Rollup merge of #63492 - eddyb:cvarargs, r=nagisa,matthewjasper

Remove redundancy from the implementation of C variadics.

This cleanup was first described in https://github.com/rust-lang/rust/issues/44930#issuecomment-497163539:

* AST doesn't track `c_variadic: bool` anymore, relying solely on a trailing `CVarArgs` type in fn signatures
* HIR doesn't have a `CVarArgs` anymore, relying solely on `c_variadic: bool`
  * same for `ty::FnSig` (see tests for diagnostics improvements from that)
  * `{hir,mir}::Body` have one extra argument than the signature when `c_variadic == true`
  * `rustc_typeck` and `rustc_mir::{build,borrowck}` need to give that argument the right type (which no longer uses a lifetime parameter, but a function-internal scope)
* `rustc_target::abi::call` doesn't need special hacks anymore (since it never sees the `VaListImpl` now, it's all inside the body)

r? @nagisa / @rkruppe cc @dlrobertson @oli-obk

1 files changed, 4 insertions, 3 deletions

diff --git a/src/libsyntax/parse/parser.rs b/src/libsyntax/parse/parser.rs
index cc582819b6b..f22fd5ad703 100644
--- a/src/libsyntax/parse/parser.rs
+++ b/src/libsyntax/parse/parser.rs
@@ -1194,7 +1194,7 @@ impl<'a> Parser<'a> {
     }
 
     fn parse_fn_params(&mut self, named_params: bool, allow_c_variadic: bool)
-                     -> PResult<'a, (Vec<Param> , bool)> {
+                     -> PResult<'a, Vec<Param>> {
         let sp = self.token.span;
         let mut c_variadic = false;
         let (params, _): (Vec<Option<Param>>, _) = self.parse_paren_comma_seq(|p| {
@@ -1218,6 +1218,8 @@ impl<'a> Parser<'a> {
                             let span = p.token.span;
                             p.span_err(span,
                                 "`...` must be the last argument of a C-variadic function");
+                            // FIXME(eddyb) this should probably still push `CVarArgs`.
+                            // Maybe AST validation/HIR lowering should emit the above error?
                             Ok(None)
                         } else {
                             Ok(Some(param))
@@ -1245,7 +1247,7 @@ impl<'a> Parser<'a> {
                           "C-variadic function must be declared with at least one named argument");
         }
 
-        Ok((params, c_variadic))
+        Ok(params)
     }
 
     /// Returns the parsed optional self parameter and whether a self shortcut was used.
@@ -1414,7 +1416,6 @@ impl<'a> Parser<'a> {
         Ok(P(FnDecl {
             inputs: fn_inputs,
             output: self.parse_ret_ty(true)?,
-            c_variadic: false
         }))
     }