Add contract variable declarations

Contract variables can be declared in the `requires` clause and can be referenced both in `requires` and `ensures`, subject to usual borrow checking rules. This allows any setup common to both the `requires` and `ensures` clauses to only be done once.

compiler/rustc_ast/src/ast.rs

@@ -3700,6 +3700,9 @@ pub struct TraitImplHeader {
 
 #[derive(Clone, Encodable, Decodable, Debug, Default, Walkable)]
 pub struct FnContract {
+ /// Declarations of variables accessible both in the `requires` and
+ /// `ensures` clauses.
+ pub declarations: ThinVec<Stmt>,
  pub requires: Option<Box<Expr>>,
  pub ensures: Option<Box<Expr>>,
 }

compiler/rustc_ast_lowering/src/block.rs

@@ -27,7 +27,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
  hir::Block { hir_id, stmts, expr, rules, span: self.lower_span(b.span), targeted_by_break }
  }
 
- fn lower_stmts(
+ pub(super) fn lower_stmts(
  &mut self,
  mut ast_stmts: &[Stmt],
  ) -> (&'hir [hir::Stmt<'hir>], Option<&'hir hir::Expr<'hir>>) {

compiler/rustc_ast_lowering/src/contract.rs

@@ -18,6 +18,11 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
  body: impl FnOnce(&mut Self) -> rustc_hir::Expr<'hir>,
  contract: &rustc_ast::FnContract,
  ) -> rustc_hir::Expr<'hir> {
+ // The order in which things are lowered is important! I.e to
+ // refer to variables in contract_decls from postcond/precond,
+ // we must lower it first!
+ let contract_decls = self.lower_stmts(&contract.declarations).0;
+
  match (&contract.requires, &contract.ensures) {
  (Some(req), Some(ens)) => {
  // Lower the fn contract, which turns:
@@ -27,6 +32,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
  // into:
  //
  // let __postcond = if contract_checks {
+ // CONTRACT_DECLARATIONS;
  // contract_check_requires(PRECOND);
  // Some(|ret_val| POSTCOND)
  // } else {
@@ -45,8 +51,11 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
  let precond = self.lower_precond(req);
  let postcond_checker = self.lower_postcond_checker(ens);
 
- let contract_check =
- self.lower_contract_check_with_postcond(Some(precond), postcond_checker);
+ let contract_check = self.lower_contract_check_with_postcond(
+ contract_decls,
+ Some(precond),
+ postcond_checker,
+ );
 
  let wrapped_body =
  self.wrap_body_with_contract_check(body, contract_check, postcond_checker.span);
@@ -68,15 +77,15 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
  // let ret = { body };
  //
  // if contract_checks {
+ // CONTRACT_DECLARATIONS;
  // contract_check_ensures(__postcond, ret)
  // } else {
  // ret
  // }
  // }
-
  let postcond_checker = self.lower_postcond_checker(ens);
  let contract_check =
- self.lower_contract_check_with_postcond(None, postcond_checker);
+ self.lower_contract_check_with_postcond(contract_decls, None, postcond_checker);
 
  let wrapped_body =
  self.wrap_body_with_contract_check(body, contract_check, postcond_checker.span);
@@ -91,12 +100,13 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
  //
  // {
  // if contracts_checks {
+ // CONTRACT_DECLARATIONS;
  // contract_requires(PRECOND);
  // }
  // body
  // }
  let precond = self.lower_precond(req);
- let precond_check = self.lower_contract_check_just_precond(precond);
+ let precond_check = self.lower_contract_check_just_precond(contract_decls, precond);
 
  let body = self.arena.alloc(body(self));
 
@@ -145,9 +155,12 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
 
  fn lower_contract_check_just_precond(
  &mut self,
+ contract_decls: &'hir [rustc_hir::Stmt<'hir>],
  precond: rustc_hir::Stmt<'hir>,
  ) -> rustc_hir::Stmt<'hir> {
- let stmts = self.arena.alloc_from_iter([precond].into_iter());
+ let stmts = self
+ .arena
+ .alloc_from_iter(contract_decls.into_iter().map(|d| *d).chain([precond].into_iter()));
 
  let then_block_stmts = self.block_all(precond.span, stmts, None);
  let then_block = self.arena.alloc(self.expr_block(&then_block_stmts));
@@ -164,10 +177,13 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
 
  fn lower_contract_check_with_postcond(
  &mut self,
+ contract_decls: &'hir [rustc_hir::Stmt<'hir>],
  precond: Option<rustc_hir::Stmt<'hir>>,
  postcond_checker: &'hir rustc_hir::Expr<'hir>,
  ) -> &'hir rustc_hir::Expr<'hir> {
- let stmts = self.arena.alloc_from_iter(precond.into_iter());
+ let stmts = self
+ .arena
+ .alloc_from_iter(contract_decls.into_iter().map(|d| *d).chain(precond.into_iter()));
  let span = match precond {
  Some(precond) => precond.span,
  None => postcond_checker.span,

compiler/rustc_builtin_macros/src/contracts.rs

@@ -17,7 +17,7 @@ impl AttrProcMacro for ExpandRequires {
  annotation: TokenStream,
  annotated: TokenStream,
  ) -> Result<TokenStream, ErrorGuaranteed> {
- expand_requires_tts(ecx, span, annotation, annotated)
+ expand_contract_clause_tts(ecx, span, annotation, annotated, kw::ContractRequires)
  }
 }
 
@@ -29,7 +29,7 @@ impl AttrProcMacro for ExpandEnsures {
  annotation: TokenStream,
  annotated: TokenStream,
  ) -> Result<TokenStream, ErrorGuaranteed> {
- expand_ensures_tts(ecx, span, annotation, annotated)
+ expand_contract_clause_tts(ecx, span, annotation, annotated, kw::ContractEnsures)
  }
 }
 
@@ -130,42 +130,17 @@ fn expand_contract_clause(
  Ok(new_tts)
 }
 
-fn expand_requires_tts(
+fn expand_contract_clause_tts(
  ecx: &mut ExtCtxt<'_>,
  attr_span: Span,
  annotation: TokenStream,
  annotated: TokenStream,
+ clause_keyword: rustc_span::Symbol,
 ) -> Result<TokenStream, ErrorGuaranteed> {
  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, feature_span)),
- Spacing::Joint,
- ));
- new_tts.push_tree(TokenTree::Token(
- token::Token::new(token::TokenKind::OrOr, attr_span),
- Spacing::Alone,
- ));
- new_tts.push_tree(TokenTree::Delimited(
- DelimSpan::from_single(attr_span),
- DelimSpacing::new(Spacing::JointHidden, Spacing::JointHidden),
- token::Delimiter::Brace,
- annotation,
- ));
- Ok(())
- })
-}
-
-fn expand_ensures_tts(
- ecx: &mut ExtCtxt<'_>,
- attr_span: Span,
- annotation: TokenStream,
- annotated: TokenStream,
-) -> Result<TokenStream, ErrorGuaranteed> {
- 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, feature_span)),
+ token::Token::from_ast_ident(Ident::new(clause_keyword, feature_span)),
  Spacing::Joint,
  ));
  new_tts.push_tree(TokenTree::Delimited(

compiler/rustc_parse/src/parser/expr.rs

@@ -4036,6 +4036,30 @@ impl<'a> Parser<'a> {
  self.mk_expr(span, ExprKind::Err(guar))
  }
 
+ pub(crate) fn mk_unit_expr(&self, span: Span) -> Box<Expr> {
+ self.mk_expr(span, ExprKind::Tup(Default::default()))
+ }
+
+ pub(crate) fn mk_closure_expr(&self, span: Span, body: Box<Expr>) -> Box<Expr> {
+ self.mk_expr(
+ span,
+ ast::ExprKind::Closure(Box::new(ast::Closure {
+ binder: rustc_ast::ClosureBinder::NotPresent,
+ constness: rustc_ast::Const::No,
+ movability: rustc_ast::Movability::Movable,
+ capture_clause: rustc_ast::CaptureBy::Ref,
+ coroutine_kind: None,
+ fn_decl: Box::new(rustc_ast::FnDecl {
+ inputs: Default::default(),
+ output: rustc_ast::FnRetTy::Default(span),
+ }),
+ fn_arg_span: span,
+ fn_decl_span: span,
+ body,
+ })),
+ )
+ }
+
  /// Create expression span ensuring the span of the parent node
  /// is larger than the span of lhs and rhs, including the attributes.
  fn mk_expr_sp(&self, lhs: &Box<Expr>, lhs_span: Span, op_span: Span, rhs_span: Span) -> Span {

compiler/rustc_parse/src/parser/generics.rs

@@ -312,25 +312,48 @@ impl<'a> Parser<'a> {
  /// Parses an experimental fn contract
  /// (`contract_requires(WWW) contract_ensures(ZZZ)`)
  pub(super) fn parse_contract(&mut self) -> PResult<'a, Option<Box<ast::FnContract>>> {
- let requires = if self.eat_keyword_noexpect(exp!(ContractRequires).kw) {
+ let (declarations, requires) = self.parse_contract_requires()?;
+ let ensures = self.parse_contract_ensures()?;
+
+ if requires.is_none() && ensures.is_none() {
+ Ok(None)
+ } else {
+ Ok(Some(Box::new(ast::FnContract { declarations, requires, ensures })))
+ }
+ }
+
+ fn parse_contract_requires(
+ &mut self,
+ ) -> PResult<'a, (ThinVec<rustc_ast::Stmt>, Option<Box<rustc_ast::Expr>>)> {
+ Ok(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()?;
- Some(precond)
+ let mut decls_and_precond = self.parse_block()?;
+
+ let precond = match decls_and_precond.stmts.pop() {
+ Some(precond) => match precond.kind {
+ rustc_ast::StmtKind::Expr(expr) => expr,
+ // Insert dummy node that will be rejected by typechecker to
+ // avoid reinventing an error
+ _ => self.mk_unit_expr(decls_and_precond.span),
+ },
+ None => self.mk_unit_expr(decls_and_precond.span),
+ };
+ let precond = self.mk_closure_expr(precond.span, precond);
+ let decls = decls_and_precond.stmts;
+ (decls, Some(precond))
  } else {
- None
- };
- let ensures = if self.eat_keyword_noexpect(exp!(ContractEnsures).kw) {
+ (Default::default(), None)
+ })
+ }
+
+ fn parse_contract_ensures(&mut self) -> PResult<'a, Option<Box<rustc_ast::Expr>>> {
+ Ok(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()?;
  Some(postcond)
  } else {
  None
- };
- if requires.is_none() && ensures.is_none() {
- Ok(None)
- } else {
- Ok(Some(Box::new(ast::FnContract { requires, ensures })))
- }
+ })
  }
 
  /// Parses an optional where-clause.

tests/ui/contracts/contracts-disabled-side-effect-declarations.rs

@@ -0,0 +1,17 @@
+//@ run-pass
+#![feature(contracts)]
+//~^ WARN the feature `contracts` is incomplete and may not be safe to use and/or cause compiler crashes [incomplete_features]
+
+extern crate core;
+use core::contracts::requires;
+
+#[requires(*x = 0; true)]
+fn buggy_add(x: &mut u32, y: u32) {
+ *x = *x + y;
+}
+
+fn main() {
+ let mut x = 10;
+ buggy_add(&mut x, 100);
+ assert_eq!(x, 110);
+}

tests/ui/contracts/contracts-disabled-side-effect-declarations.stderr

@@ -0,0 +1,11 @@
+warning: the feature `contracts` is incomplete and may not be safe to use and/or cause compiler crashes
+ --> $DIR/contracts-disabled-side-effect-declarations.rs:2:12
+ |
+LL | #![feature(contracts)]
+ | ^^^^^^^^^
+ |
+ = note: see issue #128044 <https://github.com/rust-lang/rust/issues/128044> for more information
+ = note: `#[warn(incomplete_features)]` on by default
+
+warning: 1 warning emitted
+

tests/ui/contracts/contracts-disabled-side-effect-ensures.rs

@@ -5,7 +5,7 @@
 extern crate core;
 use core::contracts::ensures;
 
-#[ensures({*x = 0; |_ret| true})]
+#[ensures(*x = 0; |_ret| true)]
 fn buggy_add(x: &mut u32, y: u32) {
  *x = *x + y;
 }

tests/ui/contracts/declared-vars-referring-to-params.rs

@@ -0,0 +1,19 @@
+//@ run-pass
+//@ compile-flags: -Zcontract-checks=yes
+#![feature(contracts)]
+//~^ WARN the feature `contracts` is incomplete and may not be safe to use and/or cause compiler crashes [incomplete_features]
+
+extern crate core;
+use core::contracts::{ensures, requires};
+
+// checks that variable declarations are lowered properly, with the ability to
+// access function parameters
+#[requires(let y = 2 * x; true)]
+#[ensures(move |ret| { *ret == y })]
+fn foo(x: u32) -> u32 {
+ x * 2
+}
+
+fn main() {
+ foo(1);
+}

tests/ui/contracts/declared-vars-referring-to-params.stderr

@@ -0,0 +1,11 @@
+warning: the feature `contracts` is incomplete and may not be safe to use and/or cause compiler crashes
+ --> $DIR/declared-vars-referring-to-params.rs:3:12
+ |
+LL | #![feature(contracts)]
+ | ^^^^^^^^^
+ |
+ = note: see issue #128044 <https://github.com/rust-lang/rust/issues/128044> for more information
+ = note: `#[warn(incomplete_features)]` on by default
+
+warning: 1 warning emitted
+

tests/ui/contracts/declared-vars-used-in-ensures.rs

@@ -0,0 +1,17 @@
+//@ run-pass
+//@ compile-flags: -Zcontract-checks=yes
+#![feature(contracts)]
+//~^ WARN the feature `contracts` is incomplete and may not be safe to use and/or cause compiler crashes [incomplete_features]
+
+extern crate core;
+use core::contracts::{ensures, requires};
+
+#[requires(let y = 1; true)]
+#[ensures(move |_ret| { y == 1 })]
+fn foo(x: u32) -> u32 {
+ x * 2
+}
+
+fn main() {
+ foo(1);
+}

tests/ui/contracts/declared-vars-used-in-ensures.stderr

@@ -0,0 +1,11 @@
+warning: the feature `contracts` is incomplete and may not be safe to use and/or cause compiler crashes
+ --> $DIR/declared-vars-used-in-ensures.rs:3:12
+ |
+LL | #![feature(contracts)]
+ | ^^^^^^^^^
+ |
+ = note: see issue #128044 <https://github.com/rust-lang/rust/issues/128044> for more information
+ = note: `#[warn(incomplete_features)]` on by default
+
+warning: 1 warning emitted
+

tests/ui/contracts/declared-vars-used-in-requires-and-ensures.rs

@@ -0,0 +1,19 @@
+//@ run-pass
+//@ compile-flags: -Zcontract-checks=yes
+#![feature(contracts)]
+//~^ WARN the feature `contracts` is incomplete and may not be safe to use and/or cause compiler crashes [incomplete_features]
+
+extern crate core;
+use core::contracts::{ensures, requires};
+
+// checks that variable declarations are lowered properly, with the ability to
+// refer to them *both* in requires and ensures
+#[requires(let y = 2 * x; y > 0)]
+#[ensures(move |ret| { *ret == y })]
+fn foo(x: u32) -> u32 {
+ x * 2
+}
+
+fn main() {
+ foo(1);
+}