auto merge of #19870 : mdinger/rust/align_error, r=nick29581

#### Updated 1/12/2014

I updated the multi-line testcase to current but didn't modify the others. The spew code was broke by the `matches!` macro no longer working and I'm not interested in fixing the testcase.

I additionally added one testcase below.

Errors will in general look similar to below if the error is either `mismatched types` or a few other types. The rest are ignored.

---

#### Extra testcase:
```rust
pub trait Foo {
    type A;
    fn boo(&self) -> <Self as Foo>::A;
}

struct Bar;

impl Foo for i32 {
    type A = u32;
    fn boo(&self) -> u32 {
        42
    }
}

fn foo1<I: Foo<A=Bar>>(x: I) {
    let _: Bar = x.boo();
}

fn foo2<I: Foo>(x: I) {
    let _: Bar = x.boo();
}


pub fn baz(x: &Foo<A=Bar>) {
    let _: Bar = x.boo();
}


pub fn main() {
    let a = 42i32;
    foo1(a);
    baz(&a);
}
```

#### Multi-line output:
```cmd
$ ./rustc test3.rs
test3.rs:20:18: 20:25 error: mismatched types:
 expected `Bar`,
    found `<I as Foo>::A`
(expected struct `Bar`,
    found associated type)
test3.rs:20     let _: Bar = x.boo();
                             ^~~~~~~
test3.rs:31:5: 31:9 error: type mismatch resolving `<i32 as Foo>::A == Bar`:
 expected u32,
    found struct `Bar`
test3.rs:31     foo1(a);
                ^~~~
test3.rs:31:5: 31:9 note: required by `foo1`
test3.rs:31     foo1(a);
                ^~~~
test3.rs:32:9: 32:11 error: type mismatch resolving `<i32 as Foo>::A == Bar`:
 expected u32,
    found struct `Bar`
test3.rs:32     baz(&a);
                    ^~
test3.rs:32:9: 32:11 note: required for the cast to the object type `Foo`
test3.rs:32     baz(&a);
                    ^~
error: aborting due to 3 previous errors
```

---

This is a continuation of #19203 which I apparently broke by force pushing after it was closed. I'm attempting to add multi-line errors where they are largely beneficial - to help differentiate different types in compiler messages. As before, this is still a simple fix.

#### Testcase:
```rust
struct S;

fn test() -> Option<i32> {
    let s: S;

    s
}

fn test2() -> Option<i32> {
    Ok(7) // Should be Some(7)
}

impl Iterator for S {
    type Item = i32;
    fn next(&mut self) -> Result<i32, i32> { Ok(7) }
}

fn main(){ 
    test();
    test2();

}
```

---

#### Single-line playpen errors:
```cmd
<anon>:6:5: 6:6 error: mismatched types: expected `core::option::Option<int>`, found `S` (expected enum core::option::Option, found struct S)
<anon>:6     s
             ^
<anon>:10:5: 10:10 error: mismatched types: expected `core::option::Option<int>`, found `core::result::Result<_, _>` (expected enum core::option::Option, found enum core::result::Result)
<anon>:10     Ok(7) // Should be Some(7)
              ^~~~~
<anon>:14:5: 14:55 error: method `next` has an incompatible type for trait: expected enum core::option::Option, found enum core::result::Result [E0053]
<anon>:14     fn next(&mut self) -> Result<uint, uint> { Ok(7) }
              ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
error: aborting due to 3 previous errors
playpen: application terminated with error code 101
```

---

#### Multi-line errors:
```cmd
$ ./rustc test.rs
test.rs:6:5: 6:6 error: mismatched types:
 expected `core::option::Option<i32>`,
    found `S`
(expected enum `core::option::Option`,
    found struct `S`)
test.rs:6     s
              ^
test.rs:10:5: 10:10 error: mismatched types:
 expected `core::option::Option<i32>`,
    found `core::result::Result<_, _>`
(expected enum `core::option::Option`,
    found enum `core::result::Result`)
test.rs:10     Ok(7) // Should be Some(7)
               ^~~~~
test.rs:15:5: 15:53 error: method `next` has an incompatible type for trait: expected enum `core::option::Option`, found enum `core::result::Result` [E0053]
test.rs:15     fn next(&mut self) -> Result<i32, i32> { Ok(7) }
               ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
error: aborting due to 3 previous errors
```

---

#### Positive notes
* Vim worked fine with it: #19203 (comment)
* `make check` didn't find any errors
* Fixed *backtick* placement suggested by @p1start at #19203 (comment)

#### Negative notes
* Didn't check Emacs support but also wasn't provided a testcase...
* Needs to be tested with macro errors but I don't have a good testcase yet
* I would like to move the `E[0053]` earlier (see #19464 (comment)) but I don't know how
* It might be better to indent the types slightly like so (but I don't know how):
```cmd
test.rs:6:5: 6:6 error: mismatched types:
          expected `core::option::Option<int>`,
             found `S`
         (expected enum `core::option::Option`,
             found struct `S`)
test.rs:6     s
```
* Deep whitespace indentation may be a bad idea because early wrapping will cause misalignment between lines

#### Other
* I thought that compiler flags or something else (environment variables maybe) might be required because of comments against it but now that seems too much of a burden for users and for too little gain.
* There was concern that it will make large quantities of errors difficult to distinguish but I don't find that an issue. They both look awful and multi-line errors makes the types easier to understand.

---

#### Single lined spew:
```cmd
$ rustc test2.rs 
test2.rs:161:9: 170:10 error: method `next` has an incompatible type for trait: expected enum core::option::Option, found enum core::result::Result [E0053]
test2.rs:161         fn next(&mut self) -> Result<&'a str, int> {
test2.rs:162             self.curr = self.next;
test2.rs:163             
test2.rs:164             if let (Some(open), Some(close)) = Parens::find_parens(self.all, self.next) {
test2.rs:165                 self.next = if self.all.char_at(self.next) == '(' { close }
test2.rs:166                 else { open }
             ...
test2.rs:164:21: 164:31 error: mismatched types: expected `core::result::Result<uint, int>`, found `core::option::Option<_>` (expected enum core::result::Result, found enum core::option::Option)
test2.rs:164             if let (Some(open), Some(close)) = Parens::find_parens(self.all, self.next) {
                                 ^~~~~~~~~~
test2.rs:164:33: 164:44 error: mismatched types: expected `core::result::Result<uint, int>`, found `core::option::Option<_>` (expected enum core::result::Result, found enum core::option::Option)
test2.rs:164             if let (Some(open), Some(close)) = Parens::find_parens(self.all, self.next) {
                                             ^~~~~~~~~~~
test2.rs:169:40: 169:76 error: mismatched types: expected `core::result::Result<&'a str, int>`, found `core::option::Option<&str>` (expected enum core::result::Result, found enum core::option::Option)
test2.rs:169             if self.curr != self.len { Some(self.all[self.curr..self.next]) } else { None }
                                                    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
test2.rs:169:86: 169:90 error: mismatched types: expected `core::result::Result<&'a str, int>`, found `core::option::Option<_>` (expected enum core::result::Result, found enum core::option::Option)
test2.rs:169             if self.curr != self.len { Some(self.all[self.curr..self.next]) } else { None }
                                                                                                  ^~~~
test2.rs:205:14: 205:18 error: mismatched types: expected `core::result::Result<uint, int>`, found `core::option::Option<uint>` (expected enum core::result::Result, found enum core::option::Option)
test2.rs:205             (open, close)
                          ^~~~
test2.rs:205:20: 205:25 error: mismatched types: expected `core::result::Result<uint, int>`, found `core::option::Option<uint>` (expected enum core::result::Result, found enum core::option::Option)
test2.rs:205             (open, close)
                                ^~~~~
test2.rs:210:21: 210:31 error: mismatched types: expected `core::result::Result<uint, int>`, found `core::option::Option<_>` (expected enum core::result::Result, found enum core::option::Option)
test2.rs:210             if let (Some(open), _) = Parens::find_parens(self.all, 0) {
                                 ^~~~~~~~~~
test2.rs:210:13: 212:28 error: mismatched types: expected `core::option::Option<&'a int>`, found `core::option::Option<&str>` (expected int, found str)
test2.rs:210             if let (Some(open), _) = Parens::find_parens(self.all, 0) {
test2.rs:211                 Some(self.all[0..open])
test2.rs:212             } else { None }
test2.rs:299:48: 299:58 error: mismatched types: expected `Box<translate::Entity>`, found `collections::vec::Vec<_>` (expected box, found struct collections::vec::Vec)
test2.rs:299         pub fn new() -> Entity { Entity::Group(Vec::new()) }
                                                            ^~~~~~~~~~
test2.rs:359:51: 359:58 error: type `&mut Box<translate::Entity>` does not implement any method in scope named `push`
test2.rs:359                 Entity::Group(ref mut vec) => vec.push(e),
                                                               ^~~~~~~
test2.rs:366:51: 366:85 error: type `&mut Box<translate::Entity>` does not implement any method in scope named `push`
test2.rs:366                 Entity::Group(ref mut vec) => vec.push(Entity::Inner(s.to_string())),
                                                               ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
error: aborting due to 12 previous errors
```

---

#### Multi-line spew:

```cmd
$ ./rustc test2.rs 
test2.rs:161:9: 170:10 error: method `next` has an incompatible type for trait:
 expected enum `core::option::Option`,
    found enum `core::result::Result` [E0053]
test2.rs:161         fn next(&mut self) -> Result<&'a str, int> {
test2.rs:162             self.curr = self.next;
test2.rs:163             
test2.rs:164             if let (Some(open), Some(close)) = Parens::find_parens(self.all, self.next) {
test2.rs:165                 self.next = if self.all.char_at(self.next) == '(' { close }
test2.rs:166                 else { open }
             ...
test2.rs:164:21: 164:31 error: mismatched types:
 expected `core::result::Result<uint, int>`,
    found `core::option::Option<_>`
(expected enum `core::result::Result`,
    found enum `core::option::Option`)
test2.rs:164             if let (Some(open), Some(close)) = Parens::find_parens(self.all, self.next) {
                                 ^~~~~~~~~~
test2.rs:164:33: 164:44 error: mismatched types:
 expected `core::result::Result<uint, int>`,
    found `core::option::Option<_>`
(expected enum `core::result::Result`,
    found enum `core::option::Option`)
test2.rs:164             if let (Some(open), Some(close)) = Parens::find_parens(self.all, self.next) {
                                             ^~~~~~~~~~~
test2.rs:169:40: 169:76 error: mismatched types:
 expected `core::result::Result<&'a str, int>`,
    found `core::option::Option<&str>`
(expected enum `core::result::Result`,
    found enum `core::option::Option`)
test2.rs:169             if self.curr != self.len { Some(self.all[self.curr..self.next]) } else { None }
                                                    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
test2.rs:169:86: 169:90 error: mismatched types:
 expected `core::result::Result<&'a str, int>`,
    found `core::option::Option<_>`
(expected enum `core::result::Result`,
    found enum `core::option::Option`)
test2.rs:169             if self.curr != self.len { Some(self.all[self.curr..self.next]) } else { None }
                                                                                                  ^~~~
test2.rs:205:14: 205:18 error: mismatched types:
 expected `core::result::Result<uint, int>`,
    found `core::option::Option<uint>`
(expected enum `core::result::Result`,
    found enum `core::option::Option`)
test2.rs:205             (open, close)
                          ^~~~
test2.rs:205:20: 205:25 error: mismatched types:
 expected `core::result::Result<uint, int>`,
    found `core::option::Option<uint>`
(expected enum `core::result::Result`,
    found enum `core::option::Option`)
test2.rs:205             (open, close)
                                ^~~~~
test2.rs:210:21: 210:31 error: mismatched types:
 expected `core::result::Result<uint, int>`,
    found `core::option::Option<_>`
(expected enum `core::result::Result`,
    found enum `core::option::Option`)
test2.rs:210             if let (Some(open), _) = Parens::find_parens(self.all, 0) {
                                 ^~~~~~~~~~
test2.rs:210:13: 212:28 error: mismatched types:
 expected `core::option::Option<&'a int>`,
    found `core::option::Option<&str>`
(expected int,
    found str)
test2.rs:210             if let (Some(open), _) = Parens::find_parens(self.all, 0) {
test2.rs:211                 Some(self.all[0..open])
test2.rs:212             } else { None }
test2.rs:229:57: 229:96 error: the trait `core::ops::Fn<(char,), bool>` is not implemented for the type `|char| -> bool`
test2.rs:229                                              .map(|s| s.trim_chars(|c: char| c.is_whitespace()))
                                                                     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
test2.rs:238:46: 239:75 error: type `core::str::CharSplits<'_, |char| -> bool>` does not implement any method in scope named `filter_map`
test2.rs:238                                             .filter_map(|s| if !s.is_empty() { Some(s.trim_chars('\'')) }
test2.rs:239                                                             else { None })
test2.rs:237:46: 237:91 error: the trait `core::ops::Fn<(char,), bool>` is not implemented for the type `|char| -> bool`
test2.rs:237                 let vec: Vec<&str> = value[].split(|c: char| matches!(c, '(' | ')' | ','))
                                                          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
test2.rs:238:65: 238:77 error: the type of this value must be known in this context
test2.rs:238                                             .filter_map(|s| if !s.is_empty() { Some(s.trim_chars('\'')) }
                                                                             ^~~~~~~~~~~~
test2.rs:299:48: 299:58 error: mismatched types:
 expected `Box<translate::Entity>`,
    found `collections::vec::Vec<_>`
(expected box,
    found struct `collections::vec::Vec`)
test2.rs:299         pub fn new() -> Entity { Entity::Group(Vec::new()) }
                                                            ^~~~~~~~~~
test2.rs:321:36: 322:65 error: type `core::str::CharSplits<'_, |char| -> bool>` does not implement any method in scope named `filter_map`
test2.rs:321                                   .filter_map(|s| if !s.is_empty() { Some(s.trim_chars('\'')) }
test2.rs:322                                                   else { None })
test2.rs:320:36: 320:81 error: the trait `core::ops::Fn<(char,), bool>` is not implemented for the type `|char| -> bool`
test2.rs:320             let vec: Vec<&str> = s.split(|c: char| matches!(c, '(' | ')' | ','))
                                                ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
test2.rs:321:55: 321:67 error: the type of this value must be known in this context
test2.rs:321                                   .filter_map(|s| if !s.is_empty() { Some(s.trim_chars('\'')) }
                                                                   ^~~~~~~~~~~~
test2.rs:359:51: 359:58 error: type `&mut Box<translate::Entity>` does not implement any method in scope named `push`
test2.rs:359                 Entity::Group(ref mut vec) => vec.push(e),
                                                               ^~~~~~~
test2.rs:366:51: 366:85 error: type `&mut Box<translate::Entity>` does not implement any method in scope named `push`
test2.rs:366                 Entity::Group(ref mut vec) => vec.push(Entity::Inner(s.to_string())),
                                                               ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
error: aborting due to 24 previous errors
```

Closes #18946 #19464
cc @P1start @jakub- @tomjakubowski @kballard @chris-morgan

Author: bors

src/compiletest/runtest.rs

@@ -966,6 +966,16 @@ fn check_expected_errors(expected_errors: Vec<errors::ExpectedError> ,
         line.starts_with( prefix )
     }
 
+    // A multi-line error will have followup lines which will always
+    // start with one of these strings.
+    fn continuation( line: &str) -> bool {
+        line.starts_with(" expected") ||
+        line.starts_with("    found") ||
+        //                1234
+        // Should have 4 spaces: see issue 18946
+        line.starts_with("(")
+    }
+
     // Scan and extract our error/warning messages,
     // which look like:
     //    filename:line1:col1: line2:col2: *error:* msg
@@ -981,7 +991,7 @@ fn check_expected_errors(expected_errors: Vec<errors::ExpectedError> ,
                        ee.kind,
                        ee.msg,
                        line);
-                if prefix_matches(line, prefixes[i].as_slice()) &&
+                if (prefix_matches(line, prefixes[i].as_slice()) || continuation(line)) &&
                     line.contains(ee.kind.as_slice()) &&
                     line.contains(ee.msg.as_slice()) {
                     found_flags[i] = true;

src/librustc/lib.rs

@@ -36,6 +36,7 @@ extern crate fmt_macros;
 extern crate getopts;
 extern crate graphviz;
 extern crate libc;
+extern crate regex;
 extern crate rustc_llvm;
 extern crate rustc_back;
 extern crate serialize;

src/librustc/middle/ty.rs

@@ -4702,7 +4702,7 @@ pub fn ty_sort_string<'tcx>(cx: &ctxt<'tcx>, ty: Ty<'tcx>) -> String {
         }
         ty_tup(ref tys) if tys.is_empty() => ::util::ppaux::ty_to_string(cx, ty),
 
-        ty_enum(id, _) => format!("enum {}", item_path_str(cx, id)),
+        ty_enum(id, _) => format!("enum `{}`", item_path_str(cx, id)),
         ty_uniq(_) => "box".to_string(),
         ty_vec(_, Some(n)) => format!("array of {} elements", n),
         ty_vec(_, None) => "slice".to_string(),
@@ -4714,7 +4714,7 @@ pub fn ty_sort_string<'tcx>(cx: &ctxt<'tcx>, ty: Ty<'tcx>) -> String {
             format!("trait {}", item_path_str(cx, inner.principal_def_id()))
         }
         ty_struct(id, _) => {
-            format!("struct {}", item_path_str(cx, id))
+            format!("struct `{}`", item_path_str(cx, id))
         }
         ty_unboxed_closure(..) => "closure".to_string(),
         ty_tup(_) => "tuple".to_string(),

src/librustc/session/mod.rs

@@ -15,6 +15,8 @@ use metadata::filesearch;
 use session::search_paths::PathKind;
 use util::nodemap::NodeMap;
 
+use regex::Regex;
+
 use syntax::ast::NodeId;
 use syntax::codemap::Span;
 use syntax::diagnostic::{self, Emitter};
@@ -71,7 +73,58 @@ impl Session {
         self.diagnostic().handler().fatal(msg)
     }
     pub fn span_err(&self, sp: Span, msg: &str) {
-        self.diagnostic().span_err(sp, msg)
+        // Conditions for enabling multi-line errors:
+        if !msg.contains("mismatched types") &&
+           !msg.contains("type mismatch resolving") &&
+           !msg.contains("if and else have incompatible types") &&
+           !msg.contains("if may be missing an else clause") &&
+           !msg.contains("match arms have incompatible types") &&
+           !msg.contains("structure constructor specifies a structure of type") {
+            return self.diagnostic().span_err(sp, msg);
+        }
+
+        let first  = Regex::new(r"[( ]expected").unwrap();
+        let second = Regex::new(r" found").unwrap();
+        let third  = Regex::new(
+                     r"\((values differ|lifetime|cyclic type of infinite size)").unwrap();
+
+        let mut new_msg = String::new();
+        let mut head = 0u;
+
+        // Insert `\n` before expected and found.
+        for (pos1, pos2) in first.find_iter(msg).zip(
+                            second.find_iter(msg)) {
+            new_msg = new_msg +
+            // A `(` may be preceded by a space and it should be trimmed
+                      msg[head..pos1.0].trim_right() + // prefix
+                      "\n" +                           // insert before first
+                      &msg[pos1.0..pos1.1] +           // insert what first matched
+                      &msg[pos1.1..pos2.0] +           // between matches
+                      "\n   " +                        // insert before second
+            //           123
+            // `expected` is 3 char longer than `found`. To align the types, `found` gets
+            // 3 spaces prepended.
+                      &msg[pos2.0..pos2.1];            // insert what second matched
+
+            head = pos2.1;
+        }
+
+        let mut tail = &msg[head..];
+        // Insert `\n` before any remaining messages which match.
+        for pos in third.find_iter(tail).take(1) {
+            // The end of the message may just be wrapped in `()` without `expected`/`found`.
+            // Push this also to a new line and add the final tail after.
+            new_msg = new_msg +
+            // `(` is usually preceded by a space and should be trimmed.
+                      tail[..pos.0].trim_right() + // prefix
+                      "\n" +                       // insert before paren
+                      &tail[pos.0..];              // append the tail
+
+            tail = "";
+        }
+
+        new_msg.push_str(tail);
+        self.diagnostic().span_err(sp, &new_msg[])
     }
     pub fn span_err_with_code(&self, sp: Span, msg: &str, code: &str) {
         self.diagnostic().span_err_with_code(sp, msg, code)

src/test/compile-fail/array-not-vector.rs

@@ -9,8 +9,18 @@
 // except according to those terms.
 
 fn main() {
-    let _x: isize = [1is, 2, 3]; //~ ERROR expected isize, found array of 3 elements
+    let _x: isize = [1is, 2, 3];
+    //~^ ERROR mismatched types
+    //~| expected `isize`
+    //~| found `[isize; 3]`
+    //~| expected isize
+    //~| found array of 3 elements
 
     let x: &[isize] = &[1, 2, 3];
-    let _y: &isize = x; //~ ERROR expected isize, found slice
+    let _y: &isize = x;
+    //~^ ERROR mismatched types
+    //~| expected `&isize`
+    //~| found `&[isize]`
+    //~| expected isize
+    //~| found slice
 }

src/test/compile-fail/associated-types-eq-3.rs

@@ -30,7 +30,12 @@ fn foo1<I: Foo<A=Bar>>(x: I) {
 }
 
 fn foo2<I: Foo>(x: I) {
-    let _: Bar = x.boo(); //~ERROR mismatched types
+    let _: Bar = x.boo();
+    //~^ ERROR mismatched types
+    //~| expected `Bar`
+    //~| found `<I as Foo>::A`
+    //~| expected struct `Bar`
+    //~| found associated type
 }
 
 
@@ -41,6 +46,12 @@ pub fn baz(x: &Foo<A=Bar>) {
 
 pub fn main() {
     let a = 42is;
-    foo1(a); //~ERROR expected usize, found struct Bar
-    baz(&a); //~ERROR expected usize, found struct Bar
+    foo1(a);
+    //~^ ERROR type mismatch resolving
+    //~| expected usize
+    //~| found struct `Bar`
+    baz(&a);
+    //~^ ERROR type mismatch resolving
+    //~| expected usize
+    //~| found struct `Bar`
 }

src/test/compile-fail/associated-types-path-2.rs

@@ -25,7 +25,9 @@ pub fn f2<T: Foo>(a: T) -> T::A {
 
 pub fn f1_int_int() {
     f1(2is, 4is);
-    //~^ ERROR expected usize, found isize
+    //~^ ERROR type mismatch resolving
+    //~| expected usize
+    //~| found isize
 }
 
 pub fn f1_int_uint() {
@@ -46,7 +48,11 @@ pub fn f1_uint_int() {
 
 pub fn f2_int() {
     let _: isize = f2(2is);
-    //~^ ERROR expected `isize`, found `usize`
+    //~^ ERROR mismatched types
+    //~| expected `isize`
+    //~| found `usize`
+    //~| expected isize
+    //~| found usize
 }
 
 pub fn main() { }

src/test/compile-fail/bad-const-type.rs

@@ -8,7 +8,10 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-// error-pattern:expected `collections::string::String`, found `isize`
-
 static i: String = 10is;
+//~^ ERROR mismatched types
+//~| expected `collections::string::String`
+//~| found `isize`
+//~| expected struct `collections::string::String`
+//~| found isize
 fn main() { println!("{}", i); }

src/test/compile-fail/block-must-not-have-result-do.rs

@@ -8,10 +8,12 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-// error-pattern:mismatched types: expected `()`, found `bool`
-
 fn main() {
     loop {
-        true
+        true //~  ERROR mismatched types
+             //~| expected ()
+             //~| found bool
+             //~| expected ()
+             //~| found bool
     }
 }

src/test/compile-fail/block-must-not-have-result-res.rs

@@ -8,13 +8,15 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-// error-pattern:mismatched types: expected `()`, found `bool`
-
 struct r;
 
 impl Drop for r {
     fn drop(&mut self) {
-        true
+        true //~  ERROR mismatched types
+             //~| expected ()
+             //~| found bool
+             //~| expected ()
+             //~| found bool
     }
 }