptr.stderr

@@ -12,7 +12,7 @@ note: function defined here
   --> $DIR/suggest-null-ptr.rs:7:8
    |
 LL |     fn foo(ptr: *const u8);
-   |        ^^^
+   |        ^^^ ---
 help: if you meant to create a null pointer, use `std::ptr::null()`
    |
 LL |         foo(std::ptr::null());
@@ -32,7 +32,7 @@ note: function defined here
   --> $DIR/suggest-null-ptr.rs:9:8
    |
 LL |     fn foo_mut(ptr: *mut u8);
-   |        ^^^^^^^
+   |        ^^^^^^^ ---
 help: if you meant to create a null pointer, use `std::ptr::null_mut()`
    |
 LL |         foo_mut(std::ptr::null_mut());
@@ -52,7 +52,7 @@ note: function defined here
   --> $DIR/suggest-null-ptr.rs:11:8
    |
 LL |     fn usize(ptr: *const usize);
-   |        ^^^^^
+   |        ^^^^^ ---
 help: if you meant to create a null pointer, use `std::ptr::null()`
    |
 LL |         usize(std::ptr::null());
@@ -72,7 +72,7 @@ note: function defined here
   --> $DIR/suggest-null-ptr.rs:13:8
    |
 LL |     fn usize_mut(ptr: *mut usize);
-   |        ^^^^^^^^^
+   |        ^^^^^^^^^ ---
 help: if you meant to create a null pointer, use `std::ptr::null_mut()`
    |
 LL |         usize_mut(std::ptr::null_mut());