Rollup merge of #136835 - compiler-errors:contracts-span-hack, r=celinval

Stop using span hack for contracts feature gating

The contracts machinery is a pretty straightforward case of an *external* feature using a (perma-unstable) *internal* feature within its implementation. There's no reason why it needs to be implemented any differently than other features by using global span tracking hacks to change whether the internals are gated behind the `contracts` or `contracts_internals` feature gate -- for the case of macro expansions we already have `allow_internal_unstable` for exactly this situation.

This PR changes the internal, perma-unstable AST syntax to use the `contracts_internals` gate always, and adjusts the macro expansion to use the right spans so that `allow_internal_unstable` works correctly.

As a follow-up, there's really no reason to have `contracts` be a *compiler feature* since it's at this point fully a *library feature*; the only reason it's a compiler feature today is so we can mark it as incomplete, but that seems like a weak reason. I didn't do anything in this PR for this.

r? ``@celinval``

compiler/rustc_builtin_macros/src/contracts.rs

@@ -1,11 +1,9 @@
-#![allow(unused_imports, unused_variables)]
-
 use rustc_ast::token;
 use rustc_ast::tokenstream::{DelimSpacing, DelimSpan, Spacing, TokenStream, TokenTree};
 use rustc_errors::ErrorGuaranteed;
 use rustc_expand::base::{AttrProcMacro, ExtCtxt};
 use rustc_span::Span;
-use rustc_span::symbol::{Ident, Symbol, kw, sym};
+use rustc_span::symbol::{Ident, Symbol, kw};
 
 pub(crate) struct ExpandRequires;
 
@@ -121,23 +119,19 @@ fn expand_contract_clause(
         }
     }
 
-    // Record the span as a contract attribute expansion.
-    // This is used later to stop users from using the extended syntax directly
-    // which is gated via `contracts_internals`.
-    ecx.psess().contract_attribute_spans.push(attr_span);
-
     Ok(new_tts)
 }
 
 fn expand_requires_tts(
-    _ecx: &mut ExtCtxt<'_>,
+    ecx: &mut ExtCtxt<'_>,
     attr_span: Span,
     annotation: TokenStream,
     annotated: TokenStream,
 ) -> Result<TokenStream, ErrorGuaranteed> {
-    expand_contract_clause(_ecx, attr_span, annotated, |new_tts| {
+    let feature_span = ecx.with_def_site_ctxt(attr_span);
+    expand_contract_clause(ecx, attr_span, annotated, |new_tts| {
         new_tts.push_tree(TokenTree::Token(
-            token::Token::from_ast_ident(Ident::new(kw::ContractRequires, attr_span)),
+            token::Token::from_ast_ident(Ident::new(kw::ContractRequires, feature_span)),
             Spacing::Joint,
         ));
         new_tts.push_tree(TokenTree::Token(
@@ -155,14 +149,15 @@ fn expand_requires_tts(
 }
 
 fn expand_ensures_tts(
-    _ecx: &mut ExtCtxt<'_>,
+    ecx: &mut ExtCtxt<'_>,
     attr_span: Span,
     annotation: TokenStream,
     annotated: TokenStream,
 ) -> Result<TokenStream, ErrorGuaranteed> {
-    expand_contract_clause(_ecx, attr_span, annotated, |new_tts| {
+    let feature_span = ecx.with_def_site_ctxt(attr_span);
+    expand_contract_clause(ecx, attr_span, annotated, |new_tts| {
         new_tts.push_tree(TokenTree::Token(
-            token::Token::from_ast_ident(Ident::new(kw::ContractEnsures, attr_span)),
+            token::Token::from_ast_ident(Ident::new(kw::ContractEnsures, feature_span)),
             Spacing::Joint,
         ));
         new_tts.push_tree(TokenTree::Delimited(

compiler/rustc_parse/src/parser/generics.rs

@@ -302,26 +302,16 @@ impl<'a> Parser<'a> {
     pub(super) fn parse_contract(
         &mut self,
     ) -> PResult<'a, Option<rustc_ast::ptr::P<ast::FnContract>>> {
-        let gate = |span| {
-            if self.psess.contract_attribute_spans.contains(span) {
-                // span was generated via a builtin contracts attribute, so gate as end-user visible
-                self.psess.gated_spans.gate(sym::contracts, span);
-            } else {
-                // span was not generated via a builtin contracts attribute, so gate as internal machinery
-                self.psess.gated_spans.gate(sym::contracts_internals, span);
-            }
-        };
-
         let requires = if self.eat_keyword_noexpect(exp!(ContractRequires).kw) {
+            self.psess.gated_spans.gate(sym::contracts_internals, self.prev_token.span);
             let precond = self.parse_expr()?;
-            gate(precond.span);
             Some(precond)
         } else {
             None
         };
         let ensures = if self.eat_keyword_noexpect(exp!(ContractEnsures).kw) {
+            self.psess.gated_spans.gate(sym::contracts_internals, self.prev_token.span);
             let postcond = self.parse_expr()?;
-            gate(postcond.span);
             Some(postcond)
         } else {
             None

compiler/rustc_session/src/parse.rs

@@ -208,10 +208,6 @@ pub struct ParseSess {
     pub config: Cfg,
     pub check_config: CheckCfg,
     pub edition: Edition,
-    /// Places where contract attributes were expanded into unstable AST forms.
-    /// This is used to allowlist those spans (so that we only check them against the feature
-    /// gate for the externally visible interface, and not internal implmentation machinery).
-    pub contract_attribute_spans: AppendOnlyVec<Span>,
     /// Places where raw identifiers were used. This is used to avoid complaining about idents
     /// clashing with keywords in new editions.
     pub raw_identifier_spans: AppendOnlyVec<Span>,
@@ -260,7 +256,6 @@ impl ParseSess {
             config: Cfg::default(),
             check_config: CheckCfg::default(),
             edition: ExpnId::root().expn_data().edition,
-            contract_attribute_spans: Default::default(),
             raw_identifier_spans: Default::default(),
             bad_unicode_identifiers: Lock::new(Default::default()),
             source_map,

tests/ui/contracts/internal_machinery/internal-feature-gating.stderr

@@ -1,18 +1,18 @@
 error[E0658]: contract internal machinery is for internal use only
-  --> $DIR/internal-feature-gating.rs:16:45
+  --> $DIR/internal-feature-gating.rs:16:28
    |
 LL |     fn identity_1() -> i32 contract_requires(|| true) { 10 }
-   |                                             ^^^^^^^^^
+   |                            ^^^^^^^^^^^^^^^^^
    |
    = note: see issue #128044 <https://github.com/rust-lang/rust/issues/128044> for more information
    = help: add `#![feature(contracts_internals)]` to the crate attributes to enable
    = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
 
 error[E0658]: contract internal machinery is for internal use only
-  --> $DIR/internal-feature-gating.rs:18:44
+  --> $DIR/internal-feature-gating.rs:18:28
    |
 LL |     fn identity_2() -> i32 contract_ensures(|_| true) { 10 }
-   |                                            ^^^^^^^^^^
+   |                            ^^^^^^^^^^^^^^^^
    |
    = note: see issue #128044 <https://github.com/rust-lang/rust/issues/128044> for more information
    = help: add `#![feature(contracts_internals)]` to the crate attributes to enable

tests/ui/feature-gates/feature-gate-contracts.rs

@@ -3,9 +3,7 @@
 #[core::contracts::requires(x > 0)]
 pub fn requires_needs_it(x: i32) { }
 //~^^  ERROR use of unstable library feature `contracts`
-//~^^^ ERROR contracts are incomplete
 
 #[core::contracts::ensures(|ret| *ret > 0)]
 pub fn ensures_needs_it() -> i32 { 10 }
 //~^^  ERROR use of unstable library feature `contracts`
-//~^^^ ERROR contracts are incomplete

tests/ui/feature-gates/feature-gate-contracts.stderr

@@ -9,7 +9,7 @@ LL | #[core::contracts::requires(x > 0)]
    = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
 
 error[E0658]: use of unstable library feature `contracts`
-  --> $DIR/feature-gate-contracts.rs:8:3
+  --> $DIR/feature-gate-contracts.rs:7:3
    |
 LL | #[core::contracts::ensures(|ret| *ret > 0)]
    |   ^^^^^^^^^^^^^^^^^^^^^^^^
@@ -18,26 +18,6 @@ LL | #[core::contracts::ensures(|ret| *ret > 0)]
    = help: add `#![feature(contracts)]` to the crate attributes to enable
    = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
 
-error[E0658]: contracts are incomplete
+error: aborting due to 2 previous errors
-  --> $DIR/feature-gate-contracts.rs:3:1
-   |
-LL | #[core::contracts::requires(x > 0)]
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   |
-   = note: see issue #128044 <https://github.com/rust-lang/rust/issues/128044> for more information
-   = help: add `#![feature(contracts)]` to the crate attributes to enable
-   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
-
-error[E0658]: contracts are incomplete
-  --> $DIR/feature-gate-contracts.rs:8:1
-   |
-LL | #[core::contracts::ensures(|ret| *ret > 0)]
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   |
-   = note: see issue #128044 <https://github.com/rust-lang/rust/issues/128044> for more information
-   = help: add `#![feature(contracts)]` to the crate attributes to enable
-   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
-
-error: aborting due to 4 previous errors
 
 For more information about this error, try `rustc --explain E0658`.