diff --git a/src/librustc_typeck/check/mod.rs b/src/librustc_typeck/check/mod.rs index ae0ed81ac77..59f3ac739e0 100644 --- a/src/librustc_typeck/check/mod.rs +++ b/src/librustc_typeck/check/mod.rs @@ -415,15 +415,16 @@ impl Diverges { } #[derive(Clone)] -pub struct BreakableCtxt<'gcx, 'tcx> { - unified: Ty<'tcx>, - coerce_to: Ty<'tcx>, - break_exprs: Vec<&'gcx hir::Expr>, +pub struct BreakableCtxt<'gcx: 'tcx, 'tcx> { may_break: bool, + + // this is `null` for loops where break with a value is illegal, + // such as `while`, `for`, and `while let` + coerce: Option>, } #[derive(Clone)] -pub struct EnclosingBreakables<'gcx, 'tcx> { +pub struct EnclosingBreakables<'gcx: 'tcx, 'tcx> { stack: Vec>, by_id: NodeMap, } @@ -3547,60 +3548,66 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> { tcx.mk_nil() } hir::ExprBreak(destination, ref expr_opt) => { - if let Some(target_id) = destination.target_id.opt_id() { - let coerce_to = { - let mut enclosing_breakables = self.enclosing_breakables.borrow_mut(); - enclosing_breakables.find_breakable(target_id).coerce_to - }; + if let Some(target_id) = destination.target_id.opt_id() { + let (e_ty, cause); + if let Some(ref e) = *expr_opt { + // If this is a break with a value, we need to type-check + // the expression. Get an expected type from the loop context. + let opt_coerce_to = { + let mut enclosing_breakables = self.enclosing_breakables.borrow_mut(); + enclosing_breakables.find_breakable(target_id) + .coerce + .as_ref() + .map(|coerce| coerce.expected_ty()) + }; - let e_ty; - let cause; - if let Some(ref e) = *expr_opt { - // Recurse without `enclosing_loops` borrowed. - e_ty = self.check_expr_with_hint(e, coerce_to); - cause = self.misc(e.span); - // Notably, the recursive call may alter coerce_to - must not keep using it! - } else { - // `break` without argument acts like `break ()`. - e_ty = tcx.mk_nil(); - cause = self.misc(expr.span); - } + // If the loop context is not a `loop { }`, then break with + // a value is illegal, and `opt_coerce_to` will be `None`. + // Just set expectation to error in that case. + let coerce_to = opt_coerce_to.unwrap_or(tcx.types.err); - let mut enclosing_breakables = self.enclosing_breakables.borrow_mut(); - let ctxt = enclosing_breakables.find_breakable(target_id); + // Recurse without `enclosing_breakables` borrowed. + e_ty = self.check_expr_with_hint(e, coerce_to); + cause = self.misc(e.span); + } else { + // Otherwise, this is a break *without* a value. That's + // always legal, and is equivalent to `break ()`. + e_ty = tcx.mk_nil(); + cause = self.misc(expr.span); + } - let result = if let Some(ref e) = *expr_opt { - // Special-case the first element, as it has no "previous expressions". - let result = if !ctxt.may_break { - self.try_coerce(e, e_ty, ctxt.coerce_to) - } else { - self.try_find_coercion_lub(&cause, || ctxt.break_exprs.iter().cloned(), - ctxt.unified, e, e_ty) - }; + // Now that we have type-checked `expr_opt`, borrow + // the `enclosing_loops` field and let's coerce the + // type of `expr_opt` into what is expected. + let mut enclosing_breakables = self.enclosing_breakables.borrow_mut(); + let ctxt = enclosing_breakables.find_breakable(target_id); + if let Some(ref mut coerce) = ctxt.coerce { + if let Some(ref e) = *expr_opt { + coerce.coerce(self, &cause, e, e_ty); + } else { + assert!(e_ty.is_nil()); + coerce.coerce_forced_unit(self, &cause); + } + } else { + // If `ctxt.coerce` is `None`, we can just ignore + // the type of the expresison. This is because + // either this was a break *without* a value, in + // which case it is always a legal type (`()`), or + // else an error would have been flagged by the + // `loops` pass for using break with an expression + // where you are not supposed to. + assert!(expr_opt.is_none() || self.tcx.sess.err_count() > 0); + } - ctxt.break_exprs.push(e); - result - } else { - self.eq_types(true, &cause, e_ty, ctxt.unified) - .map(|InferOk { obligations, .. }| { - // FIXME(#32730) propagate obligations - assert!(obligations.is_empty()); - e_ty - }) - }; - match result { - Ok(ty) => ctxt.unified = ty, - Err(err) => { - self.report_mismatched_types(&cause, ctxt.unified, e_ty, err).emit(); - } - } + ctxt.may_break = true; + } else { + // Otherwise, we failed to find the enclosing loop; this can only happen if the + // `break` was not inside a loop at all, which is caught by the loop-checking pass. + assert!(self.tcx.sess.err_count() > 0); + } - ctxt.may_break = true; - } - // Otherwise, we failed to find the enclosing breakable; this can only happen if the - // `break` target was not found, which is caught in HIR lowering and reported by the - // loop-checking pass. - tcx.types.never + // the type of a `break` is always `!`, since it diverges + tcx.types.never } hir::ExprAgain(_) => { tcx.types.never } hir::ExprRet(ref expr_opt) => { @@ -3645,51 +3652,59 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> { expr.span, expected) } hir::ExprWhile(ref cond, ref body, _) => { - let unified = self.tcx.mk_nil(); - let coerce_to = unified; - let ctxt = BreakableCtxt { - unified: unified, - coerce_to: coerce_to, - break_exprs: vec![], - may_break: true, - }; - self.with_breakable_ctxt(expr.id, ctxt, || { - self.check_expr_has_type(&cond, tcx.types.bool); - let cond_diverging = self.diverges.get(); - self.check_block_no_value(&body); + let ctxt = BreakableCtxt { + // cannot use break with a value from a while loop + coerce: None, + may_break: true, + }; - // We may never reach the body so it diverging means nothing. - self.diverges.set(cond_diverging); - }); + self.with_breakable_ctxt(expr.id, ctxt, || { + self.check_expr_has_type(&cond, tcx.types.bool); + let cond_diverging = self.diverges.get(); + self.check_block_no_value(&body); - if self.has_errors.get() { - tcx.types.err - } else { - tcx.mk_nil() - } + // We may never reach the body so it diverging means nothing. + self.diverges.set(cond_diverging); + }); + + self.tcx.mk_nil() } - hir::ExprLoop(ref body, _, _) => { - let unified = self.next_ty_var(TypeVariableOrigin::TypeInference(body.span)); - let coerce_to = expected.only_has_type(self).unwrap_or(unified); - let ctxt = BreakableCtxt { - unified: unified, - coerce_to: coerce_to, - break_exprs: vec![], - may_break: false, - }; + hir::ExprLoop(ref body, _, source) => { + let coerce = match source { + // you can only use break with a value from a normal `loop { }` + hir::LoopSource::Loop => { + let coerce_to = expected.only_has_type_or_fresh_var(self, body.span); + Some(CoerceMany::new(coerce_to)) + } - let (ctxt, ()) = self.with_breakable_ctxt(expr.id, ctxt, || { - self.check_block_no_value(&body); - }); - if ctxt.may_break { - // No way to know whether it's diverging because - // of a `break` or an outer `break` or `return. - self.diverges.set(Diverges::Maybe); + hir::LoopSource::WhileLet | + hir::LoopSource::ForLoop => { + None + } + }; - ctxt.unified - } else { - tcx.types.never - } + let ctxt = BreakableCtxt { + coerce: coerce, + may_break: false, // will get updated if/when we find a `break` + }; + + let (ctxt, ()) = self.with_breakable_ctxt(expr.id, ctxt, || { + self.check_block_no_value(&body); + }); + + if ctxt.may_break { + // No way to know whether it's diverging because + // of a `break` or an outer `break` or `return. + self.diverges.set(Diverges::Maybe); + } + + // If we permit break with a value, then result type is + // the LUB of the breaks (possibly ! if none); else, it + // is nil. This makes sense because infinite loops + // (which would have type !) are only possible iff we + // permit break with a value [1]. + assert!(ctxt.coerce.is_some() || ctxt.may_break); // [1] + ctxt.coerce.map(|c| c.complete(self)).unwrap_or(self.tcx.mk_nil()) } hir::ExprMatch(ref discrim, ref arms, match_src) => { self.check_match(expr, &discrim, arms, expected, match_src) diff --git a/src/test/compile-fail/issue-27042.rs b/src/test/compile-fail/issue-27042.rs index f31389f1337..23afa4b6296 100644 --- a/src/test/compile-fail/issue-27042.rs +++ b/src/test/compile-fail/issue-27042.rs @@ -12,14 +12,14 @@ fn main() { let _: i32 = - 'a: //~ ERROR mismatched types - loop { break }; + 'a: // in this case, the citation is just the `break`: + loop { break }; //~ ERROR mismatched types let _: i32 = 'b: //~ ERROR mismatched types - while true { break }; + while true { break }; // but here we cite the whole loop let _: i32 = 'c: //~ ERROR mismatched types - for _ in None { break }; + for _ in None { break }; // but here we cite the whole loop let _: i32 = 'd: //~ ERROR mismatched types while let Some(_) = None { break }; diff --git a/src/test/compile-fail/loop-break-value.rs b/src/test/compile-fail/loop-break-value.rs index d4f29597486..a4143218992 100644 --- a/src/test/compile-fail/loop-break-value.rs +++ b/src/test/compile-fail/loop-break-value.rs @@ -40,37 +40,40 @@ fn main() { loop { break 'while_loop 123; //~^ ERROR `break` with value from a `while` loop - //~| ERROR mismatched types break 456; break 789; }; } - 'while_let_loop: while let Some(_) = Some(()) { + while let Some(_) = Some(()) { if break () { //~ ERROR `break` with value from a `while let` loop - break; - break None; - //~^ ERROR `break` with value from a `while let` loop - //~| ERROR mismatched types } + } + + while let Some(_) = Some(()) { + break None; + //~^ ERROR `break` with value from a `while let` loop + } + + 'while_let_loop: while let Some(_) = Some(()) { loop { break 'while_let_loop "nope"; //~^ ERROR `break` with value from a `while let` loop - //~| ERROR mismatched types break 33; }; } - 'for_loop: for _ in &[1,2,3] { + for _ in &[1,2,3] { break (); //~ ERROR `break` with value from a `for` loop break [()]; //~^ ERROR `break` with value from a `for` loop - //~| ERROR mismatched types + } + + 'for_loop: for _ in &[1,2,3] { loop { break Some(3); break 'for_loop Some(17); //~^ ERROR `break` with value from a `for` loop - //~| ERROR mismatched types }; } diff --git a/src/test/ui/loop-break-value-no-repeat.rs b/src/test/ui/loop-break-value-no-repeat.rs new file mode 100644 index 00000000000..790f796fae0 --- /dev/null +++ b/src/test/ui/loop-break-value-no-repeat.rs @@ -0,0 +1,25 @@ +// Copyright 2016 The Rust Project Developers. See the COPYRIGHT +// file at the top-level directory of this distribution and at +// http://rust-lang.org/COPYRIGHT. +// +// Licensed under the Apache License, Version 2.0 or the MIT license +// , at your +// option. This file may not be copied, modified, or distributed +// except according to those terms. + +#![feature(loop_break_value)] +#![allow(unused_variables)] + +use std::ptr; + +// Test that we only report **one** error here and that is that +// `break` with an expression is illegal in this context. In +// particular, we don't report any mismatched types error, which is +// besides the point. + +fn main() { + for _ in &[1,2,3] { + break 22 + } +} diff --git a/src/test/ui/loop-break-value-no-repeat.stderr b/src/test/ui/loop-break-value-no-repeat.stderr new file mode 100644 index 00000000000..0d99abd3907 --- /dev/null +++ b/src/test/ui/loop-break-value-no-repeat.stderr @@ -0,0 +1,8 @@ +error[E0571]: `break` with value from a `for` loop + --> $DIR/loop-break-value-no-repeat.rs:23:9 + | +23 | break 22 + | ^^^^^^^^ can only break with a value inside `loop` + +error: aborting due to previous error +