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

3 files changed, 2 insertions, 5 deletions

diff --git a/src/libsyntax/parse/parser/expr.rs b/src/libsyntax/parse/parser/expr.rs
index c776704b285..23674ad589d 100644
--- a/src/libsyntax/parse/parser/expr.rs
+++ b/src/libsyntax/parse/parser/expr.rs
@@ -1176,7 +1176,6 @@ impl<'a> Parser<'a> {
         Ok(P(FnDecl {
             inputs: inputs_captures,
             output,
-            c_variadic: false
         }))
     }
 
diff --git a/src/libsyntax/parse/parser/item.rs b/src/libsyntax/parse/parser/item.rs
index 370030d02c7..92b19b73e57 100644
--- a/src/libsyntax/parse/parser/item.rs
+++ b/src/libsyntax/parse/parser/item.rs
@@ -1292,13 +1292,12 @@ impl<'a> Parser<'a> {
 
     /// Parses the argument list and result type of a function declaration.
     fn parse_fn_decl(&mut self, allow_c_variadic: bool) -> PResult<'a, P<FnDecl>> {
-        let (args, c_variadic) = self.parse_fn_params(true, allow_c_variadic)?;
+        let args = self.parse_fn_params(true, allow_c_variadic)?;
         let ret_ty = self.parse_ret_ty(true)?;
 
         Ok(P(FnDecl {
             inputs: args,
             output: ret_ty,
-            c_variadic,
         }))
     }
 
diff --git a/src/libsyntax/parse/parser/ty.rs b/src/libsyntax/parse/parser/ty.rs
index b4c006ca2b1..c52d3733b5e 100644
--- a/src/libsyntax/parse/parser/ty.rs
+++ b/src/libsyntax/parse/parser/ty.rs
@@ -292,12 +292,11 @@ impl<'a> Parser<'a> {
         };
 
         self.expect_keyword(kw::Fn)?;
-        let (inputs, c_variadic) = self.parse_fn_params(false, true)?;
+        let inputs = self.parse_fn_params(false, true)?;
         let ret_ty = self.parse_ret_ty(false)?;
         let decl = P(FnDecl {
             inputs,
             output: ret_ty,
-            c_variadic,
         });
         Ok(TyKind::BareFn(P(BareFnTy {
             abi,