Fix bad-c-variadic error being emitted multiple times

If a function incorrectly contains multiple `...` args, and is also not foreign or `unsafe extern "C"`, only emit the latter error once.

Author: nicholasbishop

compiler/rustc_ast_passes/src/ast_validation.rs

@@ -485,6 +485,18 @@ impl<'a> AstValidator<'a> {
  /// Reject C-variadic type unless the function is foreign,
  /// or free and `unsafe extern "C"` semantically.
  fn check_c_variadic_type(&self, fk: FnKind<'a>) {
+ let variadic_spans: Vec<_> = fk
+ .decl()
+ .inputs
+ .iter()
+ .filter(|arg| matches!(arg.ty.kind, TyKind::CVarArgs))
+ .map(|arg| arg.span)
+ .collect();
+
+ if variadic_spans.is_empty() {
+ return;
+ }
+
  match (fk.ctxt(), fk.header()) {
  (Some(FnCtxt::Foreign), _) => return,
  (Some(FnCtxt::Free), Some(header)) => match header.ext {
@@ -499,11 +511,7 @@ impl<'a> AstValidator<'a> {
  _ => {}
  };
 
- for Param { ty, span, .. } in &fk.decl().inputs {
- if let TyKind::CVarArgs = ty.kind {
- self.err_handler().emit_err(errors::BadCVariadic { span: *span });
- }
- }
+ self.err_handler().emit_err(errors::BadCVariadic { span: variadic_spans });
  }
 
  fn check_item_named(&self, ident: Ident, kind: &str) {

compiler/rustc_ast_passes/src/errors.rs

@@ -271,7 +271,7 @@ pub struct ExternItemAscii {
 #[diag(ast_passes_bad_c_variadic)]
 pub struct BadCVariadic {
  #[primary_span]
- pub span: Span,
+ pub span: Vec<Span>,
 }
 
 #[derive(Diagnostic)]

tests/ui/c-variadic/issue-86053-1.stderr

@@ -50,13 +50,7 @@ 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
@@ -76,6 +70,6 @@ help: you might be missing a type parameter
 LL | fn ordering4 < 'a , 'b, F > ( a : , self , self , self ,
  | +++
 
-error: aborting due to 11 previous errors
+error: aborting due to 10 previous errors
 
 For more information about this error, try `rustc --explain E0412`.

tests/ui/parser/variadic-ffi-semantic-restrictions.rs

@@ -49,11 +49,9 @@ impl X {
  //~| 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 `...` 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 `...` must be the last argument of a C-variadic function
 }
 

tests/ui/parser/variadic-ffi-semantic-restrictions.stderr

@@ -116,91 +116,79 @@ error: only foreign or `unsafe extern "C"` functions may be C-variadic
  --> $DIR/variadic-ffi-semantic-restrictions.rs:50:13
  |
 LL | fn i_f3(..., x: isize, ...) {}
- | ^^^
-
-error: only foreign or `unsafe extern "C"` functions may be C-variadic
- --> $DIR/variadic-ffi-semantic-restrictions.rs:50:28
- |
-LL | fn i_f3(..., x: isize, ...) {}
- | ^^^
+ | ^^^ ^^^
 
 error: `...` must be the last argument of a C-variadic function
- --> $DIR/variadic-ffi-semantic-restrictions.rs:54:13
- |
-LL | fn i_f4(..., x: isize, ...) {}
- | ^^^
-
-error: only foreign or `unsafe extern "C"` functions may be C-variadic
- --> $DIR/variadic-ffi-semantic-restrictions.rs:54:13
+ --> $DIR/variadic-ffi-semantic-restrictions.rs:53:13
  |
 LL | fn i_f4(..., x: isize, ...) {}
  | ^^^
 
 error: only foreign or `unsafe extern "C"` functions may be C-variadic
- --> $DIR/variadic-ffi-semantic-restrictions.rs:54:28
+ --> $DIR/variadic-ffi-semantic-restrictions.rs:53:13
  |
 LL | fn i_f4(..., x: isize, ...) {}
- |   ^^^
+ | ^^^ ^^^
 
 error: only foreign or `unsafe extern "C"` functions may be C-variadic
- --> $DIR/variadic-ffi-semantic-restrictions.rs:61:23
+ --> $DIR/variadic-ffi-semantic-restrictions.rs:59:23
  |
 LL | fn t_f1(x: isize, ...) {}
  | ^^^
 
 error: only foreign or `unsafe extern "C"` functions may be C-variadic
- --> $DIR/variadic-ffi-semantic-restrictions.rs:63:23
+ --> $DIR/variadic-ffi-semantic-restrictions.rs:61:23
  |
 LL | fn t_f2(x: isize, ...);
  | ^^^
 
 error: C-variadic function must be declared with at least one named argument
- --> $DIR/variadic-ffi-semantic-restrictions.rs:65:13
+ --> $DIR/variadic-ffi-semantic-restrictions.rs:63:13
  |
 LL | fn t_f3(...) {}
  | ^^^
 
 error: only foreign or `unsafe extern "C"` functions may be C-variadic
- --> $DIR/variadic-ffi-semantic-restrictions.rs:65:13
+ --> $DIR/variadic-ffi-semantic-restrictions.rs:63:13
  |
 LL | fn t_f3(...) {}
  | ^^^
 
 error: C-variadic function must be declared with at least one named argument
- --> $DIR/variadic-ffi-semantic-restrictions.rs:68:13
+ --> $DIR/variadic-ffi-semantic-restrictions.rs:66:13
  |
 LL | fn t_f4(...);
  | ^^^
 
 error: only foreign or `unsafe extern "C"` functions may be C-variadic
- --> $DIR/variadic-ffi-semantic-restrictions.rs:68:13
+ --> $DIR/variadic-ffi-semantic-restrictions.rs:66:13
  |
 LL | fn t_f4(...);
  | ^^^
 
 error: `...` must be the last argument of a C-variadic function
- --> $DIR/variadic-ffi-semantic-restrictions.rs:71:13
+ --> $DIR/variadic-ffi-semantic-restrictions.rs:69:13
  |
 LL | fn t_f5(..., x: isize) {}
  | ^^^
 
 error: only foreign or `unsafe extern "C"` functions may be C-variadic
- --> $DIR/variadic-ffi-semantic-restrictions.rs:71:13
+ --> $DIR/variadic-ffi-semantic-restrictions.rs:69:13
  |
 LL | fn t_f5(..., x: isize) {}
  | ^^^
 
 error: `...` must be the last argument of a C-variadic function
- --> $DIR/variadic-ffi-semantic-restrictions.rs:74:13
+ --> $DIR/variadic-ffi-semantic-restrictions.rs:72:13
  |
 LL | fn t_f6(..., x: isize);
  | ^^^
 
 error: only foreign or `unsafe extern "C"` functions may be C-variadic
- --> $DIR/variadic-ffi-semantic-restrictions.rs:74:13
+ --> $DIR/variadic-ffi-semantic-restrictions.rs:72:13
  |
 LL | fn t_f6(..., x: isize);
  | ^^^
 
-error: aborting due to 34 previous errors
+error: aborting due to 32 previous errors