From fe09dbfcba0ba812d671f2c255a986bbabdd878d Mon Sep 17 00:00:00 2001 From: varkor Date: Tue, 16 Oct 2018 14:56:39 +0100 Subject: [PATCH 1/3] Allow explicit matches on ! without warning --- src/librustc_typeck/check/_match.rs | 5 ----- .../ui/unreachable/unwarned-match-on-never.rs | 18 +++++++++++++++ .../unwarned-match-on-never.stderr | 22 +++++++++++++++++++ 3 files changed, 40 insertions(+), 5 deletions(-) create mode 100644 src/test/ui/unreachable/unwarned-match-on-never.rs create mode 100644 src/test/ui/unreachable/unwarned-match-on-never.stderr diff --git a/src/librustc_typeck/check/_match.rs b/src/librustc_typeck/check/_match.rs index c9158af178f..b4c969447de 100644 --- a/src/librustc_typeck/check/_match.rs +++ b/src/librustc_typeck/check/_match.rs @@ -608,10 +608,6 @@ https://doc.rust-lang.org/reference/types.html#trait-objects"); self.check_expr_has_type_or_error(discrim, discrim_ty); }; - // If the discriminant diverges, the match is pointless (e.g., - // `match (return) { }`). - self.warn_if_unreachable(expr.id, expr.span, "expression"); - // If there are no arms, that is a diverging match; a special case. if arms.is_empty() { self.diverges.set(self.diverges.get() | Diverges::Always); @@ -620,7 +616,6 @@ https://doc.rust-lang.org/reference/types.html#trait-objects"); // Otherwise, we have to union together the types that the // arms produce and so forth. - let discrim_diverges = self.diverges.get(); self.diverges.set(Diverges::Maybe); diff --git a/src/test/ui/unreachable/unwarned-match-on-never.rs b/src/test/ui/unreachable/unwarned-match-on-never.rs new file mode 100644 index 00000000000..0c160615c8b --- /dev/null +++ b/src/test/ui/unreachable/unwarned-match-on-never.rs @@ -0,0 +1,18 @@ +#![deny(unreachable_code)] +#![allow(dead_code)] + +#![feature(never_type)] + +fn foo(x: !) -> bool { + // Explicit matches on the never type are unwarned. + match x {} + // But matches in unreachable code are warned. + match x {} //~ ERROR: unreachable expression +} + +fn main() { + return; + match () { //~ ERROR: unreachable expression + () => (), + } +} diff --git a/src/test/ui/unreachable/unwarned-match-on-never.stderr b/src/test/ui/unreachable/unwarned-match-on-never.stderr new file mode 100644 index 00000000000..969c24a07e8 --- /dev/null +++ b/src/test/ui/unreachable/unwarned-match-on-never.stderr @@ -0,0 +1,22 @@ +error: unreachable expression + --> $DIR/unwarned-match-on-never.rs:10:5 + | +LL | match x {} //~ ERROR: unreachable expression + | ^^^^^^^^^^ + | +note: lint level defined here + --> $DIR/unwarned-match-on-never.rs:1:9 + | +LL | #![deny(unreachable_code)] + | ^^^^^^^^^^^^^^^^ + +error: unreachable expression + --> $DIR/unwarned-match-on-never.rs:15:5 + | +LL | / match () { //~ ERROR: unreachable expression +LL | | () => (), +LL | | } + | |_____^ + +error: aborting due to 2 previous errors + From 0982be77107f9af614adb609ee6eb1c5730d8eab Mon Sep 17 00:00:00 2001 From: varkor Date: Tue, 16 Oct 2018 18:04:07 +0100 Subject: [PATCH 2/3] Remove outdated test --- ...eachable-warning-with-diverging-discrim.rs | 16 -------------- ...able-warning-with-diverging-discrim.stderr | 14 ------------- src/test/ui/reachable/expr_match.rs | 6 ------ src/test/ui/reachable/expr_match.stderr | 21 +++++++------------ 4 files changed, 7 insertions(+), 50 deletions(-) delete mode 100644 src/test/ui/match/match-unreachable-warning-with-diverging-discrim.rs delete mode 100644 src/test/ui/match/match-unreachable-warning-with-diverging-discrim.stderr diff --git a/src/test/ui/match/match-unreachable-warning-with-diverging-discrim.rs b/src/test/ui/match/match-unreachable-warning-with-diverging-discrim.rs deleted file mode 100644 index aae0f3135d8..00000000000 --- a/src/test/ui/match/match-unreachable-warning-with-diverging-discrim.rs +++ /dev/null @@ -1,16 +0,0 @@ -// 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. - -#![allow(unused_parens)] -#![deny(unreachable_code)] - -fn main() { - match (return) { } //~ ERROR unreachable expression -} diff --git a/src/test/ui/match/match-unreachable-warning-with-diverging-discrim.stderr b/src/test/ui/match/match-unreachable-warning-with-diverging-discrim.stderr deleted file mode 100644 index 10a86f92fe1..00000000000 --- a/src/test/ui/match/match-unreachable-warning-with-diverging-discrim.stderr +++ /dev/null @@ -1,14 +0,0 @@ -error: unreachable expression - --> $DIR/match-unreachable-warning-with-diverging-discrim.rs:15:5 - | -LL | match (return) { } //~ ERROR unreachable expression - | ^^^^^^^^^^^^^^^^^^ - | -note: lint level defined here - --> $DIR/match-unreachable-warning-with-diverging-discrim.rs:12:9 - | -LL | #![deny(unreachable_code)] - | ^^^^^^^^^^^^^^^^ - -error: aborting due to previous error - diff --git a/src/test/ui/reachable/expr_match.rs b/src/test/ui/reachable/expr_match.rs index 2faa262d110..73f26129805 100644 --- a/src/test/ui/reachable/expr_match.rs +++ b/src/test/ui/reachable/expr_match.rs @@ -13,12 +13,6 @@ #![allow(dead_code)] #![deny(unreachable_code)] -fn a() { - // The match is considered unreachable here, because the `return` - // diverges: - match {return} { } //~ ERROR unreachable -} - fn b() { match () { () => return } println!("I am dead"); diff --git a/src/test/ui/reachable/expr_match.stderr b/src/test/ui/reachable/expr_match.stderr index 240341232d8..fe1a0c4ea11 100644 --- a/src/test/ui/reachable/expr_match.stderr +++ b/src/test/ui/reachable/expr_match.stderr @@ -1,30 +1,23 @@ -error: unreachable expression - --> $DIR/expr_match.rs:19:5 +error: unreachable statement + --> $DIR/expr_match.rs:18:5 | -LL | match {return} { } //~ ERROR unreachable - | ^^^^^^^^^^^^^^^^^^ +LL | println!("I am dead"); + | ^^^^^^^^^^^^^^^^^^^^^^ | note: lint level defined here --> $DIR/expr_match.rs:14:9 | LL | #![deny(unreachable_code)] | ^^^^^^^^^^^^^^^^ + = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info) error: unreachable statement - --> $DIR/expr_match.rs:24:5 + --> $DIR/expr_match.rs:29:5 | LL | println!("I am dead"); | ^^^^^^^^^^^^^^^^^^^^^^ | = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info) -error: unreachable statement - --> $DIR/expr_match.rs:35:5 - | -LL | println!("I am dead"); - | ^^^^^^^^^^^^^^^^^^^^^^ - | - = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info) - -error: aborting due to 3 previous errors +error: aborting due to 2 previous errors From 26346467c52e34c730f3e924be7d635d69b4f737 Mon Sep 17 00:00:00 2001 From: varkor Date: Thu, 18 Oct 2018 00:05:19 +0100 Subject: [PATCH 3/3] Warning about unreachable arms after matching on a diverging type --- src/librustc_typeck/check/_match.rs | 6 ++++++ .../ui/unreachable/unwarned-match-on-never.rs | 10 ++++++++-- .../unreachable/unwarned-match-on-never.stderr | 16 +++++++++++----- 3 files changed, 25 insertions(+), 7 deletions(-) diff --git a/src/librustc_typeck/check/_match.rs b/src/librustc_typeck/check/_match.rs index b4c969447de..eaaf9f77430 100644 --- a/src/librustc_typeck/check/_match.rs +++ b/src/librustc_typeck/check/_match.rs @@ -614,6 +614,12 @@ https://doc.rust-lang.org/reference/types.html#trait-objects"); return tcx.types.never; } + if self.diverges.get().always() { + for arm in arms { + self.warn_if_unreachable(arm.body.id, arm.body.span, "arm"); + } + } + // Otherwise, we have to union together the types that the // arms produce and so forth. let discrim_diverges = self.diverges.get(); diff --git a/src/test/ui/unreachable/unwarned-match-on-never.rs b/src/test/ui/unreachable/unwarned-match-on-never.rs index 0c160615c8b..71f8fe3a783 100644 --- a/src/test/ui/unreachable/unwarned-match-on-never.rs +++ b/src/test/ui/unreachable/unwarned-match-on-never.rs @@ -7,12 +7,18 @@ fn foo(x: !) -> bool { // Explicit matches on the never type are unwarned. match x {} // But matches in unreachable code are warned. - match x {} //~ ERROR: unreachable expression + match x {} //~ ERROR unreachable expression +} + +fn bar() { + match (return) { + () => () //~ ERROR unreachable arm + } } fn main() { return; - match () { //~ ERROR: unreachable expression + match () { //~ ERROR unreachable expression () => (), } } diff --git a/src/test/ui/unreachable/unwarned-match-on-never.stderr b/src/test/ui/unreachable/unwarned-match-on-never.stderr index 969c24a07e8..8807e5f04e5 100644 --- a/src/test/ui/unreachable/unwarned-match-on-never.stderr +++ b/src/test/ui/unreachable/unwarned-match-on-never.stderr @@ -1,7 +1,7 @@ error: unreachable expression --> $DIR/unwarned-match-on-never.rs:10:5 | -LL | match x {} //~ ERROR: unreachable expression +LL | match x {} //~ ERROR unreachable expression | ^^^^^^^^^^ | note: lint level defined here @@ -10,13 +10,19 @@ note: lint level defined here LL | #![deny(unreachable_code)] | ^^^^^^^^^^^^^^^^ -error: unreachable expression - --> $DIR/unwarned-match-on-never.rs:15:5 +error: unreachable arm + --> $DIR/unwarned-match-on-never.rs:15:15 | -LL | / match () { //~ ERROR: unreachable expression +LL | () => () //~ ERROR unreachable arm + | ^^ + +error: unreachable expression + --> $DIR/unwarned-match-on-never.rs:21:5 + | +LL | / match () { //~ ERROR unreachable expression LL | | () => (), LL | | } | |_____^ -error: aborting due to 2 previous errors +error: aborting due to 3 previous errors