Express contracts as part of function header and lower it to the contract lang items

includes post-developed commit: do not suggest internal-only keywords as corrections to parse failures.

includes post-developed commit: removed tabs that creeped in into rustfmt tool source code.

includes post-developed commit, placating rustfmt self dogfooding.

includes post-developed commit: add backquotes to prevent markdown checking from trying to treat an attr as a markdown hyperlink/

includes post-developed commit: fix lowering to keep contracts from being erroneously inherited by nested bodies (like closures).

Rebase Conflicts:
 - compiler/rustc_parse/src/parser/diagnostics.rs
 - compiler/rustc_parse/src/parser/item.rs
 - compiler/rustc_span/src/hygiene.rs

Remove contracts keywords from diagnostic messages

2 files changed, 9 insertions, 2 deletions

diff --git a/compiler/rustc_resolve/src/def_collector.rs b/compiler/rustc_resolve/src/def_collector.rs
index 16c0a345f87..db607dbb419 100644
--- a/compiler/rustc_resolve/src/def_collector.rs
+++ b/compiler/rustc_resolve/src/def_collector.rs
@@ -174,10 +174,13 @@ impl<'a, 'ra, 'tcx> visit::Visitor<'a> for DefCollector<'a, 'ra, 'tcx> {
                 _ctxt,
                 _ident,
                 _vis,
-                Fn { sig: FnSig { header, decl, span: _ }, generics, body, .. },
+                Fn { sig: FnSig { header, decl, span: _ }, generics, contract, body, .. },
             ) if let Some(coroutine_kind) = header.coroutine_kind => {
                 self.visit_fn_header(header);
                 self.visit_generics(generics);
+                if let Some(contract) = contract {
+                    self.visit_contract(contract);
+                }
 
                 // For async functions, we need to create their inner defs inside of a
                 // closure to match their desugared representation. Besides that,
diff --git a/compiler/rustc_resolve/src/late.rs b/compiler/rustc_resolve/src/late.rs
index 4842cbd556c..e37e7e98ee7 100644
--- a/compiler/rustc_resolve/src/late.rs
+++ b/compiler/rustc_resolve/src/late.rs
@@ -1019,7 +1019,7 @@ impl<'ra: 'ast, 'ast, 'tcx> Visitor<'ast> for LateResolutionVisitor<'_, 'ast, 'r
             // Create a label rib for the function.
             this.with_label_rib(RibKind::FnOrCoroutine, |this| {
                 match fn_kind {
-                    FnKind::Fn(_, _, _, Fn { sig, generics, body, .. }) => {
+                    FnKind::Fn(_, _, _, Fn { sig, generics, contract, body, .. }) => {
                         this.visit_generics(generics);
 
                         let declaration = &sig.decl;
@@ -1046,6 +1046,10 @@ impl<'ra: 'ast, 'ast, 'tcx> Visitor<'ast> for LateResolutionVisitor<'_, 'ast, 'r
                             },
                         );
 
+                        if let Some(contract) = contract {
+                            this.visit_contract(contract);
+                        }
+
                         if let Some(body) = body {
                             // Ignore errors in function bodies if this is rustdoc
                             // Be sure not to set this until the function signature has been resolved.