Auto merge of rust-lang#5622 - elichai:2020-05-match_wild_err_arm, r=flip1995

Downgrade `match_wild_err_arm` to pedantic and update help messages

Hi,
This fixes rust-lang#3688 and downgrades `match_wild_err_arm` to pedantic.
There are a lot of different reasons in that issue, for me the biggest are:
1. Rust's errors aren't like Java's exceptions because they're type safe and in most cases the type of error can't change by itself.
2. Sometimes matching can be more ergonomic, and before the `track_caller` feature got introduced it was actually easier to track the panic location with explicit `panic!` than with `expect`.

Currently clippy is failing to build because of a breaking change in rust-lang#69171 I tried fixing it but it is too complex for my little knowledge of clippy and rustc so I'll leave that to people who know what they're doing :)

Another thing, if rustc is breaking clippy a lot then maybe it's better to use something like `miri` does, where it's hard codes the latest tested rustc commit and they keep bumping it, that way when you develop locally it should work even if there was a breaking change (https://github.com/rust-lang/miri/blob/master/rustup-toolchain#L23-L29)

changelog: Downgrade `match_wild_err_arm` to pedantic

Author: bors

clippy_lints/src/lib.rs

@@ -1141,6 +1141,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
         LintId::of(&match_on_vec_items::MATCH_ON_VEC_ITEMS),
         LintId::of(&matches::MATCH_BOOL),
         LintId::of(&matches::MATCH_WILDCARD_FOR_SINGLE_VARIANTS),
+        LintId::of(&matches::MATCH_WILD_ERR_ARM),
         LintId::of(&matches::SINGLE_MATCH_ELSE),
         LintId::of(&methods::FILTER_MAP),
         LintId::of(&methods::FILTER_MAP_NEXT),
@@ -1285,7 +1286,6 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
         LintId::of(&matches::MATCH_OVERLAPPING_ARM),
         LintId::of(&matches::MATCH_REF_PATS),
         LintId::of(&matches::MATCH_SINGLE_BINDING),
-        LintId::of(&matches::MATCH_WILD_ERR_ARM),
         LintId::of(&matches::SINGLE_MATCH),
         LintId::of(&matches::WILDCARD_IN_OR_PATTERNS),
         LintId::of(&mem_discriminant::MEM_DISCRIMINANT_NON_ENUM),
@@ -1476,7 +1476,6 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
         LintId::of(&matches::INFALLIBLE_DESTRUCTURING_MATCH),
         LintId::of(&matches::MATCH_OVERLAPPING_ARM),
         LintId::of(&matches::MATCH_REF_PATS),
-        LintId::of(&matches::MATCH_WILD_ERR_ARM),
         LintId::of(&matches::SINGLE_MATCH),
         LintId::of(&mem_replace::MEM_REPLACE_OPTION_WITH_NONE),
         LintId::of(&mem_replace::MEM_REPLACE_WITH_DEFAULT),

clippy_lints/src/matches.rs

@@ -168,7 +168,7 @@ declare_clippy_lint! {
     /// **What it does:** Checks for arm which matches all errors with `Err(_)`
     /// and take drastic actions like `panic!`.
     ///
-    /// **Why is this bad?** It is generally a bad practice, just like
+    /// **Why is this bad?** It is generally a bad practice, similar to
     /// catching all exceptions in java with `catch(Exception)`
     ///
     /// **Known problems:** None.
@@ -182,7 +182,7 @@ declare_clippy_lint! {
     /// }
     /// ```
     pub MATCH_WILD_ERR_ARM,
-    style,
+    pedantic,
     "a `match` with `Err(_)` arm and take drastic actions"
 }
 
@@ -711,7 +711,7 @@ fn check_wild_err_arm(cx: &LateContext<'_, '_>, ex: &Expr<'_>, arms: &[Arm<'_>])
                                 arm.pat.span,
                                 &format!("`Err({})` matches all errors", &ident_bind_name),
                                 None,
-                                "match each error separately or use the error output",
+                                "match each error separately or use the error output, or use `.except(msg)` if the error case is unreachable",
                             );
                         }
                     }

src/lintlist/mod.rs

@@ -1195,7 +1195,7 @@ pub static ref ALL_LINTS: Vec<Lint> = vec![
     },
     Lint {
         name: "match_wild_err_arm",
-        group: "style",
+        group: "pedantic",
         desc: "a `match` with `Err(_)` arm and take drastic actions",
         deprecation: None,
         module: "matches",

tests/ui/future_not_send.stderr

@@ -47,17 +47,32 @@ error: future cannot be sent between threads safely
   --> $DIR/future_not_send.rs:20:63
    |
 LL | async fn private_future2(rc: Rc<[u8]>, cell: &Cell<usize>) -> bool {
-   |                                                               ^^^^
+   |                                                               ^^^^ future returned by `private_future2` is not `Send`
    |
+note: captured value is not `Send`
+  --> $DIR/future_not_send.rs:20:26
+   |
+LL | async fn private_future2(rc: Rc<[u8]>, cell: &Cell<usize>) -> bool {
+   |                          ^^ has type `std::rc::Rc<[u8]>` which is not `Send`
    = note: `std::rc::Rc<[u8]>` doesn't implement `std::marker::Send`
+note: captured value is not `Send`
+  --> $DIR/future_not_send.rs:20:40
+   |
+LL | async fn private_future2(rc: Rc<[u8]>, cell: &Cell<usize>) -> bool {
+   |                                        ^^^^ has type `&std::cell::Cell<usize>` which is not `Send`
    = note: `std::cell::Cell<usize>` doesn't implement `std::marker::Sync`
 
 error: future cannot be sent between threads safely
   --> $DIR/future_not_send.rs:24:43
    |
 LL | pub async fn public_future2(rc: Rc<[u8]>) {}
-   |                                           ^
+   |                                           ^ future returned by `public_future2` is not `Send`
    |
+note: captured value is not `Send`
+  --> $DIR/future_not_send.rs:24:29
+   |
+LL | pub async fn public_future2(rc: Rc<[u8]>) {}
+   |                             ^^ has type `std::rc::Rc<[u8]>` which is not `Send`
    = note: `std::rc::Rc<[u8]>` doesn't implement `std::marker::Send`
 
 error: future cannot be sent between threads safely
@@ -117,8 +132,13 @@ error: future cannot be sent between threads safely
   --> $DIR/future_not_send.rs:66:34
    |
 LL | async fn unclear_future<T>(t: T) {}
-   |                                  ^
+   |                                  ^ future returned by `unclear_future` is not `Send`
    |
+note: captured value is not `Send`
+  --> $DIR/future_not_send.rs:66:28
+   |
+LL | async fn unclear_future<T>(t: T) {}
+   |                            ^ has type `T` which is not `Send`
    = note: `T` doesn't implement `std::marker::Send`
 
 error: aborting due to 8 previous errors

tests/ui/match_wild_err_arm.stderr

@@ -5,31 +5,31 @@ LL |         Err(_) => panic!("err"),
    |         ^^^^^^
    |
    = note: `-D clippy::match-wild-err-arm` implied by `-D warnings`
-   = note: match each error separately or use the error output
+   = note: match each error separately or use the error output, or use `.except(msg)` if the error case is unreachable
 
 error: `Err(_)` matches all errors
   --> $DIR/match_wild_err_arm.rs:17:9
    |
 LL |         Err(_) => panic!(),
    |         ^^^^^^
    |
-   = note: match each error separately or use the error output
+   = note: match each error separately or use the error output, or use `.except(msg)` if the error case is unreachable
 
 error: `Err(_)` matches all errors
   --> $DIR/match_wild_err_arm.rs:23:9
    |
 LL |         Err(_) => {
    |         ^^^^^^
    |
-   = note: match each error separately or use the error output
+   = note: match each error separately or use the error output, or use `.except(msg)` if the error case is unreachable
 
 error: `Err(_e)` matches all errors
   --> $DIR/match_wild_err_arm.rs:31:9
    |
 LL |         Err(_e) => panic!(),
    |         ^^^^^^^
    |
-   = note: match each error separately or use the error output
+   = note: match each error separately or use the error output, or use `.except(msg)` if the error case is unreachable
 
 error: aborting due to 4 previous errors