Auto merge of #66021 - tmandry:rollup-y13l6n9, r=tmandry

Rollup of 16 pull requests

Successful merges:

 - #65112 (Add lint and tests for unnecessary parens around types)
 - #65470 (Don't hide ICEs from previous incremental compiles)
 - #65471 (Add long error explanation for E0578)
 - #65857 (rustdoc: Resolve module-level doc references more locally)
 - #65902 (Make ItemContext available for better diagnositcs)
 - #65914 (Use structured suggestion for unnecessary bounds in type aliases)
 - #65946 (Make `promote_consts` emit the errors when required promotion fails)
 - #65960 (doc: reword iter module example and mention other methods)
 - #65963 (update submodules to rust-lang)
 - #65972 (Fix libunwind build: Define __LITTLE_ENDIAN__ for LE targets)
 - #65977 (Fix incorrect diagnostics for expected type in E0271 with an associated type)
 - #65995 (Add error code E0743 for "C-variadic has been used on a non-foreign function")
 - #65997 (Fix outdated rustdoc of Once::init_locking function)
 - #66002 (Stabilize float_to_from_bytes feature)
 - #66005 (vxWorks: remove code related unix socket)
 - #66018 (Revert PR 64324: dylibs export generics again (for now))

Failed merges:

r? @ghost

2 files changed, 19 insertions, 3 deletions

diff --git a/src/libsyntax/error_codes.rs b/src/libsyntax/error_codes.rs
index 17ea4767520..941df5ea570 100644
--- a/src/libsyntax/error_codes.rs
+++ b/src/libsyntax/error_codes.rs
@@ -487,7 +487,6 @@ Erroneous code example:
                                // `test_2018_feature` is
                                // included in the Rust 2018 edition
 ```
-
 "##,
 
 E0725: r##"
@@ -505,6 +504,20 @@ Delete the offending feature attribute, or add it to the list of allowed
 features in the `-Z allow_features` flag.
 "##,
 
+E0743: r##"
+C-variadic has been used on a non-foreign function.
+
+Erroneous code example:
+
+```compile_fail,E0743
+fn foo2(x: u8, ...) {} // error!
+```
+
+Only foreign functions can use C-variadic (`...`). It is used to give an
+undefined number of parameters to a given function (like `printf` in C). The
+equivalent in Rust would be to use macros directly.
+"##,
+
 ;
 
     E0539, // incorrect meta item
diff --git a/src/libsyntax/parse/parser/ty.rs b/src/libsyntax/parse/parser/ty.rs
index 86c94b680b2..e8f718a2483 100644
--- a/src/libsyntax/parse/parser/ty.rs
+++ b/src/libsyntax/parse/parser/ty.rs
@@ -197,8 +197,11 @@ impl<'a> Parser<'a> {
                 self.eat(&token::DotDotDot);
                 TyKind::CVarArgs
             } else {
-                return Err(self.fatal(
-                    "only foreign functions are allowed to be C-variadic"
+                return Err(struct_span_fatal!(
+                    self.sess.span_diagnostic,
+                    self.token.span,
+                    E0743,
+                    "only foreign functions are allowed to be C-variadic",
                 ));
             }
         } else {